Effects of hydrogen sulfide on the corrosion behavior of high strength steel in Alkaline solutions

In-situ electrochemical corrosion measurements were performed for high-strength low-alloy steels in 5 %wt. NaCl solutions of pH 7.5, 10.6, and 12.3 at 85 °C. It was observed that the corrosion typically reached a steady state by 60 hours. The corrosion rate at steady state was slower at higher pH, regardless of H₂S concentration. The addition of H₂S accelerated the corrosion rates of UD-165 at pH 7.5 and 12.3, but decreased the corrosion rate at pH 10.6. This could have been related to the autocatalytic effect of H₂S and the nature of the corrosion product film on the surface. Both the Pourbaix diagrams and the surface analyses suggested that the corrosion products shifted from iron sulfides to iron oxides as the solution pH was increased.