Effect of Sulfuric Acid on Corrosion and Passivation of 316 SS in Organic Solution

Organic solvents like methanol have potential application in fuel cells, chemical and surface treatment processes. The corrosion investigation of austenitic stainless steels in methanol containing reducing acids (HCl, H 2 SO 4 etc.) is very limited, in particular the passivation and pitting kinetics. In this work, the corrosion, passivation and pitting kinetics of 316 stainless steel (SS) have been investigated in methanolic solutions containing LiCl, HCl and mixture of HCl and H 2 SO 4 by polarization, EIS, SEM and XPS. The rate of corrosion was higher in HCl solutions as compared to LiCl solutions. Passivation was promoted in methanol–HCl + H 2 SO 4 solutions with molar ratio of H 2 SO 4 to HCl ≥ 10: 1. The presence of anions, water content and solution acidity were the key factors determining the stability of passive film. Pit nucleation was inhibited with increasing H 2 SO 4 concentration. Primary components of the passive film were iron/chromium oxyhydroxides with incorporated and ions.