Review of Hydrogen Induced Cracking of Mid-Wall Defects

There is the potential to demand more of existing infrastructure and introduce uncommon integrity threats as a result of societal challenges to building new cross-country pipelines, the need to traverse more challenging terrain, and the momentum for a hydrogen economy increases. One such threat is hydrogen induced cracking (HIC) of mid-wall defects. HIC is commonly defined in the literature as cracking that initiates within the mid-wall from reformation of molecular hydrogen at mid-wall defects, such as stringers, or microscopic voids in the line pipe steel. In 2020, the Pipeline Research Council International, Inc. (PRCI) funded a project, PRCI Project NDE-1-10, to review the pipeline industry’s current understanding of mid-wall HIC and to identify a potential management strategy for HIC as an integrity threat. The project included a literature review of key factors influencing HIC and of the capabilities of non-destructive inspection technologies (both in-line and in the field) to detect, identify, and size mid-wall defects and any potential radial cracking associated with HIC. A summary of the key factors as well as non-destructive inspection technologies with the potential to detect and size the mid-wall defects with radial cracking was compiled. As a result of the literature review, gaps in knowledge and experience with HIC were identified. It was determined that there is opportunity to better understand hydrogen exposure, both the amount of hydrogen present in the environment and the amount of time in which the line pipe materials are exposed, required to initiate HIC. The literature review also identified improvement opportunities related to non-destructive inspection technologies with the ability to reliably and consistently detect and size HIC. A management framework was developed, based upon the key factors that were identified, data offered through case studies by the steering committee, as well as industry subject matter expert interviews and feedback. The framework is comprised of traditional integrity management components with a focus on threat susceptibility, integrity assessment, severity determination, and assessment response. Using the segment’s threat history, environmental factors, and pipe material factors, a high-level threat susceptibility process was developed that categorizes pipeline or dynamic segments into high-high, high, moderate, low, and not covered priorities. A response for each categorization was also developed that ranges from performing an integrity assessment as soon as practical to opportunistic monitoring. This paper provides a high-level summary of the key factors for the threat of HIC, the gaps identified through the literature reviewed as well as industry outreach, and the integrity management framework developed as a result.