IPC2012-90021

Proceedings of the 2012 9th International Pipeline Conference IPC2012 September 24-28, 2012, Calgary, Alberta, CanadaIPC2012-90021 THE ROLE OF EFFECTIVE COLLABORATION IN THE ADVANCEMENT OF EMAT INLINE INSPECTION TECHNOLOGY FOR PIPELINE INTEGRITY MANAGEMENT: A CASE STUDY Jeff. Sutherland PII Pipeline Solutions 4908 52nd St SE Calgary AB, T2B3R2 Phone: 1 403 204 5255 [email protected] Richard Kania, TransCanada PipeLines Ltd. 450 – 1st Street S.W., Calgary, AB T2P 5H1 Phone 1 403 920-6032, [email protected] Jim Marr TransCanada PipeLines Ltd. 450 – 1st Street S.W., Calgary, AB T2P 5H1 Phone 1-403- 920-5410, [email protected] Gabriela Rosca TransCanada PipeLines Ltd. 450 – 1st Street S.W., Calgary, AB T2P 5H1 Phone 1-403- 920-2929, [email protected] Stephan Tappert PII Pipeline Solutions Lorenzstrasse 10, D-76297 Stutensee, Germany, Phone ++49-7244/732-185, [email protected] Karlheinz Kashammer, PII Pipeline Solutions Lorenzstrasse 10, D-76297 Stutensee, Germany, Phone ++49-7244/732-222 [email protected] Andrew Mann PII Pipeline Solutions Atley Way, NE23 1WW Cramlington, Great Britain, Phone ++44-191/247-3463, [email protected] Clint Garth. TransCanada PipeLines Ltd. 450 – 1st Street S.W., Calgary, AB T2P 5H1 Phone 1-403- 920-7930 [email protected] ABSTRACT Over the past three years there has been increasing industry interest and profile regarding the role and pipeline integrity management potential of EMAT crack inspection technology in the Oil & Gas pipeline industry. This paper outlines the stages and results of the effective collaboration of a major pipeline operator and a service company to advance the true predictive performance of the EMATScan Gen III crack inspection technology. The paper will also summarize and provide examples of lessons-learned from this collaboration across all stages of EMAT based SCC integrity management program. The paper will similarly outline ongoing work in progress regarding the assessment of the ILI data relative to hydrotesting equivalency, detection of injurious defects and the related analysis and reporting improvements made over the past three years. NOMENCLATURE EMAT: Electro Magnetic Acoustic Transducer CD: Crack Detection ILI: In Line Inspection SCC: Stress Corrosion Cracking SH: Shear Horizontal Wave RH: Rayleigh Wave POD: Probability Of Detection POI: Probability Of Identification 1 Copyright © 2012 by ASME INTRODUCTION In 1995, following the National Energy Board’s (NEB) inquiry into SCC, one of the recommendations was to develop an inline inspection (ILI) tool to detect and quantify stress corrosion cracking (SCC). The application of the traditional ultrasonic piezoelectric transducers for in-line inspection requires a liquid couplant for ultrasonic energy and signal transfer into the pipe wall. Filling a gas pipeline with a liquid product or by batching the tool in a liquid slug is not feasible from a cost-efficient, technical and operational perspective. Liquid filled wheel probes had been developed to overcome the issue, however the experiences of poor defect discrimination forestalled acceptance and use of this technology [1]. Electro Magnetic Acoustic Transduction technology, known as EMAT, does not require a coupling medium, is based on ultrasonic inspection methods and was targeted for natural gas pipeline environments. The first generation in-line inspection EMAT tool was launched for 36-inch diameter pipelines in 2002. The experience with this tool was the subject of papers delivered at IPC in Calgary 2002 and 2004 [3], [4]. The initial inspection was considered a success based on the comparative ability to locate reference crack features identified earlier by running the ultrasound crack detection tool (USCD) in the same section of the pipeline within a water batch. Further inspections between 2002 and 2005 contained a larger population of pipeline features with broader variety in pipe conditions and environment [6], which uncovered certain limitations in the tool design. Some further developments were progressed leading to a second generation release; However some fundamental developments were considered to be needed to achieve the expected inspection performance relative to benchmarked ultrasound crack detection CD technology. The third generation design (“Gen III”) was started in 2005 and launched in 2008, with key the objectives to 1) Maintain and even improve POD, 2) Improve and ensure reliable POI, and 3) Match USCD sizing abilities for features in weld. Similarly the operational range, diameters and general robustness were improved as outlined in Table 1. Table 1: Performance comparison of EMAT GEN I and GEN III ILI systems The early experiences with the latest generation of the EMAT crack detection