Impact of Hydrogen Concentration Distribution in Hydrogen-Blended Gas on Fatigue Crack Growth Rate of Pipeline Steels

Abstract The methods to achieve large-scale and long-distance hydrogen transport are primarily to blend hydrogen with another gas, such as natural gas. Due to the significant difference of the densities of hydrogen and those of other gases, the distribution of hydrogen-blended gas becomes uneven during pipeline transportation. Mechanical properties of pipeline steels are normally degraded due to the internal hydrogen environment, and thus fatigue and fracture of pipelines that transport hydrogen-blended gases are likely to occur. This paper aims to investigate the impact of the heterogeneous hydrogen volume fraction of hydrogen-blended gas on the hydrogen induced fatigue crack growth rate of pipeline steels using the cyclic cohesive zone model (CCZM). A dynamic surface hydrogen concentration is used to simulate the heterogeneous hydrogen volume fraction of hydrogen-blended gas during transportation. In the CCZM, not only the degradation of cohesive strength but also the degradation of accumulated cohesive length is considered to incorporate the impact of hydrogen embrittlement (HE) on the fatigue crack growth. The predicted results are compared with the fatigue crack growth rate where the hydrogen volume fraction is constant and the most prone locations in pipeline steels where HE may occur are discussed. The results tend to provide a valuable reference for future designs of hydrogen-blended gas pipelines.