Inhibitory Effect of Oxygen and Carbon Monoxide Impurities on Hydrogen Assisted Fatigue Crack Growth in API X65 Linepipe Steels

Abstract Hydrogen is a promising energy carrier for achieving a carbon-neutral society, with pipeline systems being the cost-effective method for transporting gaseous hydrogen. However, the degradation of material properties in linepipe steels poses a significant threat to pipeline integrity and a challenge for repurposing existing pipeline infrastructure. The addition of impurities such as oxygen (O2) and carbon monoxide (CO) has been reported to mitigate hydrogen embrittlement in linepipe steels exposed to high-pressure gaseous hydrogen. However, the results and implications for mitigating hydrogen embrittlement are still under debate. This study investigates the inhibitory effects of O2 and CO impurities on hydrogen-assisted fatigue crack growth (HAFCG) under high pressure H2 gaseous environments at the pressures relevant for H2 pipeline transportation. Initially, the effect of frequency on HAFCG was examined under the loading conditions of Kmax = 44 MPa √m and ΔK = 22 MPa √m to understand the kinetics of the inhibitory effect of impurities. Subsequently, HAFCG was evaluated as a function of ΔK at the selected frequency under different environments. In this paper we present the initial results of HAFCG and advanced characterization of the tested coupons.