Quantifying Conservatism in ASME B31.12 Option A for Hydrogen Pipeline Repurposing

Hydrogen is a key enabler of the energy transition, and repurposing existing natural gas pipelines offers a costeffective pathway for large-scale hydrogen transport. However, hydrogen embrittlement raises integrity concerns, and current design standards such as ASME B31.12 Option A adopt highly conservative safety margins without a quantified reliability basis. This study evaluates whether the conservative safety margins in ASME B31.12 Option A for hydrogen pipelines can be safely relaxed. A semi-elliptical flaw (depth 0.25t, length 1.5t) is assessed using the Failure Assessment Diagram (FAD) method and Monte Carlo simulations with up to 2.5 × 107 iterations. Fracture toughness is fixed at 69.3 MPa√m, while wall thickness and yield strength vary statistically. Three design scenarios explore safety factor products from 0.388 to 0.720 at 0 ◦C and 20 ◦C. Results show that flaw acceptability is maintained in all deterministic cases, and the probability of failure remains below 10− 6 . No failures occur when the safety factor product drops below 0.637. The analysis uses only codified flaw assumptions and public material data. These findings confirm that Option A provides a highly conservative envelope and demonstrate the value of a reliability-based approach for assessing hydrogen pipeline repurposing while addressing the gap between prescriptive standards and quantified reliability. This integrated FAD–probabilistic framework demonstrates that Option A includes significant conservatism and supports a reliability-based approach to evaluate hydrogen pipeline repurposing without experimental inputs.