Thermodynamically modeling the interactions of hydrogen,stress and anodic dissolution at crack-tip during near-neutral pH SCC in pipelines

A thermodynamic model was developed to clarify the interactions of hydrogen, stress and anodic dissolution at crack-tip during near-neutral pH stress corrosion cracking in pipelines by comprehensively considering the electrochemical reactions occurring in the pipeline steel in deoxygenated, near-neutral pH solution. By analyzing the change of the free-energy of steel due to the presence of hydrogen and stress, it is demonstrated that a synergism of hydrogen and stress promotes the cracking of steel. The enhanced hydrogen concentration in the stressed steel significantly accelerates the crack growth. An exact expression of the hydrogen concentration factor, i.e., the dependence of anodic dissolution rate of steel at crack-tip on the hydrogen concentration, is essential at the quantitative prediction of the crack growth rate.