Best Practices Manual for Prestressed Concrete Pipe Condition Assessment: What Works? What Doesn t? What s Next?

Transcription

1 Best Practices Manual for Prestressed Concrete Pipe Condition Assessment: What Works? What Doesn t? What s Next? Subject Area: Infrastructure

2 Best Practices Manual for Prestressed Concrete Pipe Condition Assessment: What Works? What Doesn t? What s Next?

3 About the Water Research Foundation The Water Research Foundation is a member-supported, international, 501(c)3 nonprofit organization that sponsors research that enables water utilities, public health agencies, and other professionals to provide safe and affordable drinking water to consumers. The Foundation s mission is to advance the science of water to improve the quality of life. To achieve this mission, the Foundation sponsors studies on all aspects of drinking water, including resources, treatment, and distribution. Nearly 1,000 water utilities, consulting firms, and manufacturers in North America and abroad contribute subscription payments to support the Foundation s work. Additional funding comes from collaborative partnerships with other national and international organizations and the U.S. federal government, allowing for resources to be leveraged, expertise to be shared, and broad-based knowledge to be developed and disseminated. From its headquarters in Denver, Colorado, the Foundation s staff directs and supports the efforts of more than 800 volunteers who serve on the board of trustees and various committees. These volunteers represent many facets of the water industry, and contribute their expertise to select and monitor research studies that benefit the entire drinking water community. Research results are disseminated through a number of channels, including reports, the Website, Webcasts, workshops, and periodicals. The Foundation serves as a cooperative program providing subscribers the opportunity to pool their resources and build upon each others expertise. By applying Foundation research findings, subscribers can save substantial costs and stay on the leading edge of drinking water science and technology. Since its inception, the Foundation has supplied the water community with more than $460 million in applied research value. More information about the Foundation and how to become a subscriber is available at

4 Best Practices Manual for Prestressed Concrete Pipe Condition Assessment: What Works? What Doesn t? What s Next? Prepared by: Mehdi S. Zarghamee, Rasko P. Ojdrovic, and Peter D. Nardini Simpson Gumpertz & Heger Inc., 41 Seyon Street, Bldg 1, Suite 500, Waltham, MA Jointly sponsored by: Water Research Foundation 6666 West Quincy Avenue, Denver, CO and U.S. Environmental Protection Agency Washington D.C. Published by:

5 DISCLAIMER This study was jointly funded by the Water Research Foundation (Foundation) and the U.S. Environmental Protection Agency (EPA) under Cooperative Agreement No. EM The Foundation and EPA assume no responsibility for the content of the research study reported in this publication or for the opinions or statements of fact expressed in the report. The mention of trade names for commercial products does not represent or imply the approval or endorsement of the Foundation or EPA. This report is presented solely for informational purposes. Copyright 2012 By Water Research Foundation ALL RIGHTS RESERVED. No part of this publication may be copied, reproduced or otherwise utilized without permission. ISBN Printed in the U.S.A.

6 CONTENTS LIST OF TABLES... ix LIST OF FIGURES... xi FOREWORD... xiii ACKNOWLEDGMENTS...xv EXECUTIVE SUMMARY... xvii CHAPTER 1: INTRODUCTION...1 Purpose of the Project and the Manual... 1 Scope... 1 Method of Approach of Investigation... 1 Background Data... 2 PCCP Performance History... 4 PCCP Failure Modes... 5 Causes of PCCP Failure... 5 Design deficiency... 5 Manufacturing deficiency... 6 Installation deficiency... 6 Adverse environment... 6 Operation... 6 CHAPTER 2: RISK AND ASSET MANAGEMENT...7 Failure Risk Analysis... 7 Asset Management Process... 7 CHAPTER 3: SUMMARY OF TECHNOLOGIES...13 Condition Assessment Technologies Internal Visual Inspection External Inspection of Pipe Surface Leak Detection Advanced NDT Technologies for Condition Assessment Over-the-line Corrosivity and Corrosion Surveys Monitoring Technologies Periodic Inspection Advanced NDT Technologies for Monitoring Uncertainties in NDT Technologies Failure Margin Analysis Methods Failure Margin Analysis Using Risk Curves Technology Risk Ranking Neural Network v

7 vi Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Fuzzy Markov Approach Cost CHAPTER 4: CONDITION ASSESSMENT TECHNOLOGIES...31 Internal Inspection Description Application Internal Visual Inspection Summary External Inspection of Pipe Surface Description Application External Inspection of Pipe Surface Summary Leak Detection Description Application Leak Detection Summary Electromagnetic Inspection Description Application Electromagnetic Evaluation Summary Stress Wave Analysis Description Application Stress Wave Analysis Summary Over-the-line Corrosivity and Corrosion Surveys Description Application Over-the-line Corrosivity and Corrosion Surveys Summary CHAPTER 5: MONITORING TECHNOLOGIES...73 Acoustic Monitoring Description Application Acoustic Monitoring Summary CHAPTER 6: METHODS OF FAILURE MARGIN ANALYSIS AND REMAINING SERVICE LIFE ESTIMATION...79 Failure Margin Analysis Using Risk Curves Technology Description Application Summary Failure Margin Analysis Using Risk Curves Technology Risk Ranking Description Application Risk Ranking Summary... 88

8 Contents vii CHAPTER 7: WHAT WORKS?...91 How Do I Select Pipelines/Sections for Condition Assessment? How Do I Select a Technology for Condition Assessment? How Frequently Should a Pipeline Be Inspected? Is Field Verification of NDT Results Needed? If Yes, How? What Do I Do with the Results of Condition Assessment? How Do I Reduce the Risk of Failure? CHAPTER 8: WHAT DOESN T WORK?...97 Ignoring Consequences of Rupture in Planning Asset Management Not having a proper asset management program Use of Condition Assessment Technologies with Unverified Accuracy Use of Technologies for Failure Margin Analysis and Determination Repair Priority with Unverified Accuracy Overkill in Rehabilitation CHAPTER 9: WHAT S NEXT?...99 Pipeline Asset Management Determining Pipeline Criticality Acceptable Risk PCCP Design Improvements Build Robustness in Design of PCCP Analysis Improvements Ability to Estimate Remaining Service Life without Long History of Site-specific Data Electromagnetic Inspection and Large Uncertainties NDT Signal Interpretation Verification of Acoustic Monitoring Results Future Developments Condition Assessment Technologies for PCCP with Wire Breaks Caused by Hydrogen Embrittlement Accurate Method for Detecting Broken Wires on Excavated LCP and ECP with Shorting Strap Ability of Fiber Optic Cable to Perform Wire Break and Leak Detection Simultaneously Detection of Joint Defects Other Condition Assessment Technologies APPENDIX A: RESULTS OF QUESTIONNAIRE APPENDIX B: MINUTES OF THE WATERRF WORKSHOP REFERENCES ABBREVIATIONS...139

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10 LIST OF TABLES Table 2.1. Rehabilitation cost data based on industry survey...10 Table 3.1. Documented experience of utilities using technologies for condition assessment and monitoring...21 Table 3.2. Documented verification of condition assessment technologies by utilities...22 Table 3.3. Comparison of primary characteristics of technologies for condition assessment and monitoring...23 Table 3.4. Comparison of primary characteristics of technologies for failure margin analysis and remaining service life estimation...29 Table 3.5. Approximate costs of condition assessment, monitoring, and failure margin analysis/service life estimation based on utility experiences...30 Table A.1. Responding utility, consultant, and service provider Table A.2. Summary of current condition assessment technology Table A.3. Summary of number of verified results for different technologies Table A.4. Summary of PCCP condition assessment cost data Table A.5. Summary of current gaps in PCCP condition assessment technology Table A.6. Summary of monitoring technology experience Table A.7. Summary of PCCP monitoring cost data Table A.8 Summary of current gaps in PCCP monitoring technology Table A.9. Summary of failure margin analysis/service life estimation experience Table A.10. Summary of failure margin analysis/service life estimation techniques Table A.11. Summary of current gaps in PCCP failure margin analysis/service life estimation Table A.12. Summary of the risk mitigation strategies ix

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12 LIST OF FIGURES Figure 2.1. Asset manangement and pipeline condition assessment approach...11 Figure 4.1. Internal visual and sounding inspection of PCCP detected a longitudinal crack in the inner concrete core...33 Figure 4.2. Leak detected during internal visual and sounding inspection of PCCP...33 Figure 4.3. Hole cut in the outer core of PCCP showing crack going completely through the outer core, exposing the steel cylinder to the environment...40 Figure 4.4. Wire continuity measurements along the top of PCCP...41 Figure 4.5. Half-cell potential measurement being taken on PCCP...41 Figure 4.6. Magnified (100X) image of coating of a PCCP showing moderate to severe alteration in microstructure resulting from leaching due to acid attack, dissolution, and bicarbonation of the paste matrix (light-colored areas)...42 Figure 4.7. Tethered Sahara acoustic leak detection system...47 Figure 4.8. Free-swimming SmartBall acoustic leak detection system...47 Figure 4.9. Comparison of images from infrared and standard video collected during IR survey...48 Figure Schematic of impact echo test setup...61 Figure Impact echo test being performed on top of a concrete pressure pipe...61 Figure SASW test method diagram...62 Figure Pipe-to-soil potential measurements...68 Figure Laboratory soil resistivity measurements...68 Figure Induction-type electromagnetic soil conductivity meter (EM31-MK2 ground conductivity meter)...69 Figure 6.1. Example risk curves for a specific ECP design subjected to a specific height of cover and bedding and backfill condition...81 Figure 6.2. Strains in outer core at failure of cracked outer core...82 Figure 6.3. Hydrostatic testing of PCCP with broken prestressing wires...82 xi

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14 FOREWORD The Water Research Foundation (Foundation) is a nonprofit corporation that is dedicated to the implementation of a research effort to help drinking water utilities respond to regulatory requirements and address high-priority concerns of the water sector. The research agenda is developed through a process of consultation with Foundation subscribers and other drinking water professionals. Under the umbrella of a Strategic Research Plan, the Board of Trustees and Board-appointed volunteer committees prioritize and select research projects for funding based upon current and future needs, applicability, and past work. The Foundation sponsors research projects through the Focus Area, Emerging Opportunities, and Tailored Collaboration programs, as well as various joint research efforts with organizations such as the U.S. Environmental Protection Agency and the U.S. Bureau of Reclamation. This publication is a result of one of these sponsored studies, and it is hoped that its findings will be applied in communities throughout the world. The following report serves not only as a means of communicating the results of the water industry's centralized research program but also as a tool to enlist the further support of the nonmember utilities and individuals. Projects are managed closely from their inception to the final report by the Foundation's staff and large cadre of volunteers who willingly contribute their time and expertise. The Foundation serves a planning and management function and awards contracts to other institutions such as water utilities, universities, and engineering firms. The funding for this research effort comes primarily from the Subscription Program, through which water utilities subscribe to the research program and make an annual payment proportionate to the volume of water they deliver and consultants and manufacturers subscribe based on their annual billings. The program offers a cost-effective and fair method for funding research in the public interest. A broad spectrum of water supply issues is addressed by the Foundation's research agenda: resources, treatment and operations, distribution and storage, water quality and analysis, toxicology, economics, and management. The ultimate purpose of the coordinated effort is to assist water suppliers to provide the highest possible quality of water economically and reliably. The true benefits are realized when the results are implemented at the utility level. The Foundation's trustees are pleased to offer this publication as a contribution toward that end. Roy L. Wolfe, Ph.D. Chair, Board of Trustees Water Research Foundation Robert C. Renner, P.E. Executive Director Water Research Foundation xiii

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16 ACKNOWLEDGMENTS The authors of this report would like to thank those water utilities, service providers, and consultants who contributed to the project through responses to questionnaires and participation in the workshop. Respondents and/or participants are Aurora Water, Calleguas Municipal Water District, Central Arizona Project, Chicago Department of Water Management, City of Calgary, City of Ottawa, City of Montreal, Cleveland Division of Water, Donahue Associates, Greater Cincinnati Water Works, Greater Lawrence Sanitary District, Halifax Water, Howard County Department of Public Works, Jason Consultants, Metropolitan Water District of Southern California, NDT Corporation, North Shore Sanitary District, North Texas Municipal Water District, Pressure Pipe Inspection Company, Pure Technologies, San Diego County Water Authority, San Patricio Municipal Water District, and Tarrant Regional Water District. In addition, the authors would like to thank the WaterRF project manager Jian Zhang and the Project Advisory Committee members Gary Burkhardt of Southwest Research Institute, Jon Kennedy of Tampa Bay Water, Brandy Kelso of City of Phoenix Water Services Department, and Alex Margevicius of Cleveland Division of Water. The authors would like to thank Albert Saul and Joan Cunningham of Simpson Gumpertz & Heger Inc. (SGH) for assistance with the literature search and Elizabeth Carroll of SGH for formatting and preparing this report. xv

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18 EXECUTIVE SUMMARY OBJECTIVES This Manual is intended to be a user-friendly Best Practices Manual for condition assessment, monitoring, and remaining service life/failure margin analysis of prestressed concrete cylinder pipe (PCCP). The Manual provides an overview of available technologies, summarizes best current practices for condition-assessment and prediction of remaining service life, and provides assistance to utilities in identifying the most appropriate technologies for their system. It is also intended to provide an understanding of the limits of applicability of the available technologies and trends in future developments in PCCP condition assessment and determination of failure margin and repair priority. The manual is based on literature review and the results of questionnaires distributed to, and a follow up workshop of, water utilities, service providers, and consultants. BACKGROUND PCCP lines have been used for water transmission for more than 65 years and represent the backbone of many water systems in the U.S., Mexico, Canada, and overseas. PCCP was the pipe of choice for large diameter transmission lines throughout the U.S. in the years between the mid-1960s and the end of the 1980s. By then nearly 100 million feet of pipe had been installed throughout the United States and Canada (Clift 1991). A few ruptures of PCCP in the early 1990s created a sudden apprehension about the use of the pipe. The failures of PCCP were in general catastrophic due to their large diameter and high internal pressure. A recent study sponsored by WaterRF indicates that nearly 19,000 miles or about 5 million pipe pieces had been produced in the U.S. between 1940 and 2006 (WRF Report ). Results of electromagnetic inspection of about 175,962 pipes (nearly 700 miles or about 3.5% of all installed PCCP) in North America indicated 6,431 distressed pipes with 1 or more broken wires (Semanuik and Mergelas 2006), corresponding to 3.7% of the total number of pipes inspected. This indicates that on the average about 96.3% of inspected pipes do not have any broken wires. The prevalence of distress in any given pipeline may differ significantly from this average rate based on a number of factors including pipe design, manufacture, aggressiveness of the environment to PCCP, and frequency and magnitude of actual transient pressure events and loads experienced by the pipeline. Distressed pipes having a small number of broken wires were providing service at the time of inspection, and would likely continue to deliver service with a risk of rupture that may initially be very low and gradually increase with time, leading ultimately to rupture. In general, distressed pipes may continue to provide service at very low risk of rupture for years or decades after the onset of distress. Based on the experience of the authors, the number of distressed pipes with high risk of failure is typically about an order of magnitude less than the number of distressed pipes. For this reason, the goal of the condition assessment process is to identify those distressed pipes with unacceptably high risk of failure and repair or replace them before they rupture, thus maintaining the desired pipeline reliability. xvii

19 xviii Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment APPROACH The method of approach included the following: Perform a literature review of published papers on PCCP condition assessment, performance monitoring, and service life estimation/failure margin analysis. Perform an industry survey through a questionnaire sent to pipeline operators, inspection companies, and consultants on the current state of PCCP condition assessment, performance monitoring, and determination of failure margin and remaining service life. Conduct a workshop to gather and assess utility experiences, utility needs, and utilities perception of gaps in knowledge for future research. Evaluate the existing condition assessment technologies based on their accuracy in identifying distressed pipe, accuracy in estimating the level and location of distress, and the usefulness of results for rational determination of failure margin and estimation of time to failure. Synthesize the gathered data into a best practice guidance manual to assist water utilities in selecting the appropriate condition assessment and monitoring technologies, frequency of inspection and monitoring, and appropriate methods for maintaining a failure margin that ensures acceptable pipeline reliability. Identify further research needed to improve condition assessment techniques and service life estimates. RESULTS/CONCLUSIONS What Works In general, what works is a program of pipeline asset management aimed to maintain the pipeline risk of failure at an acceptable level. It generally includes periodic condition assessment, failure margin analysis, identification of pipe pieces with unacceptable failure risk, and repair or replacement of such pipes. Selection of pipelines or sections of pipelines for condition assessment should be based on criticality. Criticality accounts for the pipeline likelihood of failure, consequences of failure, and system constraints. Selection of inspection frequency and condition assessment technology is different for low, medium, and high criticality pipelines. Higher criticality pipelines require more frequent inspection and the use of advanced NDT technologies for locating and predicting the level of distress. The results from inspection using the selected NDT technology must be verified through comparison to the results from another technology or field-verification unless substantial verification of the results has already been made and is available. Once distressed pipes have been detected and the extent of distress estimated, it is necessary to determine the likelihood of failure, failure risk, and repair priority of the distressed pipes. The method of failure margin analysis used to evaluate the likelihood of failure must be based on a calibrated and verified model and must account for the uncertainties in the results of NDT technologies used for condition assessment. Risk of failure of the pipeline can be reduced in a number of ways, including rehabilitation of individual pipes or pipeline sections with

20 Executive Summary xix unacceptably high risk of failure, reduction of maximum internal pressure, or cathodic protection of an electrically continuous pipeline. What Doesn t Work In general, what doesn t work are not having a proper asset management program or having a program that does not properly account for system constraints and consequences of failure, does not accurately quantify the likelihood of failure, and/or does not prioritize rehabilitation based on failure risk. The consequences of rupture may include quantifiable cost due to property damage, repair, investigation, water loss, and service interruption and non-quantifiable costs, such as risk of loss of life, loss of public trust, and political fallout that should be accounted for. Ignoring or inadequately accounting for these consequences of rupture results in improper assignment of risk and misallocation of resources. Use of technologies with unverified accuracy in detecting distressed pipes and in quantifying the level of distress in such pipe can result in data that cannot be used to establish the failure margin of the distressed pipe. Inaccuracy in detection of distressed pipe can be either costly as good pipes are repaired unnecessarily or ineffective as bad pipes go undetected. Similarly, use of technologies with unverified accuracy for determination of failure margin and repair priority can lead to error in determining how close the pipe is to rupture, resulting in either unnecessary repair or failure to prioritize highly distressed pipe for repair, thus increasing the risk of pipeline failure. With limited resources, asset management by repairing all of the distressed pipe identified by an NDT inspection procedure or replacing a part of the line or an entire line with limited distress comparable to the distress level of the pipelines managed successfully by others does not work. In most cases, PCCP with limited number of wire breaks can safely perform under the design loads and pressures for many years. Replacing a section of pipeline with limited distress and a low-to-moderate risk of failure constitutes an inefficient use of scarce resources in a system that could have been managed at a fraction of cost. What s Next The technologies needed by the utilities for improved condition assessment and pipeline asset management can be categorized into (1) pipeline asset management, (2) design improvements, (3) analysis improvements, and (4) future developments. The research needed for the development of the new technologies requires collaboration and financial support of the utilities. Utilities should pool their resources to fund the needed research to solve the challenging problems ahead. Pipeline asset management needs include methods to determine pipeline criticality using the existing data and establishment of a utility-specific acceptable level of risk. Design improvements include building robustness into PCCP design to account for future distress. Analysis improvements include the ability to estimate remaining service life without a long history of site-specific data, understanding the uncertainties of the electromagnetic inspection results near the pipe ends and for special pipes, and verification of acoustic monitoring results. Future development needs to include condition assessment technologies for PCCP that distinguish between random wire breaks caused by hydrogen embrittlement and clustered wire

21 xx Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment breaks caused by corrosion, an accurate method for detecting broken wires on excavated LCP and ECP with shorting strap, ability of fiber optic cable to perform wire break and leak detection simultaneously, detection of joint defects, and other condition assessment technologies. APPLICATIONS/RECOMMENDATIONS Effective pipeline management requires allocating resources to the high risk areas of the pipeline where they are needed and not wasting scarce resources on low risk areas of the pipeline. This Manual can be used by water utilities to develop a program of condition assessment, monitoring, and rehabilitation of their PCCP lines based on pipeline criticality and failure risk. Utilities with existing pipeline management programs can use this Manual to evaluate and improve their current program. Economic Implications. Allocating scarce resources in a systematic, risk-based manner can lower the cost of pipeline management while reducing the risk of pipeline failure. The cost of properly managing a critical pipeline with distressed pipes is typically significantly less than the costs associated with pipeline failure or overly conservative rehabilitation strategies. The costs of periodic inspection and rehabilitation of pipelines with high failure risk can be spread over time to allow planning and budgeting. Management Concerns. Understanding the pipeline likelihood of failure, consequences of failure, and system constraints allows operators of pipelines to quantify their exposure and prioritize condition assessment and rehabilitation actions. Understanding the capabilities and limitations of condition assessment, monitoring, and failure margin analysis technologies allows operators to confidently select technologies that satisfy their inspection expectations and system constraints. This Manual provides a pipeline management approach that accounts for system constraints and pipelines likelihood of failure and consequences of failure. It also provides descriptions of technologies - including their primary applications, benefits, limitations, and access requirements. Technological Advancements. Water utilities that currently have pipeline management plans in place can use this manual to evaluate their current plan and the technologies they employ for condition assessment, monitoring, and failure margin analysis. Utilities may opt to select different technologies that are better suited for their system or have more reliable verification results. This Manual identifies areas of future technological development that utilities or other stakeholders might choose to support financially or consider using once the technologies have been developed.

22 CHAPTER 1: INTRODUCTION PURPOSE OF THE PROJECT AND THE MANUAL The goal of prestressed concrete cylinder pipe (PCCP) condition assessment is to identify distressed pipes and to identify and repair those pipes with unacceptable failure risk at minimum cost while keeping the pipeline reliability at an acceptable level. The overall objective of this project is to provide utilities with a best practices manual based on the available state-of-the-art condition assessment and service life estimation approaches for PCCP lines. The purpose of this manual is to provide operators of PCCP lines with an overview of available PCCP condition assessment and monitoring technologies, to summarize the best current practices for condition assessment and service life estimation, and to help operators identify the most appropriate technologies for the given constraints in their system. The manual also provides an understanding of the limits of applicability of available technologies and trends and future developments in PCCP condition assessment and determination of failure margin and repair priority. SCOPE The manual synthesizes utility experiences within North America with PCCP condition assessment technologies, monitoring technologies, and methods for determination of remaining service life/failure margin and identifies needs for future research and development based on the following: Literature review. More than 200 published papers were reviewed. Industry survey. A questionnaire was distributed to water utilities, service providers, and consultants (Appendix A). Workshop. A workshop was conducted with 17 participants from water utilities, consultants, and service providers to discuss and share utility experiences, needs, and practical technologies (Appendix B). METHOD OF APPROACH OF INVESTIGATION The method of approach included the following: Perform a literature review of published papers on PCCP condition assessment, performance monitoring, and service life estimation/failure margin analysis. Perform an industry survey through a questionnaire sent to pipeline operators, inspection companies, and consultants on the current state of PCCP condition assessment, performance monitoring, and determination of failure margin and remaining service life. Conduct a workshop to gather and assess utility experiences; utility needs; technologies successfully employed for assessment, monitoring, determination of failure margin and remaining service life of PCCP; and utilities perception of gaps in knowledge for future research. 1

23 2 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Evaluate the existing condition assessment technologies for different types of pipes (e.g., LCP, ECP, ECP without shorting straps, non-cylinder pipe, etc.) based on the accuracy in identifying distressed pipe, especially identifying highly distressed pipe, prevalence of false negatives (calling bad pipe good) or false positives (calling good pipe bad). o False positive, although conservative, increases cost of repair unnecessarily and erodes owner confidence and false negative negates the purpose of assessment. o Accuracy in estimation of the level and location of distress, e.g., extent of corrosion, number of wire breaks, corrosion state of steel cylinder. o Usefulness of results for rational determination of failure margin and estimation of time to failure considering the uncertainties in inspection results and pipeline operation, e.g., determine the existing number of wire breaks and the rate of wire breakage. Synthesize the gathered data into a best practice guidance manual, referred to as the manual, to assist water utilities in selecting the appropriate condition assessment and monitoring technologies, frequency of inspection and monitoring, and appropriate methods for maintaining a failure margin that ensures acceptable pipeline reliability. Identify further research needed to improve condition assessment techniques and service life estimates. BACKGROUND DATA PCCP lines have been used for water transmission for more than 65 years and represent the backbone of many water systems in the U.S., Mexico, Canada, and overseas. PCCP was the pipe of choice for large diameter transmission lines throughout the U.S. in the years between the mid-1960s and to the end of the 1980s. By then, nearly 100 million feet of pipe had been installed throughout the United States and Canada, with approximately one-half manufactured by Interpace (Clift 1991). A few ruptures of PCCP in the early 1990s created a sudden apprehension about the use of the pipe. The failures of PCCP were in general catastrophic due to large diameter and high internal pressure in the pipe. Internal and external inspection of the failed pipelines showed that other pipes in the line had internal cracks, sounded hollow when tapped, and when excavated, were found to be in a distressed state close to rupture. Water utilities with PCCP pipelines became concerned about the risk of rupture of their PCCP pipelines and some started on a program of condition assessment of their PCCP lines. Forensic investigations performed to determine the cause(s) of rupture found that some wires at the rupture site were corroded, some exhibited ductile fracture, and some exhibited brittle fracture with characteristic sharp and jagged surface. In addition, the wires on many pipes showed longitudinal splits, characteristic of dynamic strain aging resulting from the drawing process of extremely high strength wires. It was found that wires with higher tensile strength are more susceptible to brittle fracture. Brittle fracture was observed primarily on pipes manufactured during the 1970s by Interpace using extremely high strength Class IV wires, and to a lesser extent on the high strength Class III wires. PCCP was first manufactured as a lined cylinder pipe (LCP) and installed in AWWA approved a Tentative Standard Specifications for Reinforced Concrete Water Pipe Steel Cylinder Type, Prestressed in 1949 (also referred to as AWWA C301-49) covering

24 Chapter 1: Introduction 3 materials and fabrication of 16 inches to 48 inches diameter pipe. The first AWWA C301 standard appeared in 1952 and increased the maximum diameter of LCP to 54 inches. Embedded cylinder pipe (ECP) was developed after LCP and was first installed in In 1955, a Tentative Standard AWWA C301-55T introduced ECP with up to 72 inches diameter. Maximum standard pipe diameter was increased to 96 inches in AWWA C It included an empirical design procedure based on hydrostatic pressure tests and three edge bearing tests of each pipe design with cubic parabola interaction curve between the two (Appendix A, used primarily in eastern states) and a stress analysis design method (Appendix A, used primarily in western states). AWWA C increased the maximum standard diameter of ECP to 144 inches and included numerous changes in material specification and fabrication. AWWA C (1979) increased the maximum standard diameter of LCP to 60 inches. AWWA C (1964) through -79 allowed the use of prestressing wires (referred to hereafter as wires ) with higher strength than Class III wires. AWWA C (1984) introduced changes in material and fabrication specifications and eliminated a provision that allowed higher tensile strength of wires. In 1992, AWWA C301 was revised to incorporate new and more detailed testing of virtually every aspect of the pipe manufacturing process, including controls on wire and on mortar coating. AWWA also introduced Standard C (1992) for design of PCCP, which replaced Method A and Method B design procedures. Since 1992, changes in AWWA C301 or AWWA C304 have been less significant. The prestressing wire specified by AWWA C301 between 1949 and 1972 conformed to the requirements of ASTM A227 Standard Specifications for Hard-drawn Steel Spring Wire. ASTM A specified wire with a tensile strength in the range of 192 to 221 ksi for gage 6 and 200 to 230 ksi for gage 8 wire. In 1964, higher strength Class II wire was introduced with a tensile strength in the range of 222 to 251 ksi for gage 6 and 231 to 261 ksi for gage 8 wire. In 1972, ASTM A648 Standard Specification for Steel Wire, Hard Drawn for Prestressing Concrete Pipe (2011) was introduced. This standard specified the minimum tensile strength for Class I, II, and III wires. The minimum tensile strength of Class III wire was specified at 252 ksi for gage 6 and 262 ksi for gage 8 wire. In 1984, A648 was revised to provide both minimum and maximum tensile strengths for Class I, II, and III wires. For example, the maximum tensile strength of Class III wire was specified at 290 ksi for gage 6 and 297 ksi for gage 8. Class IV wire, although in use, was not referenced in this standard. In 1986, a supplemental splitting test using a bolt cutter was added, and in 1990 Class I wire and gage 8 wire were deleted from the standard. In 1995, a wire relaxation test was added and the splitting test by bolt cutter was removed. In 2004, ASTM A648 cautioned that strain aging caused by elevated temperature during the drawing process that lasts for more than 5 seconds at 400 F or 20 seconds at 360 F can reduce the wire ductility and increase its susceptibility to hydrogen embrittlement. In addition, a supplementary requirement was added in which hydrogen embrittlement susceptibility of the wire can be tested in accordance with ASTM A1032 in ammonium thiocyanate solution. The more significant changes in the material and the fabrication process of PCCP over the years are summarized below: Wire classes have changed over the years. Class I wire was used initially, and Classes II, III, and IV were gradually introduced by the manufacturers of PCCP over the years. Use of Class IV wire ended in the early 1980s due to concerns about its susceptibility to embrittlement and premature breakage. Currently the wire standard A-648 allow the use of only Class II and Class III with additional requirements to

25 4 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment reduce brittle fracture of the wire, including a supplemental requirement for testing susceptibility to hydrogen embrittlement. Minimum wire diameter was increased from gage 8 to gage 6 in 1992 due to the additional susceptibility of gage 8 wire to corrosion. Minimum wire spacing was changed to 2.0 wire diameters for ECP and 2.75 wire diameters for LCP in 1992 to prevent delamination of the coating. Coating thickness was changed several times over the years from 5/8 inch over the wire to the current minimum value of 3/4 inch over the wire. The use of cast concrete coating, which was an option from beginning, was ended in Electric continuity in the form of shorting straps laid beneath the wires and bonding of joint rings of adjacent pipes were introduced as options in the late 1970s. PCCP PERFORMANCE HISTORY Performance history of PCCP has been recently studied and summarized in WRF Report (2008). The results indicate that nearly 19,000 miles or about 5 million (4,979,837) pipe pieces have been produced in the U.S. between 1940 and The average failure rate based on reported pipe ruptures and leaks and other types of failure (significant structural weakness discerned by inspection and loss of service) is 1 rupture in 3,000 miles per year and 1 failure other than rupture in 50 miles per year. Results of electromagnetic inspection of about 175,962 pipes (nearly 700 miles or about 3.5% of all installed PCCP) in North America by the Pressure Pipe Inspection Company indicated 6,431 distressed pipes with 1 or more broken wires (Semanuik and Mergelas 2006), corresponding to 3.7% of the total number of pipes inspected. This indicates that on the average more than 96.3% of inspected pipes do not have any broken wire. The prevalence of distress in a pipeline may differ significantly from this average rate depending on pipe design, manufacture, aggressiveness of environment to PCCP, and frequency and magnitude of actual transient pressure events experienced by the pipeline. The distress rate is typically higher in pipelines manufactured by LockJoint during the 1970s with Class IV wire and poor coating, and lower in PCCP manufactured prior to 1970 and after 1990 (WRF Report 91214, 2008). The distressed pipes having one or more broken wires were providing service at the time of inspection, and continue to deliver service with a risk of rupture that is initially very low and gradually increases as the number of broken wires grows with time, leading ultimately to rupture when the distress level (number of broken wires) reaches a limit, depending on the pipe design, when the maximum pressure in the pipe exceeds the capacity of distressed pipe with broken wires. In general, distressed pipes may continue to provide service at very low risk of rupture for years or decades after the onset of distress, i.e., the first wire break. Based on the experience of the authors, the number of distressed pipes with high risk of failure is typically about an order of magnitude less than the number of distressed pipes. For this reason, the goal of condition assessment process is to identify those distressed pipes with unacceptably high risk of failure and repair or replace them before they rupture, and thus maintain the desired pipeline reliability.

26 Chapter 1: Introduction 5 PCCP FAILURE MODES Failure of PCCP may occur circumferentially or longitudinally. The failure process in the circumferential failure mode includes initiation of corrosion and ensuing wire breaks, or wire breaks caused hydrogen embrittlement, followed by cracking and delamination of the coating, loss of prestress as corrosion and wire breaks progress, cracking of the core, exposure of embedded steel cylinder to the environment, corrosion of the steel cylinder, and eventual rupture. Initiation of distress in the circumferential failure mode may be related to design, manufacture, installation, operation, or aggressive environment. Once the corrosion inhibiting properties of high alkaline cement mortar has diminished (say by cracking and/or delamination or loss of alkalinity of coating), corrosion of wire can start. In addition to the corrosion, hydrogen embrittlement of the wires with high tensile strength can occur and lead to progressive breakage of wires. Concomitant with wire breaks is loss of prestress in the core, which can lead to cracking of the core. In ECP, cracking of the core will expose the steel cylinder to corrosive elements in the soil. In LCP, the corrosion of the steel cylinder can begin with the corrosion of the wires, and pipe rupture may or may not be preceded by leakage, depending on pipe design and pressures. Longitudinal failure occurs typically due to inadequate hydraulic thrust restraint at elbows, tees, or bulkheads; differential soil settlements; or seismic ground motion due to blasts or earthquake. Poisson s effect of circumferential strains from internal pressure and thermal loads also can contribute to the longitudinal effects. The longitudinal failure process begins with the pipe movement resulting in opening of joints or circumferential cracking of the concrete core, exposure of the steel cylinder to corrosion, yielding and rupture of steel cylinder, and failure of the outer concrete core. The process can result in leakage or rupture and may occur with or without corrosion of the steel cylinder. CAUSES OF PCCP FAILURE The causes of PCCP failure can be divided into 5 categories of design, manufacture, installation, environment, and operation. Design deficiency Design deficiency includes improper selection of the pipe type for the exposure environment and inadequate structural design of the pipe resulting from deficiencies either in the design methodology (e.g., the requirements of the standard used such as use of very high tensile strength wire, specification of too thin a coating over the wire, or insufficient cylinder thickness or harness length for pressure-induced thrust restraint) or in the loads (e.g., improper selection of the design working and transient pressures, design earth load, and design live load). Inadequate design may also result from improper design of corrosion protection for the exposure environment.

