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 H-2 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 H-2/CO2 environment but showed a significant difference in H-2/CO2/steam environment. The fracture was a ductile fracture mode in N-2 environment and a brittle fracture mode in H-2/CO2/steam environment. The reason for the severe plasticity loss of 3Cr in H-2/CO2/steam environment was probably that the steam has a preferential adsorption onto the 3Cr surface compared with H-2 and CO2. Consequences in CO2 combined with H2O to form H2CO3, which accelerated the anodic dissolution of 3Cr, and the physical adsorption of H-2 on steel was enhanced.