A Novel Non Destructive Technology for Pipe Grade Determination and MAOP/Design Pressure Validation of Operating Pipelines

Transcription

1 19 th World Conference on Non-Destructive Testing 2016 A Novel Non Destructive Technology for Pipe Grade Determination and MAOP/Design Pressure Validation of Operating Pipelines Thomas EIKEN 1, Werner THALE 1 1 ROSEN Technology and Research Center GmbH, Lingen, Germany Contact teiken@rosen-group.com Abstract. When establishing a pipelines maximum allowable operating pressure (MAOP), many pipeline operators face uncertainties regarding the yield strength of the respective pipeline material. This specifically concerns pre-regulatory pipelines which, for example, constitute approximately 66% of all gas transmission pipelines in the U.S. as well as new pipelines to ensure laid steel pipes meet the contracted steel grade. Conventional ILI technologies are capable of delivering relevant information for MAOP calculation, such as wall thickness and diameter. However, as missing element, in the past there have been no economic means for accurately measuring yield strength. Therefore ROSEN has developed and tested a novel non-destructive system for measuring yield strength of pipeline steel. This paper introduces the fundamental principles of this new system and outlines first results. Laboratory test results are obtained from samples covering the typical range of pipeline steels. The sensor readings are correlated with reference yield strengths of certified steels where the yield strength was determined by destructive tensile tests. Initial pipe tests with the novel non-destructive system measurement are compared with the available yield strengths and tensile strengths according to the inspection certificates of the test pipes. Introduction Investigations on major incidents drive national regulations in the issue of ageing pipelines. Uncertainties in design requirements from the area of pipe line construction due to gaps in pipeline records enforce the industry efforts in the development of new approaches in the ILI technology. The objective of material property tools is to provide major variables for MAOP (Maximum Allowable Operating Pressure), MOP calculation. This includes diameter, wall thickness and specified minimum yield strength. In contrast to the most other ILI technologies measurements of strength will need a combination of several technologies to reveal this material property. A first Eddy Current approach was developed by the ROSEN-GROUP. This service called RoMat PGS (Pipe Grade Sensor) uses an Eddy Current approach for the measurement of absolute values of tensile strength and yield strength. License: 1 More info about this article:

2 The use of ILI material property tools will increase the safety within the pipeline industry and will be an essential part in the risk assessment. This novel approach in the In-Line inspection technology was awarded with the Global Pipeline Award of ASME s Global Pipeline Division during the Rio Pipeline Conference Nomenclature EC ILI MAOP UTS YS SG HA WT a.u. eddy current inline inspection maximum allowable operation pressure ultimate tensile strength yield strength steel grade hardness wall thickness arbitrary units Background of Sensor Development Different methods have been identified as ILI potential to determine the steel grade as e.g. applying nonlinear harmonic sensors which partially determines the magnetic hysteresis curve. We are presenting a method based on eddy current testing. Figure 1 shows a schematic stress vs. strain curve of steel with the mechanical key parameter YS which also denotes the Steel Grade. From this point the transition to plastic deformation begins. The maximum stress that the sample can withstand external forces without failing is denoted as the UTS point. Fig. 1. Schematic stress-strain curve of steel denoting the mechanical quantities YS, UTS and ultimate strain 2

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4 Table 1. Samples used for testing and calibration Sample # Form of manufacture Steel Grade Manufacturing Specification Yield Strength [MPa] ) 1 Tensile Strength [MPa] ) 1 1 Plate S235JR+AR EN Pipe A516 Gr. 70 ASTM A 672 CL Plate S355MC EN Pipe X65 API 5L Pipe SAWL 465 IFD DNV OS F ) 1 according to the pipe manufacturer s inspection certificates Steel samples (plate segments and pipe pieces) with a broad variety of material strength level were used for the development of the eddy current measurement technique as presented in Table 1. The five steel samples cover a range which is comparable to the API 5L grade classes from Grade B to X70. The samples were scanned with varying set ups. Figure 3 shows the experimental set up in the laboratory. )* 4

5 After optimization of the eddy current technique a good correlation between EC response and YS was obtained as shown in Figure 4. Fig. 4. Eddy current response in arbitrary units versus yield strength The observed correlation between EC response and UTS presents Figure 5. As the UTS is directly proportional to the hardness, this measured value could be checked directly during dig verifications with mobile hardness testing [2,3]. The measurement performance of this sensor is the same in different liquids and in gas since the influence of the medium on the EC signal is negligible. Further measurements are planned with a larger number of samples to confirm this approach, and if necessary perform optimizations or modifications. Fig. 5. Eddy current response versus ultimate tensile strength 5

