Study on the synergistic effect of welding residual stress and hydrogen diffusion on fatigue crack growth of X80 steel pipeline

During the service of X80 high-strength pipeline steel, the combined effects of welding residual stress, cyclic loading, and hydrogen complicate the prediction of pipeline fatigue life. This article combines ABAQUS and FRANC3D finite element software to analyze the fatigue crack growth laws of the X80 pipeline with thickness of 22 mm under the combined condition. After heat treatment, the fatigue life of pipelines with annular and axial cracks increased by 19 % and 83 %, indicating that post-weld heat treatment significantly improves the fatigue life of the pipeline. When the crack grows to the outer surface of the pipeline, the fatigue life of a pipeline with a 10 % hydrogen doping ratio is reduced by 77 % compared to one with a 1.5 % hydrogen doping ratio. These findings indicate that toughness of the crack front region is significantly reduced by hydrogen concentration, the crack propagation rate is accelerated, and the fatigue life of the pipeline is significantly reduced.