27 6 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Manufacturing deficiency Manufacturing deficiency includes improper material used in the fabrication process, improper fabrication processes such as welding, or improper labeling of the manufactured pipe, and improper quality control. Examples of improper materials include: Class IV wire. One of the failure modes of wire is brittle fracture of wires due to embrittlement. Very high strength Class IV wires manufactured between the early 1970s and the early 1980s and to a lesser extent some higher strength Class III wires have exhibited sensitivity to embrittlement. Sensitivity to embrittlement depends on strain aging as described earlier in this chapter (Benedict and Lewis 1999). Porous or thin mortar coating. Wire must be protected from the potentially aggressive environment by dense and durable cement mortar coating (hereafter referred to as coating ). The increased permeability of a porous coating results in a higher rate of migration of corrosive chloride ions from the environment to the steel wire. Other manufacturing anomalies that have occurred rarely in the past include absence of adequate tension in the wire; use of dented steel cylinder; very close spacing of wire wraps near the joint rings, resulting in coating delamination; incorrect labeling of pipe class; and deficient welds at seams in the steel cylinder or between the steel cylinder and joint ring. Installation deficiency Installation deficiencies that have caused failures in the past include inadequate bedding and backfill (especially in rocky terrain), installation of wrong pipe (e.g., lower class pipe in a higher pressure zone), coating damage during transportation, handling and installation (e.g., scraping of coating during handling or compaction, impact damage, hard joining), or improper installation of thrust restraint (e.g., not fully seated harness clamps or deficiently welded joints). Adverse environment Adverse environment is the most common cause of PCCP distress. Pipes installed in aggressive environments may require additional protection measures. AWWA Manual M9 identifies aggressive environments as those containing highly corrosive soils (soils characterized by low resistivity and high chloride or high sulfate content), severe acidic conditions, aggressive carbon dioxide, or stray currents. Operation Improper operation of pipeline can cause high stresses in the pipe resulting in distress in the form of core and coating cracking and wire break. The most common operation causes are allowing large transient pressures to occur in the pipeline or heavy earth load or live load beyond the loads for which the pipe was designed. Another common operation cause for pipelines that are cathodically protected is improper cathodic protection that typically causes rapid rate of wire break. Third party damage in some pipelines has caused rupture of PCCP.

28 CHAPTER 2: RISK AND ASSET MANAGEMENT FAILURE RISK ANALYSIS The purpose of failure risk analysis is to allow effective pipeline management by allocating resources to the high-risk areas of the pipeline where they are needed and not wasting scarce resources on low risk areas of the pipeline asset. The failure risk of a pipeline is typically expressed as the product of the likelihood of failure and consequence of failure. Evaluating the likelihood of failure of a pipeline requires initial information of the pipeline condition, which can be obtained from information about its design, manufacturing, installation, and operation, as well as the existing inspection results. The criticality of a pipeline is determined from the failure risk of the pipeline with due consideration of system constraints. Based on the criticality of each pipeline in the system (or each section of the pipeline), inspection priority and the need for the use of advanced condition assessment technologies (i.e., technologies that provide information about individual distressed pipe and usually at higher cost) are determined. Asset Management Process Failure risk can be re-analyzed using the condition assessment results from the advanced technologies and decisions regarding pipeline repairs and monitoring priorities can be made. Each step in this asset management process is shown in Figure 2.1 and discussed below. Consequences of Failure The first step in the process of asset management is to assess the consequences of failure, including life safety, property damage, service interruption, public trust, and political cost. Some of these are expressible in dollar value and others are not. The result of this assessment is categorization of a pipeline or a part of a pipeline to have low, medium, or high consequence of failure. Likelihood of Failure The second step is to evaluate the likelihood of failure based on available pipe data. 1. Circumferential Direction. The likelihood of failure in the circumferential direction is determined from: a. pipe age, b. past performance issues of the pipeline in the form of leaks or ruptures, c. known factors in pipe design, manufacturing, installation (including the bedding condition), environment, and operation that may increase the likelihood of failure, d. the available results of conventional condition assessment techniques, such as internal visual inspection, external inspection, and over the line corrosivity and corrosion surveys, and 7

29 8 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment e. failure margin of the distressed pipe. Based on the above factors, the pipeline can be classified into low likelihood, medium likelihood and high likelihood of failure. This process can be formalized by assigning an index approach. 2. Longitudinal Direction. The likelihood of failure in the longitudinal direction is determined from: a. the thrust restraint design of the pipeline, b. pressure in the line, and c. soil type. Furthermore, excessive differential settlement can cause failure. Temperature and Poisson effect (shortening of the pipe length from the radial expansion of the pipe wall due to hoop stress caused by internal pressure) also contribute to longitudinal stresses, but they tend to disappear as the pipe develops circumferential cracks. The thrust restraint design of pipelines for pressures in the line follows the AWWA Manual M9, Manual of Water Supply Practices for Concrete Pressure Pipe. This manual, including the procedure for design of thrust restraint, underwent significant change in The past design procedures were successful in protecting pipelines installed in stiff soils against failure, but some pipes installed in soft, plastic soils did fail. Therefore, pipelines designed and installed in soft soils prior to 2009 have higher likelihood of failure due to longitudinal effects of high internal pressure. The new M9 Manual accounts for pipe-soil interaction and for joint restraint type (mechanically restrained joints or welded joints). Unavoidable settlement of the pipeline results in longitudinal stresses in the pipe and the joint opening that should be safely resisted by the pipeline System constraints The third step is to evaluate system constraints, including (1) system redundancy, (2) the total time the line can be out of service, (3) time required for condition assessment work inside the pipeline, (4) access availability and the time and cost of constructing the needed access for the line, and (5) dewatering time and cost. Evaluation of the access should account for assessment of the in-line valves operability and the need for their repair. Criticality The results of the above three steps is integrated to determine the criticality of the pipeline. Use of advanced condition assessment technologies If a pipeline is critical, use of advanced NDT technologies such as electromagnetic inspection, leak detection, and acoustic monitoring may be justified for locating and predicting the level of distress. This information needs to be used to reevaluate the failure risk and repair priority of the pipe with the level of distress identified by the NDT technologies.

30 Chapter 2: Risk and Asset Management 9 Updated failure risk Using the results of the advanced condition assessment technologies, the failure margin or likelihood of the failure of the pipeline should be determined from the distress level data obtained for individual distressed pipe and the loads acting on the distressed pipe. Based on these data, the risk of failure and repair priority of the individual distressed pipe needs to be established and the risk of failure of the pipeline needs to be reevaluated. The method of failure margin analysis used to evaluate the likelihood of failure must be based on a calibrated and verified model and must account for the uncertainties in the results of NDT technologies used for condition assessment. Rehabilitation The rehabilitation of the pipeline can be either in the form of repair or replacement of the individual distressed pipe with high risk of failure and hence high repair priority, or in the form of replacement of one or more sections of the pipeline which shows high rate of distress and high likelihood of failure. The determination of individual pipe repair or replacement of a highly distressed section of the pipeline must be based on the economic and structural evaluation of different rehabilitation alternatives. Monitoring The monitoring of a distressed pipeline can be in the form of either periodic inspection of the line or active acoustic monitoring of the line. The results of monitoring can be used to periodically update the likelihood of failure of distressed pipes for re-evaluation of the risk of failure to decide on future rehabilitation and condition assessment. Maintaining a pipeline at an acceptable risk of failure requires either rehabilitation of pipes with unacceptable risk of failure under the existing loads or reduction of the internal working pressure, transient pressure, earth load, and live load acting on the pipeline. Rehabilitation methods for individual distressed pipe pieces include, but are not limited to, pipe replacement with a closure piece, external post-tensioning, lining with carbon fiber reinforced polymer (CFRP), and installation of a steel liner. When multiple distressed pipes in close proximity of each other are interspersed with undistressed pipe, rehabilitation of the entire pipeline section may be more economical than repair of individual distressed pipes. Rehabilitation methods for pipeline sections include, in addition to those listed for individual pipe repair, replacement of the pipeline section and slip lining using steel pipe, high-density polyethylene (HDPE) pipe, or HOBAS pipe. Other methods such as robotically applied CFRP liner and cured-in-place CFRP liner are under development. Cost data and technical benefits and limitations of rehabilitation strategies collected from our industry survey are presented below in Table 2.1.

31 10 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table 2.1. Rehabilitation cost data based on industry survey Rehabilitation Strategy Technical Benefit Technical Limitation Replacement of Effective for limited number Requires excavation of the pipe. individual of highly distressed pipes. May require field welding of distressed pipe with No reduction in internal closure piece. closure piece diameter. Requires extensive work area. CFRP lining of individual pipe pieces Slip lining of a section Pipeline section replacement External posttensioning of individual or a short section of distressed pipe and shotcrete coating Requires limited work area; excavation is required. Minimal reduction of internal diameter. Reduction of surface roughness. Effective for repair of nearly straight sections of pipelines. Minimized welding inside the pipe. Effective for repair of pipeline sections. No reduction in internal diameter. Effective for limited number of distressed pipes. No pipeline dewatering. Re-establishes the prestress in the distressed pipe. No reduction of internal diameter. Relatively rapid installation for pipes with low soil cover. Requires monitoring of CFRP installation. Reduction in diameter may result in loss of flow capacity. Requires extensive work area and removal of several pipes. Requires excavation of the pipe. May require field welding of closure piece. Requires extensive work area along the pipeline alignment. Requires excavation of the pipe. Typically requires pipeline depressurization. Cost (Comparative) $$$ $$$$ $ $$$ $$$

32 Chapter 2: Risk and Asset Management 11 Chapter 2: Risk and Asset Management 11 Figure 2.1. Asset manangement and pipeline condition assessment approach

33

34 CHAPTER 3: SUMMARY OF TECHNOLOGIES This chapter provides a summary of each condition assessment, monitoring, and failure margin/remaining service life estimation technology currently in use by utilities based on literature review and industry survey. Additional detail about each technology based on literature review is available in Chapters 4, 5, and 6, and additional detail based on industry survey results is available in Appendix A. This chapter serves as a guide to concisely describe each technology, its primary use, its benefits and limitation, its usage by utilities, and its comparative cost to assist readers in focusing their attention to the topics of their choice in Chapters 4, 5, and 6. Utility usage of each technology is identified as high, medium, or low in the following sections of this Manual based on the results of the utility survey and literature search moderated by our experience to account for bias in literature for newer technologies. High usage corresponds to documented usage by 15 or more utilities or documented inspection of at least 500 miles. Similarly, medium usage corresponds to 5 up to 15 utilities or 200 to 500 miles, and low usage corresponds to fewer than 5 utilities and less than 200 miles. Documented experience of utilities using condition assessment and monitoring technologies is summarized in Table 3.1. Documented verification results for condition assessment technologies are summarized in Table 3.2. Many technologies have no published verification results. Some technologies, such as impact echo and Sahara leak detection, have only limited results that may be biased because of their size. Pipe rupture is typically preceded by gradual deterioration manifested by corrosion, wire breakage from corrosion or embrittlement, loss of prestress and the resulting core cracking, separation of the concrete core from steel cylinder, and corrosion and perforation of the steel cylinder and possibly leakage (particularly in the case of LCP). Condition assessment and monitoring technologies are aimed at identifying manifestations of the deterioration in distressed pipes. Failure margin analysis of distressed pipes is used to estimate pipe margin to failure and repair priorities from the results of the condition assessment technologies used. Uncertainties in wire break data and in maximum pressure (working plus transient pressure) are included in failure margin analysis. The uncertainties may be reduced by verification of the results of condition assessment and monitoring technologies through external inspection of the identified distressed pipe and/or by performing transient analysis for improved maximum pressure estimation. Leakage in pipelines may occur at the joints or in the pipe barrel, away from the joints. Joint leakage may be a result of improper gasket installation, gasket deterioration, improper installation (especially improper bedding that causes pipe settlement), failure of joint harness (mechanical or welded), soil settlement, seismic motion, surge events, etc. Leakage in the pipe barrel occurs due to loss of water tightness of the steel cylinder due to corrosion or due to rupture caused by differential settlement or inadequate thrust restraint design near elbows, tees, or bulkheads. Corrosion of LCP, with steel cylinder and wires having the same exposure to the permeating chloride ions through the coating, is typically manifested in the form of leakage from the pipe wall before rupture (Erbay et al. 2007), especially if the internal pressure is not very high. This early warning system allows detection of distressed LCP by leak surveys; however, in PCCP under high pressure, rupture of distressed pipe typically occurs soon after the onset of leakage. 13

35 14 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment CONDITION ASSESSMENT TECHNOLOGIES Condition assessment technologies have evolved rapidly in the past 15 years. Conventional condition assessment technologies prevalent until the late 1990s were internal inspection for cracks and hollow sounding inner concrete core and corrosivity or corrosion surveys followed by excavation and exposure of the suspect pipe to verify pipe distress. Recent nondestructive inspection technologies, such as electromagnetic inspection and acoustic monitoring methods, detect and locate wire breaks in the pipe. Signal distortions in electromagnetic inspection can be used to estimate the extent of wire break. Technologies for leak detection have also evolved from detection of the acoustic signal generated by a leak from microphones attached to the pipeline at a manhole to in-line acoustic detection probes that can accurately detect and locate small leakages. See Chapter 4 for detailed descriptions of condition assessment technologies. Internal Visual Inspection (Usage: High) The purpose of internal visual inspection is to identify and document visible cracks (location, geometry, length and width) on the inside surface of the pipe, joint openings, and hollow-sounding areas (location and geometry) found when the surface of the pipe is sounded with a light hammer (generally 1 to 2 pounds) or similar instrument. Simultaneous occurrence of longitudinal cracks and hollow sounding of the inner concrete core is an indication of an advanced state of distress and significant loss of prestress in the pipe; however, individually, they may not be related to pipe distress as hollow sound in the inner core can occur near the joint rings, in low prestress ECP, ECP subjected to differential shrinkage, or ECP with dented steel cylinder and longitudinal cracking can be caused by transient events or shrinkage. Other types of anomalies, such as circumferential cracking and joint openings, observed during internal inspection may or may not be indicative of distress in PCCP. Circumferential cracks and /or joint openings may be nonstructural and caused by temperature and shrinkage of concrete, or they may be structural and caused by inadequate thrust restraint design near bends or by differential settlement near rigid concrete encasements or changes in foundation stiffness. AWWA C (2007) considers circumferential or helical cracks in the inner concrete core less than inches in width as acceptable. Circumferential cracks exceeding inches in width, multiple closely spaced circumferential cracks located near bends or areas of potential settlement, or cracks showing signs of corrosion require special investigation. External Inspection of Pipe Surface External Visual and Sounding (Usage: Medium) Failure of PCCP in a corrosive environment generally begins with loss of prestress due to wire corrosion (or wire and steel cylinder corrosion) and wire breakage. Due to the expansive nature of the corrosion process, delamination and cracking of the coating often occur in corrosion areas. Visual inspection and sounding of the coating can identify these areas for further investigation. Mode of wire breakage (corrosion or embrittlement) is determined by

36 Chapter 3: Summary of Technologies 15 visual inspection of wires after removal of coating and opening a window in the coating for inspection of wires. Wire Continuity (Usage: Medium) Continuity of the wire for non-shorting strap ECP can be determined by measuring resistance between adjacent wire wraps. A broken wire results in a high measured resistance between adjacent wire wraps. Wire continuity measurements require excavation of a 2-foot width on the top of the pipe and localized removal of the coating at the crown of the pipe to expose the wires in a strip along the full length of the pipe and approximately 2 inches wide circumferentially. Measurement of electrical resistance between the exposed portions of adjacent wraps can identify wire breaks at any location around the pipe circumference. Wire continuity testing requires a digital multimeter with test leads, equipment to remove a strip of coating along the top of the pipe to locally expose the wires, and equipment to clean the prestressing to obtain a bright, clean metal surface for electrical connection between the wire and the multimeter test lead. Care must be taken to minimize damage to the wires during removal of the coating strip. Wire continuity measurements cannot be performed on ECP with shorting straps or LCP due to the electrical continuity of the wires provided by the shorting strap or the steel cylinder, respectively. Linear Polarization and Galvanostatic Pulse Measurement (Usage: Low) Linear polarization and galvanostatic pulse measurement are technologies for determining active corrosion in a pipe by estimating corrosion rate based on the relationship between electrochemical potential, current flow, and time. They were developed for determining the corrosion rate of reinforcement in concrete and for overcoming difficulties in interpretation of half-cell potential data. Half-Cell Potential Measurements (Usage: Medium) Half-cell potential measurements can be used to detect the existence of corrosion underneath the coating or areas with higher propensity for corrosion by measuring the difference between potential of the coating surface and the steel. The magnitude of the potential and the potential contours can be used to locate areas with higher likelihood of corrosion at the time of measurement for removal of coating and visual inspection of the conditions of wires. Potential measurement locations are generally located on a grid of points spaced 1 foot to 2 feet apart. Interpretation of half-cell potential measurements must consider temperature, moisture, delaminations, surface coatings, and other conditions that may be present and that may influence the resulting potential measurements. The half-cell potential measurement system, as defined by ASTM C876 (2009), consists of a reference electrode, an electrical junction device, an electrical contact solution, a volt meter, and electrical lead wires. Petrography and Coating Testing(Usage: Medium) The prestressing wire is protected from the corrosive environment by the high alkalinity of the cement coating applied over the wire. Wire corrosion can occur if the quality of the

37 16 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment coating is compromised. Quality of the mortar can be determined using concrete petrography, absorption testing, and chloride profile testing through the thickness of the coating. Poor quality of coating is a likely cause of wire corrosion and pipe deterioration. Leak Detection Walking the Line (Usage: High) Leaks in a pipeline typically find their paths to the ground surface; however, the exact location of leakage in the pipeline may not be at the point where it surfaces. Leakage of pipeline under pressure typically generates a sound related to the turbulence at the orifice that is detectable by trained ears when sources of other noise are absent. Walking the pipeline alignment during the day for visual signs of leakage or during the night for leakage noise has proven useful. Ground Microphones (Usage: Medium) Ground microphones are acoustic leak detection sensors that locate leaks from the ground surface by detecting the distinct acoustic signal generated by the pressurized water leaking from the pipe. Ground microphone systems include the ground microphone, a sensor, and headphones. Correlator Systems (Usage: Low) A correlator system has multiple acoustic leak detection sensors that identify leaks by detecting the acoustic signal generated by pressurized water leaking from the pipe, and locate the leak by comparing the arrival time of the acoustic signal to the different sensors. The sensors are placed on the pipe wall or inserted into the stream at different locations. The acoustic signals received by each sensor are then correlated. Correlator systems include at least two sensors, two transmitters, a receiver, and a data acquisition system. In-Line Acoustic Probes (Usage: Medium) In-line acoustic leak detection probes move through the pipeline and locate the sound generated by a leak. The intensity of the sound generated is related to leak size. These systems have very high detection accuracy. The acoustic leak detection probes are either tethered or freeswimming. Systems used for acoustic leak detection in large diameter pipelines include a tethered microphone with a radar system to locate the signal, and a microphone with GPS system placed inside a free-swimming ball. The location of the probe in the pipeline is monitored using receiver units on the ground surface. Leak locations are determined on the ground surface either by stopping the tethered probe at the leak location and marking the location on the ground surface or by correlating the acoustic and location data of untethered probes.

38 Chapter 3: Summary of Technologies 17 Infrared Thermography (Usage: Low) Infrared thermography (IR) can be used to detect pipeline leaks based on changes in temperature and emissive properties of the soil. Fluid leaking from a pipeline changes the temperature of the soil (Maser and Zarghamee 1997). IR survey systems require an infrared camera, a standard camcorder, and a means to survey the pipeline from a high elevation, e.g., a helicopter. Ground-Penetrating Radar (Usage: Low) Ground-penetrating radar (GPR) can be used to determine soil properties and the depth of buried objects based on the transmission and reflection properties of electromagnetic waves induced in the soil. The speed and amplitude of the transmitted and reflected electromagnetic waves are dependent on the dielectric constant and the conductivity of the soil and any objects within the soil. Increase in the soil moisture content causes an increase in the conductivity and the dielectric constant of the soil, resulting in decreased attenuation and velocity of the transmitted and reflected wave. The time delay and amplitude of the received signal appears as a distortion of the pipe compared to locations with dry soil (Maser and Zarghamee 1997). GPR survey systems require a radar, one or more antennas, and a data acquisition system. Advanced NDT Technologies for Condition Assessment Electromagnetic Inspection (Usage: High) Electromagnetic (EM) inspection is a nondestructive technology that can detect broken wires in PCCP and their locations, and estimate the number of broken wires. The location of broken wires along the pipe length and the number of broken wires at each location are predicted by analysis of distortions in the EM signal collected during inspection. EM inspection tools have been developed for pipes ranging in diameter from 16 inches to 252 inches for: manned and unmanned internal inspection of dewatered pipelines, unmanned internal inspection of in-service pipelines, and external inspection of in-service pipelines. The system consists of an exciter, a detector, a data acquisition system, a power supply (batteries), and an odometer all mounted on a customized tool that travels inside or outside the pipeline. Results of EM inspection can be used directly to assess the condition of a pipeline at the time of inspection and to obtain a measure of its remaining service life when used jointly with failure margin analysis to determine how close a distressed pipe with a number of broken wires and a maximum internal pressure is to failure. Prediction of distress level has been subject to uncertainties involved in the interpretation of signal distortions. The uncertainties are exceptionally higher for ECP without shorting strap. Unlike the pipes with shorting straps that show a linear relationship between the actual number of broken wires and the distortion of the signal, the pipes without shorting straps show a large distortion for a single broken wire and a lower resolution as the number of broken wires

39 18 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment increases. Another source of uncertainty is steel cylinder thickness. Electromagnetic waves are affected by the steel cylinder thickness, which typically varies along the length of the pipeline and near bends, tees, and bulkheads. Thicker steel cylinders may completely obscure signal distortions. Absence of accurate design information and pipe location can adversely influence the results of EM inspection. Additional uncertainties have been related to electromagnetic properties of the steel cylinder and the method of anchoring the prestressing wire to the concrete core and steel cylinder. The presence of shorting strap and the pipe design properties must be known prior to conducting the electromagnetic inspection. The appropriateness of EM inspection for PCCP without shorting strap should be evaluated after review of calibration results that show the actual number of broken wires and the corresponding measure of signal distortion. External EM inspection improves the resolution as it allows the use of higher frequency waves because the signal does not need to pass through the steel cylinder. High frequency waves provide improved estimation of the number of wire breaks near the pipe joints and away from the joints. Stress Wave Analysis (Usage: Low to Medium) Stress wave analysis is a group of nondestructive inspection techniques that use a controlled impact to the pipe surface to generate stress waves within the pipe wall that are detected by one or more sensors on the pipe surface spaced a known distance away from the impact location. Properties of the pipe wall and locations of defects can be determined based on the stress wave velocity and the dominant frequencies of the response. Two general types of stress wave analysis currently in use in different forms are impact echo (IE) and spectral analysis of surface waves (SASW). IE is used to identify delamination at the interface of the concrete core with either the steel cylinder or the coating. SASW is based on the premise that microcracking and cracking of concrete reduce its modulus; SASW is used to determine wave velocities in concrete, from which the modulus of concrete is determined. Over-the-line Corrosivity and Corrosion Surveys Pipe-to-Soil Potential (Usage: Medium to high) Pipe-to-soil potential measurement is an over-the-line survey used to detect areas of active corrosion by measuring the difference in potential between the soil and an electrically continuous pipeline. Potential is measured using a voltmeter with one lead connected to the pipeline and the second lead connected to an electrode that is placed on the soil over the pipeline at regular intervals. The corrosion in the pipeline occurs where current leaves the pipeline; such areas have a more negative potential than the surrounding area; therefore, areas with significantly more negative potentials relative to the surrounding areas are likely sites of active corrosion. The system for pipe-to-soil potential measurement consists of a fixed lead that is electrically connected to the pipeline, a movable lead connected to an electrode that is placed on the surface of the soil at regular intervals along the pipeline, a high impedance voltage meter, and a reliable way to measure distances along the pipeline.

40 Chapter 3: Summary of Technologies 19 Cell-to-Cell Potential Measurements (Usage: Low) Cell-to-cell potential measurement is an over-the-line survey used to detect corrosion in a pipeline that is not electrically continuous by measuring the difference in potential between locations on the surface of the soil. Potentials are measured at fixed intervals directly above the centerline of the pipeline (with reference to a stationary electrode) and at fixed distance from the pipeline centerline to determine if current flows toward or away from the pipeline. Higher negative potential at the centerline of the pipeline compared to points away from the center of pipeline is an indication of likely local corrosion. The system for cell-to-cell potential measurements consists of one stationary reference electrode, two moving electrodes, a high impedance voltage meter, and a reliable way to measure distances along the pipeline. Soil Resistivity Survey (Usage: High) Over-the-line surveys of soil resistivity can be used to identify areas where the environment may be corrosive to PCCP. Measurement of soil resistivity can be used as an initial indicator of the presence of potentially aggressive ions. Soil resistivity measurements can be made either in the laboratory using samples collected in the field or in the field using either electrodes in contact with the ground surface (Wenner four-point testing) or induction-type electromagnetic conductivity meters, which do not require direct contact with the soil. Chemical Analysis of Soil and Groundwater (Usage: High) Over-the-line surveys using chemical analyses of soil and groundwater are used to determine corrosivity of the environment to PCCP. AWWA M9 identifies environments with high chloride or sulfate content, acid conditions or dissolved carbon dioxide in the groundwater (produced from rainwater or humic acid from vegetation decay) aggressive to PCCP. Chemical analyses of soil and groundwater are generally performed in localized areas identified as containing active corrosion or as being potentially aggressive to PCCP based on over-the-line surveys. Soil and/or groundwater samples taken near the pipeline are analyzed in the laboratory to further quantify the aggressiveness of the environment toward PCCP and try to identify the cause. Protective measures or supplemental corrosion protections are generally recommended for pipes located in soils containing resistivity below 1,500 ohm-cm and more than 400 ppm water soluble chloride at the same location, soils containing over 2,000 ppm sulfates, or soils with a ph below 5. MONITORING TECHNOLOGIES Monitoring technologies in the context of this Manual are those technologies that monitor changes in the condition of the pipeline. Periodic inspection is the most common means of monitoring used, and acoustic monitoring is an advanced monitoring technology that provides direct data about the change in the condition of the pipeline. See Chapter 5 for a detailed description of acoustic monitoring.

41 20 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Periodic Inspection (Usage: High) Periodic inspection using the same technologies employed for condition assessment is the most common approach for determining changes in the condition of the pipeline. For pipeline of low criticality, periodic inspection should be performed every 10 or fewer years. For pipelines with medium to high criticality, periodic inspection should be performed every 3 to 5 years, depending on the condition of the pipeline and expected change in the condition of the pipeline. Advanced NDT Technologies for Monitoring Acoustic Monitoring (Usage: Medium) Acoustic monitoring (AM) of pipelines is a nondestructive monitoring technology in which wire break events are identified and localized as they occur in a pipeline through detection of the acoustic waves generated by a wire break. Several different AM systems have been developed including hydrophone stations, hydrophone arrays, piezoelectric sensors, and fiber optic cables. The system consists of either an array of sensors installed at discrete points on the pipe wall, tethered along a cable that is placed inside the pipe through a tap, or an optical cable placed inside the pipeline, a data acquisition system, signal processing equipment, an energy supply, and a communication system for transmitting the data collected. Use of AM alone for condition assessment is limited to the identification of pipes with higher acoustic activity than other parts of the line. Higher acoustic activity is expected in severely distressed pipes that are about to fail. The results of analysis of data collected by the authors from several utilities and major users of PCCP over a span of a decade show that for wire breaks caused by corrosion, the rate of wire break does not change significantly with the level of distress in the pipe, except for pipes in the process of rupture (Zarghamee et al. forthcoming). The rate of wire break is significantly more in pipes subjected to stray current. Integration of AM data on the rate of wire breakage with electromagnetic inspection and failure margin analysis that relates the number of broken wires to pipe proximity to rupture can provide the proper basis for predicting the remaining life to rupture for distressed pipe and thus for the pipeline. UNCERTAINTIES IN NDT TECHNOLOGIES The determination of failure margin of a distressed pipe or its failure risk cannot be performed without consideration of the uncertainties in the condition assessment technology used. In general, the NDT results are in the form of signals that need to be interpreted to detect distressed pipe or to estimate the distress level and location. The uncertainty in detection or in estimation of distress level may have two sources: (1) the inherent resolution of the NDT technology in estimating the distress level in the pipe and (2) the uncertainty in the interpretation of signals where there is good resolution of the signal. Examples of the first source of uncertainty are: uncertainty in estimating the distress level from internal inspection results; uncertainty in detecting distress near the joints from the results of electromagnetic inspection of ECP; and uncertainty in estimating the distress level from the results of electromagnetic inspection of ECP without shorting straps. An example of the second source of uncertainty is the uncertainty in interpreting the number of broken wires away from joints from the results of

42 Chapter 3: Summary of Technologies 21 electromagnetic inspection of ECP with shorting straps or LCP. Due to the inherent resolution of the technology, there may exist situations where the signal is not sensitive to distress, such as the uncertainty in estimating distress level from the results of internal inspection with limited hollow sound and longitudinal cracks, the uncertainty in detection of distress levels near the joints by electromagnetic inspection, or the uncertainty in the estimates of distress level for ECP pipe without shorting strap by electromagnetic inspection. The first uncertainty source is inherent to the technology and requires verification, such as field excavation and external inspection of a sample of pipe to determine the level of uncertainty in the results. The second uncertainty source is random in nature and should be accounted for in failure margin analysis and determination of likelihood of failure. In this case, uncertainty should be accounted for by consideration of the error in NDT from calibration testing, the corrosion condition of the wires adjacent to broken wires, and propagation rate of distress in the pipe until the pipe is reinspected or repaired. These are all random variables with mean values and standard deviations from which the likelihood of failure in future years can be determined. Table 3.1. Documented experience of utilities using technologies for condition assessment and monitoring Technology No. of Utilities Using the Technology Total Inspection Length (miles) Electromagnetic Inspection Acoustic monitoring Internal Visual and Sounding Chemical analysis of soil and groundwater In-line acoustic probes External visual and sounding 10 4 Soil resistivity Pipe-to-soil potential survey (Close Interval Potential Survey CIPS) Stress wave analysis 5 4 Wire continuity 5 1 Cell-to-cell potential survey 3 63 Correlator systems 2 17 Half-cell potential measurements 2 <1 Ground microphones 1 19

43 22 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table 3.2. Documented verification of condition assessment technologies by utilities Technology Category Electromagnetic Inspection Internal Visual and Sounding Stress Wave Analysis In-Line Leak Acoustic Detection Probes 1 Technology Commercial Name RFTC P-Wave Internal IE Sahara SmartBall No. of pipes with verified results No. (%) of false identification of good pipes (false negative) 0 (0) 12 (27) 3 (14) 0 (0) 0 (0) 0 (0) No. (%) of false identification of distressed pipes (false positive) 1 (1.7) 6 (13) 5 (23) 0 (0) 1 (33) 0 (0) No. of distress areas, e.g., BWZs, hollow sounding areas, leaks, etc No. (%) of areas with accurate estimation of distress level 42 (49) 13 (21) 13 (59) 2 (100) 0 (0) 4 (33) No. (%) of areas with overestimated distress level 33 (39) 9 (14) 6 (27) 0 (0) 1 (33) 0 (0) No. (%) of areas with under estimated distress level 10 (12) 41 (65) 3 (14) 0 (0) 0 (0) 0 (0) No. (%) of areas where predicted location Not was accurate (within 1 ft) 63 (74) 10 (16) available 2 (100) 2 (67) 12 (100) 1 Limited verification data is available for leak detection. Most published verification exercises do not quantify the leakage rate. The authors experience in several projects has shown that Sahara is highly accurate.

