A group of eight gas transmission pipeline operators, responsible collectively for operating over 160,000 miles of pipelines in North America, has participated in a Joint Industry Project (JIP) to examine the current status of Stress Corrosion Cracking (SCC) Threat Management. Many of these operators had previously participated in a JIP addressing the Integrity Management of SCC in High Consequence Areas. Completed in 2006, the JIP developed experience-based guidance for the conduct of hydrostatic testing and excavations, for the assessment of the severity of discovered defects, and for establishing the interval before the next assessment. The outcome was published in ASME STP-PT-011, and formed the basis for proposed revisions to ASME B31.8S. In this second phase of the work, the operational experiences and threat management experiences during the five years since 2006 have been reviewed. From an operational viewpoint, the situation has been very satisfactory; only three in-service failures (ruptures or leaks) due to SCC have been experienced during this period, a considerable reduction compared to the preceding years. However, there is still a legacy of SCC to be managed in older pipelines; for example, 80 near-critical cracks have been removed by hydrostatic testing, and around 100 cracks that would probably have failed a hydrostatic test have been discovered by crack detection ILI. From the threat management viewpoint, a consistent overall framework for addressing SCC is beginning to be established, within which the wide range of operational experience can be addressed using mitigation strategies that are appropriate, proportionate, and timely. Most operators, particularly those with a legacy of SCC in older pipelines, make use of hydrostatic testing. Several now make use of SCC Direct Assessment, following its acceptance as a formal process in around 2005, but mostly for addressing segments with low relative risk of SCC and/or no history of SCC. Many are exploring the application of crack detection ILI; among the JIP members around 45 runs totalling nearly 3000 miles have been completed using EMAT ILI vehicles, and more are scheduled. Almost all the JIP members are using two or more of these approaches in combination as part of their SCC Threat Management strategies. There are areas where the experiences of SCC Threat Management over the last five years point to opportunities for improvement. For SCC Direct Assessment, the use of feedback from excavations to refine the relative rankings for segment prioritisation and dig site selection will become an increasingly important aspect of process improvement. For crack detection ILI, the main issues are the accuracy and reliability of information determining the flaw size and shape for use in predictions of failure pressure and assessments of defect severity. As Threat Management moves from baseline assessment to regular re-assessment, issues that arise include determination of the re-assessment interval, particularly when using SCC Direct Assessment and crack detection ILI. There is also an issue about how best to actively monitor those segments where there is low relative risk and no experience of SCC.

The use of the Electro-Magnetic Acoustical Transducer (EMAT) technology for crack detection by In-Line Inspection (ILI) tools has increased over the last few years. Rigorous validation of the technology leading from the initial application of EMAT inline inspection tools through to determining Probability of Detection (POD) and Identification (POI) has contributed to improved confidence and reliability. EMAT results are being utilized to determine SCC valve section severity, to review and modify hydrostatic test schedules and intervals and could potentially be implemented as a viable alternative to hydrostatic testing. This paper describes the development of an EMAT ILI based program and the related validation process applied by the vendor, pipeline operator and in-ditch personnel. This process is illustrated by demonstrating the performance of the EMAT tool in two 20″ diameter natural gas pipelines which have a documented history of SCC. The tool identified hundreds of features in the two pipelines which were validated both in the ditch and via detailed anomaly sizing.

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 hydro-testing equivalency, detection of injurious defects and the related analysis and reporting improvements made over the past three years.

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Stress Corrosion Cracking (SCC) Direct Assessment in accordance with the guidance set out in NACE SP0204 is an accepted method for assessing the threat of SCC in High Consequence Areas in the US, as prescribed for gas transmission pipelines by CFR 192 Sub-part O. Although operators have used excavations as part of their integrity management strategies for SCC for many years, the formalized method for gathering, interpretation and application of information that is set out in NACE SP0204 has only been applied for less than ten years. During a recent Joint Industry Project involving eight major North American natural gas transmission operators, the current status and application of SCC Direct Assessment has been reviewed. Several of these operators have developed in-house procedures incorporating the relevant guidance from NACE, CEPA and ASME, and over 160 SCC Direct Assessment excavations in accordance with the requirements of NACE SP0204 have been undertaken during the last five years. This paper reviews the development of the procedures, their in-field application and the use of the interpreted data to further refine the SCC Direct Assessment processes.