A Study of Galvanic Corrosion in Stagnant Ammonium Bisulfide Solution

Galvanic corrosion of carbon steel (CS) coupled to four different alloys, namely, 316 SS, 321 SS, Incoloy 825, and 2205 SS, was studied in deaerated 3.5% ammonium bisulfide solution (ABS) at 60°C by electrochemical techniques under stagnant condition. The electrochemical work included the measurements of the potential of separate alloys as well as the measurements of galvanic potential and galvanic current as a function of time and Evans (polarization) diagrams of coupled metals. The impact of galvanic coupling on the anodic and cathodic reaction rates was determined. It was found that the CS suffered galvanic corrosion when it was coupled to all of the selected alloys but at different rates; so, it is recommended to avoid the galvanic coupling of CS with any of the noble alloys in stagnant deaerated 3.5% ABS at 60°C. Results indicated that the best alloy to be used with the CS in stagnant deaerated 3.5% ABS solution at 60°C is SS 2205 since the galvanic couple has the lowest CR with a less negative Ecorr value, indicating that CS corrodes at a lower rate when it is coupled to SS2205 in this environment.