44 Chapter 3: Summary of Technologies 23 Internal visual inspection (Usage: High) Table 3.3. Comparison of primary characteristics of technologies for condition assessment and monitoring Technology Primary Use Major Technical Benefits Identify pipes with severe distress External visual and sounding (Usage: Medium) Wire continuity (Usage: Medium) Linear polarization/ galvanostatic pulse measurement (Usage: Low) Half-cell potential measurements (Usage: Low) Walking the line (Usage: High) Verification of nondestructive inspection results and validation of pipe design parameters Verification of nondestructive inspection results and validation of pipe design parameters Detection of active corrosion Detection of areas where corrosion of wire is more likely to occur from the exterior surface of the pipe Identify and locate leaks Can readily identify pipes with severe distress and close to failure Can be performed simultaneously with other manned internal inspection methods Direct inspection of pipe distress Allow wire continuity testing for ECP without shorting strap Can confirm mode of failure for exposed wires Can collect soil, groundwater, and coating samples for additional forensic investigation Direct measurement of the number of broken wires Confirm the results of nondestructive testing Can determine the rate of corrosion Data is not affected by wetness of concrete as half-cell potential measurement Can identify areas where wires are likely to have corrosion and need to be examined visually. Identify potential leak sites for further investigation Major Technical Limitations Cannot readily identify pipes with lower levels of distress Does not provide a direct estimate of the existing number of broken wires and their locations Subject to experience and skill of inspector Removal of coating may be required to determine extents of distress and mode of wire failure Cannot be performed on pipes with shorting straps or on lined cylinder pipe It is difficult to apply Delamination of the coating interrupts the electrical circuit of half-cell measurements Surface dielectric coatings prevent current flow and should be removed by abrasion prior to measuring half-cell potentials Subjectivity Leak detection is subject to noise from surrounding environment Cannot detect leaks in pipes under deep soil cover Access Requirements Confined space procedures must be planned, approved, and properly implemented Need dewatering to allow safe passage by inspection personnel Excavation of pipe is required Pressure reduction may be required Excavation required to expose top of pipe and removal of coating over 2 in. wide band along the pipe length No dewatering of pipeline required Excavation of pipe is required Pressure reduction may be required Excavation of pipe is required Pressure reduction may be required Pipeline remains in service No excavation required Cost (Comparative) $$ $$ to $$$ depending on excavation costs $$ to $$$ depending on excavation costs $$ to $$$ depending on excavation costs $$ to $$$ depending on excavation costs $ (continued)

45 24 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Ground microphones (Usage: Medium) Correlator (Usage: Low) In-line acoustic probes (Usage: Medium) Infrared thermography (Usage: Low) Ground penetrating radar (Usage: Low) Electromagnetic inspection (Usage: High) Identify and locate leaks Identify and locate leaks Identify and locate leaks Identify and locate leaks Identify likelihood of leaks and their likely locations from ground surface over the pipeline Identify distressed pipes and predict the number and location of broken wires Table 3.3 (Continued) Direct technology that can identify and locate leaks Direct technology that can identify and locate leaks Direct technology that can identify, locate, and quantify leaks Can detect small leaks because they travel through the pipeline very near to the leak Free-swimming probes can inspect long lengths of pipeline (10 or more miles) in one deployment Tethered probes can inspect up to 1 mile in one deployment Calibration performed by simulating leaks using existing valves Can be performed over long lengths of pipeline to identify potential leak sites for further investigation Can be performed over long lengths of pipeline to identify potential leak sites for further investigation Direct measurement of pipe distress Can accurately identify PCCP with broken wires Results can be used directly in failure margin analysis Leak detection is subject to noise from surrounding environment Cannot detect leaks in pipes under deep soil cover Sensitivity decreases with increasing pipe diameter and with increasing distance between correlators Internal pressure and fluid flow rate must be within the ranges specified by the manufacturer Indirect technology that requires further investigation to confirm presence of a leak Requires a means to survey the pipeline from a high elevation, e.g., a helicopter Indirect technology that requires further investigation to confirm presence of a leak Requires knowledge of depth of cover Uncertainty in the results is high for sporadic wire breaks and broken wire zones in close proximity of joint rings Less accuracy in pipe without shorting strap Pipeline remains in service No excavation required Pipeline remains in service Sensors can be placed on the pipe wall or inserted through the flow through taps in the pipe wall Pipeline remains in service, but pressure and/or velocity may need to be modified during inspection Tethered probes can usually be inserted into and extracted from the pipeline through a tap Free-swimming probe can be inserted into the pipeline at a tape and retrieved downstream by a net deployed downstream. Pipeline remains in service Performed over ground surface above pipeline Pipeline remains in service Manned internal inspection requires dewatering Unmanned internal and external inspections do not require dewatering External inspections require excavation $ $$ $$$ $$ $$ In-service: $$$ Dewatered: $$$$ (continued)

46 Chapter 3: Summary of Technologies 25 Stress wave analysis (Usage: Low to Medium) Pipe-to-soil potential survey (Close Interval Potential Survey CIPS) (Usage: Medium to High) Cell-to-cell potential survey (Usage: Low) Soil resistivity (Usage: High) Identify delaminations within pipe wall and condition of concrete core Detection of areas where corrosion is more likely Detection of areas where corrosion is more likely from measurements at the ground surface Assessment of soil corrosivity to PCCP Table 3.3 (Continued) IE can detect delamination within the pipe wall from the exterior or interior surface SASW can determine the elastic properties of each layer of the composite pipe wall Can be used periodically for monitoring changes purpose Can identify potentially corroding areas for further condition assessment work Can identify potentially corroding areas for further condition assessment work Can be applied to pipelines that are not electrically continuous Can be used as a first step in condition assessment either to prioritize sections for assessment or to identify areas for more detailed inspection Neither IE nor SASW detects corrosion or provides a direct estimate of the existing number of broken wires and their locations Data obtained cannot be used for pipeline asset management, must be augmented by other technologies Does not provide any direct information regarding the level of distress on the pipeline Requires that the pipeline be electrically continuous Depends on the soil moisture content and cannot be performed on dry soil Potential field around the pipe can be affected by stray currents, other buried objects, and depth of burial and other factors that affect soil resistivity Unable to detect corrosion at the bottom of the pipe in large diameter pipe Does not provide any direct information regarding the level of distress on the pipeline Depends on the soil moisture content and cannot be performed on dry soil Potential field around the pipe can be affected by stray currents, other buried objects, and depth of burial and other factors that affect soil resistivity. Unable to detect corrosion at the bottom of the pipe Does not provide any direct information regarding the level of distress on the pipeline Depends on the soil moisture content and cannot be performed on dry soil The pipe must either be dewatered for internal access or excavated for external access Require access and electrical contact to the ground surface above the pipeline Require connection to pipeline (usually done at manholes) and electrical continuity of the pipeline Pipeline remains in service Require access and electrical contact to the ground surface above the pipeline Pipeline remains in service Requires access to the ground surface above the pipeline Does not require excavation Pipeline remains in service Internal: $$$ External: $$$ depending on excavation costs $ assuming pipeline is electrically continuous $ $ (continued)

47 26 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table 3.3 (Continued) Chemical analysis of soil and groundwater (Usage: High) Periodic inspection (Usage: High) Assessment of soil and groundwater corrosivity to PCCP Determining changes in the condition of the pipeline Can be used as a first step in condition assessment either to prioritize sections for assessment or to identify areas for more detailed inspection Condition assessment technology and inspection interval may be selected based on pipeline criticality Does not provide any direct information regarding the level of distress in the pipeline Does not provide any information regarding the level of distress in the pipeline between inspections Requires localized excavation or borings to collect samples Pipeline remains in service Depends on condition assessment technologies used $ to $$ depending on the cost associated with getting soil and groundwater samples near the springline of the pipe. $ to $$$$ depending on the condition assessment technology used Allows for periodic update of the likelihood of failure Acoustic monitoring (Usage: Medium) Identify and localize wire break events as they occur in a pipeline Direct detection of wire breaks Provides information on the rate of wire breaks Identify individual pipes or sections of pipeline with high rate of wire breaks Does not provide an estimate of the existing number of broken wires and their locations Sufficiently long time of monitoring is required Filters must be used to distinguish wire break events from noise Pipeline remains in service Fiber optic cable needs to be installed inside the pipe Taps may be required for tethered array or for insertion of hydrophones Acoustic fiber optics: $$$ Others: $$ FAILURE MARGIN ANALYSIS METHODS Failure of PCCP typically involves wire breakage due to corrosion or hydrogen embrittlement, cracking of concrete core, and it may involve corrosion, thinning, perforation, or rupture of steel cylinder. Failure is progressive as it takes a long period of time from the first wire break until the number of broken wires becomes sufficiently large to result in pipe rupture. Breakage of wires should be viewed as a degradation process that may take many years. The purpose of failure margin analysis is to determine the margin to failure of distressed pipes and to prioritize pipe repairs. Failure margin analysis of distressed pipes can predict the likelihood of failure and determine repair priorities of distressed pipes from the estimated wire breaks from electromagnetic inspection data, the uncertainties in electromagnetic inspection results, and the maximum pressure (working plus transient pressure) in the pipe. There are several analysis methods that have been used in predicting failure margin of distressed pipe, estimating their remaining service life, and determining repair priorities. These technologies are discussed in the following sections and their primary characteristics are summarized in Table 3.4. Failure Margin Analysis Using Risk Curves Technology (Usage: High) Failure margin analysis evaluates the effect of broken wires on the performance of the pipe and on its margin to failure using risk curves corresponding to limit states related to serviceability, damage, and ultimate strength of the pipe with broken wires. Repair priorities are assigned to pipes with broken wires in order to identify pipes with unacceptable margin to failure

48 Chapter 3: Summary of Technologies 27 when subjected to the maximum internal pressure and gravity loads. These limit state curves are established using a model developed in part under a research program for PCCP Users Group in 2002 and 2003 (Zarghamee and Ojdrovic 2001; Zarghamee et al. 2003). The research done in support of the risk curves technology included hydrostatic pressure testing of PCCP with broken wires to failure, field inspection of pipes with broken wires, nonlinear finite element analyses to further substantiate and calibrate the model, and development of a procedure to construct the risk curves. The risk curves are the results of a deterministic structural analysis calculation that relates the maximum pressure to the effective number of wire breaks for different limit states of serviceability, damage, and strength. For a distressed pipe with known effective number of wire breaks subjected to a known maximum pressure, the risk curves show which limit states are exceeded and what the margin to failure is for the pipe. The effective number of wire breaks is the sum of the actual number of wire breaks determined from nondestructive inspection and the uncertainties in the estimation of the number of wire breaks. The maximum pressure is the sum of the actual working pressure plus transient pressure in the line. Remaining service life can be estimated as the ratio of the remaining number of wire breaks to rupture (calculated as the difference between the existing effective number of broken wires and the number of broken wires corresponding to the strength limit state for the maximum pressure in the pipe) to the expected rate of progression of wire breaks. The expected rate of wire breakage is a random variable that can be determined either experimentally using AM, calculated using historical results of condition assessment on the pipeline, or obtained from documented rates observed on similar pipelines in similar environments. Risk Ranking Index System (Usage: High) Index systems are based on subdividing the pipeline asset into different sections and determining the failure likelihood of each section by assigning weights and condition ratings to each attribute that may govern the condition of the pipeline. Examples of such attributes are design, construction, operation, and environmental factors. Any available results of corrosion surveys, inspections, and past failures can also be included in this type of analysis. Index systems have often been used to prioritize pipelines in a water system or sections of a pipeline at the beginning of a condition assessment program. Some utilities have developed index systems as measure of likelihood of rupture to be used with consequences of failure to predict the failure risk as discussed in Chapter 2. Finite Element Analysis Not Verified Experimentally (Usage: Low) Finite element analysis (FEA) is used to evaluate the effect of broken wires on stresses in concrete core and steel cylinder at various lengths of prestress loss and a constant internal pressure in the pipe. Such models simulate assumed failure processes, but none have been verified experimentally, calibrated against full-scale test results, or verified in the field by comparing to distressed pipes that are believed to be close to failure. The stress is used as measure of likelihood of failure.

49 28 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Based Solely on a Certain Number of Broken Wires (Usage: Medium) Methods using only the number of broken wires to evaluate pipe failure margin and remaining service life are subjective and are based solely on previous experience with the number of broken wires or rate of wire breakage that resulted in pipe rupture in the past. Empirical data of the number of wire breaks that caused a PCCP to fail in the past are generally used to determine the maximum tolerable number of broken wires. Alternatively, pipes are evaluated based on the rate of wire breakage and may be replaced if the observed rate increases beyond a tolerable threshold. Neural Network (Usage: Low) Neural Network, when applied to condition assessment of pipeline, is an artificial intelligence based procedure for detecting distressed pipe or estimating the distress level based on multitudes of parameters that influence the results. It differs from multivariable regression analysis as Neural Network technology learns from the data, develops its own rules that are not visible to the user, has the ability to generalize, and can cope with noise/error in the data. In contrast, regression analysis requires pre-specified equations, follows set rules, cannot be generalized and is not error tolerant. Neural Network is a generalized model that is based on a part of the data used for training, and is set up with no explicit rules. It is especially applicable to problems that require pattern recognition when exact formulation is too complex for traditional techniques. Neural Network has been used by the Great Man-Made River Project (GMRP) for analysis of acoustic monitoring data using 9 input parameters (i.e., monitoring period, pipe age, soil resistivity, pressure class, soil density, soil cover, number of wraps, wire diameter, and wire pitch) for estimating wire breaks. Fuzzy Markov Approach (Usage: Low) Failure risk can be categorized into states ranging from extremely high risk to extremely low risk. Deterioration process can be viewed as a Markov process in which the likelihood of a pipe to be in a given state at a particular time step depends only on the state of the same pipe in the previous time step. Fuzzy-based modeling is used because interpretation of pipe distress as shown by NDT results is subjective and fuzzy. The Fuzzy Markov approach to failure risk analysis was introduced by National Research Council of Canada for determining the risk of failure of a pipeline and selecting time for renewal. Fuzzy logic rules are used to couple the fuzzy consequences mass functions with fuzzy mass function of failure possibility to obtain mass functions that describe the risk of failure. The approach requires (1) conducting condition assessment and record distress indicators and interpreting them into a pipe condition rating; (2) using pipe condition rating to train a fuzzy Markov-based deterioration model and generate a risk projection for pipe life; (3) determining a maximum acceptable risk (MAR) and comparing the MAR with the risk projection and to select a time for renewal when MAR is exceeded.

50 Chapter 3: Summary of Technologies 29 Table 3.4. Comparison of primary characteristics of technologies for failure margin analysis and remaining service life estimation Technology Primary Use Major Technical Benefits Major Technical Limitations Cost (Comparative) Experimentally verified failure margin analysis (Usage: High) Failure margin analysis and remaining service life estimation Based on structural analysis, laboratory testing, and field inspection Accounts for uncertainties in electromagnetic inspection results Accounts for progression of wire breaks in future Provides a means to evaluate the Subject to uncertainties in the results of inspection and rate of wire breakage $$$$ Index system (Usage: High) Finite element analysis not verified experimentally (Usage: Low) Based solely on a certain number of broken wires (Usage: Medium) Neural Network (Usage: Low) Fuzzy Markov (Usage: Low) Determining pipeline criticality Failure risk analysis Failure risk analysis Determining pipeline criticality Determining pipeline criticality and failure risk analysis significance of inspection results Based on factors that may influence rupture Provides a measure of likelihood of failure Based on structural analysis Evaluates effect of broken wires on stresses in pipe wall Provides a subjective measure of likelihood of failure mostly based on experience It is easy to use Learns from a set of available data from pipelines with known criticality and determines criticality on other pipelines Ideally fit for gradual condition assessment of pipeline assets Uses fuzzy logic and Markov process to determine the failure risk of pipelines Ideal for determining criticality as degradation process lends itself very well to fuzzy mathematics Not based on direct measurements of distress Not based on structural analysis of distressed pipe Not verified or calibrated by laboratory testing of distressed pipe to rupture or by field inspection of near failure distressed pipe Not clear how uncertainties in nondestructive testing results are accounted for Lacks basis in structural analysis, laboratory testing, or field calibration The technology is at its inception The technology is at its inception $ $$$ $ $$$ $$ COST The cost of condition assessment and monitoring varies widely depending on the technology selected, length of inspection, pipe diameter, pipeline accessibility, and numerous other factors. Table 3.5 below provides approximate costs for use of various technologies based on utility experiences collected during industry survey (Appendices A and B). (Owing to absence of reliable information, valve assessment cost is not shown in Table 3.5 and should be estimated for the prevailing conditions.)

51 30 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table 3.5. Approximate costs of condition assessment, monitoring, and failure margin analysis/service life estimation based on utility experiences Inspection Technology Unit Approximate Cost 1 Comments Condition Assessment Dewatering per mile per in. diameter $300 $500 Internal visual and sounding inspection per mile $2k $3k Excluding dewatering and mobilization/demobilization External visual and sounding per pipe $10k Including excavation inspection Electromagnetic per mile $12.5k $56 Excluding dewatering (if needed) In-line acoustic leak detection per mile $11k $23k Corrosion monitoring and maintenance per mile per year $5k Stray current testing, CP maintenance and upgrades Over-the-line corrosion/ per mile $0.5k $3k corrosivity survey Acoustic Fiber Optic per mile per year $70k $170k Including installation, equipment, and monitoring, but not dewatering Hydrophone Array Installation Cost Hydrophone Station Monitoring Cost per mile per year $70k Including installation of hydrophones and monitoring per mile per 6 months $30k Including installation Failure Margin Analysis / Service Life Estimation Experimentally verified failure margin analysis per mile $7k $29k Cost depends on the mileage and distress level Finite element analysis not per pipe design $5k $7.5k verified experimentally Pipeline Decay Index per mile $10k Based solely on the number of broken wires per mile Minimal Very low cost beyond the cost of inspection and/or monitoring 1 Costs are based on industry survey and reflect utility experiences under conditions that may differ significantly from typical projects.

52 CHAPTER 4: CONDITION ASSESSMENT TECHNOLOGIES INTERNAL INSPECTION Description Definition The purpose of internal inspection is to identify and document visible cracks (location, geometry, length and width) existing on the inside surface of the pipe, joint openings, and hollow sounding areas of the inner concrete core when sounded using a light hammer (generally 1 to 2 pounds). History Internal visual inspection has been used for condition assessment of PCCP pipelines since the late 1980s and early 1990s and continues to be a useful supplement to recently developed nondestructive evaluation methods of identifying distressed pipes. Internal visual inspection as a stand-alone inspection method has been able to identify pipes containing severe loss of prestress. The accuracy of this method in detecting distressed pipes that are not on the verge of failure is not very good as it may miss less distressed pipes and it may result in numerous false positives, i.e., calling a good pipe bad, if hollow sounding and longitudinal cracking do not occur simultaneously (Zarghamee et al. 1998; Lewis and Wheatley 2003; Ojdrovic et al. 2009). Physics of Technology Failure of PCCP in a corrosive environment generally begins with corrosion of prestressing wires due to either cracking and/or debonding of the coating or permeation of chlorides through the coating. Loss of prestress occurs due to prestressing wire corrosion and breakage, followed by cracking and delamination of the concrete core as the length of prestress loss zone grows, corrosion of the steel cylinder as core crack width increases, and eventual pipe rupture. Simultaneous occurrence of longitudinal cracks (Figure 4.1) and hollow sounding of the inner concrete core are indications of advanced pipe distress and a significant loss of prestress in the pipe. Hollow-sounding areas develop when sufficient prestress loss has occurred to cause the inner concrete core to debond from the steel cylinder under internal pressure. PCCP close to rupture can be identified by internal visual and sounding inspection by locating pipes containing both longitudinal cracks and hollow sounding areas; however, pipes containing lower levels of prestress loss may not exhibit simultaneously longitudinal cracking and hollow sound. In structurally sound pipe, longitudinal cracks or hollow sound can occur without wire breaks and loss of prestress. Other types of anomalies, such as circumferential cracking and joint openings, observed during internal inspection, may or may not be indicative of damage to the PCCP (Figure 4.2). Circumferential cracks could develop in PCCP due to shrinkage of concrete, changes in temperature, settlement, or pressure induced thrust near bends. Cracking due to temperature changes or shrinkage would be distributed along the pipe length. Cracking due to pressure- 31

53 32 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment induced thrust would be concentrated near bends and may be indicative of inadequate thrust restraint design. Joint openings may occur due to pipeline thermal contraction, settlement, and movement that concentrate in the bell-and-spigot unrestrained joints, especially when joints of adjacent pipes are welded. Bell and spigot joints can accommodate some movement without leakage. If the movement becomes excessive, the joints may open sufficiently to allow leakage. Failure of PCCP may occur in a noncorrosive environment as a result of hydrogen embrittlement (HE). Wires that fail due to HE tend to develop breaks that are scattered along the pipe length and around the circumference. Since the breaks typically do not coalesce, pipe suffering from HE do not exhibit hollow sounding areas and longitudinal cracks as observed in pipes subject to corrosion. PCCP with HE induced wire breaks retain a portion of the prestress as long as the breaks remain scattered. If the breaks begin to coalesce, failure may occur rapidly. Distress in PCCP subjected to HE is difficult to identify by internal inspection alone. Inspection Process Preparation of the pipeline is required prior to any internal inspection. Existing access points must be identified and additional access points must be constructed as needed. The pipeline must be sufficiently dewatered to allow safe passage by inspection personnel. Confined space procedures must be planned and approved prior to inspection and properly implemented during inspection. The visual and sounding inspection process involves identifying any anomalies (e.g., longitudinal or circumferential cracks, joint openings, leaks, spalled concrete, etc.) on the pipe inner concrete core and sounding the inner concrete core using a 1- to 2-pound hammer, or similar, to locate areas of hollow sounding. Observations should be photographed and recorded by field notes and sketches. Pipe numbers and/or distances from the nearest pipeline features should be recorded along with any observations to assist with location of the pipe during future inspections or repair work. Benefits and Issues The benefits of the technology can be summarized as follows: Pipes with significant loss of prestress can be reliably identified. The cost of internal visual and sounding inspection is significantly less than the cost of internal inspections using electromagnetic or impact echo technologies. Internal visual and sounding inspection can be performed in dewatered pipelines simultaneously with electromagnetic inspection to identify and document the condition of the highly distressed pipes found visually or from examination of electromagnetic signal distortions. The issues with this technology include: Pipes containing levels of prestress loss lower than that required to cause longitudinal cracking and hollow sounding areas cannot be reliably detected by internal inspection.

54 Chapter 4: Condition Assessment Technologies 33 Pipes containing hollow sounding areas of the inner concrete core caused by mechanisms other than loss of prestress may be incorrectly identified as areas of broken wires. Hollow sounding inner core may occur in pipes without any prestress loss due to shrinkage in low prestress ECP, differential shrinkage of inner concrete core, dents in the steel cylinder, or other anomalies. Internal visual and sounding inspection does not provide a direct estimate of the existing number of broken wires and their locations. Figure 4.1. Internal visual and sounding inspection of PCCP detected a longitudinal crack in the inner concrete core Figure 4.2. Leak detected during internal visual and sounding inspection of PCCP

55 34 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Application Several example applications where internal visual and sounding inspection was conducted and compared to external inspection results presented below. 1. Supplemental Tunnel and Aqueduct, Providence, Rhode Island: Internal visual and sounding inspection was used in conjunction with electromagnetic inspection, external inspection, and failure margin analysis to identify distressed pipes and prioritize repairs along 9 miles of 78-inch- and 102 inch-diameter ECP. External inspection included wire continuity testing and visual inspection of the exterior of inch-diameter PCCP believed to be distressed based on internal inspection and electromagnetic inspection results. The results of continuity testing identified 10 pipes with and 7 without broken wires. Internal visual and sounding inspection identified 7 of 10 pipes with broken wires and 2 of 7 pipes with no broken wires. Three pipes with broken wires were not identified by internal inspection, and 5 pipes with no broken wires were falsely identified as having broken wires. The criterion for existence of wire break was presence of hollow sounding areas of the inner concrete core, and not necessarily accompanied by longitudinal cracking. Based on the inspection results, the paper concludes that internal inspection can identify the most-severely-distressed pipes, but may result in false positive identifications if hollow sounding areas of the inner core and longitudinal cracking do not occur simultaneously (Ojdrovic et al. 2009). 2. Baltimore County Water Transmission Main, Baltimore, Maryland: A 7,800-foot portion of the 48-inch-diameter PCCP pipeline was inspected internally using visual and sounding inspection and electromagnetic technology in November Four pipes were identified with both longitudinal cracks and hollow sounding areas. One additional pipe was identified with a 6-inch-longitudinal crack, but no further action was recommended on this pipe as no hollow sound was detected. The 4 distressed pipes identified by internal visual and sounding inspection were also identified by electromagnetic inspection as containing large numbers of broken wires and were, therefore, selected for replacement. Subsequent forensic investigation of the 4 pipes confirmed that 3 of the 4 did contain large numbers of broken wires, and 1 pipe contained only 2 broken wires, but had significant corrosion of the steel cylinder and a splice in the prestressing wire (Donaldson et al. 2006). 3. South Plainfield Water Transmission Main, Plainfield, New Jersey: A PCCP condition assessment and asset management program was initiated after Elizabethtown Water Company detected a leak in the water transmission main in October Investigation of the leak determined that the cause was corrosion of the steel cylinder exposed by removal of the inner concrete core for internal field welding of the joint. Internal visual and sounding inspection and P-Wave electromagnetic inspection were performed in November Visual inspection identified 9 additional exposed field welded joints and 1 pipe with longitudinal cracks, but without hollow sounding areas of the inner core. P-Wave inspection identified 9 pipes with broken prestressing wires, including the pipe with longitudinal cracking. External inspection of the pipe containing longitudinal cracks revealed

56 Chapter 4: Condition Assessment Technologies 35 longitudinal cracks in the coating. No hollow sounding of coating was noticed. Coating was locally removed near the longitudinal crack to expose 11 prestressing wires within an 8-inch by 13-inch window, and 10 of the 11 wires were broken (brittle fracture) with 1 wire containing 2 breaks within the opening. Based on inspection results, 400 feet of PCCP near 2 90-degree bends were replaced with new PCCP, and 1 pipe was repaired externally by application of post-tensioning strands. Verification of broken wires was not performed on the externally repaired pipe other than identification of a hollow sounding area approximately 8 inches by 16 inches (Lewis and Schaefer 2004). 4. Large diameter PCCP, San Diego, CA (SDCWA): As a part of their proactive aqueduct protection plan, SDCWA performed internal visual and sounding inspection of their large diameter PCCP to identify potentially deteriorating pipe. The sounding was performed using a hollow aluminum rod with steel caps. Based on previous experience with their failed pipes, moderate hollow sounding areas were defined as between 0.24 and 0.56 square meters without visible cracking, and severe hollowsounding areas were defined as greater than 0.56 square meters with visible cracking. Pipes with severe hollow-sounding areas were excavated for external inspection. External inspection found severe corrosion of the prestressing wires on a pipe where internal inspection identified a 1.5 square meter hollow-sounding area accompanied by longitudinal cracking. Generally, a severe hollow sounding area combined with longitudinal and circumferential cracking would cause pipe repair or replacement (Galleher and Stift 1998). Internal Visual Inspection Summary Internal visual and sounding inspection can be used to identify cracks and hollow sounding areas in the inner concrete core, joint openings, and other anomalies on the interior surface of the pipe. This method of inspection has been used since the late 1980s and early 1990s and continues to be used to identify highly distressed pipes and to supplement other nondestructive condition assessment methods. Internal visual and sounding inspection can identify pipes in advanced state of distress based on the simultaneous occurrence of longitudinal cracks and hollow sounding of the inner concrete core. Observations such as circumferential cracking, joint openings, and hollow sounding inner core in absence of longitudinal cracking need to be evaluated on an individual basis as these anomalies might not be indicative of significant distress. Preparation of the pipeline for internal inspection includes identifying access points, dewatering to allow safe passage by inspectors, and implementing planned and approved confined space procedures.

57 36 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment EXTERNAL INSPECTION OF PIPE SURFACE Description Definition External inspection verifies nondestructive inspection and failure margin analysis results, validates assumptions on pipe design parameters, and enables forensic investigation to evaluate the cause of wire breakage and pipe distress. History External inspection has been an integral part of condition assessment since internal inspection of PCCP pipelines began. External inspection has been and continues to be the most reliable way to verify the results of nondestructive evaluation methods. Physics of Technology Visual inspection and sounding: Failure of PCCP in a corrosive environment generally begins with loss of prestress due to prestressing wire corrosion and breakage. Due to the expansive nature of the corrosion process, delamination and cracking of the coating often occur in areas of corroded prestressing wires. Visual inspection and sounding of the coating can identify these areas for further investigation. Mode of wire breakage (corrosion or embrittlement) can be determined by visual inspection of exposed prestressing wires. Wire continuity measurements: Continuity of the prestressing wire for non-shorting strap embedded cylinder pipe (ECP) can be determined by measuring resistance between adjacent wire wraps. A break in the prestressing wire results in a high measured resistance. Wire continuity measurements cannot be performed on ECP with shorting straps or LCP due to the electrical continuity of the wires provided by the shorting strap or cylinder, respectively. Half-cell potential measurements: Corrosion occurs when a metal submerged in an electrolyte develops areas of differing electrical potential and undergoes anodic and cathodic reactions. The anodic reaction is one of oxidation (production of electrons) while the cathodic reaction is one of reduction (consumption of electrons), resulting in electron current flow from the anode to the cathode, i.e., conventional current flow from the cathode to the anode. It is not practical to directly measure the current flow or the potential that drives it, so the potential is measured relative to a reference electrode (Suprenant 1992). Active corrosion can be detected by measuring the electrical potential at various points on the coating surface relative to the potential of a reference electrode. The magnitude of the potential and the potential gradient can be used to determine the probability of active corrosion at the time of the measurement and identify areas for further investigation. Linear polarization resistance (LPR) and galvanostatic pulse measurement (GPM): LPR and GPM can be used to locate active corrosion in a pipe and evaluate the corrosion rate. Both methods are based on the relationship between electrochemical potential, current flow, and time. LPR works by inducing a potential between a reference electrode and the pipe and measuring the current flow, which is proportional to the corrosion rate. GPM works by inducing a short

58 Chapter 4: Condition Assessment Technologies 37 duration anodic current pulse into the wire and calculating the corrosion rate from changes in DC polarization resistance over time and the applied current. Petrographic analysis and material testing: The ability of coating to protect the prestressing wires from the surrounding environment may be inadequate as a result of either degradation due to long-term exposure to an aggressive environment or poor initial material properties. Degradation of coating may result from environmental factors such as acid attack, carbonation/bicarbonation, sulfate attack, or chloride migration (Scali et al. 2003). Poor initial material properties may include high water-to-cementitious-material ratio (w/cm), low density, or high permeability. System Components Visual inspection and sounding: External visual inspection and sounding requires a lightweight (typically 1 to 2 pounds) hammer, means to document observations, equipment to remove coating samples (if needed), and storage containers for samples collected. Wire continuity measurements: Wire continuity testing requires a digital multimeter with test leads, equipment to remove a strip of coating along the top of the pipe to expose the prestressing wires, and equipment to clean the prestressing to obtain a bright, clean metal surface to allow good contact between the probes of the multimeter and the wire. Half-cell potential measurements: The apparatus for half-cell potential measurement systems is defined by ASTM C876 and consists of a reference electrode, an electrical junction device, an electrical contact solution, a volt meter, and electrical lead wires. Linear polarization resistance and galvanostatic pulse measurement: Both LPR and GPM require a reference electrode, an electrical junction device, electrical contact solution, and a connection to the prestressing wire. Additionally, LPR requires equipment capable of applying a potential difference between the prestressing wire and the reference electrode and measuring resulting changes in the current, and GPM requires equipment capable of inducing a current pulse and measuring the resulting changes in potential with time between the wire and the reference electrode, Petrographic analysis and material testing: The required apparatus for petrographic analysis includes equipment to prepare and examine samples. Equipment required for preparation of polished sections includes a diamond saw, a lap wheel, a polishing wheel, and an oven. Thin sections are often sent out for preparation by specialized firms. Equipment required for examination of samples includes a stereomicroscope, a polarizing microscope, microscope lamps, and calibrated immersion media (ASTM C ). The required apparatus for material test will vary widely depending on the tests performed and will be specified by the applicable testing standard. System Types System types do not vary widely. Inspection Process Visual inspection and sounding: Locate the pipe by surveying, using GPS, or with respect to visible features; excavate the pipe to at least springline; and clean the outside surface

59 38 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment (typically done by a contractor). Due to the risk of rupture of a pipe under pressure with an unknown level of distress, the pipe should be depressurized prior to excavation or a failure margin analysis should be performed to determine the level of distress that may result in rupture under pressure. Visually inspect and sound the exposed surface of the pipe. Record the locations and dimensions of cracks, hollow-sounding areas, corrosion marks, coating and wire damage (if any), and other anomalies. Photograph the pipe exterior surface, and document overall and close-up details of anomalies. Select areas for removal of coating in the hollowsounding area and collect samples for laboratory analysis. Inspect and record the condition of wires within the opening in the coating. Measure and record wire diameter and spacing. Photograph ends of broken wires and collect samples of broken wires (about 2 feet in length). Observe and record location and width of cracks on the outside of the concrete core. If there are longitudinal cracks in the outer concrete core that are wider than inches, or if there is visible corrosion mark at the crack, expose a small area of the steel cylinder for inspection at the widest crack location (Figure 4.3). Use a 3- to 4-inch diameter core bit to core to within 0.5 to 1 inch of the steel cylinder. Chip the rest of the outer core using a cold chisel and hammer very carefully. Do not damage or puncture the steel cylinder. Note any corrosion stains on the surface of the core in contact with the steel cylinder and on crack faces. Use an ultrasonic thickness gauge to measure the thickness of the steel cylinder. Examine and photograph the condition of the steel cylinder. Wire continuity measurements: Expose a 2-foot width on the top of the pipe along its entire length. Since the excavation only exposes the top of the pipe, wire continuity measurements can often be performed with the pipeline in service, but a failure margin analysis should be performed to determine the level of distress that may result in rupture under pressure. Remove the coating at the crown of the pipe to expose the prestressing wires in a strip along the full length of the pipe and approximately 2 inches wide circumferentially (Figure 4.4). If the wire has surface rust, remove the rust using sand paper or a wire wheel to obtain a bright, clean surface to allow good contact between the probes of the multimeter and the wire. Set the multimeter on the lowest full-scale resistance range. Starting with the negative probe on the upstream wire and the positive probe on the downstream wire, contact the probes with selected wire wraps and measure and record the resistance in ohms, and remeasure and record the resistance value with reverse polarity of probes. Half-cell potential measurements: Measurement locations are generally located on a grid of points spaced 1 foot apart (Figure 4.5). A contact solution must be applied to the pipe surface at each measurement location to reduce the resistivity of the coating. In order to complete the electrical circuit, a prestressing wire must be exposed at one location on the pipe for connection of one lead of the voltmeter. The second lead of the voltmeter is connected to the reference electrode. Electrical continuity must be maintained throughout the circuit at each measurement location. For this reason, half-cell potential measurements are better suited for LCP compared to ECP due to the electrical continuity provided by the steel cylinder. Interpretation of half-cell potential results for buried structures is more complicated than for above-ground structures. The guidelines for interpretation provided in ASTM C were developed empirically for bridge decks and are not directly applicable to all structures. Half-cell potential readings are influenced by temperature, moisture, delaminations, surface coatings, and many other factors as discussed in ASTM C (2009) and TRL Application Guide 9. Linear polarization resistance and galvanostatic pulse measurement: LPR techniques induce various known potentials between the pipe and the reference electrode and measure the

60 Chapter 4: Condition Assessment Technologies 39 current at each potential. The corrosion rate is estimated based on the slope of the potential versus current curve. Galvanostatic pulse measurements induce a known current pulse and measure the potential between the pipe and the reference electrode during application of the current. The measured potential is a function of the applied current, the material electrical resistance, and the polarization resistance. The portion of the curve corresponding to polarization resistance will have a very shallow slope and reach a steady-state potential for active corrosion, and the curve will have a steeper slope and may not reach a steady-state potential for passive reinforcement (Frolund et al. 2002). The polarization resistance can be used to calculate the corrosion rate using the Stern-Geary equation. Petrographic analysis and material testing: Petrographic analysis of coating from PCCP includes visual and microscopic examinations on polished and/or ultrathin sections and, in some cases, scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDXS). Guidelines for performing petrographic analyses are provided in ASTM C856. Samples are cut and polished in order to conduct microscopic examinations to evaluate the general composition, condition, and overall quality of the coating. Ultrathin (< 25 µm), blue-dyed epoxy impregnated sections (Figure 4.6) are prepared from selected samples for the purpose of conducing a moredetailed petrographic examination of the coating with the aid of a polarized, transmitted light microscope at increased magnifications (Scali et al. 2003). Material testing of samples of coating includes testing physical properties such as absorption, porosity, and density in accordance with ASTM C642 (2006) and measuring chloride content in accordance with ASTM C1152 (2004), ASTM C1218 (1999 [2008]), or AASHTO T- 260 (2008). Chloride contents are measured at the inner and outer surfaces of the coating in order to evaluate the migration of chlorides through the thickness of the coating. Benefits and Issues The benefits of the technology can be summarized as follows: External visual and sounding inspection can identify areas of cracking and/or hollow sounding coating. The inspection can be extended to confirm the existence of wire corrosion and breaks and cracks in the concrete core, and determine the mode of wire breakage. Wire continuity measurements can directly determine the number of broken prestressing wires on ECP without shorting straps. Excavation of the pipeline is an opportunity for forensic evaluation of the root cause of PCCP deterioration, including collection of samples of coating, soil, and groundwater for laboratory analysis. Half-cell potential measurements, LPR measurements, and GPM can identify areas where active corrosion is occurring. LPR measurements and GPM can be used to estimate the corrosion rate. LPR measurements and GPM can measure the corrosion rate when concrete is wet. Petrographic analysis and material testing provide information regarding coating quality and degradation mechanisms that is useful for condition assessment and forensic analyses.

61 40 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment The issues with this technology include: External inspection requires excavation of buried PCCP. Wire continuity measurement requires removal of a strip of coating. Wire continuity measurement does not work on ECP with shorting straps or LCP. HCP, LPR, and GPM cannot detect areas of distress on pipes caused by hydrogen embrittlement. Delamination of the coating changes the electrical circuit of HCP, LPR, and GPM by making the current path between the steel and the electrode much longer. Delaminations are identified by sounding of the coating. Wire breaks in ECP without shorting strap affects measurements made by HCP, LPR, and GPM. Surface coatings may prevent current flow in half-cell potential measurement, LPR measurements, and GPM. Surface coatings should be removed by abrasion prior to measuring potentials. Samples of coating must be removed from the pipe in order to perform petrographic analysis and material testing. Areas of removed mortar must be patched prior to backfilling the pipe. Figure 4.3. Hole cut in the outer core of PCCP showing crack going completely through the outer core, exposing the steel cylinder to the environment The steel cylinder shows minor surface corrosion and no major pitting.

