SMALL DIAMETER, MULTIPLE DATASET INSPECTION IN LOW FLOW AND LOW PRESSURE ENVIRONMENTS

Transcription

1 WHITE PAPER SMALL DIAMETER, MULTIPLE DATASET INSPECTION IN LOW FLOW AND LOW PRESSURE ENVIRONMENTS Chuck Harris T.D. WILLIAMSON HOUSTON, TEXAS Mark Graves WILLIAMS OKLAHOMA CITY, OKLAHOMA PRESENTED AT THE PIPELINE PIGGING & INTEGRITY MANAGEMENT CONFERENCE, FEB , 2015

2 Introduction Williams subsidiary, Access Midstream (Access), is a growth-oriented midstream natural gas service provider focused on owning, operating, developing and acquiring midstream energy assets in the United States. Access owns and operates approximately 6,300 miles of natural gas gathering pipelines with an average throughput of approximately 6 billion cubic feet per day (bcf/d). Its corporate strategy is focused on long-term sustainability of its asset base. This strategy is demonstrated by the 100 miles per year, on average, that Access assesses via inline inspection (ILI), while only two miles of the system are actually regulated. This commitment further underscores the company s focus on asset integrity as many of the pipelines assessed are challenging to assess due to operating conditions. To successfully inspect and assess these lines, Access partnered with T.D. Williamson (TDW) to develop ILI tools specifically designed to operate in such environments. Due to Access s proactive, risk-based approach to pipeline integrity of their mostly non-regulated system, the company required an inline inspection device capable of geometry and metal loss inspections in extremely low pressure and flow. While some applications exist in slightly larger diameters, the company specifically required such inspections in 6-inch diameter pipelines, with pressure on the order of 100 pounds per square inch (PSI). Typical minimum pressures required in a gaseous medium, depending on the ILI service provider, range from 300 PSI to 600 PSI for a 6-inch pipeline. Creating a solution to meet Access s specific needs would be no small task. It would require a unique ILI tool design that would allow the device to be sufficiently propelled in a low pressure, low flow environment, while also providing an acceptable speed profile to ensure successful inspection of geometry and metal loss anomalies. TDW has a long history of developing pipeline integrity solutions. Specific to inline inspection (ILI), the company has evolved from caliper technology for geometry inspection of newly constructed pipelines in the early 1970s, to high resolution deformation, Magnetic Flux Leakage (MFL) and mapping technologies in the late 1990s and early 2000s; and more recently, Speed Control, Multiple Datasets (MDS), Electro-Magnetic Acoustic Transducer (EMAT) and others. Throughout TDW s history, the focus has remained on partnering with pipeline operators in an effort to help solve their inspection challenges. Inspecting 6-inch pipelines with very low pressure and flow is particularly challenging. Components contacting the pipe s internal diameter (ID), such as urethane drive cups and brushes used to transfer magnetism, create significant drag. This drag can negatively impact tool performance in compressible products such as natural gas, resulting in speed excursions outside optimal velocity ranges. These excursions can be greatly exaggerated in low pressure and low flow natural gas pipelines, thus increasing the risk of reduced data resolution. The ability to control tool speed in this environment is essential to ensure proper saturation of the pipe wall when using MFL technology. In general, the optimal velocity range for MFL tools is 4 to 7 miles per hour 1. An MFL inspection carried out at velocities above the optimum range causes a reduction in the induced magnetic field, thus negatively impacting the accuracy of reported results 2. To achieve the desired wall thickness inspection range on any ILI tool, the laws of physics require a certain volume of magnet and core material to provide an adequate magnetic circuit for pipeline saturation. Historically, ILI technologies incorporate steel brushes into the magnetic circuit as a flexible means of transferring magnetic flux from the tool to the pipe wall. These brushes also provide tool centering and support for the magnetizer. Urethane cups are used as a means to provide drive through a pipeline, via product flow, as well as for centering and support WHITE PAPER TDWILLIAMSON.COM 1

