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

This study investigated the pressure-dependent CO 2 effect on the hydrogen embrittlement of X80 and GB20# pipeline steels by combining experiments and first-principles calculations. Results revealed that the CO 2 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, CO 2 could not significantly accelerate the inherent rapid hydrogen uptake at high pressure. • Enhanced hydrogen embrittlement by CO 2 effect was pressure-dependent. • CO 2 effect at low pressure was more pronounced than that at high pressure. • CO 2 adsorption rate on iron decreased with increasing surface hydrogen coverage.