Probabilistic Fitness-for-Service Assessment of Hydrogen Pipeline Girth Welds

Repurposing of natural gas pipelines made of carbon steel for use with hydrogen blends requires a fitness-for-service analysis as part of the hydrogen use safety case. Girth welds of an unknown quality exist in the Local Transmission System (LTS). In hydrogen service these welds would have a greater susceptibility to fracture failure due to material embrittlement caused by interaction of steel material with hydrogen.Current inspection methods do not routinely inspect girth welds for defects. Deterministic defect assessment models require the use of conservative assumptions for defect sizes, material properties and loading. This can lead to overly pessimistic conclusions about the suitability of pipelines with girth welds for use with hydrogen.More detailed probability-based assessments are required to reduce the inherent pessimism in deterministic calculation methods. This would provide confidence of the safety and allow for greater use of the LTS with hydrogen and contribute to a quicker and cheaper energy transition for the UK gas network.