Abstract
Galvanic corrosion of carbon steel (CS) coupled to four different alloys, namely, 316 SS, 321 SS, Incoloy 825 and 2205 SS was studied through electrochemical techniques in flowing (3 and 5 m/s) deaerated 3.5% ammonium bisulfide solution (ABS) at 60oC collected from petroleum refinery. The electrochemical work included the Evans (polarization) diagrams of coupled alloys and the measurements of the potential of separate alloys as well as the measurements of galvanic potential and galvanic current as a function of time. The impact of galvanic coupling on the anodic and cathodic reaction rates was determined. It was found that the corrosion of CS was enhanced as the result of increasing the solution flow velocity while it was coupled to the different alloys. It showed that the best couple to be used at 5 m/s is CS/SS321 since it had the lowest corrosion current and less negative corrosion potential. The severity of galvanic corrosion increased with the increase of the solution speed (3, and 5 m/s) for all the couples. It was concluded that for all the couples, the anodic control is higher than the cathodic control, indicating that the corrosion of CS is the dominant factor in the reaction of the metallic couples in the 3.5% ABS at different speeds and at 60oC. Results indicated 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 deaerated 3.5% ABS at 60oC and at different speeds ( 3, and 5 m/s).
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Journal of Geology and Geoscience 