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8 " ; 0)2 /)3 #. 9 () %# ' ) > ) " ' ; ' (? ; '? ) " 5 4% ( ) Using the average EC readings per joint, YS and UTS were calculated applying the above mentioned calibration and then compared with the specified YS and UTS values from tensile tests as documented in the manufacturer s certificate of the different test joints, see Figure 8. & $- *3)3$ 4 The strength values determined by the ILI (both YS and UTS) are in agreement with the specified values. As a first estimation we would consider accuracies of ±40 MPa for the electromagnetic determination with our method for both tensile strength and yield strength. Furthermore, accuracies of ±9 MPa are considered for tensile strength and ±14 MPa for yield strength for the values from tensile testing according to literature [5].. ( '!*! &% # ))! 3* # A ( ()! B# /C2#!*! ) " ' (!*! ) 8

9 Outliers in pipe grade of known segments were recognized by the used ILI service RoMat PGS (pipe grade sensor) and confirmed by subsequent visual inspection of records. Fig. 9. Inspection System Result verification and discrepancy analysis Selected ILI tensile strength results were compared with 11 in-situ measurements of tensile strength by mobile hardness testing in the field. This allows further optimizations of the measuring technique and the tool design. Destructive testing is as well part of the optimization and verification process. Future cut outs and pipeline segments replacements of the inspected pipeline will be used for further validation of the process and the results. Fig. 10. Unity plot of the inspection system result verification according to the API standard 1163 at a confidence level of 80 % and a standard deviation of ±41.4 MPa (6 ksi) The results of an 30 R&D blind survey in a natural gas transmission pipeline conducted in 2015 provided addition confidence in the technology. The blind survey 9

10 delivered all pipe grades used in the investigated pipeline. In addition to this the technology shows its capabilities to uncover every pipe replacement that was done since service of the pipeline section started. Reported case studies based on available mill certs acknowledged the specified standard deviation of the technology. Ongoing field verifications will provide further verified tool data and will gain additional confidence in pipe grade determination by the use of ILI technology. The next surveys were conducted in spring 2016 and the pipe grade data evaluation is ongoing. Summary and Conclusion Conventional ILI technologies are capable of delivering relevant information for MAOP calculation, such as wall thickness and diameter. However, in the past ILI technologies have not been able to deliver the missing yield strength information needed for MAOP calculations. Until now, there has not been a cost-efficient way for accurately measuring yield strength of pipeline steel. Therefore ROSEN has developed and tested a reliable and cost-efficient ILI system for measuring the yield strength of pipeline steel. The development started with laboratory measurements of steel samples with a broad range of material properties. Initial pull tests with an ILI tool and test joints of different steel grade were compared with the specified yield strengths and tensile strengths according to the inspection certificates of the pull test pipes and showed good compliance. A large scale test further increased the data base of different steel grades. The ILI results will be compared with field measurements of the steel hardness. This will allow further optimizations of the measuring technique and the tool design. References [1] H. Haines, B. Nestleroth, NDE 4A Pipeline Discrepancy Analysis Using an ILI An Approach for Meeting the Need For Traceable, Verifiable & Complete Records for Vintage Pipelines, 2013 PRCI RESEARCH EXCHANGE MEETING February 5, 2013, Dallas, TX [2] Clark, E.B., Amend, W.E., Applications Guide for Determining the Yield Strength of In-Service Pipe by Hardness Evaluation, Final report, CRTD-Vol. 91, ASME, 2009 [3] ) #, - & %D. ASME CRTD Vol. 91, IPC [4] American Society for Nondestructive Testing, Nondestructive Testing Handbook, 2 nd Edition, Vol. 4, Electromagnetic Testing, 1986 [5] Holger Frenz et. al., Tensile Test, Results of an Inter-laboratory Comparison Test with 91 European Testing Laboratories, Materialprüfung (Material Testing) 40 (1998). [6] Borja Martinez, Daniel Molenda, Markus Brors, Calculating Pressure A novel In- Line Inspection Technology for MAOP Validation, World Pipelines 2014 [7] Daniel Molenda, Werner Thale, A Novel Approach for Pipe Grade Determination Through In-Line Inspection (ILI), Proceedings of 10 th International Pipeline Conferences, IPC