3 of additional canisters (i.e., drive, battery, CPU, etc.). In small diameter MFL tools, the limits on design volume are significant enough to force some compromises in the allocation of magnets, core and brushes. These design compromises can lead to concessions in performance in terms of navigability or wall thickness inspection capability. For brushes in particular, the design concessions often lead to very short bristle length, which results in a rigid brush with high drag and reduced tool navigability. Understanding the importance of such design considerations for ILI technologies in small diameter pipelines, TDW developed a unique approach to improve overall tool performance. These techniques would be applied to the company s 6-inch MDS platform, which includes various datasets to overcome limitations of individual technologies. In addition to the MDS arrangement, this platform could be configured to include only deformation and MFL technologies in a compact 46-inch (1.17m) length. The end result was a 6-inch inspection device with: Greater wall thickness capability Reduced drag Improved navigability Improved protection of the magnetizer TDW and Access began preliminary conversations to discuss Access s desire to achieve successful inspections in their 6-inch gathering system, with pressures around 150psi; many 6-inch MFL tools in the industry require a minimum pressure of 600psi. The new approach to the 6-inch MDS tool was discussed as a potential solution, given that its design attributes would improve performance in lower pressure natural gas lines. Since Access only required geometry and metal loss inspection, TDW would plan to employ the deformation and MFL configuration. When the tool was built and made available for internal validation, TDW tested a variety of technology configurations to address the critically defined parameters, including a comparative analysis of associated drag. Figure 1 shows the drag comparison between multiple 6-inch tool configurations: DEF+MFL: traditional geometry combined with metal loss inspection MFL: traditional stand-alone metal loss inspection MDS-based DEF+MFL: newly designed MDS tool using DEF+MFL configuration only Drive: drive body only FIGURE 1 DRAG COMPARISON OF MULTIPLE 6-INCH TOOL CONFIGURATIONS WHITE PAPER TDWILLIAMSON.COM 2

4 Testing confirmed that high drag is associated with thick short brushes and multiple cups used to support and center canisters. The unique MDS-based deformation and MFL configuration achieved the following results: Reduced tool drag by 55 percent over the stand-alone MFL tool in inch wall thickness Reduced tool drag by 59 percent over the traditional deformation and MFL tool in inch wall thickness Reduced tool drag by 61 percent over the stand-alone MFL tool in inch wall thickness Reduced drag by 68 percent over the traditional deformation and MFL tool in inch wall thickness Of note, a pull test of just the drive section minus the deformation and MFL technologies resulted in similar drag characteristics to the MDS-based deformation and MFL inspection device. This is further proof of the impact of cups on tool drag, as well as the low drag characteristics of the newly designed deformation and MFL technologies. TDW s internal validation results were shared with Access and plans were initiated to find the first 6-inch segments for field validation in low pressure and flow pipelines. Case Studies The newly designed TDW tool was run seven times on pipelines in the Barnett Shale area during late 2013 and early The pressure and flow limits of the tool were tested on each inspection with varying results. The lines assessed all operate on a gas lift system. Gas lift is a method to recover hydrocarbons when there is insufficient pressure in a reservoir to produce a well. It involves buying back the gas that is produced and injecting down hole in order to lift a column of liquids. This results in widely ranging flow characteristics for pipeline. Due to the low flow and low pressure operating conditions and anticipated surging, it is standard practice by Access for a water slug of five barrels to be placed in front of an inline inspection tool to help control speed. This section will provide run details of a selection of the lines and demonstrate differing line conditions in which a successful run was achieved. CASE STUDY 1: INITIAL RUN The initial pipeline inspected is a OD x WT line with a normal operating pressure of 156 psi. During the inspection, the line was flowing approximately one million cubic feet per day. One small section of heavier wall thickness is present in the line where a tie in from another well is made. Several 45 degree and 90 degree 3D fittings are in the line, as well as one 45 degree fitting identified as 1.5D. SPEED PROFILE The speed profile can be seen in Figure 2. The average speed was 4.5 feet/second with a maximum speed of 22 feet/second. Five areas of overspeed were experienced in this initial run. The first large speed excursion occurred at 2274 feet as the tool traveled through a 45 degree 1.5D fitting and lasted for approximately 130 feet. The second large speed excursion occurred at 6383 feet where the wall thickness was increased to at a tie-in point. The speed excursion lasted for 450 feet and ended just before the tool entered the receiver. WHITE PAPER TDWILLIAMSON.COM 3

5 FIGURE 2 CASE STUDY 1 SPEED PROFILE INITIAL RUN RESULTS All MFL, IDOD, and DEF sensors were working throughout the entire inspection resulting in 100% data capture. The speed of the tool was within tolerance for 90% of the line, which meets Access requirements for an acceptable run. Twenty internal metal loss indications were identified during the inspection. Upon excavation and NDE of the three largest indications, it was discovered that they were mill features. The successful first inspection using the TDW low drag tool provided confidence to expand its use and inspect additional lines that were previously unpiggable. CASE STUDY 2: DECREASED PRESSURE AND INCREASED FLOW The second case study is on a OD x WT line with a normal operating pressure of 120 psi. During the inspection, the flow varied between one million and two million cubic feet per day. There are two tie-in locations and two bore sections in the line where the wall thickness is increased to SPEED PROFILE The speed profile can be seen in Figure 3. The average speed was 1.1 feet/second with a maximum speed of 31.9 feet/second. 26 speed excursions were experienced during the inspection. The tool was travelling over the tolerance of 10 feet/second for 30.8% of the length of the line. The point where the tool reached the maximum speed occurred as it travelled through a heavy wall tie-in section. Additional speed excursions occurred at each instance where the tool travelled through an elbow fitting or bore section. Two speed excursions occurred in straight sections of pipe immediately following speed excursions through elbow fittings. The final speed excursion occurred in straight pipe with no wall thickness changes and ended as the tool entered the receiver trap. WHITE PAPER TDWILLIAMSON.COM 4

