Full-Scale Testing of Circumferential Stress-Corrosion Cracking Features in Pipelines: Bridging the Gap in Integrity Management

Abstract Circumferentially oriented crack-like features, particularly those associated with circumferential stress-corrosion cracking (C-SCC), have emerged as a rising integrity challenge for pipeline operators. Despite considerable advancements in testing and model validation for axially oriented features, there remains a notable gap in understanding the load-carrying capacity of pipe with circumferentially oriented crack-like features. To address this knowledge deficit and enhance integrity management understanding around circumferential cracking, a Joint Industry Project (JIP) was undertaken with 10 pipeline operators. The JIP’s second phase was recently completed, which involved comprehensive full-scale testing of pipes with both machined circumferential features and natural C-SCC features from excavated pipe sections that were donated by JIP members. The primary aim of Phase 2 of the JIP was to contribute to the integrity management of circumferential crack-like flaws identified during in-line inspection, supporting decisions such as selecting excavation sites, planning mitigation measures, determining monitoring actions, and predicting failure loads. The JIP’s focus was on assessing the load-carrying capacity of pipe affected by C-SCC in a biaxial load-state (i.e. internal pressure and axial load) by evaluating the impact of flaw dimensions, internal pressure, and natural flaws (in comparison to machined ones). The full-scale test data was also used to evaluate existing failure prediction models (see IPC2024-133091). Testing of various flaw depths and length-to-depth ratios showed a maximum axial load reduction of 35% compared to the predicted failure load of pristine pipe. There was a minimal reduction in failure load between hoop stresses of 30% and 50% specified minimum yield stress (SMYS), and a moderate reduction between 50% and 72% SMYS when assessing the effect of internal pressure. Pipes that had severe natural flaws (up to 94% of wall thickness) were still able to carry loads that were considerably higher than predicted. Additionally, burst testing confirmed that circumferentially oriented crack-like features still maintain considerable burst capacity. This paper provides a comprehensive overview of the executed test program, including the outcomes and findings. The investigation scrutinizes the impact of flaw dimensions, internal pressure, and the distinction between natural and machined flaws on the load-carrying capacity of the tested pipes. As pipeline integrity remains a paramount concern, the outcomes of this study will contribute significantly to advancing the field and improving the industry’s ability to manage and mitigate the risks associated with circumferential crack-like flaws. Completion of this phase represents a significant stride in understanding the load-carrying capacity and model limitations related to C-SCC.