62 Chapter 4: Condition Assessment Technologies 41 Figure 4.4. Wire continuity measurements along the top of PCCP Multimeter shows high resistance, indicative of broken prestressing wire. Figure 4.5. Half-cell potential measurement being taken on PCCP Electrical connection to the prestressing wire visible near joint

63 42 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Leaching Figure 4.6. Magnified (100X) image of coating of a PCCP showing moderate to severe alteration in microstructure resulting from leaching due to acid attack, dissolution, and bicarbonation of the paste matrix (light-colored areas) Application to 201 inch diameter PCCP, California: Metropolitan Water District of Southern California (MWDSC) has performed forensic examinations since 1989 on PCCP suspected of damage. Examinations have included visual inspection, sounding of the coating, measurements of corrosion potentials on the mortar, electrical continuity measurements on prestressing wires, corrosion loss measurements, mechanical and metallurgical testing of prestressing wires, and chemical analysis of mortar, concrete, and soil samples. Results of forensic examinations have identified causes of PCCP deterioration, exposed the benefits and limitations of inspection technologies, and confirmed the value in utilizing multiple inspection technologies (Harren and McReynolds 2010). 2. Central Pipeline, Santa Clara Valley, California: Five pipes were selected for external inspection based on the results of electromagnetic inspection and failure risk analysis. External inspection consisted of wire continuity measurements, visual inspection and sounding of the exposed pipe surface, and measurement of coating thickness, soil cover height, and prestressing wire diameter and spacing. Samples of coating, in-situ soil, and backfill were collected for laboratory analysis. Based on the results of field inspection, laboratory testing, and failure risk analysis, SCVWD determined that repairs were unnecessary and monitoring the line was adequate. SCVWD considers the $330,000 spent to validate electromagnetic results and evaluate the failure risk of the pipeline a good investment compared to the costs of unnecessarily repairing the 59 pipes identified as distressed by electromagnetic inspection (Dion and Zarghamee 2008). 3. Bay Division Pipeline No. 4 (SFPUC): Three ECPs without shorting strap where RFTC showed high distress were excavated for external verification. External visual

64 Chapter 4: Condition Assessment Technologies 43 inspection showed no sign of distress and sounding showed no hollow-sounding area. X-ray inspection of a segment of a pipe where high distress was observed showed only a few random broken wires. Wire continuity measurements confirm absence of high distress. The overestimation of the number of broken wires was attributed to the absence of shorting strap. The pipeline was returned to service without repairs (communication between Mehdi Zarghamee and Jonathan Chow of SFPUC). 4. Supplemental Tunnel and Aqueduct, Providence, Rhode Island: External inspection was performed on a total of 28 pipes that had been identified as containing broken prestressing wires using RFTC and/or P-Wave along 9 miles of 78- and 102-inch diameter ECP. External inspection included wire continuity measurements and visual and sounding of the exposed pipe surface. Results of wire continuity measurements were used to evaluate the electromagnetic inspection results and analyze the risk of pipe failure. Detailed external inspection was performed on 6 distressed pipes containing broken prestressing wires and large areas of delaminated coating. Areas of the outer concrete core were locally removed to inspect the steel cylinder on 2 pipes containing visible longitudinal cracks in the outer core. Little to no corrosion was observed beneath a inch-wide crack and minor corrosion was observed beneath a inch-wide crack. Petrographic analysis of the coating showed that heavily distressed pipes suffered from mild to severe acid attack evidenced by leaching and dissolution of the cement paste resulting in bicarbonation and loss of paste. Further testing showed that the coating consisted of a good mix with a low water-to-cementitious-material ratio, but had high absorption. Tensile and torsion testing of the prestressing wires showed that the wires on the 78-inch diameter pipe were susceptible to embrittlement. Testing of the soil and groundwater showed the environment was acidic (Ojdrovic et al. 2009). 5. Muskegon County Wastewater Management System, Muskegon, Michigan: External inspection was performed on the 11-mile-long, 66-inch-diameter PCCP line that could not be taken out of service without severe economic and environmental impacts. Additionally, the pipeline did not have any manholes along its length and no part of it could be isolated. A condition assessment program was developed using test pits, material testing, soil resistivity survey, soil chemical analysis, geotechnical investigation, hydraulic surge analysis, and structural analysis. Fourteen test pits were located along the pipeline at areas of high soil corrosivity, near bends, and at areas of typical conditions to establish baseline condition. Assessment at each test pit location included visual and sounding inspection of the coating, localized removal of the coating for inspection of the prestressing wires, and removal of coating and prestressing wire samples for laboratory analysis (Ojdrovic et al. 2001). External Inspection of Pipe Surface Summary External inspection can include visual and sounding inspection, wire continuity measurements, and half-cell potential, linear polarization testing, and petrography of coating. Results of external inspection can be used to verify internal nondestructive inspection results, confirm pipe design parameters, and perform forensic investigation to evaluate the cause of wire breakage and pipe distress. Wire continuity is a direct method for detecting a wire break and can be used to identify all broken wires without the need to remove the coating on ECP without

65 44 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment shorting straps. Potential measurements of the pipe on the exterior surface can identify areas where corrosion likelihood is the highest for further exploration by coating removal and visual inspection of wire condition. Excavation of the pipeline is an opportunity to collect samples of coating, soil, and groundwater for laboratory analysis. LEAK DETECTION Description Definition Locations of leaks in buried PCCP lines can be identified by visual observation, detection of acoustics generated by leakage, detection of temperature changes of soil caused by leak water properties, and radar reflection patterns in the vicinity of the leak as soil conductivity changes by moisture. Acoustic leak detection systems have been used along the ground surface over the pipeline and have been deployed inside the pipeline to directly detect leaks during operation. Thermal scans and ground penetrating radar (GPR) have been used to survey the pipeline and surrounding soil from the ground surface to identify potential leak locations. History The earliest and simplest methods of detecting leaks in a pressurized pipeline include visual observation of water over the pipeline and listening for the sound of leakage, without the use of equipment, during times of low ambient noise. Ground microphones have been used for over 50 years to locate leaks by detecting and identifying the sound generated as fluid escapes from a pressurized pipe. In the 1970s, Water Research Center (WRC) in the United Kingdom developed leak noise correlator that employed the same principle to detect and locate leaks by monitoring the pipeline at two locations and correlating the acoustic signals. In the 1990s, WRC developed Sahara inline, tethered acoustic leak detection system for use in large diameter pipelines where correlator was less effective (Webb et al. 2009, Larsen et al. 2005). Pure Technologies developed SmartBall inline, free-swimming acoustic leak detection system and began commercial use in 2007 (Elliot and Kler 2008). Physics of Technology Walking the line: Visual observation and listening, without use of any equipment, can be used for leak detection. A leak in a pressurized pipe may result in visual indications on the ground surface over the pipeline such as unexpected water ponding, erosion of soil, or water bubbling from the ground surface. Water leaking from a pressurized pipe makes a sound that may be detected for pipes under shallow soil cover from the ground surface by ear of a trained inspector. Acoustic leak detection: Acoustic leak detection technologies can locate leaks by detecting the distinct sound created by fluid escaping from a pressurized vessel. The acoustic signal is detected from the ground surface using ground microphones for pipe under shallow soil cover. The location of leaks in small diameter pipelines is determined by correlating the acoustic

66 Chapter 4: Condition Assessment Technologies 45 signals measured from two locations along the pipeline. In large diameter pipelines, correlator is less effective due to attenuation of the acoustic signal (Webb et al. 2009). Acoustic sensors deployed inside the pressurized pipeline are better suited for detecting leaks in large diameter pipelines because they come within close proximity of the leak as they travel through the pipeline. Location of leaks is determined using in-line acoustic sensors with a tracking radar system on the ground surface. Infrared thermography: IR can be used to detect pipeline leaks or voids in the soil based on changes in temperature and emissive properties of the soil. Fluid leaking from a pipeline changes the local temperature of the soil, which changes the IR emissivity of the soil (Maser and Zarghamee 1997). The IR radiation can be detected using an infrared camera. Ground penetrating radar: GPR can be used to determine soil conductivity and the depth of buried objects based on the transmission and reflection properties of electromagnetic waves propagated into the soil. Increase in the soil moisture content cause an increase in the conductivity of the soil, which can be measured by GPR (Maser and Zarghamee 1997). System Components Walking the line: No special equipment is required. Acoustic leak detection: In-line acoustic leak detection systems consist of an acoustic sensor, a transmitter, a receiver, and a data acquisition system. Correlator systems include at least two accelerometers, two transmitters, a receiver, and a data acquisition system. Ground microphone systems include the ground microphone, a sensor, and headphones. Infrared thermography: IR survey systems require an infrared camera, a standard camcorder, and a means to survey the pipeline from a high elevation, e.g., a helicopter. Ground penetrating radar: GPR survey systems require radar, at least one antenna, a data acquisition system, and a means to move the equipment over the pipeline. System Types In-line acoustic leak detection systems are either tethered or free-swimming probes. Sahara is a commonly used tethered system, and SmartBall is a commonly used free-swimming system. Systems for correlators, ground microphones, IR surveys, and GPR surveys do not vary widely. Inspection Process Walking the line: Visual observation and listening can be performed while walking the entire length of the pipeline and looking for water boils on the ground surface or on the slopes of nearby embankments and listening for sound of leakage. The water needs to be tested to verify its source. Acoustic leak detection: Acoustic leak detection microphones are placed on the ground surface over the pipeline, inserted into the pipeline at discrete locations, or deployed into inservice pipelines (in-line probes). Ground microphones locate leaks from the ground surface by detecting the distinct acoustic signal generated by pressurized water leaking from the pipe. Correlators are placed on the outside pipe wall or inserted into the pipeline through

67 46 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment appurtenances at two or more locations and leaks are located based on the acoustic signals received by each correlator. In-line acoustic leak detection probes move through the pipeline and an onboard acoustic sensor monitors for the sound generated by a leak. Tethered and free-swimming in-line acoustic leak detection probes are currently in use. Figure 4.7 shows a schematic of the Sahara system and Figure 4.8 shows the SmartBall system. The location of the probe in the pipeline is monitored using receiver units on the ground surface. Leak locations are determined on the ground surface by either stopping the tethered probe at the leak location or by correlating the acoustic and location data of untethered probes. Infrared thermography: IR surveys can be performed using an infrared camera from a helicopter early in the morning after a period of about one week without rain. This scenario ensures that no solar interference influences the measurements and that any indication of soil moisture along the pipeline can be attributed to leakage from the buried pipe. A standard video can be recorded using a camcorder mounted on top of the infrared camera to identify any features along the ground surface that may produce anomalies in the IR images (Figure 4.9). The IR images must be analyzed to identify areas of anomalous signal where additional inspection is required to determine the presence of a leak. Ground penetrating radar: GPR surveys are generally performed along the length of the pipe to identify locations for a more detailed survey transverse to the pipeline. Longitudinal GPR surveys over long lengths of pipeline may be performed by attaching multiple antennas (spaced 3 to 4 feet apart, transverse to the pipeline) to an inspection vehicle that can move along the pipeline. Transverse GPR surveys are performed by moving the antennas along the ground surface from one side of the pipe to the other. Benefits and Issues Benefits of leak detection systems are as follows: The pipeline remains in service during inspection. Acoustic leak detection is a direct technology that can identify and quantify leaks. Sahara probes can be inserted into and extracted from the pipeline through an existing tap 2-inch diameter or larger. SmartBall can be inserted and extracted through existing taps 4-inch diameter or larger. In-line acoustic probes can detect small leaks because they travel through the pipeline very near to the leak. Free-swimming in-line acoustic probes can be used to inspect long lengths of pipeline (on the order of 10 or more miles) in one deployment. Tethered in-line acoustic probes can be used with a winch system to inspect pressurized pipelines with low or zero flow velocity. Calibration of acoustic leak detection systems can be performed by simulating leaks using existing valves. IR and GPR surveys can be performed over long lengths of pipeline to identify potential leak sites for further investigation. Issues with leak detection systems include the following:

68 Chapter 4: Condition Assessment Technologies 47 Leaks identified by walking the surface may not be due to pipe leakage at the point of water boils. IR and GPR surveys are indirect leak detection technologies that require further investigation to confirm presence of a leak. Sensitivity of correlators decreases with increasing pipe diameter and with increasing distance between correlators. For in-line acoustic probes, the internal pressure and fluid flow rate must be within the ranges specified by the manufacturer. Depending on pipeline configuration, installation of additional taps may be required for correlators or in-line acoustic probes. SmartBall may be lost if retrieval is not successful. Source: Webb et al. 2009, with permission from ASCE Figure 4.7. Tethered Sahara acoustic leak detection system Source: Murray et al. 2009, with permission from ASCE Figure 4.8. Free-swimming SmartBall acoustic leak detection system

69 48 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Source: Maser and Zarghamee 1997, with permission from ASCE Figure 4.9. Comparison of images from infrared and standard video collected during IR survey Application to 42 inch diameter PCCP Lines, San Diego County, California: Field performance of an un-tethered, free-swimming acoustic leak detection system was evaluated in 3.9 miles of 30- to 42-inch-diameter pipelines by San Diego County Water Authority (SDCWA) in The device required a minimum flow rate of 0.5 fps. Receivers were located on the ground surface separated by 0.5 to 1 mile. Calibration curves were generated by holding the device in the pipeline at the retrieval outlet while various simulated leaks were generated. SDCWA simulated 3 leaks along the line and did not inform the deploying team of the size or location. The 3 leaks were detected with rates of 8, 0.75, and 3 gpm (actual simulated leakage rates not provided) (Galleher and Kurtz 2008). 2. Lake Fork Raw Water Transmission Main, Dallas, Texas: Phase I (7.3 miles) of the Lake Fork Raw Water Transmission Main was inspected for the City of Dallas Water Utilities (DWU) using Sahara leak detection in The newly constructed pipeline failed to pass hydrostatic pressure testing due to leakage that occurred when the pressure exceeded 190 psi. Since the pipeline was newly constructed, there was no flow to carry the Sahara probe through the pipeline. Sahara was deployed using a winch and a cable to pull the probe through the pipeline while a locator unit identified the probe location from the surface. Two leaks were identified (flow rate not quantified) and verified by excavation (Larsen et al. 2005) to 54 inch diameter PCCP Lines, Bay County, Florida: Four pipelines (3 PCCP and 1 HDPE) were inspected using SmartBall. No major modifications to the pipeline were required for the inspection. The SmartBall was inserted through existing 4-inch-diameter outlets. The total length of PCCP inspected was 15.4 miles. Eight leaks were detected and confirmed using ground microphones, which were applicable because of the shallow burial depth of the pipes (Murray et al. 2009). 4. Halifax, Nova Scotia, Canada: Aboveground leak surveys using ground microphone during the calm of the night were conducted along the alignment of LCP lines at 1 to 6- month intervals, depending on failure risk of pipe. Past experience of Halifax has

70 Chapter 4: Condition Assessment Technologies 49 confirmed that for the pressures involved, the distressed LCPs in these lines tend to leak prior to rupture. Fifteen leaks were identified using this simple leak detection method and the pipes were excavated and repaired/replaced. Five pipes ruptured during the time this method was in use (communication with Jamie Hannam of Halifax Water, 2010). 5. Hultman Aqueduct, Massachusetts: A leak survey was conducted using infrared thermography (IR) and ground penetrating radar (GPR) along the 16-mile-long 150-inch-, 138-inch-, and 84-inch-diameter AWWA C300 RCCP Hultman Aqueduct for Massachusetts Water Resources Authority to detect leaks. IR was performed from a helicopter over the entire pipeline alignment. GPR was performed longitudinally on 3.9 miles of the pipeline and transversely at 89 stations. Results of the combined IR/GPR survey were compared to the results of a visual leak survey. The leak survey identified 26 potential leak sites and 25 of these sites were included in the IR/GPR survey. Thirteen of the potential leak sites were confirmed by the IR/GPR survey, 9 were showed no evidence of leakage, and 3 could not be evaluated. Thirty-five additional potential leak sites were identified by the IR/GPR survey (Maser and Zarghamee 1997) mm diameter pipeline, City of Airdrie, Canada: 7.9 miles of PCCP inspected using SmartBall for detection and location of leaks in SmartBall was inserted into the pipeline through an existing 4-inch- diameter gate valve and was captured downstream at the metering station. Three leaks were identified ranging from 2 to 113 liters/min (0.5 to 30 gal/min). The largest leak was excavated and confirmed to be within about 8 inches of the predicted location (Elliot and Kler 2008) mm diameter pipeline, City of Calgary, Canada: 0.4 miles of PCCP was inspected using SmartBall in 2007 to determine the location of a known leak. The City had been unable to locate the leak using correlators due to noise from nearby traffic. SmartBall was inserted into and extracted from the pipeline through existing gate valves located away from the busy street to preclude the need for traffic interruption. The leak was identified and the location was marked on the ground surface the same day. The leak was excavated and confirmed to be within about 12 inches of the predicted location (Elliot and Kler 2008). Leak Detection Summary Leak detection technologies have identified and located leaks in buried PCCP based on visual sighting of water boils on the ground, changes in acoustic signal, thermal properties, and radar reflection patterns. Based on the published literature, the most widely used technologies are acoustic-based systems. Acoustic leak detection technologies consist of ground microphones, correlators, and in-line probes (tethered and free-swimming). SmartBall and Sahara are two of the commonly used acoustic systems that have successfully located and quantified leaks in PCCP lines. IR and GPR surveys have significantly less accuracy and are used much less frequently. They are useful for inspection of very long lengths of pipeline to identify locations of potential leaks for further investigation. The benefits and limitations of leak detection technologies must be understood prior to selecting a technology for inspection. Acoustic-based leak detection systems are direct technologies that are capable of locating and quantifying leaks, while visual, IR, and GPR surveys are indirect technologies that require further investigation to confirm the presence of

71 50 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment leaks. Selection of the appropriate leak detection technology must be based on the goals of the investigation, costs of inspection, and the constraints of the pipeline. ELECTROMAGNETIC INSPECTION Description Definition Electromagnetic (EM) inspection is a non-destructive testing technology that can detect broken prestressing wires in PCCP and their location and estimate the number of broken wires from signal distortions. EM inspection can be used as a part of a pipeline asset management program in order to identify the number and location of existing broken wires. History EM inspection of PCCP was developed by David L. Atherton of Queen s University in Kingston, Canada in Pressure Pipe Inspection Company (PPIC) was formed by Dr. Brian Mergelas in 1997 to commercialize an EM inspection technology, referred to as Remote Field Transformer Coupling (RFTC) (Mergelas and Kong 2001). Pure Technologies developed a parallel approach and refers to their EM inspection technology as P-wave. PPIC was acquired by Pure Technologies in Physics of Technology EM inspection of PCCP is a combination of the remote field eddy current technology used for inspection of metallic pipes and a transformer coupling effect used to detect breaches in the spirally wound prestressing wires. The instrument has exciter and detector induction coils driven by an AC power supply. Electric current in the exciter coil generates a magnetic field that couples the exciter and detector through two paths; one is the direct path that is attenuated rapidly by eddy currents produced in the conducting pipe wall (steel cylinder), and the other is the indirect path that diffuses outwardly through the steel cylinder and travels along the pipe, through the pipe wall, and is amplified by the prestressing wire with little attenuation. Breaks in the prestressing wire affect this amplification effect and thus cause distortions in the EM signal received (Atherton et al. 2000). The EM signal detected during RFTC inspection is influenced by 1) the pipe type and 2) the pipe design and materials used in pipe manufacture, such as thickness of steel cylinder and its electromagnetic signature. For example, EM signal distortions due to broken wires is significantly different for ECP without shorting straps compared to LCP or ECP with shorting straps, resulting in significantly higher uncertainty in the estimated number of wire breaks (see discussion later in this section).

72 Chapter 4: Condition Assessment Technologies 51 System Components The system consists of an exciter, a detector, a data acquisition system, a power supply (batteries), and an odometer all mounted on a customized tool that travels along the pipeline. System Types Several different EM inspection tools have been developed for manned, unmanned, internal, and external inspections of PCCP from 16 inches to 252 inches in diameter as follows. Manned Internal Inspection: A manned internal inspection of a dewatered pipeline is typically performed by pushing or driving the tool along the pipeline at normal walking pace. Available tools include PipeWalker and PipeRider developed by PPIC and P-Wave developed by Pure Technologies. Unmanned Internal Inspection of Dewatered Pipe: An unmanned internal inspection may be performed using a tool mounted on a tethered crawler in either a dewatered or a depressurized pipeline. The tethered crawlers come in several sizes, depending on the pipe size, length, access, and other constraints. Available tools include PipeCrawler and PipeRanger developed by PPIC and Robotic Inspection developed by Pure Technologies. Unmanned Internal Inspection of In-service Pipe: An unmanned internal inspection may be performed using a free-swimming tool developed for inspection of in-service pipelines. The tool is inserted into the pressurized pipeline through a tap and carried by the flow of water. This tool is caught by a net deployed at another tap, and thus eliminates the need to dewater (Kong et al. 2010). Available tools include PipeDiver developed by PPIC and Robotic Inspection developed by Pure Technologies. External Inspection: A manned external inspection of a pipeline may be performed using a tool that can be pushed over the exterior surface of an externally exposed pipe (Biggar 2010). Available tools include PipeScanner developed by PPIC. Inspection Process EM inspection process generally involves field inspection, analysis of the EM signal collected during inspection. During inspection of a pipeline, one of the tools described above is used to record the amplitude and phase of the EM signal along the length of the pipeline. Pipeline features are noted for later comparison to the laying schedule and pipeline drawings. The baseline electromagnetic signal of pipes without broken wires is not the same and changes with design. Furthermore, design parameters such as steel cylinder thickness, presence of shorting straps, and the method of anchoring the prestressing wire alters the signal distortion received from a distressed pipe (Mergelas et al. 2002). The estimation of the number of consecutive wire breaks is performed from comparison of signal distortions of phase and amplitude of the inspected pipes to the corresponding signal distortions obtained from calibration pipes of same or similar design with induced wire breaks of different number and pattern. Although it is highly recommended to perform calibration for each pipeline, the prohibitive cost has forced use of calibration data from a pipe of similar design.

73 52 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Analysis of the collected EM signals is needed to estimate the number and location of wire breaks. Analysis methods are proprietary technologies of the vendors, but they involve examination of amplitude and phase distortions for each pipe and comparing them to a catalog of distortions of the available calibration data. Results are generally presented in a report that includes a listing of all pipes and their lengths, location of special pipes and fittings, and listing of all distressed pipes including the axial location of each broken wire zone and estimate of the number of broken wires in each broken wire zone. Estimation of the number and location of broken wires in broken wire zones, and proximity of broken wire zones is important for analyzing the likelihood of pipe failure. Benefits and Issues The benefits of the technology can be summarized as follows: EM inspection is a nondestructive evaluation technique that can accurately identify PCCP with broken prestressing wires. Prediction of the number of broken wires for LCP or ECP with shorting straps is relatively accurate away from the pipe ends. The axial location of wire breaks can typically be reported to within +/- 6 inches along the pipe length. EM internal inspections do not require excavation except, potentially, at access points. A range of tools have been developed that allow internal inspection of dewatered pipelines of different diameters as well as of pressurized pipeline in service and external inspection of pipelines that cannot be accessed internally. The following issues with the technology have been identified on detection of the signal, analysis of the signal, and physical access to the pipeline. For ECP without shorting straps, estimates of the number of broken wires is subject to large error, as breakage of a single wire creates a large distortion that changes only a little by subsequent wire breaks. The error may be reduced, but not eliminated, by calibration. Interpretation of the EM signals is subjective, as RFTC and P-Wave may produce different results. EM inspection detects prestressing wires that are fractured through their diameter and are no longer electrically continuous. Corroded wires, even with significant loss of cross-sectional area, will not be detected if they are still electrically continuous. Prestressing wire breaks close to the ends of the pipe are not detectable with the same accuracy as the breaks away from pipe joints due to the baseline signal distortions caused by the thick steel joint rings. In pipes with multiple BWZs, the uncertainty in the predicted number and location of broken wires increases as the number of zones increase or as the distance between zones decreases due to complication of the signal analysis. Similarly, uncertainty in the predicted number of broken wires is high for pipes with sporadic broken wires distributed along the pipe length.

74 Chapter 4: Condition Assessment Technologies 53 Depending on the pipeline geometry and available access points, new manholes or taps may need to be installed to facilitate access into the pipeline for tool insertion. External inspection methods require excavation and exposure of the top half of the buried pipelines. Application EM inspection has been applied to the condition assessment of several major pipelines, some of the most significant of which are as follows: 1. Water Reclamation Supply System, Palo Verde Nuclear Generating Station, Tonopah, Arizona: Since 1999, RFTC inspections have been performed periodically on the 66 inches to 114 inches diameter, 36-mile long pipeline, constructed using electronically continuous ECP with shorting strap and bonded joints. Many pipes have been excavated and inspected to verify the predicted number and location of broken prestressing wires, including an independent external verification of 12 pipes performed by SGH in January 2002 in which fully corroded prestressing wires were found within the RFTC predicted broken wire zones. Results of electromagnetic inspection were used to evaluate the failure margin of distressed PCCP (SGH experience). 2. Cedar Creek and Richland Creek Pipelines, Tarrant County, Texas: Cedar Creek Pipeline is a 74-mile long ECP pipeline with diameters of 72 inches and 84 inches designed with bonded joints and shorting straps; thus, all steel is electrically continuous. Richland Creek Pipeline is a 78-mile-long ECP pipeline with diameters of 90 inches and 108 inches and has bonded joints and shorting straps. From 1974 until 1992, cathodic protection amplifier on the Cedar Creek pipeline provided a 1.2 V potential at Sta , resulting in wire breaks due to hydrogen embrittlement for about 20,000 feet on either side of the amplifier station. Both pipelines have been inspected multiple times using RFTC beginning in 1998 and continue to be inspected on a periodic basis. Many pipes have been excavated and inspected to verify the predicted number and location of broken prestressing wires. Results of electromagnetic inspection were used to evaluate the failure margin of distressed PCCP and prioritize repairs (Marshall et al. 2005). 3. Sarir/Sirt and Tazerbo/Benghazi pipelines, Great Manmade River Project (GMRP), Libya: Evaluation of an electrically continuous pipeline, generally 4 m (158 in.) diameter, with shorting strap and bonded joints using a combination of RFTC and close interval potential survey (CIPS). More than 560 miles (900 km) of ECP was inspected using RFTC, and about 2.5 miles (4.1 km) using CIPS. Locations of active corrosion identified using CIPS correlated well with the locations of distress identified using RFTC over the sections of pipeline where the inspections overlapped. The pipeline was excavated for external inspection by visual inspection and potential mapping to verify the results of RFTC (Abdullah et al. 2003; Essamin et al. 2005). 4. Rampart Raw Water Pipeline, Aurora, Colorado: EM inspection of 4.25 miles of 54- inch-diameter ECP without shorting straps was performed by PPIC in 2000, 2002, and 2006 and by Pure Technologies in The 2002 RFTC inspection identified a

75 54 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment high percent of distress (11% distress) over the inspected length. One pipe was excavated for verification in 2002 and 52 broken wires were found compared to the 40 breaks estimated by RFTC. The 2006 inspection also identified a high percent of distressed pipe (14.9%) over the inspected length and a significantly higher distress rate (29.7%) over a 1-mile segment. Based on external inspection of 4 pipes in 2006, locations of BWZs were found to be correct, but the number of wire breaks was significantly overestimated by RFTC. Brittle wire breaks were observed with intact wires between broken wires. P-Wave inspection in 2008 identified significantly fewer distressed pipes with more broken wires per BWZ. Five additional pipes were excavated in February and March of 2008 to verify the results of electromagnetic inspection. No false positives were identified. Correlation with the RFTC results from 2006 ranged from significant overestimation of the number of wire breaks (predicted 85 wire breaks and found 2) to good correlation (predicted 50 wire breaks and found 43). Correlation with P-Wave results from 2008 ranged from overestimation of the number of wire breaks (predicted 30 wire breaks and found 2) to underestimation (predicted 20 wire breaks and found 43) (Oligo et al. 2002; Catalano et al. 2009). 5. San Diego County Water Authority (SDCWA), San Diego, California: RFTC and P- Wave inspection technologies were used to inspect the same portion of a SDCWA pipeline (12.8 miles total) consisting of 66-inch to 96-inch- diameter ECP. External inspection of 10 selected pipes was performed. Upon external inspection, 1 pipe was identified as having a different class from that used in the analysis and is therefore excluded from this comparison. Compared to the actual NBW of the other 9 pipes inspected, PPIC underestimated the NBW on 2, overestimated on 3, and was within 5 wires on 4. Pure underestimated the NBW on 6 (with 1 false negative), overestimated on 3, and was not within 5 wires on any. SDCWA has inspected a total of 72 miles of PCCP since 1999, the majority of which has been performed by PPIC (Galleher et al. 2005). 6. Conduit No. 94, Denver, Colorado: EM inspection was performed by PPIC over 9.1 miles of Conduit No. 94 in 1999 and over 6.5 miles in The pipeline consists of 72-inch- and 66-inch-diameter PCCP without shorting strap. Calibration on the actual pipe designs was not performed. EM inspection in 1999 identified broken wires in 7% of the pipes inspected with the number of broken wires ranging from 5 to 235. Eleven pipes were removed from the pipeline in 2001 and 6 (1 of which had no predicted wire breaks) were used for external verification of EM results. EM inspection in 2003 identified broken wires in 3.5% of the pipes inspected with the number of broken wires ranging from 5 to 125. Five pipes (2 of which had no predicted wire breaks) were removed from the pipeline and used for field verification by external inspection in Based on verification of distress on the 11 pipe sections removed from the line in 2001 and 2004, pipes with no broken wires were correctly identified and locations of broken wire zones (BWZs) were found to be accurate, but the number of wire breaks was overestimated significantly. A total of 9 BWZs were predicted on the 8 distressed pipes. One BWZ was predicted to have 5 broken wires and was found to contain wire splices, which appeared as a disturbance in the EM signal, but no broken

76 Chapter 4: Condition Assessment Technologies 55 wires. One BWZ predicted to have 5 broken wires was found with 1 broken wire. Four BWZs predicted to have 25 to 50 broken wires were found to have 2 to 12 broken wires. One BWZ was predicted to contain 90 broken wires and was found to contain 13 broken wires. Two BWZs were each predicted to contain 165 broken wires and were found to contain 43 and 66 broken wires (Bambei and Lewis 2005). 7. Bay Division Pipeline (BDPL) No. 4, San Francisco, California: RFTC inspection was performed in 2004 on 8.2 miles of 96-inch-diameter ECP without shorting strap in BDPL No. 4. Calibration was not performed on the actual pipe designs in the line. Verification was performed by SGH and SFPUC on 4 distressed pipes identified by RFTC as being highly distressed. Internal visual and sounding inspection showed no longitudinal cracks or significant hollow sounds. Over-the-line and side-drain potential measurement taken along the pipeline did not indicate any areas of active corrosion. Three pipes excavated for external inspection did not show any sign of distress. X-ray inspection showed no signs of distress. The entire coating was removed. The observation showed that the actual broken wires were limited to only a few random wire breaks most likely formed after fabrication and unrelated to corrosion of the pipe or hydrogen embrittlement of the wire. Overestimation of the distress level was due to large signal distortions that result in pipes without shorting strap, sporadic locations of wire breaks, and use of calibration curves from pipes with shorting strap (Mergelas et al. 2006). 8. Central Pipeline, San Jose, California: PPIC inspected 4.2 miles of 66-inch-diameter PCCP without shorting straps using RFTC technology in 2001 and inspected 6.6 miles in The 2001 inspection identified 24 distressed pipes (about 2.2%) and the 2005 inspection identified 59 distressed pipes (about 3.4%). External inspection performed by SGH on 5 pipes found by RFTC showed 2 false positive identifications and 3 pipes with a few random breaks unrelated to corrosion or hydrogen embrittlement and with significantly overestimated numbers of broken wires. PPIC predicted 20 wire breaks at 1 location near the pipe end where uncertainty in the predicted number of broken wires is highest and 3 breaks were found distributed at 0.2, 0.8, and 2.5 feet from the joint. The pipe was given a clean bill of health (Dion and Zarghamee 2008). 9. Four PCCP Lines, California: Metropolitan Water District of Southern California (MWDSC) began using RFTC in 2000 and first used P-Wave in MWDSC s first comparison of RFTC and P-Wave occurred in 2004 when P-Wave was used to evaluate a pipeline previously inspected using RFTC. Of the 70 pipes inspected using both technologies, 6 were identified as distressed using RFTC, 14 were identified as distressed using P-Wave, and no pipes were identified as distressed by both. Verification of results was not performed. MWDSC performed a blind test of RFTC and P-Wave in 2009 over sections of 96-inch- to 162-inch-diameter ECP in 3 different pipelines, 1 with shorting straps and the other 2 without shorting straps. RFTC had been used to inspect all 3 of the pipelines previously and had performed calibration on 1 pipeline in 2006 after inspection was complete. No pipes were added to or removed from the distressed pipe list as a result of the calibration. P-Wave had not been used to inspect any of the 3 pipelines. For the test, a known number of broken wires were induced in 10 broken wire zones.