tool was the subject of an IPC paper in 2010 [1,4]. The third generation EMAT tool has now surpassed the total mileage of EMAT 2nd generation tool within the last two years of inspection with various operators in the US, Canada and Australia. The performance of these inspections has been confirmed with over 120 field verifications. A sense of confidence in the ability of the technology to detect and identify SCC has been developed. PRINCIPLES OF OPERATION Electro Magnetic Acoustic Transducers (EMAT) are based on the phenomena that an alternating current in a wire induces an eddy current in the metal surface. [2] When a specific electric current and coil configuration is combined with a static magnetic field, a force is produced, which causes the steel to oscillate, thus launching a guided ultrasonic sound wave in the pipe wall as illustrated in Figure 1. The forces mentioned are also known as a magnetostrictive phenomenon, which relates physical motion to magnetic energy. Thus a guided ultrasonic wave is generated in the pipe wall by an electromagnetic wave and not from transmission of ultrasound energy from the sensor itself. Pipe wall features such as defects and cracks will result in reflections of that ultrasound wave. Reflected wave energy encountering the magnetic field near a receiver sensor will generate a corresponding electromagnetic eddy current, which in turn, induces a current in the coil within the receiver and forms the received signal, which can be further processed, recorded and analyzed. The signal’s characteristics and its time of acquisition, when combined with that of other sensors, provides information about a given feature’s size, depth and location. 2 Copyright © 2012 by ASME (3) Lamb Waves Lamb Waves also travel in the circumferential direction around the pipe utilizing different oscillation regimes compared to the SH wave. These waves are used for discriminating between cracks and non-injurious features. Figure 1: EMAT Sensor showing generation of ultrasound waves within a pipe wall due to the generation and presence of electromagnetic waves from the sensor Figure 2 illustrates typical energy paths for the EMAT generated ultrasound waves between sensors. The ultrasonic configuration and technique used actually comprises of both pulse-echo and through-transmission signals, of which both are acquired and recorded by the tool. Figure 3. EMAT ILI tool Sensor carrier and Sensor types ROLE WITHIN INTEGRITY MANAGEMENT The EMAT inspection tool has been identified as a very promising means of ensuring integrity of SCC susceptible pipeline segments. Based on the most recent verification and validation and development work, it is quickly becoming one of the most important tools for integrity management of natural gas pipelines containing SCC. Initially, the predictive soils models enabled the recognition of susceptibility of pipelines for SCC, but could not delineate severity until large populations of sites are available for inspection. When utilized in conjunction with EMAT run, the predictive SCC model can provide the locations of areas that are deemed susceptible and over time, can help improve the analytical reliability of the model and the tool. This combination approach is simpler and less disruptive to the pipeline operation than the process required for execution of a hydrostatic testing or conventional liquid ultrasonic technology run. The EMAT technology is anticipated to delineate valve section severities (for features within the tool specifications) and have the ability to locate and discriminate severe SCC (such as class 3 and 4 colonies as per CEPA guidelines [5]) with high confidence levels. The collaborative approach for use of EMAT ILI involved multiple steps for each operation, which consisted of: Inspection Run on target pipeline segment Inspection Data Analysis 3 Copyright © 2012 by ASME Figure 2: Illustration of EMAT ultrasound energy paths as reflected and through transmission signals. The EMAT ILI tool uses a patented combination of different ultrasonic wave types for feature detection, discrimination and sizing. The sensors are shown on a sensor carrier in Figure 3. These wave types are: (1) Shear “SH” Waves SH waves are horizontal shear waves, traveling throughout the pipe wall in the circumferential direction and primarily used for detection of features. (2) Rayleigh “RH” Waves High frequency Rayleigh (RH) waves travel along the internal surface of the pipe wall and oscillating in a circular motion and used mainly used for internal/external discrimination. Direct Field NDE Examination of selected features Correlation and feedback of field NDE to Reported and relevant updates to the Data Analysis Methodology Capture and Actioning