Numerical assessment of cold crack susceptibility of X65 pipe steel during in-service repair welding of pipeline in transportation of gas-hydrogen blends

Transporting green hydrogen through existing gas pipelines presents a promising pathway for sustainable energy technologies. However, hydrogen’s interaction with pipeline steels can impact the operability and reliability of the infrastructure. Blending green hydrogen with natural gas mitigates the risk of hydrogen embrittlement, yet excess diffusible hydrogen within the pipeline material, while not significantly impairing mechanical properties, must be addressed in maintenance strategies. In-service repair welding is a viable approach for restoring pipeline integrity without interrupting gas flow. However, the risk of cold cracking due to hydrogen diffusion necessitates precautions, such as preheating or optimizing welding parameters. This study evaluates the risk of cold cracking during in-service welding on pipelines carrying gas-hydrogen blends. By employing multiphysics modelling, the analysis incorporates factors like temperature distribution, microstructural evolution, stress-strain behaviour, and hydrogen diffusion. Weibull criterion is applied to predict fracture probability based on hydrogen concentration, martensitic transformation, and tensile stress. A case study on repair welding of a corroded X65 pipeline examines the effects of diffusible hydrogen and preheating temperatures. The findings offer recommendations for ensuring safe in-service welding on pipelines transporting gas-hydrogen blends.