Compressive Strain Capacity Reliability of Hydrogen-Carrying Steel Pipelines in Permafrost

Abstract In strain-based assessment, the imposed strains on the pipeline due to ground displacement are assessed as strain demands. The pipeline capacity to resist these imposed demands are termed as strain capacities. The tensile strain capacity is often governed by the strain capacity of the girth welds, and the exceedance of tensile strain capacity can lead to a full-bore rupture. In contrast, the imposed compressive strain demand initiates the local buckling of the pipeline, and the compressive strain capacity (CSC) is defined as the average strain across the buckling location at the initiation of the buckle. In the presence of the pressurized environment of hydrogen and hydrogen-methane blends, previous studies have shown that the carbon steels may experience significant reduction in post-yield ductility along with embrittlement and reduction in material toughness. As the CSC of steel pipelines is sensitive to the post-yield strain hardening and ductility of the material, there may be reduction in CSC in hydrogen pipelines. However, there haven’t been any systematic studies to understand the sensitivity of CSC to the ductility reduction in the carbon steels and amount of tolerable loss of ductility. Furthermore, the uncertainty in the amount of ductility reduction is not been characterized in the literature. In the present study, the issues in strain-based assessment of the hydrogen pipelines are addressed with the focus on CSC. The differences in uncertainty modelling of the pipeline parameters, as well as, CSC model errors are explored. Parameters for random variable modelling and uncertainty propagation for reliability analysis when using the limit state for CSC are proposed. Additionally, sensitivity of the estimated probability of failure to the pipeline material, geometry, and model uncertainties are explored through a case study. The results of the study are expected to guide the future work in development of CSC models for the carbon steel pipelines susceptible to ductility reduction and hydrogen embrittlement.