of Lessons Learned for continued improvement. INSPECTION RUNS The first inspection of the EMAT Gen III tool occurred in autumn 2008 on a 30” 39.1 km pipeline section. Since that initial run the inspection distance has increased to a total of over 2000 kms, covering diameter sizes of 30”, 34” and 36” and in 2011 had exceeded the entire lifetime inspection mileage of the previous generations. EMAT reporting performance has been correlated in more than 75 excavated pipe joints as described further under Excavation Program section below. These results continue to confirm both high probability of detection (POD) and identification (POI) performance and refined sizing specification. INSPECTION DATA ANALYSIS The analysis and interpretation methodologies were initially based on pull-test results on joints with both manufactured and actual crack features present. Due to the presence and benefit of the new, and differing, sensor types, the data analysis methodology was newly derived as it could not be simply an update over the older generation. Table 2 outlines the evolution of the data analysis method versions as part of the collaborative feedback cycle into EMAT inspection and understanding. EXCAVATION PROGRAM Over the past three years TransCanada has conducted a significant campaign of EMAT inspection runs across their pipeline network. These efforts included an extensive excavation and examination program and day to day collaboration with the EMAT team. The excavations were intended to: Remove assumed critical features from the line Enable TransCanada’s Pipeline Integrity group to develop an understanding of the ILI tool tolerance and nature of the features. Establish correlations among ILI calls (detection and sizing of SCC features) and non-destructive examinations (NDE) to prove and improve the EMAT technology on the feature classification Enable the reliable calculation of the failure pressure of the features that will be left in the line and predict when they need to be repaired Allow development of a robust integrity management plan for inspected pipeline segments. To ensure understanding and confident future analysis process refinement, some “non-decidables” were also included in the 2010 and early 2011 excavation programs as feature characterization learnings were established. All excavation sites were verified in the field and included toe-crack features, SCC features at the seam weld, and SCC cracking in the pipe body, in various coating types. As noted in previous publications [1,8], there was considerable attention given to ensuring relevant validation results within the operator’s site assessment work. This protocol has evolved within the operator/service provider collaboration and in parallel with the recent SCC JIP guidance development [9]. This protocol includes the inspection of the entire joints excavated with the intention to detect potential true negatives, false positives and even false negatives. Any significant SCC and all SCC correlated to to EMAT reported features had their depth measured using phased array ultrasonics. Several of the reported laminations were mapped using a ultrasonic scanning. Table 2: Overview of data analysis versions utilizing field examination feedback. VALIDATION RESULTS The detection capability is referred to as the Probability of Detection, also known as POD. During the excavations the operator’s extensive protocol was used. This work included MPI (Magnetic Particle Inspection) for the entire exposed surface of each pipe joint containing reported features to further establish confidence in POD against false negatives. Some cracks were initially classified as geometry features during the analysis and were not reported. After the NDE was performed, a number of features under this classification were found to be SCC. On the basis of more than 75 excavation sites, a POD value of above 95% has been verified. Since 2010, the experience with running the tool contributed to refinement of the EMAT performance capabilities. The POI classification performance has varied between 60 and 80% as new types of particularly unique features and pipe surface characteristics have been identified. In addition, within the initial stages, a reporting category of “Nondecidable” has been used. This category was used for features whose signal characteristics were distinctly different from those known for features of interest. The extensive field verification efforts have allowed the „non-decidable“ category to be removed in 2011. 