Pressure dependence of CO2 effect on hydrogen-assisted fatigue crack growth in two pipeline steels

This study investigated the pressure-dependent CO2 effect on the hydrogen embrittlement of X80 and GB20# pipeline steels by combining experiments and first-principles calculations. Results revealed that the CO2 effect enhanced the fatigue crack growth for GB20# steel in 10 MPa CO2-enriched hydrogen mixtures. However, the improved degree by the CO2 effect at 10 MPa was less pronounced than at 0.4 MPa, which was found for the first time. This was attributed to the decreased adsorption rate of CO2 on iron as hydrogen pressure increased. Therefore, in high-pressure CO2-enriched hydrogen mixtures, CO2 could not significantly accelerate the inherent rapid hydrogen uptake at high pressure.