Electrochemical Corrosion Behavior of High Strength Carbon Steel in H₂S-Containing Alkaline Brines

The electrochemical corrosion behavior of high strength low alloy carbon steel API S-135 was investigated using in-situ electrochemical measurements, ex situ surface analyses, and software modeling in the alkaline brines at pH of 7.9, 10.7, and 12.4 and at four different P_H2S equal to 0 kPa, 0.83 kPa, 8.3 kPa, and 69 kPa at 85 ^oC. Linear polarization resistance (R_pol) at steady state increased as pH increased from 7.9 to 12.4 at lower P_H2S whereas R_pol decreased and then increased at higher P_H2S. The fastest corrosion rate (CR) was 0.26 mm yr^-1 at pH 10.7 with P_H2S 69 kPa, and the slowest CR was 0.0053 mm yr^-1 at pH 12.4 with P_H2S 0.83 kPa. The correlation between the primary species, corrosion products, localized corrosion and R_pol were discussed. The experimental CR and corrosion products were compared with the modeling CR and Pourbaix diagram.