Session: 02-05-01 Extreme Loads and Responses

Submission Number: 157472

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

Geohazards caused by frost-heave cycling in the permafrost regions have significant impact on the structural integrity of onshore buried energy transmission pipelines as the permanent differential ground displacement due to thaw settlement could result in either full-bore rupture at the girth-welds or leaks due to significant local buckling. For geohazard management of buried pipelines, strain-based design and assessment approaches are often used as the type of loading on the pipelines is displacement-controlled and thus, the structural integrity of the pipeline is maintained due to the post-yield ductile resistance.

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.

Presenting Author: Smitha Koduru University of Alberta

Presenting Author Biography: Smitha Koduru is an Adjunct Professor at the University of Alberta, Canada. Dr. Koduru has more than fifteen years of experience in application of risk and reliability concepts to evaluate structural systems and distributed infrastructure, such as buried oil and gas pipelines, facilities, underground gas storage, and authored numerous research articles and research reports related to pipeline integrity related to cracks and geohazards. She chaired the Risk and Reliability Track for the ASME International Pipeline Conference (IPC) since 2017, and volunteers on American Petroleum Institute (API) committees for the development of recommended practices related to pipeline integrity. She had a PhD from the University of British Columbia, Vancouver, Canada in applying reliability methods for performance-based engineering. She carries a Professional Engineer registration in the provinces of Alberta, and British Columbia in Canada.