4 Copyright © 2012 by ASME . Some false positive features were located or were coincident with the worst areas of narrow steep-sided external corrosion and within areas of disbonded coating. Each feature had numerous areas of external corrosion indications as in the example of Figure 7. Although the EMAT signals clearly contained characteristics normally associated with corrosion, there were linear indications with significantly high amplitudes associated with the calls, which indicated that cracking could be present and conservatism within reporting was preferred. In other cases, unique corrosion deposits were found at the location of the reported features. Very hard cathodic protection deposits were found in disbondment areas underneath asphalt and tape coated pipe sections as shown in Figure 8. The NDE inspection showed that there was no cracking associated with the reported EMAT features. As signals may be enhanced by localized coating variations, including typical deposit thicknesses and chemistries, the EMAT data at this location indicated something being physically different about this location. In these cases, the iron rich deposits seemingly caused data mis-interpretation. Localized increased seam weld indication within the EMAT data has also been experienced to be caused by lack of side wall fusion, weld inhomogeneity or pronounced amplitudes due to signal amplification as a result of coating disbondment. Figure 4: Field Photographs of critical features detected by EMAT Figure 5: Site Assessment; Various photos of stages of excavation, stripping, cleaning, MPI and UT inspection The detection capability for the minimum specified defect size of 2mm depth x 50mm length or greater was identified to be 95% on the basis of a sample set of 40 reportable cracks, 12 seam weld cracks and also 40 features below the minimum detection specification. Figure 6: Verified seam weld adjacent SCC; The Field NDE phased array peak depth was 4.3mm The ability of the tool to correctly discriminate features in the line (Probability of Identification or POI) was based on a sample size of 102 data points and was established to be 75% (Table 3) which is exceeding the initial performance target for POI of 66%. Crack Detection (POD) N confidence level 40.0 95% Figure 7: Axially aligned sharp edge corrosion seen as corrosion within EMAT data but also with sharp edge reflections leading to conservatively reported cracking call. Classification (POI) N confidence level 91.0 95% # sample # sample # Incorrect correct certainty # incorrect correct certainty 2.0 38.0 95% 23.0 68.0 75% Table 3: POD performance at 95%, POI performance at 75% 5 Copyright © 2012 by ASME Figure 9: depth sizng example; left MPI, right top phased array crack profile, right bottom B-Scan data Figure 8: A unique corrosion deposit feature detected with a very high amplitude response within EMAT data PATH TO IMPROVED REPORTING PERFORMANCE Classification As a result of the experiences and trend of over conservative classification of benign feature types, the data analysis processes were reviewed and updated including the introduction of a signal characteristics system in 2011, which is self-contained within the collected EMAT tool data (independent of other ILI data or pipe models) , and known as the attributes scorecard. An extended set of special signal attributes is applied to potential reportable features to identify their likelihood of being true positive features in final quality assurance stages of analysis. Retroactive tests on verified features confirmed a success rate of over 90% in eliminating false positives. Further EMAT correlation digs in late 2011 were completed on benign features which successfully verified the new feature evaluation process. Sizing Crack depth estimation has been provided as one of depth band categories of 2-3, 3-5, >5mm and with a tolerance of 0.5mm at 80% certainty. In practice since 2010, the depth band reporting accuracy has been found to be >90% (in comparing the depth estimate reported in a band as compared to the field NDE measurement). Although encouraging results, the banded reporting format is to be replaced in 2012 in favor of absolute depth sizing estimation as described below. The field NDE phased array depth profiles were collected in 10mm increments which has been extremely valuable to take the correlation of EMAT B-Scan signal data to new stages as shown in Figures 9 and 10. In Figure 9, there was good agreement between the deeper parts of the profile and the EMAT B-scan, where the red “clouds” signify a higher reflected signal, which prompted further efforts to generate a predicted “crack amplitude” profile as is done within USCD reporting today. Initial results have been quite encouraging as per Figure 10 and efforts are continuing in order to ensure accurate reporting. Figure 10: Comparion of actual meaured profile and “amplitude-based” estimated profile derived from EMAT data. ON-GOING DEVELOPMENTS