6 FIGURE 3 CASE STUDY 2 SPEED PROFILE CASE STUDY 2 RESULTS The data quality was affected by speed excursions and MFL sensors that experienced intermittent issues. MFL sensors covered 93.8% of the line. Deformation sensor coverage was 100% for the line. Nearly 31% of the line experienced overspeed. During those periods of overspeed, anomaly detection was available, but sizing capabilities were limited. Ten metal loss features were identified during the inspection. Five of the features were identified during periods of overspeed and five were identified while the tool was travelling within the speed tolerance. All of the features were between 10 and 14% of the wall thickness. None of the features were assessed and verified because they are below critical limits based on assumed corrosion growth rates. While the speed tolerance was exceeded during this inspection for over 30% of the line, it was still accepted as a good run due to limitations of any other technology available to assess a OD line in-service with such low pressure and flow. CASE STUDY 3: INCREASED PRESSURE AND DECREASED FLOW The third case study is on a OD x WT line with a normal operating pressure of 186 psi. During the inspection, the flow was approximately 150,000 cubic feet per day. The nominal wall thickness is constant throughout the line, but there are four 1.5D elbows present. SPEED PROFILE The speed profile can be seen in Figure 4. The average speed was 0.5 feet/second with a maximum speed of 12.2 feet per second. A single speed excursion over the 10 feet/ second tolerance was experienced during the inspection. The speed excursion occurred just after the tool passed through a 90 degree 1.5D fitting and lasted for 85 feet. No other 1.5D fittings caused the tool to exceed the speed tolerance of the tool. WHITE PAPER TDWILLIAMSON.COM 5

7 FIGURE 4 CASE STUDY 3 SPEED PROFILE TABLE 1 SUMMARY OF ASSESSMENTS CASE STUDY 3 RESULTS The speed of the tool was within tolerance for 96% of the line. One MFL sensor was sporadic throughout the entire run resulting in 99.6% coverage. Four IDOD sensors and four deformation sensors were out during the entire run resulting in 83.3% coverage for each. Even with the portion of overspeed and failed sensors, the quality of the inspection data gathered was satisfactory for a comprehensive assessment. Three external features were identified, of which the deepest was reported as 11%. None of the features were assessed and verified because they are below critical limits based on assumed corrosion growth rates. Conclusions TABLE 1 AN OVERVIEW OF THE ABOVE ASSESSMENTS THAT WERE PERFORMED USING THE LOW DRAG TOOL. Each of these small diameter assets in the Barnett area were unable to be assessed in-service with traditional MFL tool technology. While speed excursions do occur with the TDW low drag tool, they are not on the magnitude of those experienced with traditional MFL tool technology. The TDW low drag tool provided a solution to gather acceptable inline inspection data at pressures as low as 120 psi. WHITE PAPER TDWILLIAMSON.COM 6

8 ACKNOWLEDGEMENTS Chuck Harris would like to thank TDW personnel, Todd Mendenhall and Blake Owen, for their tool design expertise and contributions to this paper. Chuck would also like to thank Matt Hastings and Mark Graves, with Williams, for their support and partnership on the inspection of these challenging pipelines. Mark Graves would like to thank the entire Asset Integrity group for Williams Central Operating Area, Matt Hastings, and Sam Aulbach for their roles in the testing of this tool in exceedingly difficult operating conditions. Mark would also like to thank Chuck Harris and TDW for the development of viable technology to assess small diameter gathering pipelines. REFERENCES 1 TIM CLARK and CHUCK HARRIS. IBP1228_13_Use of Speed Control Technology to Enable Inline Inspection in High Flow Natural Gas Pipelines. Rio Pipeline 2013 Conference and Exhibition. 2 J.B. NESTLEROTH and R. J. DAVIS. The effects of velocity on magnetic flux leakage inspection of gas pipelines. Technical report, Gas Research Institute, June 1996, p. 52. WHITE PAPER TDWILLIAMSON.COM 7

9 Notes

10 SMALL DIAMETER, MULTIPLE DATASET INSPECTION IN LOW FLOW AND LOW PRESSURE ENVIRONMENTS PRESENTED AT THE PIPELINE PIGGING & INTEGRITY MANAGEMENT CONFERENCE, FEB , Copyright 2015 All rights reserved. T.D. Williamson, Inc.