77 56 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment The results of the blind test did not show good agreement between RFTC and P- Wave. RFTC identified all 10 blind test locations and predicted the number of broken wires within 10 wires in all zones and within 5 wires in 8 zones. P-Wave identified 1 of the 10 blind test locations. P-Wave identified 3 additional anomalies after being notified that broken wires exist on some pipes and 2 additional anomalies after being provided the location and quantity of the blind test locations. In addition to the blind test, the pipeline that was previously used to compare RFTC and P-Wave in 2004 was re-inspected using both technologies. Of the 417 pipes inspected, 18 were identified as distressed by RFTC, 24 were identified as distressed by P-Wave, and 2 were identified as distressed by both. Furthermore, the 14 pipes identified by P-Wave as distressed in 2004 were identified by P-Wave as containing no distress in No verification of results was performed (Harren and McReynolds 2010). 10. Providence Water Supply Board Supplemental Tunnel and Aqueduct, Providence, Rhode Island: The 9-mile-long pipeline consisting of 78-inch- and 102-inch-diameter ECP without shorting straps was inspected using P-Wave between late 2005 and early A short segment of the 102-inch-diameter PCCP was also inspected using RFTC in Internal visual and sounding inspection was performed on distressed pipes identified by electromagnetic inspection and external inspection, including wire continuity measurements and visual and sounding of the exposed pipe surface, was performed on a total of 28 pipes (17 78-inch-diameter and inch-diameter PCCP). Wire continuity measurements on the inch diameter pipes identified 10 pipes with broken wires and 7 pipes without any broken wires. P-wave correctly identified 4 of 10 pipes with broken wires (6 false negatives) and 6 of 7 pipes without broken wires (1 false positive). The numbers of broken wires predicted by P-wave on 4 distressed pipes compared to the numbers of broken wires found by continuity measurements as follows: 85 broken wires predicted compared to 115 found, 20 broken wires predicted compared to 143 found, 300 broken wires predicted compared to 272 found, and 10 broken wires predicted compared to 1 found. Wire continuity measurements on the inch diameter pipes identified 6 pipes with broken wires and 5 pipes without any broken wires. P-wave correctly identified 6 distressed pipes, but incorrectly identified the remaining 5 pipes as distressed (5 false positives). Broken wires were found in 5 of 18 BWZs predicted by P-Wave, and the number of broken wires found was within ±5 wires of the predicted number in 2 of 18 BWZs. RFTC correctly identified 6 pipes with broken wires and correctly identified the other 5 pipes as not containing broken wires. Broken wires were found in 13 of 18 BWZs predicted by RFTC, and the number of broken wires found was within ±5 wires of the predicted number in 12 of 18 BWZs (Ojdrovic et al. 2009). 11. Lake Arrowhead Pipeline, Wichita Falls, Texas: RFTC inspection was performed on 5.3 miles of 54-inch-diameter ECP without shorting straps and identified 192 distressed pipes of 1,708 inspected (11.24%). Calibration was not performed on the specific pipe designs in the line. Failure risk analysis was performed by SGH. The 44 pipes identified in Repair Priorities 1 and 2 were replaced. SGH performed field

78 Chapter 4: Condition Assessment Technologies 57 inspection to verify the results of RFTC. Four pipes were selected for inspection, but based on results of inspection and review of drawings, 1 of the pipes excavated may have been the wrong pipe. Results of verification indicate that RFTC s estimation of number of broken wires in zones with less than 15 broken wires is accurate within the normal uncertainties, RFTC s estimation of the number of broken wires in pipes categorized as DA (PPIC terminology for EM signal shift detected across entire length of pipe) appears to be overly conservative, and RFTC s estimation of the number of broken wires in zones with more than 35 broken wires appears to be conservative (Taylor et al. 2008). 12. PipeDiver inspections in Canada: PipeDiver was used to inspect 2,280 feet of 30- inch-diameter LCP in Halifax s Bedford Connector pipeline. Installation of inch-diameter hot taps was required for insertion and retrieval of the tool. External verification of the results was performed on 5 pipe segments 1.5 years after the RFTC inspection. One pipe was confirmed to have no distress as predicted, 2 pipes contained a total of 4 broken wire zones that were each within 5 wires of the predicted number of broken wires, and 2 pipes were each found to contain 1 zone with 17 broken wires instead of the 5 broken wires predicted by RFTC. 13. PipeDiver inspection in Mexico: PipeDiver was used to inspect 23 miles of 99-inchdiameter PCCP in Mexico in a single deployment. The tool was inserted from a tank on one end of the pipeline and retrieved from a tank on the other end, so no installation of taps was required. Results compared well with the RFTC results from a previous inspection on the same pipeline using a manned internal inspection system (Kong et al. 2010). 14. PipeScanner Inspection of Central Parkway Transit Tunnel Transmission Main, Greater Cincinnati Water Works (GCWW) Cincinnati, Ohio: PPIC electromagnetically inspected the exterior of a 48-inch-diameter LCP line installed inside an abandoned subway tunnel without dewatering the pipeline. The pipeline was exposed within the tunnel and subjected to dripping water containing deicing salt from the roadway above. From the 292 pipe pieces (0.85 miles) inspected using the PipeScanner external inspection system, 21 pipes were identified as distressed with broken wires (Biggar 2010). Electromagnetic Evaluation Summary EM inspection is a nondestructive evaluation method that can identify distressed pipes and predict the number and location of broken wires. Results of EM inspection can be used in failure margin analysis and determine how close is a distressed pipe with a number of broken wires and a maximum internal pressure to failure and thus obtain a measure for the remaining service life of a pipeline. The accuracy of a nondestructive technology used for condition assessment of PCCP is determined from its accuracy in identifying distressed pipe, and in predicting the level of distress. EM inspection can reliably identify PCCP that contain broken prestressing wires that are not near the joint rings. Prediction of distress level has been subject to uncertainties involved in the interpretation of signal distortions. Such uncertainties are the largest for pipes without shorting strap. The predicted number of broken wires is expected to be within about 10 wires for

79 58 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment LCP or ECP with shorting straps away from the joints. For ECP without shorting strap, the uncertainty can be much greater, especially if calibration data used for the interpretation of data is not pipe specific. The determination of the safety of the pipe inspected by EM accounting for uncertainties involved and determination of how close the pipe is to rupture and its remaining service life require failure margin analysis as described in Chapter 6. STRESS WAVE ANALYSIS Description Definition Stress wave analysis is a non-destructive inspection technique using a controlled impact to the pipe surface to generate stress waves within the pipe wall that are detected by one or more sensors on the pipe surface spaced at a distance away from the impact location. Modulus of concrete in the pipe wall and locations of voids and delaminations can be determined based on the stress wave velocity and the dominant frequencies of the response. The two general types of stress wave analysis that are currently in use in different forms are impact echo (IE) and spectral analysis of surface waves (SASW). Methods that produce stress waves in the sonic/ultrasonic band operate on the same principles, but these methods are sometimes specifically referred to as sonic/ultrasonic methods. History Use of stress waves for detection of delaminations in concrete began in 1986 with a research program at the National Bureau of Standards (now NIST) into the theoretical basis and practical application of IE (Sansalone, 1989). SASW has been used for subsurface characterization in seismic engineering for decades and has been used for measuring moduli and thickness of pavement systems since the early 1980s. IE and SASW identify concrete modulus and delaminations in the pipe wall by comparing the measured response of these stress waves and the response expected from a good pipe. Testing of IE for in-situ nondestructive testing of PCCP was performed by Sack and Olson (1994) for the U.S. Bureau of Reclamation in the early 1990s and found that IE can be used for measuring pipe wall thickness and detecting changes in wall thickness as small as 0.1 inches (Sack 1994), by Zarghamee and Maser (1997) in 1995 for Massachusetts Water Resource Authority, and by Fisk and Marshall (2006 and 2010) and Washington Suburban Sanitary Commission in the 1990s and early 2000s (Marshall and Fisk 2010). Physics of Technology An impact on the surface of a body generates 3 types of stress waves: pressure waves (Pwaves) or compression waves where the displacements are parallel to the direction of wave propagation, shear waves (S-waves) in which displacements occur perpendicular to the direction

80 Chapter 4: Condition Assessment Technologies 59 of wave propagation, and surface waves (Rayleigh waves) that travel along the surface of the body. Impact echo: IE is used to identify delamination. The controlled impact applied to either the inner or the outer surface of the pipe wall generates compressive stress waves in the pipe wall that resonate between the impact surface and the delaminated surface. The compression wave that is reflected depends on the specific acoustic impedance of concrete and any void (Carino 2001). The reflection from air voids is much more than from steel reinforcement interfaces. A transducer placed near the point of impact on the same wall surface records surface displacements caused by the reflected wave (Figures 4.10 and 4.11). The frequency spectrum of the received signal shows the resonance frequency from which depth of delamination can be estimated once the velocity of compressive wave travel through concrete is known. Compressive wave velocity can be either calculated using results of SASW or measured using an array of transducers to measure compression and shear wave velocities from the impact applied by IE. Spectral analysis of surface waves: SASW is used to obtain wave velocities through concrete, from which the condition of concrete in the pipe wall can be assessed, as distress and loss of prestress may result in microcracking and cracking, and thus reduction in wave velocity. The controlled impact applied to either the inner or the outer surface of the pipe wall generates surface waves that are detected by multiple evenly spaced transducers aligned with the point of impact and capture the signal as the waves move away from the impact point (Figure 4.12). Surface wave velocity is then calculated based on the travel time of the surface wave between the transducers. The measured velocities depend on the elastic properties of concrete, e.g. cracked, microcracked, or under high compressive stress. System Components The system consists of a source of controlled impact, at least one high fidelity transducer (one or more for IE and two or more for SASW), and a data acquisition and signal processing system. System Types The systems used to perform IE and SASW do not vary significantly. Equipment provided by various manufacturers consists of the basic components listed above. Inspection Process Inspection processes for IE and SASW are discussed separately below. IE and SASW inspection methods both require access to either the inside or outside surface of the pipe wall. Impact echo: Calculation of wall thickness (or depth of flaw) using IE requires knowledge of wave velocity in the pipe wall, which can be measured using SASW. Recommended spacing between the point of impact and the transducer is between 20% and 40% of the expected wall thickness or expected flaw depth (Carino 2001). The frequencies imparted to the pipe wall by the applied impact (the hammer) vary inversely with the duration of the impact; therefore, the hammer used must impart the frequency corresponding to the depth of delamination (see ASTM C1383, 2004, 2010).

81 60 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Waveforms received in the time domain are transformed to the frequency domain by spectral analysis. Pipe wall thickness or delamination depth can be calculated using the peak response frequency and the previously determined P-wave velocity. Spectral analysis of surface waves: Surface wave velocities vary with changes in material properties. Impacts applied to the pipe wall impart various frequencies. The signals collected by the transducers are analyzed to determine surface wave velocities associated with each frequency, and to generate plots of surface wave velocity with wavelength, called dispersion plots. Surface wave velocity is constant for a given material. Changes in material can be identified from the dispersion plots by changes in surface wave velocities, and changes in thickness can be identified by shifts in the wavelengths associated with a given frequency. Changes in the surface wave velocity at wavelengths known to correspond to sound pipe wall based on previous measurements indicate anomalies in the concrete such as cracking or microcracking. Benefits and Issues The benefits of the technology can be summarized as follows: IE and SASW are nondestructive techniques that can be applied to either the interior of the pipe wall or to its exterior when the pipeline is under pressure. IE applied from interior of the pipe can identify delaminated coating, which may be indicative of corroding prestressing wires, or delamination between the concrete core and the steel cylinder, which may be indicative of significant loss of prestress and severe distress in the pipe. SASW can be used to determine the elastic properties of concrete in both inner and outer core and whether they are microcracked or cracked. It may also be used to qualitatively assess the stiffness of the surrounding soil. The following issues with the technology were initially identified as follows: Neither IE nor SASW detects corrosion or provides a direct estimate of the existing number of broken wires and their locations. Both IE and SASW require contact with the pipe wall, so the pipe must be either dewatered for internal access or excavated for external access.

82 Chapter 4: Condition Assessment Technologies 61 Source: Reprinted, with permission, from ASTM C (2004, 2010), copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA Figure Schematic of impact echo test setup Figure Impact echo test being performed on top of a concrete pressure pipe

83 62 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Source: Sack 1998, with permission from ASCE Figure SASW test method diagram Application IE and SASW have been verified by experimental results and have been applied to the condition assessment of pipelines, as discussed below: 1. USBR Research, Aurora, Colorado: A relatively high-speed IE scanning device was developed and compared to the results obtained with the results obtained using standard IE measurements. The scanning device was capable of recording IE measurements at 4 locations around the pipe circumference as it moved through the pipe at a rate of about 20 feet per 5 minutes. IE measurements recorded with the scanner on a buried 54-inch-diameter pipeline in Aurora correlated well with standard IE measurements. Physical measurements on one section of pipe removed from the pipeline showed that the IE scanner was accurate in measuring the pipe wall thickness and was capable of detecting changes in wall thickness as small as 0.1 inches Absolute wall thickness estimation was less accurate due to differences between assumed and actual velocity of concrete. No delamination was detected on the removed pipe section and none was found by physical examination (Sack and Olson 1994). 2. Round Valley Force Main, New Jersey: Sonic/ultrasonic NDT (same theoretical basis as IE technique) was used to evaluate 1,062 PCCP segments in 1999 and Risk factors were developed for each pipe based on its condition, its deterioration between inspections, and its consequence of failure. Two pipes were replaced and externally inspected after removal from the line. Both pipes were reported as containing low levels of stress in the prestressing wires. One pipe contained a longitudinal crack along its length (Fisk and Marshall 2006).

84 Chapter 4: Condition Assessment Technologies , 66, and 48 inch diameter PCCP lines: Sonic/ultrasonic testing was used to evaluate the condition of PCCP, and the rate of decay of the pipeline as evaluated based on results of multiple inspections. Example inspection results provided for 96- inch-, 66-inch-, and 48-inch-diameter PCCP lines show variable decay rates. One 66- inch pipe segment was excavated to confirm the prediction that it had severe anomalies at the end of the pipe. Two feet of corroded prestressing wire and debonded coating was found at the end of the pipe. One 48-inch-diameter pipe was excavated to confirm that it had a significant anomaly at the end of the pipe and a 1- inch reduction in wall thickness. The coating was confirmed to have reduced thickness and was soft and friable. A large area of corroded wires and debonded coating was found at the end of the pipe (Marshall and Fisk 2010) inch diameter PCCP force main: Sonic/ultrasonic testing was performed at the 4 and 8 o clock circumferential position along the interior of 1,889 section of 48-inchdiameter PCCP. The pipe wall consists of a 3-inch-thick concrete core and a 0.8-inch minimum thickness of coating. A resonant frequency for this pipe between 20 and 24 khz indicates a composite wall with full coating thickness. Resonant frequencies lower than 20 khz indicate either a thicker wall or damaged concrete. Resonant frequencies between 24 and 26 khz indicate thinning of the coating and frequencies of 29 to 30 khz indicate delamination between the concrete core and coating. Three pipe segments that were predicted to have reduced coating thickness were excavated for verification. The pipes had soft, friable coating with reduced thickness. Twentysix pipes were identified with resonant frequencies of 29 to 30 khz, but none of these pipes were excavated for verification (Fisk and Marshall 2010). 5. Hultman Aqueduct, Massachusetts: Field investigation, nondestructive testing, and structural evaluation of the 150-inch-, 138-inch-, and 84-inch-diameter AWWA C300 RCCP. Impact-echo was used to detect delamination between the concrete core and steel cylinder based on the measured resonance frequency and the average measured concrete velocity as determine by SASW (Zarghamee and Maser 1997). The detected delaminations were accounted for in the subsequent structural analysis and failure margin analysis. Safety factors against failure were calculated for various loading conditions considering separation at the concrete/steel interface. Stress Wave Analysis Summary IE and SASW are nondestructive testing methods that have been used since the 1980s to identify delaminations within reinforced concrete and distress in concrete structures. IE can be used to identify PCCP that contain delamination at the interface of the concrete core with either the steel cylinder or the coating. SASW can be used to obtain wave velocities; low velocities are related to microcracking or cracking of concrete. Delamination and microcracking and cracking of concrete are typically consequences of distress in pipe that occur with wire breaks and loss of prestress. Results of IE and SASW can be used to identify areas for further inspection. The information on the accuracy of these NDT technologies in detecting distressed pipes and predicting the level of distress is not yet developed.

85 64 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment OVER-THE-LINE CORROSIVITY AND CORROSION SURVEYS Description Definition Over-the-line surveys are used to detect and locate corrosion in PCCP or to determine corrosivity of the soil and groundwater. Active corrosion areas in a pipeline are detected by over-the-surveys such as pipe-to-soil and cell-to-cell potential measurements. Soil and groundwater corrosivity to PCCP are detected by over-the-line surveys such as soil resistivity and chemical analyses of soil and groundwater for ph, and chloride and sulfate ion content. History Measurements of potential have been used for detecting and locating corrosion in steel pipe in the oil and gas industries since 1940s (Compton 1981). Over-the-line surveys for detecting corrosion of PCCP are similar to the techniques used for detection of corrosion in steel pipelines. Over-the-line surveys aimed to determine areas of high corrosivity and corrosion areas have been in use for condition assessment of PCCP. The ability of pipe-to-soil and cell-to-cell potential over the line surveys to detect and locate corrosion cells were tested in the 1990s by Ameron. In this test, 5 corrosion firms were asked to locate simulated corrosion cells on bonded and unbonded 48-inch-diameter PCCP buried in moist soil. Results showed that these methods could detect corrosion and that corrosion was more easily detected on bonded pipelines using pipe-to-soil potential surveys than on unbounded pipelines for which cell-to-cell potential surveys were performed. The results also showed corrosion cells at the crown of the pipe could be detected more easily than at the invert. Tests repeated on dry soil showed that results were more accurate on moist soil (Hall 1994). Physics of Technology Areas of active corrosion cells can be detected along the length of the pipeline by measuring the difference in potential between the soil and the electrically continuous pipeline or between different locations on the surface of the soil. A corroding area of an active corrosion cell in a pipeline has a more negative potential than the surrounding area; therefore, areas with significantly more negative potentials over the pipe relative to the surrounding areas are likely indications of local corrosion. In an electrically continuous line, the pipe-to-soil potential survey shows active corrosion areas as dips in the potential. For a pipeline that is not electrically continuous, cell-to-cell potential is measured along the pipeline and transverse to the pipeline. The higher negative potential over the pipeline compared to points away is an indication of likely local corrosion. Areas with significantly more positive potentials relative to the surrounding areas may be indicative of stray current discharge, which also results in corrosion. Locations along the pipeline where corrosion is more likely to occur can be identified by evaluation of the corrosivity of the soil and groundwater. AWWA M9 identifies environments with high chloride or sulfate content, acid conditions or dissolved carbon dioxide and

86 Chapter 4: Condition Assessment Technologies 65 bicarbonates in the ground water (produced from rainwater or humic acid from vegetation decay) aggressive to PCCP. Chloride ions permeate through the coating from the surrounding soil and ground water and cause corrosion of the wire of prestressing wire when it reaches the wire surface. The chloride content needed for the onset of corrosion is a function of ph of the mortar, and is thus affected by the acidity of the environment. Sulfate ions cause degradation of mortar and its ability to protect the steel wire. Dissolved carbon dioxide and bicarbonates in the ground water result in carbonation of the coating, thereby reducing coating ability to protect the wire. Acidic environments or ground water with negative Langelier Index are corrosive to concrete. Soil resistivity depends on its ion content. Therefore, measurement of soil resistivity can be used as an initial indicator of the presence of potentially aggressive ions. Chemical analysis of soil and groundwater are used to determine the presence of ions, acids, dissolved carbon dioxide, and Langelier Index. System Components Pipe-to-soil: The system for pipe-to-soil potential measurements is performed with a half-cell, a reference electrode, a high impedance voltage meter in which one electrical lead is connected to the pipeline and the other is in constant contact with the soil, and a reliable way to measure distances along the pipeline. Cell-to-cell: The system for cell-to-cell potential survey requires the same equipment except that no connection to the pipeline is required and one electrode is in contact with the soil above the pipe and the other is at a fixed distance from the first either along the pipe or transverse to the line. The electrodes are used to measure change in potential. Soil resistivity: The system for measuring soil resistivity in the field can be either an array of electrodes (Wenner four-point testing) in contact with the ground surface or an induction-type electromagnetic conductivity meter. Alternatively, measurements can be made in the laboratory using soil samples collected in the field and a soil resistivity box. Chemical analysis: Chemical analysis of soil and groundwater require that samples be collected in the field and brought back to the laboratory for analysis. Appropriate containers must be brought into the field to preserve the samples, especially for measurement of dissolved carbon dioxide, carbonate, and bicarbonates. System Types The systems used to perform pipe-to-soil and cell-to-cell potential measurements do not vary significantly. Equipment provided by various manufacturers consists of the basic components listed above. The systems used to perform soil resistivity measurements vary depending whether they are for laboratory testing or field testing as described above. Inspection Process Pipe-to-Soil: Pipe-to-soil potential surveys require access to the pipe exterior for connection to the steel components of the pipe and access over the pipe along the length of the pipeline. Potential is measured using a voltmeter with one lead connected to the pipeline and the second lead connected to an electrode that is placed on the soil over the pipeline at regular intervals as shown in Figure Surface plots of potentials along the pipeline length can be

87 66 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment used to identify areas with significantly more negative potentials relative to surrounding areas and areas where current is moving toward, away from, or past the pipeline (Compton 1981). Cathodic protection of the pipeline being inspected or stray currents from another source will affect the pipe-to-soil potential measurements. Pipe-to-soil potential measurements are also used to evaluate the effectiveness of cathodic protection. Cell-to-Cell: Cell-to-cell potential surveys use a stationary reference electrode and two moving electrodes on the ground surface to measure potentials as a function of distance from the reference electrode. Cell-to-cell potential surveys do not require access to the pipe surface and do not require that the pipeline be electrically continuous. Potentials are measured at fixed intervals directly above the centerline of the pipeline with reference to a stationary electrode that is also located directly above the centerline. Potentials are also measured perpendicular to the pipe at fixed offsets from the pipe centerline to determine if current flows toward or away from the pipeline. These potentials, called side-drain measurements, are measured with reference to a stationary electrode aligned with the side-drain measurements and located directly above the pipeline. Plots of potentials along the pipeline length are used to identify areas with significantly more negative potentials relative to surrounding areas, both longitudinally and laterally; these areas are the likely potential corrosion sites where current is leaving the pipeline. Soil Resistivity: Soil resistivity measurements can be used as a part of evaluation of the aggressiveness of soil to PCCP. Soil resistivity measurements can be obtained either in the laboratory using samples collected in the field (Figure 4.14) or in the field using either electrodes in contact with the ground surface (Wenner four-point testing) or induction-type electromagnetic conductivity meters, which do not require direct contact with the soil. The resistivity of soil is a measure of the soils ability to conduct electricity and varies with soil type and moisture content. In areas with dry soil conditions, resistivity measurements should be taken after a heavy rain or after the soil has been thoroughly moistened by other means. In areas where the resistivity of moist soil is below 1,500 ohm-cm, chemical analysis of the soil should be performed (AWWA M9). Induction-type electromagnetic conductivity meters consist of induction and receiver coils separated by a specified distance (Figure 4.15). The induction coil generates a magnetic field that induces current flow in the soil, and the current generates a secondary magnetic field that is detected by the receiver. The amplitude and phase of the received signal are related to the soil resistivity. Chemical Analysis: Chemical analyses of soil and groundwater are generally performed in localized areas identified as containing active corrosion or as being potentially aggressive to PCCP based on over-the-line surveys. Soil and/or groundwater samples taken from near the pipeline are analyzed in the laboratory to further quantify the aggressiveness of the environment toward PCCP and try to identify the cause. Soils are typically analyzed for chloride content, sulfate content, ph, and minimum laboratory resistivity. Depending on site conditions, soils might also be analyzed for presence of acids and aggressive carbon dioxide. Groundwater samples are typically analyzed for chloride content, sulfate content, ph, aggressive carbon dioxide and bicarbonates. Results of chemical analyses can be compared to the limiting values recommended by AWWA M9.

88 Chapter 4: Condition Assessment Technologies 67 Benefits and Issues The benefits of the technology can be summarized as follows: Pipe-to-soil potential surveys performed at regular intervals over an electrically continuous PCCP pipeline at regular time intervals is a direct and proven method for monitoring PCCP lines. Over-the-line surveys can be used as a first step in condition assessment of a pipeline to either prioritize sections for assessment or to identify areas for more detailed inspection. Pipe-to-soil potential, cell-to-cell potential, and soil resistivity surveys do not require excavation of the pipeline. Chemical analysis of soil and/or groundwater requires only localized excavation or boring to collect samples for laboratory analysis. Cell-to-cell potential survey does not require that the pipeline be electrically continuous. The following issues with the technology were initially identified as follows: Over-the-line surveys do not provide any direct information regarding the level of distress on the pipeline. Pipe-to-soil potential measurements require that the pipeline be electrically continuous. Pipe-to-soil potentials, cell-to-cell potentials, and soil resistivity all relate to the ability of the soil to transmit current; therefore, all 3 surveys depend on the soil moisture content and cannot be performed on dry soil. Pipe-to-soil and cell-to-soil are less likely to detect corrosion near invert of large diameter pipes. Pipe-to-soil potentials, cell-to-cell potentials, and soil resistivity all require access to the ground surface above the pipeline. Pipes buried under paved roads do not lend themselves to such surveys. Pipe-to-soil potentials, cell-to-cell potentials, and soil resistivity are affected by stray currents and by buried objects that modify the soil potential such as a corroding metal object near a pipeline. Chemical analyses require excavation or soil boring to collect samples of soil and excavations or installation of wells to collect ground-water samples at the pipe level.

89 68 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Source: Reprinted, with permission, from Rothman 1985, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA Figure Pipe-to-soil potential measurements Source: Reprinted, with permission, from ASTM G57-06, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA Figure Laboratory soil resistivity measurements

90 Chapter 4: Condition Assessment Technologies 69 Source: Geonics Limited ( Figure Induction-type electromagnetic soil conductivity meter (EM31-MK2 ground conductivity meter) Application Over-the-line surveys have been conducted for condition assessment of pipelines. The following is a summary of their applications and verifications: 1. Verification of Over-the-Line Corrosion Surveys: Pipe-to-soil potential and cell-to-cell potential surveys were tested in a controlled experiment with moist soil. Corrosion was simulated with a corrosion anode cell embedded at the crown, springline, and invert of 48-inch-diameter PCCPs. Five corrosion engineering firms were selected to attempt to locate the active corrosion cells using their choice of inspection techniques. Both bonded and unbounded pipeline were selected for this experiment. None of the firms were able to locate corrosion cells at the bottom of the pipe, so this scenario was not investigated further. All 5 firms were able to locate the corrosion at the crown and springline on the bonded pipe using pipe-to-soil potential measurements. The change in the measured potential at the corrosion location was significantly lower for corrosion at the springline (20 to 40 mv) compared to corrosion at the crown (60 to 100 mv). None of the firms used the cell-to-cell potential method on the bonded pipeline. All 5 firms were able to locate the corrosion located at the crown of the pipe on the unbonded pipe using either pipe-to-soil potential or cell-to-cell potential (fixed cell-to-moving cell or moving cell-tomoving cell) measurements. Pipe-to-soil measurements worked on these unbonded pipes only because all the pipes were at the same potential and therefore acted as a reference cell. Only one firm was able to locate the corrosion at the springline of the pipe on the unbonded pipe using fixed cell-to-moving cell potential measurements at a 10-foot offset from the pipe centerline. Erratic results were obtained when the tests were repeated on dry soil without any moistening (Hall 1994) inch diameter PCCP, Mexico: A case study on a 4-year-old 60-inch-diameter PCCP line in Mexico involved evaluation of the corrosivity of the soil and groundwater as part of condition assessment of the pipeline. Soil resistivity (Wenner Four Pin Method used because the pipeline was not electrically continuous) measurements were taken at

91 70 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment elevations down to pipe invert and used to evaluate the corrosivity of the soil along pipeline. Four 100-meter-long locations were excavated for inspection of the pipeline and chemical analysis of the soil. Three areas that were subject to cyclic wetting and drying conditions had extensive corrosion of prestressing wire and high chloride and sulfate contents. The surrounding soil consisted of layers of clay and sand. The other area had the lowest resistivity and the highest high chloride and sulfate content, but showed no corrosion because it was not subject to wetting and drying cycles (Benedict et al. 1997). 3. Corrosion Detection and Case Studies: Pipe-to-soil and cell-to-cell potential surveys performed on embedded cylinder pipelines and lined cylinder pipelines in the Southern U.S. and Virginia identified areas of corrosion that were confirmed by subsequent excavation. The cell-to-cell potential measurements showed an anodic rise of about 100 mv to 125 mv in the area of the active corrosion. The pipe-to-soil potential measurements showed an anodic rise of several hundred mv in the area of the active corrosion (Rothman and Price 1985). 4. Comparison of Electromagnetic Induction and Direct Contact Measurements of Conductivity: Soil conductivity (resistivity = 1/conductivity) results obtained using the electromagnetic induction system and the direct contact electrode system were compared. One induction-type system was used that collected 90% of its measurement data within the top 5 meters of soil, one direct contact electrode system was used that collected 90% of its measurement from the top 1.5 meters of soil, and one direct contact electrode system was used that collected 90% of its measurement from the top 300 mm of soil. Tests were conducted in two fields in Illinois and two fields in Missouri. Soil conductivity measurements at various depths were compared to the soil properties obtained from soil samples collected from multiple borings at each site. Results showed that soil conductivity was influenced by soil salinity, clay content, cation exchange capacity, clay mineralogy, soil pore size and distribution, soil moisture content, and temperature. Results showed that the two sets of conductivity measurements taken deeper in the soil differed more in layered soils. Differences in the soil conductivity measurements were attributed primarily to the differences in measurement depths and soil profiles. The best correlation existed between the induction-type system and direct contact system with deeper measurements with a coefficient of correlation between 0.74 and This research identified the importance of selecting a conductivity measurement system that operates at the soil depth of interest to the investigation (Sudduth et al. 2003). Over-the-line Corrosivity and Corrosion Surveys Summary Over-the-line corrosivity and corrosion surveys have been used in the condition assessment of PCCP and can identify areas with high corrosivity along a PCCP line (areas of likely corrosion of PCCP in future) and areas of active corrosion since the 1980s. In particular, regular pipe-to-soil potential surveys of an electrically continuous line are a useful tool for monitoring a PCCP line and identifying changes in the corrosion activity along the line. Corrosivity of soil and groundwater can be determined by resistivity measurement and chemical surveys. These areas may be sites of corrosion activity. Areas of active corrosion are identified using the results of pipe-to-soil or cell-to-cell potential surveys and generating surface plots of

92 Chapter 4: Condition Assessment Technologies 71 the results. Areas along the pipeline where the current flows away from the pipe are potential sites of active corrosion and where the current flows toward pipeline may be site of stray current and possible embrittlement. None of the over-the-line survey techniques directly provide information regarding the level of distress on the pipeline; however, the information gathered through such surveys plays an important role in identifying areas along the pipeline with higher likelihood of pipe distress

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94 CHAPTER 5: MONITORING TECHNOLOGIES ACOUSTIC MONITORING Description Definition Acoustic monitoring (AM) of pipelines is a non-destructive monitoring technology in which wire break events are identified and localized as they occur in a pipeline through the detection of the acoustic waves generated by a wire break. History Acoustic monitoring system was developed by USBR Research in 1991 for condition assessment of the 252-inch-diameter Agua Fria pipeline, after the prevalent techniques such as surface potential and visual inspection proved to provide only poor correlation between the predicted and actual conditions of the pipe. Recognizing that an acoustic event occurs when a wire breaks, USBR Research employed the event detection and classification techniques that had been developed for anti-submarine warfare. USBR Research used discrete hydrophones mounted at intervals along the pipeline to detect the sound. Although they desired to apply neural network to distinguish a wire break event from the noise generated by other sources, neural network technology was not used and distinction was made on a case-by-case basis from certain parameters of the recorded signals. Experience of AM providers shows that wire break signals can be differentiated from background noise and testing shows that differences in both amplitude and frequency can be used to differentiate between acoustic signals from wire breaks and coating delaminations (Bell and Paulson 2010).. Physics of Technology As a wire breaks, energy is released resulting in an acoustic wave that travels through the pipe wall to the water in the form of pressure waves, which in turn travel along the pipeline. The acoustic waves can be detected by discrete or continuous (fiber optic) sensors along the pipeline. Detection of the same event by multiple discrete sensors allows localization of the event. The location of the event can be calculated using the arrival time at each sensor, the distance between sensors, and the speed of sound in water for discrete hydrophone arrays or accelerometer sensors. Fiber optic sensors work by projecting a beam of light through the fiber and analyzing the light that is reflected back to the source. Detection of an event by a continuous fiber optic sensor is based on the dynamic pattern of light reflected due to stress waves in the fiber caused by acoustic waves in the water (Higgins and Paulson 2006). 73

95 74 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment System Components The system consists of sensors or optical cable located along the pipeline, data acquisition system, signal processing, energy supply, and communication system for transmitting the data collected. System Types There are several different AM systems that have been developed in the past decade as follows: Probe Station: Hydrophone probes inserted into the flow stream through taps in the pipe at manholes with a data acquisition station, power source, and data transmission station at each location. This technique is suited better for large diameter pipe where the distance between sensors can be large. Array of tethered hydrophones attached to a single long cable inserted into the water stream in the pipe through a tap in the pipe at a manhole with a single data acquisition station, power source, and data transmission station at the insertion point. This system allows sensors at reduced spacing and is especially suited for smaller diameter pipe. Accelerometers are attached using an epoxy adhesive to the exterior of the pipe wall at suitable intervals with the pipeline in service, and a data acquisition station, power source, and data transmission station are provided at each accelerometer location. The accelerometer can measure the response of the pipe wall to acoustic waves traveling in the water. Fiber optic cable installed inside a pipeline. The sensors are the long continuous fibers that run along the pipeline. Acoustic waves in the water column impart pressure waves on the fibers, which in turn generate stress waves. When the beam of light encounters a change in stress field in the fiber, the light is reflected in a dynamic pattern. The pattern of reflected light is continuously analyzed by the data acquisition system to acoustically monitor the pipeline. Fiber optic cables can run a long distance and are typically placed to collect data over a long time. Fiber optics has the advantage that the sensor is located at the acoustic signal generation point, and hence spacing of sensors is no longer an issue. Furthermore, the proximity to the source provides an advantage in distinguishing between signal and noise. The fiber optic cable is attached to a data acquisition station, power source, and data transmission station. Benefits and Issues The benefits of the technology can be summarized as follows: The technology is direct as it detects wire break events as they occur. The technology provides information on the rate of broken wires. The technology can be applied to a pipeline without the need to remove it from service. Deployment of fiber optic cables may require pipeline shutdown and

96 Chapter 5: Monitoring Technologies 75 dewatering, but deployment while the pipeline remains operational is possible in some cases. The technology, if applied to a pipe after an initial electromagnetic inspection where total number of broken wires is known initially, would provide useful information to determine the remaining life to failure, and can be used for asset management of PCCP assets. Several issues with the technology were initially identified. The technology does not provide a direct estimate of the existing number of broken wires and their locations. There exist data suggesting that the rate of broken wires is correlated to the distress in the pipe for pipes in very close proximity of rupture. However, for other distressed pipes, such a correlation has not yet been established. Spacing of the discrete sensors such as microphones and accelerometers is critical in detection as acoustic signals tend to attenuate with distance. The attenuation depends on pipe characteristics (such as pipe diameter, internal pipeline features like valves, bends, etc.), instrument characteristics (such as hydrophone and accelerometer sensitivity, and signal processing technique used to distinguish between the wire break signals and other noise. Discrete sensors may lack the needed sensitivity if they are too far apart. Deployment of fiber optic cables may require pipeline shutdown and dewatering. Monitoring period: sufficiently long time of monitoring is required. Monitoring over short time periods does not provide enough wire break signals that can be used to identify distressed pipes. Note that the rate of increase in the number of wire breaks even for highly distressed pipe is very small, unless the pipe is in the final process of rupture. Detecting signal from noise: Detection of wire break signal from noise is a challenge in acoustic monitoring. Noise occurs from sources such as air in the pipeline, turbulence, background noise such noise generated from nearby traffic, pumping noise, delamination of the coating, and the noise of slippage of already broken wires. Data acquisition equipment needs to be left in the field, and thus is subject to vandalism and elements. In the case of fiber optic systems the data acquisition equipment can be located in secure areas, such as offices, pumping stations, vaults, or other shelters. Application The AM has been applied to the condition assessment of several major pipelines, the most important of which are as follows: 1. Agua Fria Siphon, Arizona (USBR Research): AM with probes inserted into the water stream at 1000 to 2000 feet intervals were used in this 252-inch-diameter PCCP line in early 1990s, and detected active areas in 500 hours of monitoring. Distressed pipes were identified, and excavation proved the distress of pipes in active areas (Worthington and DiMarco 1996; Baron and Worthington 1997).

