Fitness-for-service Assessment of Crack-like Features for Hydrogen Pipelines

Repurposing existing natural gas pipelines for hydrogen service has emerged as a cost-effective strategy for transporting hydrogen over long distances. However, the transition to hydrogen service introduces challenges due to existing defects in these pipelines; crack-like features are particularly concerning as they act as critical stress concentrators and hydrogen atom traps, which would increase the brittle fracture risk and accelerate the fatigue crack growth. API 579-2021 emphasizes the need for extreme caution when assessing crack-like features in hydrogen-charged materials. It warns that in a hydrogen-charging environment, a subcritical crack can grow over time to a critical size, leading to unstable fracture. ASME B31.12-2023 specifies requirements of hydrogen pipelines for fracture control. CSA Z662-2023 introduces Clause 17 specifically for hydrogen and hydrogen blend pipeline systems. However, comprehensive fitness-for-service (FFS) assessment approaches are still not fully developed. This paper introduces an advanced finite element model to study hydrogen diffusion and the interaction between hydrogen and steel at crack-like features in hydrogen pipelines. It also presents an FFS assessment approach that includes failure pressure and remaining life calculations. The study aims to provide deep insights into hydrogen-induced cracking and contribute to the development of FFS assessment approaches for crack-like features in hydrogen pipelines.