Modeling of hydrogen-assisted fatigue crack growth in carbon steel pipelines

Hydrogen-assisted fatigue failure poses a significant threat to the structural integrity of pipelines that transport mixtures of hydrogen and natural gas. This study provides a phase-field framework to predict hydrogen-assisted fatigue by incorporating mechanical deformation, stress-driven diffusion, and the evolution of fatigue damage, alongside the effects of chemical strain (lattice dilation due to dissolved hydrogen). The investigation predicts the fatigue behavior of API 5 L X60 and X70 pipeline steels in air and at 6.9 MPa hydrogen gas pressure, comparing the findings with published experimental data. The model indicates that the crack growth rate increases at elevated hydrogen pressures of 55 MPa and 106 MPa. These findings, along with the modeling framework, serve as tools for assessing pipeline integrity and enhancing the safety of hydrogen transportation infrastructure.