97 76 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment 2. Elkridge Pipeline, Baltimore, Maryland: AM installed in During the monitoring period, 164 probable wire breaks were identified. No field verification of the extent of distress was performed. Areas where the rate of wire breakage was higher were identified, and a part of the pipeline was replaced (Holley et al. 2001). 3. Toll House and Ridge Road Pipeline, Maryland: AM was installed in 2000 on 18 miles of 42-inch-diameter PCCP. Inspection started with a 6000-foot array installed through a 4- inch open port valve. Once AM showed wire breaks, pipes were excavated to verify the distress and replace the pipe. Excavation showed other pipe in distress and the County decided to change the 7700 feet of pipe and continue monitoring of the rest of the line. Monitoring was done through 3-month periods. A high number of wire break events were detected at a cathodically protected gas-line crossing apparently caused by the stray current from the protected line (Diaz et al. 2005). 4. Potomac main, Maryland: Fiber optic cable was installed for continuous monitoring of 96-inch-diameter PCCP. Criteria for triggering repair was establish based on the total number of wire break acoustic events during the monitoring period, rate of wire breaks, and consequences of failure (Higgins et al. 2008). 5. Pipeline 3 and 4, San Diego County, California: Acoustic fiber optic cable was installed on 17.1 km (10.6 mi) of PCCP to determine remaining service life in First, they deployed 6 hydrophone arrays in 2005 over 7.3 km (4.5 mi) and found 19 wire breaks and third-party activity by a contractor over the pipe during the 12-month monitoring period. Pursuant to this event, 2 contracts were given out for electromagnetic inspection over a 24 km of Pipeline 3 and 9 km of Pipeline 4. Authority decided to use fiber optics that was being developed at the time, in lieu of a hydrophone array, to monitor the line for a long period of time. Fiber optic cable was installed over 17.1 km. A data acquisition system was programmed to reject acoustic events outside of the parameters established for wire break events. Two monitoring sites were established: one for 6.7 km of one pipeline and the other for 10.4 km of a second pipeline. Broken wires were detected on pipes previously found to be distressed using electromagnetic inspection. A section of pipe with 3 wire breaks during the monitoring period ruptured after experiencing a number of wire breaks in a matter of few hours. This resulted in change in protocol for reporting. The new reporting system was nearly real time. Open channel flow and high velocity of water in steep areas of the line resulted in excessive noise in the data that was difficult to handle with filtering (Gallaher et al. 2007). 6. Cypress Creek Water Transmission Main, Florida: AM was used on a 17.1-mile long, 84-inch-diameter pipeline and a 4.7-mile long, 66-inch-diameter pipeline. Pressure was cycled and wire breaks and weaker delamination signals were monitored. Pressure fluctuations increased the level of acoustic activity (Higgins et al. 2003). 7. Great Man-Made River Project, Libya: AM with hydrophone probe was used over 40 km of 4 m diameter pipeline with high distress. Performed both short and long term monitoring and developed a Pipe Criticality Index (PCI) calculated based on (1) the number of broken wires from electromagnetic and AM inspections, (2) the ratio of actual working to design pressure, (3) use of single or double prestressing wire wraps, and (4) soil resistivity, without consideration of failure margin based on risk curve technology.comparison of neural network with multi-parameter regression analysis showed the

98 Chapter 5: Monitoring Technologies 77 superiority of neural network to regression analysis for developing PCI and predicting rates of wire break in pipe (Amaitik and Amaitik 2008, Essamin and Holley 2004). 8. Great Man-Made River Project, Libya: Pipeline risk management system was developed to combine manufacture, environmental, operational, and inspection data with structural and statistical analyses to model future pipeline deterioration. AM was then extended to over 100 km, using hydrophones and surface mounted sensors; acoustic fiber optic cables were later installed for continuous monitoring. Fiber optic cables were installed at a rate of 10 km in 3 days. Wire break results were used in the pipeline risk management system to help prioritize inspections and repairs. Power requirement for the data acquisition system was met with 100W solar panels. Several distressed pipes with high rate of distress were intercepted prior to rupture. Hydrophone data and fiber optic system data were compared and determined that both systems can identify and locate breaks, but the fiber optic system is more sensitive and costs less per unit length (Lenghi et al. 2009) to 96 inch diameter pipelines, Arizona: Used electromagnetic and AM for risk management of a pipeline and to predict the remaining life to failure using a deterioration model (risk curve). Borrowing technology developed for Libya, a pipe criticality index was defined based on the following variables: the number of wire breaks from electromagnetic inspection, the ratio of actual to design working pressure, pipe wrap (single or double), and soil resistivity. Pipes were classified as (1) requiring immediate intervention, (2) requiring monitoring, or (3) being in no immediate danger of failure re-evaluate later (Elliott et al. 2006). Acoustic Monitoring Summary AM is a direct method that can provide information on the rate of wire breaks in a pipe, and identification of pipes with active distress. AM can be used for general condition assessment of a pipeline or for identifying areas with higher acoustic activity compared to the other parts of the line. AM when integrated with electromagnetic inspection and failure risk analysis that correlates number of broken wires to failure can provide a technology for asset management and predicting the remaining life to failure. AM is useful to identify the pipes that are actively deteriorating. The advent of acoustic fiber optic technology has resulted in an improvement of technology as it provides continuous sensors along the line, thus eliminating issues related to the necessary spacing of the sensors to provide adequate accuracy for detection and location of wire break events. Although high rate of wire breaks is known to be a measure of extreme distress for pipes that are very close to failure, no correlation between the rate of wire breaks and the existing distress level in the pipe has been established. In absence of information on the number of wire break before AM, the use of AM for detection of critically distressed pipe remains a technology challenge.

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100 CHAPTER 6: METHODS OF FAILURE MARGIN ANALYSIS AND REMAINING SERVICE LIFE ESTIMATION FAILURE MARGIN ANALYSIS USING RISK CURVES TECHNOLOGY Description Definition Direct failure margin analysis using the risk curves technology evaluates the effect of broken prestressing wires on the performance of the pipe and its margin to failure using a calibrated and verified model. Failure margin may be evaluated using risk curves corresponding to limit states related to serviceability, damage, and ultimate strength of the pipe with broken prestressing wires (Figure 6.1). Repair priorities are assigned to pipes with broken prestressing wires in order to identify pipes with unacceptable risk of failure when subjected to the maximum internal pressure and gravity loads. History Failure margin analysis is often performed using a model that was developed by Zarghamee in 2001 as a part of a research program on failure of PCCP with broken wires sponsored by the PCCP Users Group. An experimentally verified model was developed that relates the number of broken wires and maximum pressure in the pipe to limit states of serviceability, damage, and strength (rupture). The program included, field investigations, nonlinear finite element analyses (Figure 6.2), and hydrostatic pressure testing (Figure 6.3) from which a practical failure margin analysis procedure was developed. The results of this research program were published in Zarghamee and Ojdrovic (2001), Zarghamee et al. (2002), and Zarghamee et al. (2003). Experimental verification was published by Zarghamee (2003). The accuracy of the risk curves technology was verified by comparing the predicted number of broken wires and maximum pressure corresponding to failure of the pipe with the actual value for highly distressed pipes prior to failure and failed pipes (Ojdrovic et al. 2011). The application of the procedure to LCP was published by Erbay et al. (2007). Other failure margin analysis methods using limit states curves have been developed, but no experimental verification of these methods have been published or made available. Physics of Technology The failure scenario of PCCP with broken prestressing wires progresses as follows: (1) microcracking of the concrete core (serviceability limit state) occurs within the prestress loss zone as tensile stresses increase, (2) visible longitudinal cracking of the concrete core (damage limit state) occurs within the prestress loss zone as the core expands radially, (3) circumferential cracking of the concrete core occurs at the center and the edges of the broken wire zone, and (4) the ultimate strength of the distressed pipe is reached, when the steel cylinder yields, cracked concrete core reach its strength, and soil resistance is overcome (ultimate strength limit state). 79

101 80 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Analysis Process The first step in failure margin analysis of a pipeline is collection of pipeline data including pipe design, maximum pressures expected in the pipeline, soil cover heights, and any available information regarding past performance, inspections, and aggressiveness of the environment toward PCCP. Risk curves are then constructed for each pipe design class using the earth load corresponding to the actual soil cover height (usually within about ±2 feet). The serviceability limit state is based on the onset of concrete core cracking, the damage limit state is based on structural cracking of the core and on increase in wire stress adjacent to the BWZ, and the strength limit state is based on the ultimate strength of the pipe (Zarghamee et al. 2003). Thinning of the steel cylinder due to corrosion is accounted for in analysis of LCP (Erbay et al. 2007), but is generally not included in analysis of ECP unless identified as a concern based on the pipe design or external inspection. The risk curves divide the plots of pressure versus number of broken wires into repair priority zones, as shown in Figure 6.1 for ECP. Repair priorities are calculated for each pipe containing broken wires using the maximum expected pressure in the pipe and an effective number of broken wires that accounts for the estimated number of broken wires from NDT data, uncertainties in estimation of the number of broken wires, and progression of broken wires with time. The expected rate of wire breaks can be either calculated using historical results of condition assessment on the same pipeline or obtained from documented rates observed on other similar pipelines. Each pipe containing broken wires is assigned a repair priority, depending on the margin of pipe failure and the need for repair. Due to the uncertainties in the numbers of wires predicted with the nondestructive condition assessment technologies, the results of failure margin analysis are considered to be preliminary until verification of the predicted number of broken wires is performed on selected pipes through external inspection. After verification is complete, the failure margin analysis and repair prioritization are adjusted as needed and final recommendations are made regarding the future management of the pipeline. Benefits and Issues The benefits of the technology can be summarized as follows: Technology is based on structural analysis, hydrostatic pressure testing to failure, and field verification. Accounts for uncertainties in electromagnetic inspection results and condition of wires adjacent to the broken wire zone. Accounts for progression of wire breaks using rates calculated from historical inspection data or from similar pipelines in similar environments. Provides a means to evaluate the structural significance of inspection results. Allows prioritization of repair of distressed pipe.

102 Chapter 6: Methods of Failure Margin Analysis and Remaining Service Life Estimation 81 Strength with contribution of soil Strength without contribution of soil Serviceability Damage Figure 6.1. Example risk curves for a specific ECP design subjected to a specific height of cover and bedding and backfill condition

103 82 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Source: Zarghamee et al. 2003, with permission from ASCE Figure 6.2. Strains in outer core at failure of cracked outer core Figure 6.3. Hydrostatic testing of PCCP with broken prestressing wires Application Failure margin analysis has been performed on PCCP pipelines since 2001 and is used as part of condition assessment and asset management program that includes periodic re-inspection and repairs/replacement of pipes at high likelihood of failure. Some sample applications are as follows:

104 Chapter 6: Methods of Failure Margin Analysis and Remaining Service Life Estimation Central Arizona Project, Arizona: Nonlinear finite-element analysis was used to predict the performance of 252-inch-diameter non-cylinder prestressed concrete pipe (NCP) and 72-inch-diameter PCCP, both subjected to combined effects of internal pressure, pipe and fluid weights, and earth load as it loses prestress due to gradually increasing number of broken wires. The model incorporates a nonlinear stress-strain relationship for concrete that includes compressive crushing, tensile softening and cracking. The results of analysis for 252-inch NCP show that the final failure mode of the pipe is in fact in form of progression of wire breaks due to the increase in the stresses in the wires, rather than concrete crushing or major leakage. The results of analysis for the 72-inch-diameter PCCP subjected to a prestress loss and increasing internal pressure show that interlocking strength of cracked outer core and steel cylinder ultimate strength, rather than progression of wire breakage, governs the strength of pipe. For pipe with large number of wire breaks, structural cracking can occur exposing the steel cylinder to corrosive soil environments. Corrosion of the steel cylinder can result in leakage and premature failure of the steel cylinder. The results of the nonlinear finite element analyses are used to validate engineering criteria and procedures used for risk analysis and repair priorities determination of pipes with broken wires and for comparison with confirmation testing of the pipe with broken wires (Zarghamee et al. 2002). 2. Cedar Creek Pipelines and Richland Chambers Pipelines, Tarrant Regional Water District, Texas: Beginning in 1989, Tarrant Regional Water District (TRWD) recognized that 2 of their 75-mile-long, large diameter PCCP lines were deteriorating. A high percentage of pipes in the Cedar Creek pipeline that were under impressed cathodic protection were found to have wire breaks due to hydrogen embrittlement. TRWD participated in the Prestressed Concrete Pipe User s Group and, along with a number of other agencies, funded a study by SGH to develop a simplified finite element analysis to determine the residual strength of damaged pipes. TRWD employed SGH to develop specific models and risk curves for their 2 pipelines and to calibrate the model for wire failure due to hydrogen embrittlement. As a part of calibration, several pipes with embrittlement were pressure tested to failure. Results of the study showed that pipes with embrittlement had high residual strength. Using the risk curves technology with and without embrittlement, SGH prioritized pipes for repair and TRWD was able to focus repairs on the pipes at highest risk of failure. TRWD s approach of predictive maintenance and replacement of pipes at high risk of failure allowed repair costs to be spread over decades to minimize the impact on budget and operation (Marshall et al. 2005). 3. Central Pipeline, Santa Clara Valley, California: PPIC inspected 4.2 miles of PCCP without shorting straps using RFTC technology in 2001 and inspected 6.6 miles in The 2001 inspection identified 24 distressed pipes (about 2.2%) and the 2005 inspection identified 59 distressed pipes (about 3.4%). SGH performed failure margin analysis of the distressed pipes using results of RFTC inspection and the maximum pressures in the pipes. Preliminary results of failure margin analysis were used to select 5 distressed pipe pieces for external inspection to verify the results of RFEC/TC and to reduce the uncertainties in the failure margin analysis. External inspection consisted of wire continuity measurements, visual inspection and sounding of the exposed pipe surface, and measurement of coating thickness, soil cover height, and prestressing wire diameter

105 84 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment and spacing. External inspection revealed absence of active corrosion and lower numbers of broken wires than predicted by RFTC. Failure margin analysis was revised based on the results of field inspection, and SCVWD determined that repairs were unnecessary and monitoring the line was adequate. SCVWD considers the $330,000 spent to validate electromagnetic results and evaluate the failure margin of the pipeline a good investment compared to the costs of unnecessarily repairing the 59 pipes identified as distressed by electromagnetic inspection (Dion and Zarghemee 2008). 4. Lake Arrowhead Pipeline, Wichita Falls, Texas: RFTC inspection was performed on 5.3 miles of 54-inch-diameter non-shorting strap PCCP in Lake Arrowhead Pipeline and identified 192 distressed pipes of 1708 inspected (11.24%). SGH performed failure margin analysis of the distressed pipes and field inspection to verify the results of RFTC. Results of verification indicate that RFTC s estimation of number of broken wires in zones with less than 15 broken wires is accurate within the normal uncertainties, RFTC s estimation of the number of broken wires in pipes categorized as DA (PPIC terminology for EM signal shift detected across entire length of pipe) appears to be overly conservative, and RFTC s estimation of the number of broken wires in zones with more than 35 broken wires appears to be conservative. The City of Wichita Falls decided to replace the 44 pipes identified as Repair Priorities 1 and 2 due to their geographic proximity. The cost of the inspection plus the cost of the repairs was only a fraction of the cost of replacing the pipeline. The use of RFTC inspection technology and failure margin analysis enabled the City to prioritize repairs and replacements and to determine that significant useful life remaining in its pipeline (Taylor 2008) inch diameter ECP Aqueduct, Providence, Rhode Island: A pipe failure occurred in 1996 prior to failure margin analysis and a heavily distressed pipe was identified by internal nondestructive inspection in External inspection confirmed that the distressed pipe contained approximately 150 broken prestressing wires. The maximum expected operating pressure for these pipes was about 65 psi. Risk curves developed specifically for the pipe design of the failed pipe and the distressed pipe showed that the strength limit state curve passes very near to the failed pipe, indicating that the strength limit state curve predicts the failure reasonably well. The pressure and observed number of broken wires in the distressed pipe exceed the damage limit state, but are below the ultimate strength limit state. Observations of a inch-wide crack in the concrete core, delamination between the steel cylinder and concrete core, and minor surface rust on the steel cylinder correlate well with the level of distress expected on a pipe exceeding the damage limit state (Ojdrovic et al. 2009). Summary Failure Margin Analysis Using Risk Curves Technology The failure margin of PCCP with broken wires depends on the number and location of wire break zones, the number of broken wires in each zone, pipe design, maximum pressure in the pipe, earth load, and pipe and fluid weights. The vast majority of pipes with broken wires do not have a short time to failure. In fact, an objective of pipeline condition assessment is to identify the relatively small number of pipes that have an unacceptably high failure risk and repair them before they fail. Maintaining an acceptable failure risk of distressed pipe with broken wires is accomplished by performing failure margin analysis to determine their failure

106 Chapter 6: Methods of Failure Margin Analysis and Remaining Service Life Estimation 85 risk and by subsequent repair of such pipes. This form of proactive maintenance can result in an overall improved reliability of the pipeline and reduced cost of maintenance and repair. The failure margin analysis using risk curves technology provides, for each distressed pipe, relationships between the number of broken wires and the maximum internal pressure corresponding to certain limit states on serviceability, damage, and strength (rupture). These risk curves are used to determine the failure margin of the pipe based on the number of broken wires, the cover height, gravity effects, and the maximum pressure in the pipe. Reliability of pipe depends on the uncertainty in the number and location of broken wires detected, nature of wire breakage (corrosion or hydrogen embrittlement), and the rate of increase in the number of broken wires in the future if the pipe is not repaired immediately. Field verification of distressed pipe reduces the uncertainty in the predicted number of broken wires and in the failure margin analysis. Uncertainty analysis allows importance factors to be assigned to parts of the pipeline where consequence of failure is great. These uncertainties are used to calculate the effective number of broken wires and pipe repair priorities at present and at several years into the future, within which time the pipeline may be reinspected or repaired. RISK RANKING Description Definition Risk ranking identifies individual pipes or sections of pipelines that have high failure risk, based on evaluation of parameters that are believed to correlate to pipe distress. Such methods include risk index systems, finite element models that are not based on experimental verification, and criteria based solely on the predicted number of broken wires. Risk index systems evaluate failure margin by assessment of design, construction, operation, and environmental parameters that may result in higher risk of wire breakage. Finite element methods evaluate the effect of broken wires on the performance of the pipe using a model that has not been experimentally verified or calibrated against full-scale testing. Methods using only the number of broken wires to evaluate pipe failure margin and remaining service life are based solely on previous experience with the number of broken wires or rate of wire breakage that resulted in pipe failure in the past. History The risk ranking methods have been developed since mid-2000 by various consultants or utilities in an attempt to determine what actions need to be taken after performing inspection of a pipeline and identifying distressed pipes and estimating the distressed level in such pipes. Their success has not been documented and remains unknown.

107 86 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Physics of Technologies Risk index systems account for environmental conditions that are aggressive to PCCP and concludes that the likelihood of broken wires is higher in areas where environmental conditions are more aggressive, containing high chloride concentrations, high sulfate concentrations, severe acids, and/or high levels of dissolved carbon dioxide (AWWA Manual M9). Finite element models developed to capture the behavior of PCCP with broken prestressing wires can identify the stress in the pipe in a relative basis, but have not been shown to be able to capture all failure modes and predict the failure of distressed pipes accurately through experimental means. Analysis Process Risk Index System: Risk index systems (e.g., Pipeline Decay Index or Pipe Criticality Index) determine criticality of pipeline section or a pipe based on the varying physical characteristics of the PCCP and environment along the pipeline. Factors taken into account include design parameters, original construction practices, modes of operation, maintenance procedures, results of corrosion surveys, results of internal inspections and results of acoustic monitoring of the line. Finite Element Analysis: FEA methods are based on a finite-element model of the pipe subjected to internal pressure and possibly gravity loads and prestressing, including loss of prestress. In general these FEA methods define a measure of distress as a function of the number of broken wires. Depending on the complexity of their model, they may also provide a measure for failure margin of the distressed pipe, but may not be able to predict neither the failure margin nor time to failure with any accuracy. An FEA model was developed for the analysis of an aqueduct in Mexico and used to calculate the stresses in the concrete core and steel cylinder at various lengths of prestress loss and for a constant internal pressure (Gomez et al. 2004). No experimental basis or verification data is provided for this model. One FEA method assumes incremental decrease in the prestress level along the entire pipe in order to establish the sensitivity of pipe design to wire breaks over a large area and determines the effect of prestress loss on performance of the pipe using limit state criteria from AWWA C304. There are other proprietary methods with no information provided to allow evaluation (Marshall 2009, Loera 2007). Specified Number of Broken Wires: Using this method, failure margin and remaining service life of a pipe is based only on the estimated number of broken wires or on the observed rate of wire breaks from NDT data. Empirical data of the number of wire breaks that causes a PCCP to fail in the past are generally used to determine the maximum tolerable number of broken wires. Alternatively, pipes are evaluated based on the rate of wire breakage and are replaced if the observed rate increases beyond a threshold.

108 Chapter 6: Methods of Failure Margin Analysis and Remaining Service Life Estimation 87 Benefits and Issues The benefits of the risk ranking technologies can be summarized as follows: FEA methods are based on structural analysis, and provide a relative sensitivity of the pipe to loss of prestress. Risk index method and specified number of wire breaks provide a low cost method for determining the relative failure risk of distressed pipe. All technologies allow for prioritization of repairs. Use of index systems and decisions made based solely on the number of broken wires are relatively low cost after the data collection. The following limitations of the risk ranking technology have been identified: The correlation between the actual failure margin and predictions of these technologies has not been documented. Subject to uncertainties in the results of inspection and rate of wire breakage. No published literature discusses how uncertainties in nondestructive testing results are accounted for in the use of these technologies. Application Risk ranking methods have been used as a part of condition assessment and asset management program to identify high-risk pipes. The following is a sample of their applications: 1. Cutzamala Aqueduct, Mexico City, Mexico: Two ruptures in the 99-inch-diameter PCCP line prompted a study to develop a methodology for prediction of PCCP failure due to loss of prestress. 2D models of the steel cylinder alone and of the steel cylinder with concrete core were used for preliminary calibration of the analyses. The final 3D model used for prediction of failure did not include earth load and was analyzed for a single internal pressure. Existing prestress outside the prestress loss zone was modeled by applying an external pressure equal to the original prestress minus the internal pressure. Within the prestress loss zone, the full internal pressure was applied to the pipe. Bonding of the broken wires was modeled by assuming that the wire has a development length of 30 inches. The length of prestress loss was increased incrementally until the prescribed failure condition of cracking of the inner concrete core and yielding of the steel cylinder occurred. The model showed that 42 broken prestressing wires resulted in the prescribed failure condition at the internal pressure of 1 MPa (142 psi) (Gomez et al. 2004). 2. Large diameter PCCP, San Diego, California: SDCWA developed a proactive aqueduct protection plan (APP) to ensure that their pipelines remain in service to provide safe and reliable drinking water. APP consists of inspection, data analysis and condition assessment, and implementation. Inspection consists of corrosion surveys, internal visual and sounding inspection, external inspections, and forensic investigations. Results of over-the-line surveys and internal and external inspections are organized in a database. The data is analyzed to determine required further actions. The following common

109 88 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment characteristics were identified for pipe sections that have been replaced: soil resistivity less than 2,000 ohm-cm, exposed to cycles of wetting and drying, chloride content of soil greater than 1,400 ppm, and bedding and backfill were less dense than the surrounding native soil. Prioritization of remedial actions takes into account pipe design and construction data; results of internal, external, and corrosion inspections; redundancy; transient pressures; and changes to the surrounding environment (Galleher and Stift 1998). 3. Large diameter PCCP, Phoenix, Arizona: The City of Phoenix developed a method for prioritization of sections of a 150-mile-long pipeline system for condition assessment. The system was subdivided into pipelines 3 to 5 miles long based on operational constraints and installation date. The likelihood of failure consequence of failure relative to other sections was determined using only readily available information. Installation date, proximity of the pipeline to waterways (prone to wetting and drying cycles), and soil corrosivity were used to rank the pipes according to likelihood of failure. Adjacent land use, pipeline diameter (measure of the number of people affected by rupture), and proximity to major roads and railways were used to assess consequence of failure. Pipelines were prioritized using a relative margin assessment matrix (Williams et al. 2007). 4. Potomac Transmission Main, Maryland: A study was performed on 6.5 miles of 96-inchdiameter PCCP in the Montgomery County Main Zone. At the time of evaluation, the pipeline had been in operation for 40 years and had suffered several ruptures. The study included condition assessment, Performance Analysis, and consequence of failure evaluation. Condition assessment included internal visual, electromagnetic, Sonic- Ultrasonic, and acoustic assessments. Continuous sonic-ultrasonic data was collected inside the pipe at the 4 o clock and 8 o clock positions on the pipe circumference. Results of condition assessment were used in Performance Analysis to predict structural safety factors. No description of how Performance Analysis was performed or how the level of distress predicted using the Performance Curves compared to the Sonic- Ultrasonic results. All PCCP with broken wires should be repaired, and the timing of repairs should be based on the observed and anticipated levels of distress (Marshall et al. 2009). 5. PCCP force mains, Wilmington, North Carolina: The City of Wilmington developed a method for prioritization of sections of a pipeline system for condition assessment. Step 1 is to identify the condition (likelihood of failure) and criticality (consequence of failure) factors that will be used to assess the system. Step 2 is to collect the data to evaluate the factors identified in Step 1. Step 3 is to assign numerical rankings to each factor. Step 4 is to assign a numerical rating (a risk index) to each pipeline using the numerical rankings and relative importance of each factor. Step 5 is to use the numerical ratings (the risk index) to prioritize the system (Miles et al. 2007). Risk Ranking Summary Risk ranking methods have been used to identify high-risk sections of pipeline for rehabilitation or further condition assessment investigation. The methods that have been used are risk index systems, finite element analyses, and criteria based solely on the predicted number

110 Chapter 6: Methods of Failure Margin Analysis and Remaining Service Life Estimation 89 of broken wires. Risk index systems have often been used initially to prioritize sections of a pipeline or a system for use of advanced condition assessment technologies. Numerous finite element analysis methods have been developed aimed at establishing a relative measure for failure margin of the distressed pipe, but not an accurate measure as they have not been experimentally verified and cannot predict the rupture of a distressed pipe accurately. Methods using only the number of broken wires to evaluate pipe failure margin and remaining service life are the simplest approach, but are based solely on previous pipe failure experiences.

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112 CHAPTER 7: WHAT WORKS? In general, what works is a program of pipeline asset management aimed to maintain the pipeline risk of failure at an acceptable level. It generally includes periodic inspection, failure margin analysis, and identification of pipe pieces with unacceptable failure risk, and repair or replacement of such pipes. HOW DO I SELECT PIPELINES/SECTIONS FOR CONDITION ASSESSMENT? Selection of pipelines or sections of pipelines for condition assessment should be based on the criticality as discussed in Chapter 2. Determine the criticality of the pipeline as follows: Determine the consequences of failure of each pipeline from public safety hazard, service interruption, political cost, and cost of loss of public trust. Determine the likelihood of failure, using all available data, including age, design standard under which the pipe was designed and manufactured, installation data, past performance data, failure history, pressure level in the pipeline, and the results of failure analysis, inspections, corrosion surveys, and failure margin analysis. In addition, determine if there are any issues in design, manufacturing, construction, environment, and operation that affect the likelihood of failure. A preliminary failure margin analysis may be conducted to determine level of damages necessary for pipe rupture. Determine the likelihood of failure using a rating system or other techniques. If the likelihood of failure is not uniform along the pipeline, subdivide the pipeline into individual pipe or pipeline segments and determine the likelihood of failure for each distressed pipe or pipeline segment. Determine system constraints, redundancy, the total time the pipeline can be out of service, valve operability, access constraints and cost, and dewatering issues and cost. Determine the criticality of the pipeline. Pipeline criticality can be high, low, or medium. Pipelines with high criticality should be inspected using advanced NDT technologies. Examples of different criticality of pipelines are given below: High criticality: A nonredundant pipeline, ECP type, passing through a populated area where failure can have life safety implication (high consequence of failure) was manufactured in the 1970s with Class IV wire. There has not been any major failure of the line. Internal inspection showed pipes with hollow sounding areas and cracking (high likelihood of failure). Condition assessment with advanced technology is required. Low criticality: A redundant pipeline passing through a field (low consequence of failure) was manufactured in the 1960s and has no failure history (low likelihood of failure). Condition assessment may be limited to periodic internal inspection. Medium criticality: A redundant pipeline passing through a lightly populated residential area (medium consequence of failure) was manufactured in the 1960s and experienced one failure a few years ago where corrosion and wire breaks were noted 91

113 92 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment along with what appeared to be coating damage (medium likelihood of failure). This pipeline would be dealt with as if it were a low criticality pipeline. If on the other hand the pipeline would be passing through a school yard, condition assessment with either advanced technology or multiple conventional technologies, with high repair priority given to distressed area near the school yard, would be appropriate. HOW DO I SELECT A TECHNOLOGY FOR CONDITION ASSESSMENT? Selection of condition assessment technology is different for low, medium, and high criticality pipelines. The results of condition assessment are integrated with other available data to improve the accuracy of condition assessment and determination of failure risk. For high criticality pipelines with expected impending failure, use electromagnetic inspection or acoustic monitoring or both, depending on the importance of the line, and if the pipeline cannot be inspected by electromagnetic inspection, consider using acoustic monitoring alone in area where pipe rupture may occur. For high criticality pipelines, consider condition assessment using advanced technologies, such as electromagnetic inspection and failure margin analysis. For low criticality pipelines, consider doing nothing, or select conventional condition assessment technologies that are low in cost, such as over-the-line corrosion survey and internal inspection. For medium criticality pipelines, consider using either multiple conventional condition assessment technologies that are each low in cost or an advanced technology with higher cost and accuracy for baseline condition assessment. The selection of the technologies for condition assessment should be based on accuracy of detection of distress, especially identification of highly distressed pipe, and estimation of the extent of distress from which failure margin can be established. Detection of distressed pipe is subject to two types of errors. False positive error occurs when we identify a good pipe as bad, and a false negative error occurs when we identify a bad pipe as good. False positive error results in increased cost of repair and rehabilitation and should be kept very small for economic reasons. False negative error results in bad pipes with high risk of failure to remain in the line and continue to deteriorate and rupture; it is counterproductive to the goal set for condition assessment. Therefore, a condition for selection of a technology for condition assessment is availability of verification data that show accurate detection and estimation of distress level and accurate estimation of distress level for the pipe of interest. An example is the use of electromagnetic inspection on a pipeline with embedded cylinder pipe without shorting strap; in this case, the utility should review the results of calibration performed by the service provider on the pipeline to be inspected or a pipeline with nearly identical properties in order to understand the technology s resolution for estimating distress level before inspection. HOW FREQUENTLY SHOULD A PIPELINE BE INSPECTED? All pipelines must be periodically inspected. Typically, the inspection period should not exceed 10 years. Distressed pipelines or pipes manufactured in 1970s with Class IV wire and poor coating may need to be inspected more often, say about once every 5 years. Highly

114 Chapter 7: What Works? 93 distressed pipelines with impending rupture should be inspected more often, say once every 3 years. IS FIELD VERIFICATION OF NDT RESULTS NEEDED? IF YES, HOW? The results of NDT using a technology need to be compared to the results from another technology to verify detection accuracy, and field-verified for both accuracy in detection and accuracy in estimation of distress level, unless substantial verification of the results has already been made and is available. The uncertainty in estimation of distress level from the results of an advanced NDT technology has a component that is pipe dependent and cannot be eliminated, and a component that is related to the interpretation of signals and can be reduced through field verification. Verification of the detection accuracy requires showing that false positive and false negative errors are very small. False positive error, i.e., identifying good pipes as bad, can be detected by the same techniques used for the verification of accuracy of estimated distress levels as discussed below. However, false negative error, i.e., identifying bad pipes as good, can be detected only by comparison of the results with those of alternate inspection method. Therefore, use of multiple technologies for condition assessment is needed when likelihood of false negative is there. For example, when condition assessment relies primarily on electromagnetic inspection results, internal inspection can be used to address false negative occurrence, and external inspection can be used to address false positive occurrence. Verification of the accuracy of estimated distress levels may be performed by selecting a sample of pipes identified to be distressed by the NDT technology for examination. The examination of these pipes may include: use of a different technology; excavation and external inspection of the pipe surface for signs of corrosion, delamination, and cracks; corrosion inspection using half-cell potential or linear polarization; inspection of wire condition trough windows opened through the coating; internal inspection; and wire continuity test for ECP without shorting strap. A highly accurate procedure for field verification for PCCP without shorting strap is electric continuity test of adjacent wire wraps as described in this Manual. WHAT DO I DO WITH THE RESULTS OF CONDITION ASSESSMENT? Once the results of the condition assessment of a pipeline are available, distressed pipes have been detected, and the extent of distress estimated, it is necessary to determine the margin to failure and repair priority of the distressed pipe, i.e., how close a distressed pipe is to rupture in terms of the number of broken wires accounting for the uncertainties of NDT technology.

115 94 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment HOW DO I REDUCE THE RISK OF FAILURE? There are four ways to reduce the risk of failure: 1) pressure control, 2) spot repair, 3) rehabilitation of pipeline sections, and 4) cathodic protection. Pressure Control: For a distressed pipe, the failure margin of the pipe depends strongly on the maximum pressure that the pipe experiences in future. The maximum pressure is the total sum of the working pressure and the transient pressure. The transient pressure in a pipeline depends on the design of surge control mechanisms provided and proper maintenance of this equipment. In general, it is prudent and cost effective to reduce the maximum pressure by performing a transient surge analysis, designing and installing appropriate surge control devices, controlling surge by changing operation procedures of pumps and valves, maintaining air/vacuum valves operational, and pressure monitoring. Spot Repair: The spot repair process involves repair or replacement of those pipes with unacceptable failure risk. Spot repair would require periodic inspection, estimation of distress level for distressed pipe, failure margin analysis, risk analysis and identification of pipes with unacceptable failure risk (with high criticality), and repair or replacement of such pipe. Spot repair of pipes with unacceptable failure risk will still leave a small probability of failure of pipes with lower failure risk due to the inherent uncertainties of NDT technology used. Rehabilitation of Pipeline Section: Failure risk analysis may reveal a pipeline section where the rate of occurrence of highly distressed pipes is so high that spot repair may not be economical. The cost per foot of length for rehabilitation of a section of a pipeline is typically much smaller than the cost of spot repair or replacement. Therefore, rehabilitation of a section may be the more economical choice, although there may be many good pipes in that section. Pipe replacement in a section or lining a section with steel, CFRP, or slip-lining with HDPE or smaller diameter pipe are the options for rehabilitation. The evaluation to determine whether spot repair should be used or sections rehabilitated should be based on a hydraulic/structural/economic analysis that compares the current cost of rehabilitation of a section with the present value of the spot repair performed on pipes currently with high risk of failure and those pipes whose risk of failure becomes high in the future. Cathodic Protection: Cathodic protection (CP) of an electrically continuous pipeline reduces the corrosion rate and the subsequent corrosion risk and the future repair and re-inspection need. CP can be applied to a pipeline after the onset of corrosion. In fact many of the recently constructed pipelines are electrically continuous, i.e., with joint bonds that electrically connect the adjacent pipes together and have shorting straps that is stretched under the wires and connect the wires to the joint rings; the pipeline is initially monitored and if corrosion is noted, it is placed under cathodic protection. The cathodic protection is typically in the form of either impressed current or sacrificial anodes. In designing cathodic protection using impressed current, great care must be exercised to ensure that pipe to soil potential does not exceed in magnitude a limit beyond which hydrogen can develop at cathode, resulting in hydrogen embrittlement of wire. In designing CP with sacrificial anodes, the use of zinc anodes is recommended because magnesium anodes can create a potential greater in magnitude than the limit beyond which hydrogen can develop and result in hydrogen embrittlement of wire. When the pipeline is not electrically continuous, but has shallow cover, CP anodes can be installed at every other joint and connected to the two adjacent pipes. This is an easy process if

116 Chapter 7: What Works? 95 ground surface restoration cost is minimal and increases with depth of cover and surface restoration cost. The estimated cost of CP should include the cost of establishing continuity between adjacent pipes if the pipeline is not electrically continuous and the cost of construction of deep wells, shallow wells, and impressed current stations.

