Experimental Study on Hydrogen-Induced Crack Propagation of X80 Steel Under Alternating Pressure Fluctuations

When hydrogen is transported in a pipeline, the fatigue loading in the pipeline will enhance hydrogen accumulation and diffusion, thus increasing the risk of hydrogen-induced fracture. In this study, specimens are subjected to cyclic loading within an autoclave, where hydrogen gas pressure is varied to examine its impact on fatigue crack growth. The influence of hydrogen pressure and stress variations on the fatigue crack growth rate is investigated. The findings show that as hydrogen pressure increases, the crack growth rate also rises, and at 3 MPa hydrogen pressure the rate is elevated by one order of magnitude compared to that in air, reaching 10^-2 mm/cycle. In hydrogen, the fatigue crack propagation rate decreases with increasing loading frequency. When the frequency is 0.02 Hz, the crack propagation rate reaches a maximum of 10^-2 mm/cycle, whereas at 0.5 Hz, the fatigue crack propagation rate is generally below 10^-3 mm/cycle. With the maximum stress held constant during cyclic loading, the fatigue crack growth rate increases as the stress range widens, and when the stress ratio reaches 0.5, the crack propagation rate can increase to a maximum of 10^-1 mm/cycle. Based on these experimental results, a predictive model is proposed to estimate the crack growth rate under different hydrogen pressures and loading conditions, and the average relative errors of predictive values and experimental data are limited below 10%.