Influence of Ni on corrosion and trench formation of low alloy steel in low H2S content sour corrosion environments

Abstract The influence of Ni content on corrosion and trench formation of low alloy steel in a low H 2 S containing sour corrosion environment was investigated. The results show that Ni decreases the total amount of corrosion by forming a passive film containing Ni components, such as NiS and Ni 3 S 2 on the steel surface as a result of long‐term corrosion and suppressing the anodic dissolution reaction, while increasing the trench depth. It was also identified that the Ni content had a more dominant effect on trench formation in steel regardless of the tested sour environments with 0.01 bar H 2 S gas (pH 4.0) and 0.001 M Na 2 S 2 O 3 (pH 2.7) in this study. Based on the experimental findings, the mechanism of trenching propagation by Ni was discussed from the viewpoint of changes in surface film properties and associated difference of corrosion resistance between trench‐tip and bulk surface due to the variation in Ni content.