Effect of cathodic protection potential on stress corrosion susceptibility of X80 steel

By simulating the different electrochemical characteristics of the crack tip and crack wall in the stress corrosion process of X80 steel through the dynamic potential polarization test with different scanning rates, it is reasonable to predict that the crack tip of tensile sample might still be in anodic dissolution state even under cathodic protection, and meanwhile, the hydrogen atoms generated by the cathodic reaction would have a facilitating effect on the anodic dissolution of crack tip. Thus, with the cathodic potential being negatively shifted, the hydrogen-promoted anodic dissolution and the cathodic protection effect may compete at the crack tip of steel, simultaneously. Combined with the results of electrochemical hydrogen permeation and SSRT (Slow strain rate tensile test), the authors quantitatively analyzed the effect of cathodic polarization potential on the kinetics of anodic dissolution at the crack tip, and the results showed that the cathodic protection effect on the specimen at the critical potential (about-950 mV) for stress corrosion of X80 steel is sufficient to offset the hydrogen-promoted anodic dissolution effect caused by the enrichment of hydrogen atoms at the crack tip, compared to that of the free-corrosion condition. Therefore, the dominant factor that caused a significant increase in stress corrosion cracking (SCC) susceptibility, which was indicated by the comprehensive loss rate I sigma > 20% of X80 steel and brittle fracture morphology obtained through SEM, was the hydrogen embrittlement mechanism rather than the anodic dissolution mechanism.