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118 CHAPTER 8: WHAT DOESN T WORK? IGNORING CONSEQUENCES OF RUPTURE IN PLANNING ASSET MANAGEMENT Rupture of a large diameter PCCP, due to its large size and higher pressures in the line, releases a large volume of water under pressure, which has an immense destructive power. The destructive power of the released water drives the total cost of rupture up. The consequences of rupture may include quantifiable cost such as property damage, repair cost, failure investigation expenses, and cost of water lost and of service interruption downstream of failure point. Service interruption may result in business losses, which can be quite substantial, depending on system redundancy. In addition, there are non-quantifiable costs such as risk of loss of life, loss of public trust, and political fallout that should be accounted for. Using the quantifiable and non-quantifiable costs of rupture, one can determine the failure risk. Resources then are allocated to the different pipelines or sections of pipelines in accordance with their failure risk. Ignoring consequences of rupture, i.e., its quantifiable costs and nonquantifiable consequences and fallouts, results in improper expenditure of resources without achieving the reliability desired, and does not work. On the other hand, assigning unrealistically high cost to the consequences of rupture in a line results in unnecessary repairs and loss of reliability of the pipelines to which the needed resources were not allocated. Multiple failures in a pipeline, without a publicly acceptable explanation, increase the non-quantifiable cost of rupture and expose the utility to negligence allegations. Multiple breaks can result in significant reduction of public trust, increased public scrutiny, and political fallouts. In some cases, multiple ruptures have resulted in court-mandated actions that bind the utilities to a course of action that may not be the most prudent. NOT HAVING A PROPER ASSET MANAGEMENT PROGRAM Not having an asset management program or having one that does not properly account for system constraints, consequence of failure, likelihood of failure, and ensuing risk of failure does not work. USE OF CONDITION ASSESSMENT TECHNOLOGIES WITH UNVERIFIED ACCURACY The use of condition assessment technologies with unverified accuracy does not work. Understanding the limitation of a technology in an application (e.g., inability of electromagnetic inspection to detect broken wires near the joints) is essential. Use of technologies with unverified accuracy in detecting distressed pipes and in quantifying the level of distress in such pipe can result in data that cannot be used to establish the failure margin of the distressed pipe, its failure risk and repair priority. Inaccuracy in detection of distressed pipe can be either costly as good pipes are repaired unnecessarily or ineffective in condition assessment as bad pipes go undetected. Failure in accurately estimating the extent of distress will cause errors in determining how close the pipe is to rupture, and results in either unnecessary repairs resulting in wasting of scarce resources or loss of reliability and failure of the pipeline as highly distressed pipes remain unrepaired. An example is the use of electromagnetic inspection of ECP without 97

119 98 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment shorting strap when calibration does not exist or when existing calibration does not support the resolution needed. USE OF TECHNOLOGIES FOR FAILURE MARGIN ANALYSIS AND DETERMINATION REPAIR PRIORITY WITH UNVERIFIED ACCURACY The use of technologies for determination of failure margin and repair priority with unverified accuracy can result in error in determining how close the pipe is to rupture. Not knowing the proximity of the pipe to rupture can result either in unnecessary repair or in failure to prioritize highly distressed pipe for repair, thus increasing the likelihood of rupture and its ensuing risk of failure. In summary, the use of technologies for failure margin analysis that have not been verified for accuracy does not work. OVERKILL IN REHABILITATION With limited resources, asset management by (a) repairing all of the distressed pipe identified by an NDT inspection procedure without understanding the cause of failure and without adequate field verification of the NDT results and (b) replacing a part of the line or an entire line with limited distress comparable to the distress level of the pipelines managed successfully by others does not work. We should recognize that corrosion and wire break are manifestations of the degradation process of a PCCP. Typically, degradation process of PCCP takes many years to mature and reach a critical stage that causes rupture under the applied loads. In some cases, the cause of failure is something other than the pipe which can be eliminated or reduced, such as stray current, improper cathodic protection, and local environment. In such cases, repair without solving the root cause problem is not wise. In most cases, PCCP with limited number of wire breaks can safely perform under the design loads and pressures for many years. Therefore, repair of all distressed pipes that exist at a point is not consistent with the best use of limited resources, as new distressed pipes will appear shortly after such a radical action. Replacement or rehabilitation of a section of a pipeline with low to moderate risk of failure usually stems from assigning unnecessarily high cost to rupture and the misunderstanding that distress and risk of failure grows very rapidly. This argument is not valid, because there is now 60 years of experience with PCCP that shows distress grows gradually. In fact, on the average, the fraction of distressed pipes in a line is about 3.7% of the total and the number of distressed pipes with high risk of failure is an order of magnitude less than the number of distressed pipes. In other words, PCCP is not like an apple box where a rotten apple causes the entire box of apples to rot in a short time. Therefore, replacing a section of pipeline with limited distress and a low-to-moderate risk of failure does not work and constitutes an inefficient use of scarce resources in a system that could have been managed at a fraction of cost.

120 CHAPTER 9: WHAT S NEXT? In the following sections, we have described the technologies needed by the utilities for improved condition assessment and pipeline asset management. We have categorized these technologies into (1) pipeline asset management, (2) PCCP design improvements, (3) analysis improvements, and (4) future developments. The research needed for the development of the new technologies requires collaboration and financial support of the utilities. Utilities should pool their resources to fund the needed research to solve the challenging problems ahead. PIPELINE ASSET MANAGEMENT Determining Pipeline Criticality Determining the criticality of a pipeline or a section of a pipeline and the need for application of advanced technologies using the existing data is an important step in condition assessment. Several index systems currently in use, such as pipe criticality index by GMRP, pipeline decay index developed by Raz Konyalian, engineering consultant for SDCWA, or the index developed by SGH in a closed-form functional for EPRI (Buried Pipe Reference Guide, EPRI, Palo Alto, CA: , to be published by EPRI in 2011), are examples of attempts to determine criticality from the existing data. The use of artificial intelligence approach using neural networks and fuzzy mathematics using fuzzy Markov processes has already been tried in limited cases. More work is needed to verify the results of the actual condition of a large number of pipelines where advanced technologies have been used with the results obtained from such procedures, and to develop a better index or procedure to determine the criticality of a specific pipeline. Acceptable Risk Is there an acceptable level of risk? Utilities have different risk aversions and do not believe that there is a single acceptable risk that can be defined for all utilities; rather, the acceptable risk depends on many factors that differ from utility to utility and should be defined for each utility. More work is needed in this area to help the utilities better define their risk aversion. PCCP DESIGN IMPROVEMENTS Build Robustness in Design of PCCP The tolerance of PCCP to distress, expressed in terms of broken wire, is quite different for different pipe with different design loads and pressures. There is a need for building tolerance for certain levels of distress in the design of PCCP so as to reduce sensitivity of rupture to distress. Currently, the design of PCCP considers the pipe to be free from distress. 99

121 100 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment ANALYSIS IMPROVEMENTS Ability to Estimate Remaining Service Life without Long History of Site-specific Data The remaining service life of a pipe can be established from knowledge of failure margin in terms of the number of wire breaks to rupture and the rate of wire breaks expected to occur. Data on the rate of failure for a specific pipeline can be obtained by multiple electromagnetic inspections or by AM. In absence of site-specific data, the rate of wire break for estimation of remaining service life can be obtained from sites of similar characteristics (Zarghamee et al. 2011). More work is needed on the rate of wire break through the life of PCCP. Electromagnetic Inspection and Large Uncertainties Electromagnetic inspection accuracy near the joint is far from adequate. Many false positive and false negative errors occur in detection of distressed pipe and in estimating the distress level due to uncertainty of the current technology near the ends. Similarly, the accuracy of the detection and estimation of distress level is subject to uncertainties for special pipes, such as pipes with outlet, pipes with thicker cylinder, and pipes with multiple wraps. There is a need for understanding by utilities and the consultants of the uncertainties of the electromagnetic inspection results near the pipe ends and for special pipes so that the uncertainty can be considered in failure risk analysis. NDT Signal Interpretation Understanding the capabilities, accuracy, and uncertainties of each NDT technology is a responsibility of utilities. Furthermore, understanding the intricate relationships between the signal of an NDT technology and the actual level of distress in the pipe (from which failure probability, failure margin, or time to failure can be estimated) is an essential part of successful condition assessment. This relationship needs to be made clear to the utilities and the users of technologies. Practical limitations and uncertainties in the application of NDT technologies should be identified and eliminated through research. Verification of Acoustic Monitoring Results There is a need to show the accuracy of AM results. For this purpose, a series of distressed pipes should be subjected to SGH wire continuity test before and after a period of time in which multiple wire breaks have been recorded and located. At each time the pipes are excavated and electric continuity test is performed to determine the actual wire breaks and their locations. Comparison of the results with AM test will reveal the accuracy in detection and location of wire breaks by AM during the monitoring period.

122 Chapter 9: What s Next? 101 FUTURE DEVELOPMENTS Condition Assessment Technologies for PCCP with Wire Breaks Caused by Hydrogen Embrittlement Hydrogen embrittlement breaks, unlike the wire breaks caused by corrosion, do not align and occur randomly along the length and around the circumference of the pipe. This has been observed in pressure testing to failure of pipe with more than 120 broken wires where pressure at rupture was not significantly affected relative to a good pipe. This is due to the fact that random wire breaks result in residual prestress in the pipe that prevents the core from cracking. Such a technology should be able to detect accurately the number of broken wires and the stiffness of the pipe wall. For hydrogen embrittlement wire breaks, distress is not then defined solely on the number of wire breaks but on the combination of pipe wall stiffness and number of wire breaks. There is a need to distinguish between random wire breaks caused by hydrogen embrittlement and clustered wire breaks caused by corrosion. Accurate Method for Detecting Broken Wires on Excavated LCP and ECP with Shorting Strap SGH has developed a simple wire continuity test of adjacent wire wraps to identify the breaks in the wire wraps for ECP without shorting strap. For this test, the top of the pipe is exposed, the coating is removed over a 2-inch-wide strip, and resistance of adjacent wire wraps is measured. This procedure is highly accurate for identifying and locating individual wire breaks, but it is not applicable to ECP with shorting strap or to LCP. There is a need to develop a similar test that shows accurately where wire breaks are located in an ECP with shorting strap or in an LCP. Ability of Fiber Optic Cable to Perform Wire Break and Leak Detection Simultaneously Since wire break and leak detection are both acoustic, it is reasonable to expect that a technology can be developed to perform both wire break detection and localization and leak detection and localizations simultaneously. As a first step to this goal, the ability of fiber optics to resolve the acoustic event from turbulence noise in high velocity lines need to be developed and demonstrated. Detection of Joint Defects The joint defects in the form of poorly grouted joints expose the joint rings to corrosion. The corrosion of joint rings may result in brittle wire breaks as hydrogen is released at the cathode. There is a need for a technology that can be used to detect joint defects in PCCP lines. Other Condition Assessment Technologies Average pipe wall stiffness: Areas of reduced pipe wall stiffness have been detected in cast iron pipe and asbestos cement pipe by measuring the velocity of a wave traveling through

123 102 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment the water in a pipeline. A controlled wave induced in the pipe travels as a compression wave in the water along the pipeline and dilates the pipe. The wave velocity decreases in areas of reduced pipe wall stiffness, and the average velocity between two points can be used to calculate the average pipe wall stiffness using established relationships between pipe stiffness and water bulk density (Bracken and Johnston 2009). Verification of stress wave propagation inspection results: Impact echo inspection results have been verified by Sack and Olson (1994) and by Zarghamee and Maser (1997); however, the use of SASW for determining concrete core modulus and pipe stiffness and detection of distressed pipe has not been verified. There is a need for such verification. Once the technology is verified, pipe stiffness measured by SASW can be used for detection of distressed pipe. Inductive scan imaging: Detection of defects (fractures or corrosion) in steel embedded in concrete is a developing area for application of the inductive scan imaging technique. Experiments performed on pipelines in Libya show that the technique is able to identify broken or corroding prestressing wire from the exterior of the pipe and locate the distress in the circumferential direction. PCCP vibration frequency: Prestress loss due to prestressing wire breakage may result in reduction of pipe stiffness and changes in the natural frequency of vibration. Work on the correlation of the natural frequency of PCCP with broken wire length has been reported (Alavinasab et al. 2010). Detection of cylinder corrosion by electromagnetic inspection: Development is underway for electromagnetic inspection technology to detect corrosion of the steel cylinder in LCP (Pure Workshop statement). Laser profiling: Geometric evaluation of a pipeline interior surface can be performed using laser profiling technology. A model of the pipeline interior can be reconstructed using the data collected during inspection and can be used to quantitatively evaluate the pipe interior surface for irregularities such as spalling, deterioration of inner core, and inside joint mortar loss (Kwak et al. 2007).

124 APPENDIX A: RESULTS OF QUESTIONNAIRE SURVEY OF PCCP CONDITION EVALUATION PRACTICES Background and Objectives As a part of the industry survey process, a questionnaire was sent to utilities, consultants, and service providers in order to get a broad perspective on the engineering practices on PCCP condition assessment, performance monitoring, and service-life estimation in the past 12 years. The questionnaire was sent out to 64 water utilities, 23 consultants, and 10 service providers. Fifteen utilities, 1 consultant, and 1 provider responded (Table A.1). These responses often were presented in sentence fragments; in that case, an attempt has been made to complete the view expressed in the comment with a minimum of editing. The survey questions fall into 4 categories: condition assessment technology, monitoring technology, failure margin analysis/service life estimation, and risk mitigation. The following synthesis of the survey responses is organized accordingly. Table A.1. Responding utility, consultant, and service provider Responding Utilities Abbreviation The City of Calgary Calgary North Texas Municipal Water District NTMWD Cleveland Division of Water CDW Greater Cincinnati Water Works GCWW San Patricio Municipal Water District SPMWD Howard County Department of Public Works HCDPW San Diego County Water Authority SDCWA Metropolitan Water District of Southern California MWDSC Aurora Water Aurora Central Arizona Project CAP Halifax Water Halifax Calleguas Municipal Water District Calleguas Tarrant Regional Water District TRWD Greater Lawrence Sanitary District GLSD City of Montreal, Québec, Canada Montreal Chicago Department of Water Management Chicago Responding consultant Abbreviation Jason Consultants Jason Responding provider Abbreviation NDT Corporation NDTC Synthesis of Survey Responses To be consistent with the arrangement of the questionnaire, all survey responses are summarized in tables and presented in four parts below: Part I - Condition Assessment Technology Experience Overview Part II - Monitoring Technology Experience Overview 103

125 104 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Part III Failure Margin Analysis/Service Life Estimation Experience Overview Part IV Risk Mitigation Overview Part I Condition Assessment Technology Experience Overview Part I of the questionnaire was focused on PCCP condition assessment technologies used by the responding utility during the past 12 years. For each technology used, the utility was asked to complete a form included at the end of the questionnaire to provide more details and comments regarding the technology. These responses for 18 technologies currently in use by the responding utilities are summarized in Tables A.2 through A.4. Part I also contained an openended question concerning gaps in the existing condition assessment technologies. Answers to this question are presented in Table A.5. Table A.2. Summary of current condition assessment technology Technology Category Condition Assessment Technology No. of Utilities Using the Technology Length of Pipeline (mi) Most Recent Year Used General Usefulness Limitations Electromagnetic Inspection RFTC Was able to identify pipes with broken wires and to locate distress. Helpful in setting up the repair priorities. Reliable in identifying wire breaks. The most quantifiable method and extremely cost effective. Most effective when used to find pipes with a lot of wire breaks. Limited in detecting wires that are almost completely corroded. Cost is considered extremely high. Limited by need for shut down and access. The technology is limited by traction in the pipe lessening the percentage coverage of the pipeline. Limitations were due to slope and access. Large variances with external inspection results for some very large diameter noncylinder pipe. (continued)

126 Appendix A: Results of Questionnaire 105 Table A.2 (Continued) Technology Category Condition Assessment Technology No. of Utilities Using the Technology Length of Pipeline (mi) Most Recent Year Used General Usefulness Limitations Internal Visual Inspection and sounding Stress Wave Analysis Over-the-line Surveys Pipe External Inspection P-Wave With robotics, exceptional for entering and exiting the pipe. Displayed that pipes in areas of concern from soil samples and criticality have no wire breaks, and allowed one or two pipes in poor condition to be targeted. Internal Very useful in helping prioritize the replacements. Proven to be effective in advanced stage of deterioration. Very effective in identifying corrosion occurring from inside the pipe. Heavily damaged segments were found. Impact Echo (IE) Index System Pipe-to-Soil Potential Provides areas where pipeline needs to be catholically protected. Identifies areas of stray currents. Soil Resistivity Soil Chemical Analysis Cell-to-Cell Potential Good first screening to determine areas that have a risk of failure due to soil condition. The results had a very low level of correlation with RFTC results. Very limited in identifying corrosion of the wires occurring from the outside. Cathodic protection masks almost all the issues. Sulfates typically are in small pockets and sampling intervals can miss these pockets The time spent did not merit using the test. Geotech Half-Cell Potential External Inspection A clean and easy way to verify corrosion of wires and their conditions. Gauss Field 1 < The gauss test was very slow. Wire Continuity Can detect broken wires and locations with high accuracy in ECP without shorting strap Can be used only in ECP without shorting strap (continued)

127 106 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Technology Category Condition Assessment Technology No. of Utilities Using the Technology Table A.2 (Continued) Length of Pipeline (mi) Most Recent Year Used General Usefulness Limitations Leak Detection Ground Microphones Has been successfully used to detect leaks in LCP Correlators SmartBall Very effective at locating and quantifying leaks. Sahara The general usefulness of the procedure is good. Saved pot holing to look for leaks. Limited due to access into the pipe. Limitations were bends and valves. Technology Name No. of pipes with verified results Table A.3. Summary of number of verified results for different technologies No. of distress areas, e.g., BWZs, hollow sounding areas, leaks, etc. No. (%) of false identification of distressed pipes (False positive) No. (%) of areas with accurate distress quantification No. (%) of areas with overestimated distress quantification No. (%) of areas with underestimated distress quantification No. (%) of areas accurately predicted location (within 1 ft) RFTC (52%) 20 (45%) 1 (2%) 42 (95%) P-Wave (75%) 1(10%) (10%) Internal (100%) N/A Impact Echo (100%) 0 0 N/A Sahara SmartBall Results of only one verification test were provided for each Sahara and SmartBall leak detection systems. These technologies have been shown to be successful for leak detection based on experience of SGH and as documented by literature review.

128 Appendix A: Results of Questionnaire 107 Inspection Technology Name Length of Pipeline Inspected (mi) Table A.4. Summary of PCCP condition assessment cost data Cost (per mi unless otherwise noted) Utility Comment Internal 148 $10k TRWD Staff inspects 0.6 to 2.5 $56k Halifax Manned and PipeDiver used for inspection. Additional $32k per mile in utility costs. 0.5, 0.17, 0.5, $13k MWDSC Tests for side-by-side comparison with P-Wave to 9 $12 to $16k MWDSC RFTC $15k SDCWA Total inspection length not provided. 148 $10k TRWD 10.1 $50k NTMWD Including cost of dewatering, cleaning, ventilation, inspection, testing and external inspection for verification $64k Calgary PipeWalker, PipeRanger, and PipeCrawler used for inspection. Response does not specify if access costs are included $28k Aurora With internal inspection by provider. 0.5, 0.17, 0.5, $19k MWDSC Tests for side-by-side comparison with RFTC. P-Wave $64k Calgary P-Wave and Wet P-Wave used for inspection. Response does not specify if access costs are included. Pipe-to-Soil 148 $0.5k TRWD Resistivity Cell-to-Cell Localized external inspection for verification. Cost of access Chemical 27.8 $2k San Patricio exceeded cost of inspection. Geotech External Chemical 44 $3k Calgary 334 samples collected at a cost of about $400 each. SmartBall 10.1 $11k Calgary Sahara 2.7 $23k Calleguas No access costs necessary. External 10 $5k TRWD 8 pipes $10k per pipe Calgary Excavated pipe, inspected pipe coating, and hydroblasted coating to expose prestressing wires. Notes: 1) No adjustment made for exchange rate at time of inspection 2) No adjustments for year of inspection

129 108 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table A.5. Summary of current gaps in PCCP condition assessment technology Subject of Response Response Author Accurate method to detect A good method for finding wire breaks after excavating pipe sections broken wires on excavated based upon internal testing methods. CAP Allow economical assessment without removing large diameter pipelines from service. SDCWA Capability to perform RFTC needs to be less intrusive to the system (no shut down for Halifax condition assessment with pipeline in service access). Positive progress with PPIC PipeDiver. In-the-wet electromagnetic testing for very large diameter pipe CAP Current ability to perform condition assessment while pipeline is under pressure and/or low flow velocity is a significant limitation. 1 GCWW Calibration data used to estimate the number of wire breaks require destroying a pipeline; calibration data must be determined for both Non-destructive GCWW ECP and LCP for differing pressure classes (prestressing strand electromagnetic inspection spacing) and diameters. calibration RFTC: Degree of accuracy is dependent on calibrating to actual SDCWA pieces of pipe. Electromagnetic inspection accuracy near joints Electromagnetic inspection accuracy on pipe with nonstandard properties Understanding of sensitivities and uncertainties in electromagnetic inspection results RFTC wire break sensitivity and quantification accuracy near joints. MWDSC RFTC does not pick up wire breaks near joints. Calleguas RFTC technology is suspect in joint areas of the pipe. SDCWA RFTC needs to be more accurate at bell and spigot ends. Halifax RFTC wire break sensitivity and quantification in pipes with thick MWDSC cylinder, and other non- standard PCCP fabrication configurations. RFTC technology is suspect in double wrap pipe. SDCWA Large variances with external inspections results, both underestimating and overestimating the number of wire breaks in 252-inch-diameter pipe and several false positive results in smaller CAP diameter non-cylinder pipe. Correlation between P-Wave technology and accurately locating distressed pipe areas and estimating number of wire breaks. Aurora Lack of / unacceptable correlation between RFTC and P-Wave wire break existence predictions; limited availability of P-Wave wire MWDSC breaks prediction verifications. Clarification of minimum RFTC WB sensitivity in non-shorting strap PCCP: 1 WB or sufficiently rusty splice reported as 5 WB, which presents potential to overestimate by a factor of 5, especially with MWDSC multiple break regions. Clarification of minimum RFTC WB sensitivity in shorting strap PCCP may be 5 20 WB depending on position; higher potential to MWDSC underestimate or miss WB, especially near joints. Remote Eddy Current Evaluation Reliability of number of wire breaks. GCWW 1 Technologies are currently available to perform electromagnetic inspection of in service pipelines. See Chapter 4 for details of the available technologies. (continued)

130 Table A.5 (Continued) Appendix A: Results of Questionnaire 109 Subject of Response Response Author Electromagnetic inspection cost Failure margin analysis Corrosion detection and probability with time Detection of joint defects Differentiation between wire breaks due to corrosion and embrittlement Verification of stress wave propagation inspection results Unmanned visual inspection of in-service pipeline Distinguish multiple wire breaks in short distance from a few wire breaks spread across the same area. Aurora Lack of certainty in number of wire breaks with electromagnetic inspection. CDW RFTC: More verification of survey results is required. SDCWA RFTC needs to be lower cost. Halifax Remote Eddy Current Evaluation what does it really mean and at what point is the information able to determine whether or not a GCWW pipeline is bad or in jeopardy. RFTC can t detect wire corrosion. CDW Inability to detect levels of corrosion on prestressing wires. Chicago Corrosion probability versus time to initiation of or existence of corrosion; locating small, but structurally significant corroded areas MWDSC on PCCP. No technology other than visual is available to identify separated, damaged, seeping, and leaking joints during internal inspections. MWDSC Rapid determination of embrittlement versus corrosion damage. TRWD Verification of test results of stress wave propagation methods. This would greatly improve data interpretation of test results and add creditability to the testing industry. Visual internal inspection of force mains that are too small for human entry without dewatering. NDTC Jason Part II Monitoring Technology Experience Overview Part II of the questionnaire was focused on PCCP condition monitoring technologies used by the responding utility during the past 12 years. For each method used, the utility was asked to complete a form included at the end of the questionnaire to provide more detailed experience and comments regarding the technologies. These responses for the 5 monitoring technologies in use by the responding utilities are summarized in Table A.6 and Table A.7. Part II also contained an open-ended question concerning gaps in the existing condition monitoring technologies. Answers to this question are presented in Table A.8.

131 110 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Monitoring Technology Name No. of Utilities Using Technology Table A.6. Summary of monitoring technology experience Length of Pipeline Inspected (miles) Acoustic Fiber Optics Hydrophone Arrays Hydrophone Station Pressure Surface Mounted Piezoelectric Sensors Most Recent Year of Use General Usefulness Benefits of real time reporting. Used in conjunction with baseline inspection information to determine break rate and threshold for repair /replacement. Cost-effective for monitoring longer distance (1km or greater). Used in conjunction with baseline info to determine break rate and threshold for repair/replacement. Cost effective for short length and short time period. Helpful in identify the magnitude of the failing pipes. Helpful for gathering information on time frequency of wire break event to predict rate of deterioration in localized area. Cost effective for monitoring shorter distances (~450m or less) or point monitoring. Used in conjunction with baseline info to determine break rate and threshold for repair/replacement. Limitations Impractical for short distances or point monitoring. Life-cycle costs are extremely high. Insertion was restricted by the number of bends in the pipeline. Not designed to continuously monitor for long periods of time. Impractical for long distances.

132 Appendix A: Results of Questionnaire 111 Inspection Technology Name Length of Pipeline Inspected (mi) Table A.7. Summary of PCCP monitoring cost data Cost Utility (per mi per year) Comment Acoustic Fiber Optics Hydrophone Arrays Hydrophone Station Surface Mounted Piezoelectric Sensors 2.2 to 11.9 $70k - SDCWA Includes installation and monitoring. $100k $130k- $170k MWDSC Includes installation, equipment, and monitoring, but not dewatering. Response specifies duration as long term. 7.1 $13k Howard County Monitoring cost only, does not include installation or equipment 2.25 $70k SDCWA Five sites including installation and monitoring. Response does not specify duration. $30k per MWDSC Includes installation and monitoring. Costs reduce as mi per 6 monitoring period extends beyond 6 months. Response does months not specify the total length of pipeline monitored. 0.7 $25k per 110 yds per year Calgary Solar powered units used at monitoring station. Does not include installation costs. Hydrovac used to access main for sensor installation. Table A.8 Summary of current gaps in PCCP monitoring technology Part II - What gaps currently exist in PCCP monitoring technology? Subject of Response Response Author High cost of repeated electromagnetic inspection Ability of Fiber Optic to perform wire break and leak detection simultaneously Verification of acoustic monitoring results Baseline estimate of number of wire breaks needed High cost of Fiber Optic ownership RFTC: High cost and inconvenience of repeated inspection. Ability of Fiber Optic to perform wire break and leak detection from same system. Good R&D by Pure Technologies in this area. Need verification of wire breaks predicted by acoustic monitoring. Fiber Optic: Need to obtain verification of monitoring results with excavation of suspect pipes. Acoustic monitoring differentiation between wire breaks versus other sources of acoustic events, such as wire slips. AET from Apr-Oct 2008 failed to confirm any wire breaks in the test area previously considered an area of increasing concern. Acoustic monitoring identifying corrosion breaks versus brittle type breaks. Acoustic monitoring wire break location resolution. Acoustic monitoring requires baseline RFTC for most accurate WB assessment. Lower cost of ownership for in pipe Fiber Optic solution. Acoustic monitoring requires continuous monitoring to capture all wire breaks, cost is very high. Fiber Optic: Life-cycle costs are extremely high. Halifax Halifax MWDSC SDCWA MWDSC Aurora MWDSC MWDSC MWDSC Halifax MWDSC SDCWA High cost of Fiber Optic Wet deployment of fiber optic sensors in a force main. Jason (continued)

133 112 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table A.8 (Continued) Installation Need Inexpensive installation of fiber optic sensors. Calgary Provide real time wire break results Improve capabilities of Fiber Optic in high velocity/pressure lines Fiber Optic: It is considered very expensive to install. Providing real-time monitoring results for short distance/point monitoring. Fiber Optic: There have been limitations due to high velocities. Part III Failure Margin Analysis/Service Life Estimation Experience Overview SDCWA Calgary SDCWA Part III of the questionnaire was focused on PCCP failure margin analysis/service life estimation methods. For each method used, utilities were asked to complete a form included at the end of the questionnaire to provide more details and comments regarding the particular method(s) they have used. These responses are summarized in Table A.9 and A.10. Answers to the open-ended question in Part III, regarding gaps currently existing in PCCP service life estimation method, are presented in Table A.11. Table A.9. Summary of failure margin analysis/service life estimation experience Failure Margin Analysis/Service Life Estimation Procedure No. of utilities using the technology Most recent inspection Date Pipe Types Inspected (ECP/LCP/NCP) SGH failure risk curves technology 9 November 2010 ECP/LCP/NCP Method based on structural 5 November 2010 ECP/LCP evaluation w/existing distress Method based on structural ECP evaluation w/o existing distress Method based solely on the number 4 November 2010 ECP/LCP/NCP of broken wires Other methods ECP/LCP

134 Appendix A: Results of Questionnaire 113 Method Risk curve technology for failure margin analysis Table A.10. Summary of failure margin analysis/service life estimation techniques Description of the method From RFTC, the tool adds uncertainty and continued deterioration Risk curves developed for 252-inch-diameter NCP The measure for service life estimation RFTC inspection results; pressure data; original lay schedule. Structural analysis and collateral damage potential. Available data on wire breaks; Working plus transient pressure and earth load. Subject of Response Verification Accuracy in of the correlating measure for with service life inspection estimation results Not really; a pipe not analyzed in 2004 failed in We had a pipe fail 6 months after prediction said it would. This winter we will be excavating and evaluating pipes identifies by SGH. Did not perform verification. Very good. Cost of servicelife estimation $29,400 (4.25 mi, ECP) Several hundred thousand dollars $100k (7.1 mi, ECP and LCP) Usefulness and limitations Allowed us to prioritize repairs. Limited by RFTC s uncertain data at times. Useful for preparing our replacement plan. Risk curves were critical to put true value to wire break information. Condition based replacement is the most cost effective procedure. Allows us a rational approach on which pipe sections need repair and to protect critical structures from damage. Used Author CDW Aurora Halifax TRWD HCDPW CAP (continued)

135 114 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Method Based on structural evaluation of pipes with known distress Based solely on the number of broken wires Description of the method Performed on two pipes and then extrapolated the results for the entire pipe system to build criteria for pipe repair or monitoring. First run a C304 Analysis of the PCCP assume incremental decrease in prestress level. Provide general indication of the sensitivity of pipe design to wire breaks. Then for designs that are sensitive to wire breaks, run nonlinear FE analysis to determine effect of increasing wire breaks on state of stress/strain vs. limit state criteria in C304. Used empirical data of the number of wire breaks that caused a feedermain to fail to build criteria. Monitoring event using hydrophone arrays and fiber optic cables to identify failure pipes. The measure for service life estimation Number of broken wires on an individual pipe. When wire breakage in conjunction with operating loads, results in a case where the stress/strain have exceeded the strength limit criteria then end of life has occurred. Assume linear rate of wire break to estimate time to failure. Number of broken wires on an individual pipe None; we usually repair it when we see a problem. The pipes show activities are usually few, so it is better to Table A.10 (Continued) Subject of Response Verification of the measure for service life estimation Previous observation of number of wire breaks that caused feedermain to fail, while adding in a factor of safety. No Previous observation of number of wire breaks that caused feedermain to fail, while adding in a factor of safety. Accuracy in correlating with inspection results Appear to be accurate. Fairly good correlation between internal visual inspection and the results of electromagne tic surveys. Appear to be accurate Very accurate Cost of servicelife estimation $25k (LCP, pipeline length not provided) $5.0K- 7.5K per design. Minimal Only the time need to evaluate the data received; The cost is in the monitoring Usefulness and limitations Provided more accurate criteria for determining our course of action for a pipe. Industry needs an accepted method for statistically using collected data in a probability analysis to estimate remaining life. Gave quick results and seemed accurate enough for starting our condition assessment program. Simplicity and low costs. Author Calgary Jason Calgary HCDPW (continued)

136 Appendix A: Results of Questionnaire 115 Method Description of the method The measure for service life estimation prioritize and schedule the repairs. Table A.10 (Continued) Subject of Response Verification of the measure for service life estimation Accuracy in correlating with inspection results Cost of servicelife estimation. Usefulness and limitations Author Others Methods Based upon Pipeline Decay Index (PDI) which is developed by considering design features, construction practices, operation modes, maintenance procedures, external environments, corrosion survey, internal inspections, and soil conditions. Excavation and inspection of existing pipe with known corrosion problems Based on several iterations of condition assessments, forensics, and pipeline construction. Pipeline Decay Index (PDI) Expanded database of assessment findings, changes from previous inspections, causes, and rates of deterioration, fabrication, ages, and corrosion conditions. No Service life estimation is not verified; However, inspection results (RFTC wire breaks) have provided some verification of the priority list. Close correlation between pipe s condition and its expected service life. Somewhat correlated to our 1998 corrosion priority list. $2/ft Useful in setting the timeline for replacement /rehabilitation. But you really do not know what the pipe s condition is. This study is based on bits of information and trusting technology that is relatively new. SDCWA SPMWD MWDSC

137 116 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table A.11 Summary of current gaps in PCCP failure margin analysis/service life estimation Part III What gaps currently exist in PCCP service life estimation methods? Subject of Response Uncertainties in inspection data and progression of failures Long history of data needed to estimate service life Response Assumptions that have to be made and accuracy of data. Uncertainties in assessment information or limited condition assessment information can limit ability to reliably predict service-life of a particular distressed pipe section. Lack of consolidated and detailed information on utility experiences with PCCP failures, repairs, forensics, causes, and discovery and rates of deterioration predicted by latest assessment methods. Based upon RFTC inspections, so some uncertainty from base data. Doesn t know about unique situations for a specific segment of pipe. More project experience from utilities to consolidate on best practice. Reliable pipeline service-life estimate requires several iterations of inspections, evaluation of corrosion information, failure and repair history, external evaluations, forensics, causes and rates of deterioration, risk associated with fabrication, backfill, age, etc. - may take 15 years based on 5-8 year inspection cycle and adequate capture of measureable stages of deterioration. Inspections require pipeline shutdowns, which are typically coordinated with other pipeline maintenance, construction, agency requests, etc. Impact Echo measurements have indicated outer mortar delamination in several (~10) pipe sections in which RFTC has detected minor (5) or no wire breaks. Some have heavy gage cylinder, some have standard cylinder, some are adjacent to previous repairs. We have verified outer mortar delamination at one location and plan to repair within a year and further evaluate condition of wires at that time. We plan to re-inspect the other locations for wire break development. This may potentially provide useful deterioration rate information in some areas exposed to certain conditions. More data is needed to evaluate service life. This will only come with time. Author CAP MWDSC MWDSC CDW Halifax MWDSC MWDSC HCDPW Probability of failure model based on measured degradation Consideration of pipe design properties Estimates need to be updated as new data is obtained. What s missing is a probabilistic model based on Weibull distribution to estimate probability of a failure for PCCP. We use the information on the wire breaks to have an idea of the remaining service life of the pipe. Now we are in the process of acquiring an asset management software and for that, we are validating the information in our database; this information includes: the type of material, date of installation, history of failure, pressure zone and other factors that might affect the remaining service life of the pipes. The next step will be the estimation of the remaining service life of our pipes by using a deterioration model and we will use the results to target our rehabilitation project. Consideration of value of additional external coating systems (such as loose-wrap polyethylene). This can make a very large difference in service life of the line is specific applications (low resistivity clays and presence of moderately saline shallow ground water). SDCWA Jason Montreal SPMWD

