Study on the Hydrogen Embrittlement and Fatigue Performance of In-Service X60 Pipeline Steel in Hydrogen-Blended Environments

With the increasing urgency of hydrogen blending transportation in in-service natural gas pipelines in the development demand of hydrogen energy utilization， in-service pipeline materials will face the safety risk of running in hydrogen environment.To investigate the hydrogen embrittlement properties of in-service natural gas pipelines under hydrogen blending conditions， the slow strain rate tensile test and fatigue crack growth test of pipeline steel in hydrogen environment were carried out on X60 pipeline steel of an in-service natural gas pipeline， the effect of hydrogen on the tensile and fatigue properties of the tube was analyzed.The results indicated that under a total pressure of 6.4 MPa and a hydrogen blending ratio of 5%， the hydrogen embrittlement sensitivity of the in-service X60 pipe was relatively low， with fractures exhibiting mostly ductile fracture characteristics.The 5%hydrogen blending ratio did not affect the fracture characteristics.In the same hydrogen blending environment， however， the fatigue crack growth rate of X60 pipeline steel was influenced by the hydrogen environment and the stress intensity factor range at the crack tip.When the stress intensity factor range exceeded a certain threshold， the fatigue crack growth rate of X60 pipeline steel increased dramatically.The fatigue crack growth mode transitioned from ductile fracture dominated by plastic deformation at the crack tip to a mixed fracture of brittle and ductile fracture under the combined effects of hydrogen and cyclic loading.The hydrogen embrittlement sensitivity and fatigue performance of the X60 bend pipe material will be key evaluation indicators for hydrogen blended natural gas transportation in in-service pipelines.