A key development has been the introduction of model-based depth sizing which replaces the depth banded reporting format. Results of testing to date are shown in Figure 11 and expresses +/-1 mm with a certainty of 85%. This new approach utilizes the full sensor configuration abilities of the Gen III design which includes overlap normalization, mode interpretation and individual sensor- based efficiencies factors. Figure 11: Unity Plot for depth sizing performance 6 Copyright © 2012 by ASME There are two hardware/firmware developments in progress, both of which are targeting further enhancements to signal quality. One program is looking to expand and optimize the information content collected and contained within the on-board recorded data. As such, it then enables in post-processing data analysis, enhanced signal-to-noise (S/N), and further abilities for wave mode separation as shown in Figure 12. Thus fundamental performance is expected to further improve for detection, discrimination, and sizing. An overall POD value of >95% was determined. The EmatScan CD system to date has achieved a POI of >75% for crack features. The EMAT technology is anticipated to delineate valve section severities (within tool specification) and have the ability to locate and discriminate severe SCC. ACKNOWLEDGEMENTS The authors would like to thank their respective companies for permission to author and publish this paper. As well the authors would like to acknowledge that the EMAT efforts have been a truly global effort, with the development projects managed by the Ultrasonics Center of Excellence based in Stutensee, Germany, with expertise from its Sensors Group based in Cramlington, UK, and with the EMAT Analysis team and the TCPL team based in Calgary, Canada. REFERENCES [1] Marr J. , San Juan E. , Jiangang S., Mann A., Tappert S., Weislogel J. ”Validation of latest generation EMAT Inline Inspection Technology for SCC management”, International Pipeline Conference 2010, Calgary. [2] A.H.Harker, “Elastic Waves in Solids: With Applications to Nondestructive Testing of Pipelines”, CRC Pr I Llc, 1988 [3] Yeomans M., Ashworth B., Strohmeier U., Hugger A., Wolf T., “Development of 36” EmatScan™ Crack Detection (CD) Tool” International Pipeline Conference 2002, Calgary [4] Kothari M., Tappert S., Strohmeier U., Larios J., Ronsky D., “Validation of Emat In-Line Inspection Technology for SCC Management” International Pipeline Conference 2004, Calgary. [5] CEPA Canadian Energy Pipeline Association, Stress Corrosion Cracking Recommended Practices Second Edition, December 2007. [6] Tappert S., Allen Lee D., Mann A., Balzer M., Van Boven G., “ Inline inspection for cracks in gas pipelinesEnhancements Derived from 5 Years’ Operational Experience” International Pipeline Conference 2008, Calgary [7] Wooldridge A B. “Demonstrating the capability and reliability of NDT inspections” WCNDT 14 Vol. 1: 169-173 [8] Slaughter, M, Spencer, K, Dawson, J, Senf, P. “Comparison of multiple crack detection inline inspection data for crack growth”, Pipeline Pigging and Integrity Management Conference, 2011, Houston. [9] Batte, D., Fessler, R., Marr, J., Rapp, S. “A new Joint Industry Project addressing the Integrity Management of SCC in Gas Transmission Pipelines” Pipeline Pigging and Integrity Management Conference, 2012, Houston. Raw Data signal is processed into separate individual wave modes Figure 12: Example of new format data processing with mode separation of combined signal into individual wave mode components. Moreover another ongoing program involves a new sensor design that has successfully passed initial tests in early 2012. This design will increase the signal efficiency and be more robust to influences of environment and tool dynamics on data quality. NEXT STEPS Collaborative efforts continue in 2012 within field operation, analysis and overall improvements in EMAT technology as a part of pipeline integrity management. This includes: Further definition and segmentation of POD characterization for various crack types and sizes. Testing of automated detection and characterization algorithms to allow timely, efficient and accurate reporting. Further characterization and improvement of absolute depth estimation performance. Initial studies into resolution & refinement of Crack Field assessments. Dig Feedback program within 2012. 1st re-inspection, necessitating methods and means for detailed feature and Gen III run comparisons. SUMMARY This paper presents the progress achieved in the third generation EMAT ILI tool through the collaboration of a pipeline operator and the inline inspection company. An overview has been provided of identified features, excavation results and practices. 7 Copyright © 2012 by ASME