Effect of pH and applied stress on hydrogen sulfide stress corrosion behavior of HSLA steel based on electrochemical noise analysis

The influence mechanism of pH and the externally applied stress on sulfide stress corrosion cracking behavior based on the joint analysis of the in situ electrochemical noise and microstructure was studied. The results showed that H+ in solution changes the composition and structure of corrosion product film by affecting the concentration of S2- and Fe2+ near the anode surface. When the pH increased from 2.6 to 3.6 and 4.6, the corrosion product film changed from porous Mackinawite to dense and stable FeS. The change in corrosion product type delayed the crack initiation time by 10.5 and 45.5 h, while the uniform corrosion time was prolonged by 6.1 and 46 h, respectively, delaying SSC behavior. After increasing the applied stress, the local plastic deformation on the material surface increases the porosity and crack rate of the corrosion product film and becomes a fast propagation channel for SSC cracks. When the applied stress is 110% of the actual yield strength of the material, the initiation time of stress corrosion cracking is 6 and 18.1 h earlier than that of 90% and 100%, respectively. The local corrosion time was extended by 23.5 and 8.2 h, respectively, accelerating SSC behavior.