138 Appendix A: Results of Questionnaire 117 Part IV Risk Mitigation Overview Part IV of the questionnaire includes three open-ended questions on PCCP risk mitigation. Utilities responses to these questions are summarized in the Table A.12 below. Table A.12 Summary of the risk mitigation strategies Subject of Response Response Author Part IV. a What strategies have you used for extension of service life? Pipe replacement Calleguas Pipe replacement Repair with steel liner Repair with carbon fiber reinforce polymer liner Repair with externally applied post-tensioning tendons Replaced 4.5 miles of 252-inch-diameter Agua Fria, New River, and Salt River siphons by Replace distressed pipe sections with steel Replacement of single "high priority" pipes. Repair or remove damaged segments based on condition assessment Replacement of high risk pipes with steel pipe. Replaces PCCP with steel pipe on those sections deemed to be severely distressed. If the pipe location allows for open cut excavation, the pipe will be excavated and replaced. We are replacing 24-inch pipe with PVC after a service life of 57 years. Removing pipes with excessive wire breaks and replacing them with steel. Highly distressed pipe have been sliplined with steel pipe Steel liner was applied to 1,000 ft of 252-inch diameter NCP Line distressed pipelines with steel Steel liner installation The Water Authority s preferred choice to extending PCCP service life is steel slip-lining. Of 82 miles of PCCP, approximately 27 miles have currently been slip-lined with the remaining to be lined by The remaining schedule for relining is based on the condition assessment reports, RFTC surveys, and acoustical monitoring. Carbon fiber relining of PCCP to rehabilitate those sections of PCCP deemed severe in which replacement with steel sections is not feasible due to economic or environmental concerns. Carbon fiber lining Carbon fiber lining Carbon Fiber Wrap Carbon Fiber Repairs If the pipe location does not allow for open cut excavation, the pipe will be carbon fiber repaired (CFR). Highly distressed pipe have been repaired using carbon fiber lamination Line distressed segments with carbon fiber Post tensioning of pipe sections with excessive wire breaks. Post-tensioning tendon repair of 252-inch-diameter pipe between External reinforcement CAP MWDSC Halifax TRWD Aurora SDCWA HCDPW SPMWD Calgary Jason CAP MWDSC Calleguas SDCWA SDCWA Calleguas Montreal CDW CAP HCDPW Jason MWDSC GLSD CAP Montreal (continued)

139 118 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Subject of Response Response Author Cathodic protection with sacrificial zinc anodes Halifax Added cathodic protection TRWD Continue corrosion monitoring; add or upgrade cathodic protection and stray MWDSC Cathodic protection current mitigation systems as determined by corrosion monitoring and findings during repairs/forensics Cathodic protection, using impressed current, of 30 miles of PCCP ranging in CAP diameter from 62 in. to 144 in. Installed pressure regulator Montreal Pressure reduction Pressure reduction Montreal One power plant operator has reduced pressure so that cylinder strength is not Jason exceeded as way of coping with wire breaks. Others Inspection and monitoring program No solution once corrosion has started Table A.12 (Continued) Wire splice repair Externally coating with coal tar epoxy Inspection and monitoring program Determine cause and extent of damage (corrosion from corrosive soils, stray current, isolated damaged, isolated or area settlement, etc.). Re-inspect with RFTC, visual, and impact-echo within 5-8 years depending on previous inspection findings, failures, repairs, forensics, corrosion data, settlement concerns. Repair distressed PCCP segments based on structural analysis of recent wire break findings, changes from previous inspections, suspect cause, corrosion evaluation, historical inspection information, historical repair and failure information, consequence of failure, operations, service, and reliability requirements. Occasionally add adjacent pipe section(s) with no distress if primary distress pipe has WBs near joint(s), add pipes with initial/minor/no distress indications if they are between or adjacent to distressed pipes and suspected cause is aggressive soil conditions, stray current, settlement in an area; constructability considerations, repair/shutdown schedule are factors in how much is repaired in addition to primary distressed pipe(s). Performed RFEC/TC testing to identify number of wire breaks and replace sections of distressed pipe as necessary. Less-distressed pipes are being monitored using acoustic fiber optic cables or reinspected to determine rate of increase in distress (wire break) before rehabilitation. We have not found any viable strategy for extension of service life once corrosion of the cylinder and wires has started. Part IV. b How has each strategy affected pipeline performance? Replacement with steel pipe: performance was not adversely affected. Pipe replacement: successful. Pipe replacement: It has extended the pipelines useful life. Successful extension of service life using pipe replacement Removing pipes with excessive wire breaks and replacing with steel pipe: appears to be unaffected. Replacement: To date, we have not had an unplanned outage. CAP Montreal MWDSC MWDSC MWDSC Chicago Jason SPMWD Aurora Calleguas HCPWD Calgary CAP Successful extension of service life using CFRP repairs Carbon Fiber Repairs: Repair of individual pipes, coupled with monitoring or reinspection of less-distressed pipes, has allowed the PCCP pipe owner to continue to operate the transmission mains while still controlling the risk of an unexpected failure. Very effective approach. Repaired with CFRP: It has extended the pipeline useful life. Jason HCPWD (continued)

140 Appendix A: Results of Questionnaire 119 Subject of Response Response Author Carbon Fiber Repairs: To date, we have not had an unplanned outage. CAP Successful extension of service life using steel lining repairs Table A.12 (Continued) Repaired with CFRP: The sections wrapped in 2004 have not had further wire breaks per our 2009 inspection. Carbon fiber lining: successful. When we apply the carbon fiber lining, the structural strength considerably increased. Steel sliplining: Repair of individual pipes, coupled with monitoring or reinspection of less-distressed pipes, has allowed the PCCP pipe owner to continue to operate the transmission mains while still controlling the risk of an unexpected failure. Very effective approach. Steel sliplining: The Water Authority designs the new steel lining to last 50 years. The reduction in diameter results in negligible changes in the operation of the pipeline, and these changes are included in their Regional Master Plan. Steel Liners: To date, we have not had an unplanned outage. CDW Calleguas Montreal Jason SDCWA CAP Successful extension of service life using post-tensioning repairs Temporary service life extension using CFRP repairs Success using reduction of transient pressures Success using cathodic protection Successful extension of useful life by iterative inspection, repair of distressed pipes, and occasional repair of nondistressed pipe in high-risk areas. General Comments related to risk mitigation Steel liner installation: successful. Post Tensioned: To date, we have not had an unplanned outage. Post tensioning of pipe section with excessive wire breaks: still operating after 30 years of operation. Carbon-fiber: Currently, the Water Authority considers relining with carbon fiber a temporary repair until the section can be sliplined with steel. Once a service life has been determined for carbon fiber, the repaired sections will be re-evaluated to determine whether it is or it can be made into a permanent repair. To date, there have been 13 pipe sections repaired with carbon fiber. Transient pressure monitoring of pipe acoustic monitoring of pipeline: still operating after 30 years of operation. Dramatically reduced failure rate. Zinc anodes appear to have significantly halted corrosion and wire breaks versus unprotected pipes. Reduced the potential for catastrophic failures by this approach and replacing the most distressed pipes. Overall strategy of inspection iterations, utilizing multiple methods (RFTC, visual, Impact Echo, forensics, corrosion evaluation, etc.), and repairing distressed pipes and occasionally neighboring pipes has significantly reduced likelihood of pipeline failures and assured reliability. To date, we have made repairs in 12 of our 27 PCCP pipelines, which amount to 0.65% of the PCCP in our system. Nearly 70 percent of the repairs are in one pipeline, in a few areas that were subjected to severe corrosion / stray current conditions. Since adding RFTC in 2000, we had two failures: One failure in 2002 due to settlement, two years after inspection (15 WB) One failure in 2004 due to settlement before first inspection of the pipeline. When we perform inspection and when we monitor our pipe that helps us to target our rehabilitations and at the same time increase the pipe performance. Calleguas CAP GLSD SDCWA GLSD TRWD Halifax Chicago MWDSC MWDSC MWDSC Montreal (continued)

141 120 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table A.12 (Continued) Subject of Response Response Author We have a few high pressure zones and in the case we have to reduce the pressure in the pipe because of its condition, we need to install new pump station, or use bypass to maintain the pressure in the distribution lines. Montreal Costs and benefits of CFRP repair Finally when the self-pressure regulator is installed, the pressure is limited in the sector and we note low pressure when we have high consumption. And in some cases we might have to rethink the distribution system in this area. Part IV. c What are the costs and benefits associated with each strategy used? Replacement of two pipes at a time is very expensive, but easy to budget because we have very few high risk pipes. Open cut replacement costs roughly $30,000 to $40,000 per spool. Pipe replacement: costly but we ve very experienced in this method. Requires extensive work area and sometimes traffic control. Costs of steel replacement: Estimate: $20/(LF - in diameter); $1,920/LF for typical 96 in. PCCP Costs and benefits of Benefits of steel replacement: significantly reduce risk of failure and improve pipe replacement reliability of pipeline; provides opportunity to conduct full forensics on distressed pipe; no loss of ID. Replacement with steel pipe: Eliminates the need for replacing the entire pipeline and allows steel to be used in areas with soils with known high sulphate content. The cost of a steel pipe replacement is approximately $100k to $200k depending on location and is for construction costs only. Benefit is long life expectancy to localized (single pipe) repairs. A section of pipe can be replaced in a short period of time, typically 6-10 days. Carbon fiber: most expensive but quick and easy to construction. Limited work area is required. The carbon fiber wrap is expensive, but it appears that it s working so far. Unfortunately a segment we didn t wrap failed in Did we prevent a segment from failing by wrapping it, most likely, but we still didn t prevent the main from failing. The cost of a carbon fiber reline is approximately $6,580/lf (based on 96 in. pipe). Benefit is minimal impact to communities or environment. Sections can be repaired in 3-4 days. Costs and benefits of steel lining repair Carbon fiber lining increases considerably the structural strength of the pipe and doesn t need a lot of subsequent maintenance, but it remains a costly method Cost of carbon fiber liner: Estimate (6 layers): $40-50/(LF in diameter); $4,800/LF for typical 96 in. PCCP. Benefits of carbon fiber liner: excavation not required, beneficial where excavation or steel liner is difficult; reduce risk of failure and improve reliability of pipeline. CFR in the past has costs $50,000 to $65,000 per spool. The cost for carbon fiber can be quite expensive and is only a reasonable repair solution when the added cost of disruption from replacement is considered. Steel liner installation: cheapest method but some work area is required. The cost of sliplining with steel is increasing yearly. In 2003, about $660/lf, in 2004, $830/ft2, in 2005, $915/ft2, and in 2006, $1,040/ft2. Current estimate is about $1,400/lf. The benefit is that it is the most long term solution for large section of a pipeline. Montreal Aurora HCDPW Calleguas MWDSC MWDSC Calgary SDCWA Calleguas CDW SDCWA Montreal MWDSC MWDSC HCDPW Jason Calleguas SDCWA (continued)

142 Table A.12 (Continued) Appendix A: Results of Questionnaire 121 Subject of Response Response Author Cost of steel liner: Estimate: $14/(LF in diameter); $1,344/LF for typical 96 in. MWDSC PCCP. Benefits of steel liner: significantly reduce risk of failure and improve reliability MWDSC of pipeline; minimize excavations; most cost effective method for long stretches. Costs and benefits of post-tensioning repair Post Tensioned Tendon Repairs, Carbon Fiber Repairs, Steel Liners, Replacement, RFEC Monitoring, Acoustic Monitoring, Internal visual inspection and numerous internal tests: We have spent over $100 Million taking care of our pipeline assets. CAP Costs and benefits of cathodic protection Costs and benefits of transient pressure regulation Costs and benefit of combined cathodic protection and selective replacement/repair of damaged pipe Costs and benefits of monitoring Cost of cathodic protection: Estimate (construction only) deep well, impressed current - $50k-$100k per location depends on location, power availability; shallow well costs not readily available. Cost of sacrificial anode and stray current drain station: Estimate (construction only), city location: $50k. Benefits of Corrosion monitoring and cathodic protection: identify and reduce corrosion risks and reduce future repair and re-inspection requirements. CP is relatively cost effective for a pipe in good condition and with minimal depth of bury. Our pipe is 4 to 5 ft deep, and our anodes were installed at each joint due to lack of electrical continuity. Easy process along gravel shoulder of road in our case. Increasing costs as depth increases and surface restoration costs increase. Very easy if pipeline is electrically continuous. Self-pressure regulator is a good strategy which avoids the pipe to fail because of high pressure but we have to consider, shut down cost, installation cost and the impact on the customers. When the pressure is reduced, we are sure to reduce the stress in the pipe, and at the same time reduce the risk of catastrophic failure but to maintain a level of service we might have to install new distribution lines, it s almost the same scenario than the self-pressure regulator. Estimate $14 million cost for program. Benefit: extended life of 2 75 mile long large diameter lines by decades. Cost of corrosion monitoring: $1/LF, or ~$500k annual standard monitoring, stray current testing, identification of CP requirements, upgrades, stray current mitigation system monitoring and maintenance. Cost of internal inspection: MWDSC contract fees for RFTC services have varied from $12,500 to $16,500 per mile, depending on inspection distance per mobilization, and planned inspections of miles over 3-4 years. Full internal inspection estimate: $10/LF, based on $12-17k per mile RFTC, 2-3 visual inspection engineers, ventilation and inspection support crews ($2-3k per mile), and typical $30k per mile dewatering (planning, shutdown, post work). Annual total internal inspection costs based on 6 years to cycle thru 163 miles (27 mi/year): $1.2M. MWDSC MWDSC MWDSC Halifax Montreal Montreal TRWD MWDSC MWDSC MWDSC MWDSC (continued)

143 122 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Table A.12 (Continued) Subject of Response Response Author Costs of acoustic monitoring: Acoustic fiber optic long term monitoring estimates: $10-$12/ft cable installation, $12-18/ft (27-40 DACs) and $2.5/ft monitoring annual. Does not include cost of dewatering for installation or maintain cable (add ~ $5.60/ft). MWDSC Annual estimated costs to Fiber Optic monitor all PCCP based on 6 year system life: $ M (+1 or more shutdowns per pipeline reach for installation, requirements uncertain, add $0.9M to annual). Point insertion hydrophone short term monitoring estimates: $6/ft installation and monitoring; costs reduced as monitoring period extends beyond 6 months (system intended for short term). Benefits of inspection / re-inspection: most cost-effective approach to assess all PCCP and identify distressed pipe sections, determine repair requirements, causes and rates of deterioration. Acoustic monitoring is also very cost-effective if a base line has already been established using electromagnetic tools. Benefit of monitoring: When we monitor our pipes, we are able to know their condition and avoid a catastrophic failure. In this case we have good benefits associated to this strategy. Even if the cost is high, if we compare to the rehabilitation cost or the impact of a failure, the monitoring program is a good strategy. Transient pressure monitoring of pipe acoustic monitoring of pipeline; condition assessment with p-wave; post tensioning of pipe sections with excessive wire breaks: The program implemented is less costly than the complete replacement of pipeline, to date. MWDSC MWDSC MWDSC Jason Montreal GLSD

144 APPENDIX B: MINUTES OF THE WATERRF WORKSHOP MINUTES OF THE WATERRF WORKSHOP, 20 OCTOBER 2010 Attendees Jian Zhang, Water Research Foundation (WaterRF) Gary Burkhardt, Southwest Research Institute (SWRI) Susan Folsom, Tampa Bay Water (Tampa Bay) Alex Margevicius, Cleveland Division of Water (CDW) Larry Smith, City of Phoenix Water Services Department (Phoenix) Jamie Hannam, Halifax Water (Halifax) Tom Gorman, Halifax Water (Halifax) Reid Campbell, Halifax Water (Halifax) Brian Dorn, North Shore Sanitary District (NSSD) Jai Gupta, North Shore Sanitary District (NSSD) Brian Jensen, Donahue Associates (Donahue) Mark Holley, Pure Technologies (Pure) Xiangjie Kong, Pressure Pipe Inspection Company (PPIC) Pamela Harren, Metropolitan Water District of Southern California (MWDSC) David Marshall, Tarrant Regional Water District (TRWD) Serge Paul, City of Montreal (Montreal) Shelly McDonald, City of Ottawa (Ottawa) Mehdi Zarghamee, Simpson Gumpertz & Heger Inc. (SGH) Rasko Ojdrovic, Simpson Gumpertz & Heger Inc. (SGH) Peter Nardini, Simpson Gumpertz & Heger Inc. (SGH) Location SGH office, Waltham, Massachusetts Date and Time 20 October 2010, 9:00 a.m. 4:30 p.m. Opening Remarks M. Zarghamee (SGH) welcomed the attendees Presentations Introduction by M. Zarghamee (SGH) Findings from literature review by R. Ojdrovic (SGH) Findings from questionnaire responses by P. Nardini (SGH) Discussion Session 1 Selection of Technology for Condition Assessment and Repair Prioritization of Pipelines Discussion led by M. Zarghamee (SGH) D. Marshall (TRWD): Noted importance of knowing what is in the ground and pipeline history, including inventory - catalog pipeline data, review of construction records, changes in environment and loading, and understanding what has changed since installation and what activities have been done over time. 123

145 124 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment S. McDonald (Ottawa): Criticality must include importance of pipeline. Rank importance of pipelines in system. J. Hannam (Halifax): Preliminary screening of whole system to identify areas of high priority. Don t focus only on current problem. Screening/criticality is very important for longterm planning. A. Margevicius (CDW): Prioritization of pipelines is critical. Risk is the product of the probability of failure times the consequence of failure; both the probability and the consequences of failure are important. Perform cohort analysis. D. Marshall (TRWD): Romer and Bell work with risk matrix vs. design standard and age P. Harren (MWDSC): Requested that the pipeline data for the WRSS example shown by M. Zarghamee be made available as it may be useful to others. She asked the participating utilities to share pipeline data and results of multiple inspections. M. Holley (Pure): Growth in number of wire breaks may be linear or step-wise S. Paul (Montreal): High risk, old pipelines with no redundancy located in downtown. S. Folsom (Tampa Bay): High risk pipelines with no redundancy and obstructions in line. Has a pipeline that cannot be taken out of service. M. Holley (Pure): Acoustic fiber optics (AFO) has been installed with pipeline in service. J. Gupta (NSSD): Assessing criticality of the whole system is not an option due to time. In general, we are forced to deal with emergencies. B. Jensen (Donahue): Identified uncertainty in inspection results as a problem, developing a long-term-approach as a problem, technical and analysis as not a problem. Utilities face political pressures: Repair pipes when may not be needed Location of pipes Efficiency in repairing reaches of pipe rather than individual segments. Need for a longterm approach and with limited financial resources. CFRP costs are about $5k / ft. J. Hannam (Halifax): Analyze the whole system including pipelines of other materials while maintaining focus on current issues. Currently, Halifax is developing an asset management system. Public opinion of utility is affected when multiple failures occur (implied negligence), resulting in increased consequence of failure. The public may consider the first failure as an act of God, but the second failure may be interpreted as negligence. X. Kong (PPIC): PPIC has done correlation between distress and pipeline data (age, design, etc.) and not all pipelines have correlation. Uncertainties may vary by utility. Growth varies on a pipe-by-pipe basis (including WRSS) J. Hannam (Halifax): Don t develop black box method. Can t increase uncertainty indefinitely if uncertainty is too high, why inspect replace all.

146 Appendix B: Minutes of the WaterRF Workshop 125 M. Holley (Pure): Apply multiple technologies to address high uncertainties for different technological strengths S. McDonald (Ottawa): No black box method. Uncertainties may not be averaged over the pipeline as they may be significantly higher at some locations. Discussion and specific investigation are necessary. L. Smith (Phoenix): Assessment of lines to prioritize repairs. Raising rates for funding is a political issue. Scheduling for shutdowns may be a problem try to schedule with plant shutdowns. System constraints we may have to replace large valves that may not work to enable shutdowns Discussion Session 2 Condition Assessment Technologies Issues discussed: Condition assessment technology Monitoring technology Service life/failure risk Needs of utilities Discussion led by M. Zarghamee (SGH) Discussion of utility experiences with condition assessment technologies, monitoring technologies, remaining service life/failure margin analysis techniques, and utility needs. J. Hannam (Halifax): Electromagnetic inspection (EM) provides good insight to pipe problems and is good for mid-pipe length. Halifax is pleased with the technological advancement of RFTC. It is common for corrosion to enter through joint (migration of chlorides) and the failure mode to start from the end of the pipe. Halifax has experienced underestimation of the number of broken wires within 1-2 feet of the joint as well as false negatives at pipe ends. Repair segment lengths with multiple bad pipes. Work with providers to reduce uncertainties on analysis side. Continue to work with Pure and work with SGH to include uncertainty within a reasonable manner. Pipes may leak before failure success in finding leaks with BW practical monitoring tool for lined cylinder pipe (LCP). Use acoustic detectors (no Sahara or SmartBall TM ) walk over distressed every two weeks with a microphone. Failures have occurred on pipes where no leaks detected two weeks prior. Was leak missed, or did failure progress quickly? Acoustic monitoring and leak detector system may be useful. Typical to have leakage before failure in LCP, so leak monitoring is useful to intercept failures; understanding of the failure mechanism of pipe design is important. CP used on some portions of line D. Marshall (TRWD): Pipe-to-soil measurements can be used to supplement other NDT. Pipe-to-soil potential indicates location of corrosion, but it also has false positive indications, i.e., calling a good pipe bad.

147 126 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment X. Kong (PPIC): EM can detect cylinder corrosion (pipe diver) useful for LCP and BWP. Using Sahara to measure wall thickness is under development using two sensors (used for metallic pipe). This technology is similar to Echologics wall thinning assessment procedure. M. Holley (Pure): One technology cannot solve all problems but reduce uncertainty. Working to differentiate between wire breaks on good pipe and degraded pipe. Acoustics of wire breaks change as pipe loses prestress. Not commercially available. Data may be mined to extract more information beyond just break or not break. D. Marshall (TRWD): Collaboration of end-users (utilities) to fund research to establish relationship between signal (AET and EM) and pipe properties and distress. Utilities can pool money to fund research to solve end effect issues P. Harren (MWDSC): Handle uncertainties near joint by internal inspection and judgment. Brian Dorn (NSSD): Repaired all 60 distressed pipes identified by EM. Five years later, EM identified 30 more distressed pipes. Two years later, Repair Priority 1 pipes have not been repaired and no rupture yet. We have non-shorting strap pipe with no field verification due to deep cover. We suspected hydrogen embrittlement (HE) with multiple BWZs along pipe length observed by RFTC. We need a better way to resolve contiguous versus random breaks. SS? M. Zarghamee (SGH): Can we reduce signal distortion due to single WB on pipe without Can we differentiate between contiguous BWZ and discrete breaks for non-ss pipe? X. Kong (PPIC): Conductivity between the concrete, wire, and mortar is an important variable in applying electromagnetic technologies to pipe without shorting strap. PPIC did calibrator pipes and found variation within the same pipeline (a source of uncertainty). P. Harren (MWDSC): Good RFTC results on NSS pipe. 80% of their pipe is NSS RFTC was mostly accurate with good predictions. Calibration and verification is more important for NSS pipe. M. Zarghamee (SGH): Probability of bad results is higher for NSS pipe. We could perform conductivity testing on samples of mortar coating. X. Kong (PPIC): Coating on wire a factor also. P. Harren (MWDSC): Insufficient data predict the estimated life of a pipe. Some pipes go from 0 to 80 WB in a couple of years How can you say pipes with 0 break are okay? Other factors need to be considered. Seismic effects joint problems WB is now occurring near joints, years later. Fix good pipes in vicinity of bad pipes if they suspect minor damage and minor wire breaks. Acceptable level of risk will be different for all utilities. M. Zarghamee (SGH): Rapid rate of wire breaks is usually associated with occurrence of stray current.

148 Appendix B: Minutes of the WaterRF Workshop 127 J. Hannam (Halifax): Acceptable risk varies. Political decision also. P. Harren (MWDSC): Operates about 160 miles of PCCP. Average rate of distress is somewhat misleading. Some areas have >10%. Service life estimation is the area for development. Future developments lifetime estimation based on experience, validated with real data D. Marshall (TRWD): Operates about 160 miles of PCCP. TRWD had no engineer on staff at the time of pipe installation. D. Marshall is the first engineer. 1,174 damaged pipes out of 33, % distress in area of high CP voltage. Need to differentiate HE breaks from corrosion. TRWD added CP and modified pump and valve operation. Some pipes still jump from 0 to 80+ between inspections. We are now comfortable with hydrogen embrittlement WBs because of residual prestress resulting from random wire breaks. We have replaced pipes/year (1 day to repair 1 pipe) Knowledge of consequential damages can push funding. We encountered torn cylinder due to thrust when accidentally pumped against closed valve. Welding of additional joints didn t help and lead to changing of the thrust restraint design methodology in the M9 manual. We reduced water hammer. A. Margevicius (CDW): PPIC RFTC inspection identified 60 distressed pipes with 25 highly distressed. CFRP repaired 25 highly distressed pipes. Another pipe not identified as highly distressed failed. 25 sections CFRP cost $1.3 mil S. Folsom (Tampa Bay): Cost of inspection critical. We need ability to inspect line in service. Cost will play a big factor in selection of technologies. Whoever does work has to stand by it legally. M. Zarghamee (SGH): Can an acceptable level of risk be defined? Oil and gas industry accepts 1 failure/1000 km/year. J. Hannam (Halifax): Risk calculations of public safety may not be accepted, but utilities can t repair all distressed pipes caught in the middle. Consensus: Acceptable risk will vary per utility. S. Paul (Montreal): Acceptable risk varies with time and location. Combination of AET and EM identifies highly distressed pipe. 72-inch pipe was being monitored with acoustic fiber optics. Several s indicating wire breaks in one day prompted the city to conduct RFTC and resulted in replacement of the pipe combine technologies. J. Hannam (Halifax): Agrees that a standard acceptable probability of failure should be established. We would promote an acceptable frequency of failure. A. Margevicius (CDW): Operates 400 miles of transmission mains (PCCP and cast iron). Many years of data needed to establish failure rate with any statistical significance. Categorize types of failures. Leakage is different from rupture. Typically has one failure per year cast iron has twice the failure rate.

149 128 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment L. Smith (Phoenix): Operates 180 miles of PCCP. Phoenix is in infancy of condition assessment. Not good records of pipe designs. 60-inch-diameter main ruptured, but had redundancy. Broken valves found at time of shutdown for rupture. We have a lining program in place. Not much service life estimation. Everything goes back to the cost. D. Marshall (TRWD): 1 failure in 60-inch line did not affect customers. $15 million property damage S. McDonald (Ottawa): Assessed 2 miles of pipeline (48-inch diameter) post-failure 5 segments in Priority 2 will be rehabilitated next year. New large diameter mains are being installed. Pipe diver inspection is coming up. We are deciding whether or not to install AFO in new line we are leaning to not installing it due to cost. We are concerned whether or not the technology of today will be applicable in a few years? There is km condition assessment work coming up. Funding may not be available for repairs once found. 550 pipes were inspected and 700m long segment of pipe needs to be repaired (full segment). We are also assessing C300 pipe using leak detection Discussion Session 3 Cost of Condition Assessment and Other Topics J. Hannam (Halifax): EM expensive, but has value and is more efficient with unmanned system. Reasonable value. Cost prohibitive with excavation, added manholes, confined space entry. AFO wasn t cost effective for short length of inspection. Appreciates contribution of AFO, but fast turnaround of WB data wasn t a primary concern. AFO may be more valuable for longer lengths. D. Marshall (TRWD): In 1 year, $225k per year increased to $4.9 million per year on inspection. TRWD invests funds in research. Growth rates need research. Pipe scanner to infer corrosion or HE based on spacing of breaks. Inspections by PPIC cost $300k (15-20 miles) / year for years reducing to $100 k (5 miles) / year. Growth has been unusual - troubled by embrittlement vs. corrosion. No need to monitor full time. TRWD intends to put AFO in trench on new line. X. Kong (PPIC): Resolution of EM on outside of pipe increased because a higher frequency can be used because the signal does not penetrate the steel cylinder. High frequency gives better resolution from the outside and has better resolution in joint area. D. Marshall (TRWD): Measurements of pipe wall stiffness may be able to differentiate hydrogen embrittlement from corrosion. Do baseline inspection within 10 years of installation to identify design/installation damage. P. Harren (MWDSC): $30k - $100k/mile to dewater. $1m/year for 30 mile internal inspection and support. AET not cost effective due to high number of isolated segments. May use in areas of concern. Corrosion crew of ~10 people, $10.5 million/year for external corrosion monitoring (163 mi)

150 Appendix B: Minutes of the WaterRF Workshop 129 Long-term contracts make changing course difficult Need multiple inspections to assess line, not just a snapshot Inspections are capital projects as they result in repairs A. Margevicius (CDW): Costs should be identified and discussed in manual. Use PPIC for RFTC 3 miles - $90k RFTC 60,000 feet - $18.23/ft SmartBall 32,000 feet - $6.16/ft Not including dewatering or support Take advantage of pipeline downtime for additional inspection. Should have inspected and done a more complete assessment of the pipeline during shutdown. M. Holley (Pure): Add gyroscope to enable pipe location S. Folsom (Tampa Bay): Tampa Bay has 10 miles of 48-inch-diameter PCCP for which inspection is coming up. We would advocate for a cost section in the manual. S. Paul (Montreal): $1.2m/ year budget for all work L. Smith (Phoenix): No cost data. Dewatering significant generally need to repair/replace valves. M. Holley (Pure): Return on investment analysis needed. AFO may not be cost effective in all situations. S. McDonald (Ottawa): Dewatering $300k total with $150k spent externally, $150k spent internally (in-house costs). Express costs in terms of internal/external. Pipe diver 20-50% of project cost expected to be internal M. Zarghamee (SGH): We will send minutes and literature review. D. Marshall (TRWD): Benefits of assessment compared to costs of replacing the line. Benefit will spend 9% of replacement cost and get twice the life. S. McDonald (Ottawa): Public confidence is a huge factor as the public provides the funding for the systems. M. Zarghamee (SGH): Afterthoughts on risk? J. Hannam (Halifax): Will risk discussed today affect risk curve technology? Is end effect accounted for in uncertainty analysis? Can we assume zone of wire breaks near zone (say 18 inches) and check in risk curves? How to determine joint zone? How can we provide confidence for the joint effects on distress signal? Determine blind zone size for pipe and determine the risk of missing BW near the ends X. Kong (PPIC): What if wires are heavily corroded? Does this need to be included in uncertainty analysis? S. McDonald (Ottawa): Failure due to bell ring corrosion. A. Margevicius (CDW): May be useful to involve pipe manufacturers. Price Brothers and Hanson have been helpful. Can they review drafts?

151 130 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment D. Marshall (TRWD): Build conservatism into design. Discuss uncertainties G. Burkhardt (SWRI): Discuss uncertainties in EM and other technologies. Coordinate with Pure. X. Kong (PPIC): Limitations of EM depend on information available. Closing Remarks Summary and closing remarks by M. Zarghamee (SGH)

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159 138 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment Zarghamee, M.S Hydrostatic Pressure Testing Of Prestressed Concrete Cylinder Pipe with Broken Wires. In New Pipeline Technologies, Security, and Safety, Proceedings of the ASCE International Conference on Pipeline Engineering and Construction, v 1, p Reston, VA. Zarghamee, M.S., D.W. Eggers, R.P. Ojdrovic, and B.R. Rose Risk Analysis of Prestressed Concrete Cylinder Pipe with Broken Wires. In New Pipeline Technologies, Security, and Safety, Proceedings of the ASCE International Conference on Pipeline Engineering and Construction, v 1, p Reston, VA. Zarghamee, M.S., D.W. Eggers, and R.P. Ojdrovic Finite-Element Modeling of Failure of PCCP with Broken Wires Subjected to Combined Loads. In Pipelines 2002 Beneath Our Feet: Challengers and Solutions, Proceedings of the Pipeline Division Specialty Conference. DOI: /40641(2002)66. ascelibrary.org. Zarghamee, M.S. and R.P. Ojdrovic Risk Assessment and Repair Priority of PCCP with Broken Wires. In Pipeline 2001: Advances in Pipelines Engineering & Construction - Proceedings of the Pipeline Division Specialty Conference. Reston, VA: ASCE. Zarghamee, M.S., R. P. Ojdrovic, and R. Fongemie Condition Assessment and Repair of Prestressed Concrete Pipeline. In Pipelines in the Constructed Environment: Proceedings of the 1998 Pipeline Division Conference, p Reston, VA: ASCE. Zarghamee, M.S. and K. Maser Structural Evaluation of Hultman Aqueduct. In Infrastructure Condition Assessment: Art, Science, and Practice, Proceedings of the Conference, M. Saito, ed., p , ASCE. New York, NY.

160 ABBREVIATIONS AASHTO AET AFO AM APP ASCE ASTM Aurora AWWA BDPL BW BWP BWZ Calgary Calleguas CAP CFR CFRP Chicago CIPS CP CDW Donahue DWU ECP EDXS EM EPRI FEA GCWW GLSD GMRP GPM GPR GPS Halifax American Association of State Highway and Transportation Officials Acoustic emission testing Acoustic fiber optics Acoustic monitoring Aqueduct protection plan American Society of Civil Engineers ASTM International (formerly American Society for Testing and Materials) Aurora Water American Water Works Association Bay Division Pipeline Broken wire Bar-wrapped pipe Broken wire zone City of Calgary Calleguas Municipal Water District Central Arizona Project Carbon fiber repaired Carbon fiber reinforced polymer Chicago Department of Water Management Close interval potential survey Cathodic protection Cleveland Division of Water Donahue Associates City of Dallas Water Utilities Embedded cylinder pipe Energy dispersive x-ray spectroscopy Electromagnetic Electric Power Research Institute Finite element analysis Greater Cincinnati Water Works Greater Lawrence Sanitary District Great Man-Made River Project Galvanostatic pulse measurement Ground-penetrating radar Global positioning system Halifax Water 139

161 140 Best Practices Manual: Prestressed Concrete Cylinder Pipe Condition Assessment HCDPW HDPE HE HOBAS IE IR Jason LCP LF LPR MAR Montreal MWDSC NBW NCP NDT NDTC NIST NSS NSSD NTMWD Ottawa PCCP PDI Phoenix PPIC Pure P-waves RFTC SASW SCVWD SDCWA SEM SFPUC SGH SPMWD S-waves Howard County Department of Public Works High-density polyethylene Hydrogen embrittlement HOBAS Pipe USA Impact echo Infrared thermography Jason Consultants Lined cylinder pipe Linear feet Linear polarization resistance Maximum acceptable risk City of Montreal, Québec, Canada Metropolitan Water District of Southern California Number of broken wires Non-cylinder prestressed concrete pipe Non-destructive technologies NDT Corporation National Institute of Standards and Technology Non-shorting strap North Shore Sanitary District North Texas Municipal Water District City of Ottawa Prestressed concrete cylinder pipe Pipeline decay index City of Phoenix Water Services Department Pressure Pipe Inspection Company Pure Technologies Pressure waves Remote field transformer coupling Spectral analysis of surface waves Santa Clara Valley Water District San Diego County Water Authority Scanning electron microscopy San Francisco Public Utilities Commission Simpson Gumpertz & Heger Inc. San Patricio Municipal Water District Shear waves

162 Abbreviations 141 SWRI Tampa Bay TRL TRWD w/cm WB WRC WaterRF WRSS Southwest Research Institute Tampa Bay Water Transportation Research Laboratories Tarrant Regional Water District Water-to-cementitious material ratio Wire break Water Research Center Water Research Foundation Water Reclamation Supply System