Roles of carbon dioxide and steam on the hydrogen embrittlement of 3Cr tube steel in synthetic natural gas environment

The hydrogen embrittlement behaviour of 3Cr has been investigated under mixed H₂ with CO₂ at different strain rates, hydrogen partial pressures, and in the presence/absence of steam. The slow strain rate test results show that the HE susceptibility of 3Cr increased with increasing hydrogen partial pressure, and the plasticity of 3Cr obviously decreased in the presence of steam. The effect of strain rate was negligible in H₂/CO₂ environment but showed a significant difference in H₂/CO₂/steam environment. The fracture was a ductile fracture mode in N₂ environment and a brittle fracture mode in H₂/CO₂/steam environment. The reason for the severe plasticity loss of 3Cr in H₂/CO₂/steam environment was probably that the steam has a preferential adsorption onto the 3Cr surface compared with H₂ and CO₂. Consequences in CO₂ combined with H₂O to form H₂CO₃, which accelerated the anodic dissolution of 3Cr, and the physical adsorption of H₂ on steel was enhanced.