Oxidation-sulfidation attacks on alloy 600 in supercritical water containing organic sulfides

The corrosion characteristics of alloy 600 in supercritical water containing organic sulfides was investigated after an exposure at 480 °C and 25 MPa for 72 h. A duplex-structure corrosion scale was observed, with the outer layer predominantly consisting of NiS. The inner corrosion layer was composed of Cr-rich spinel oxides and the fast channels (resulting from the interconnected sulfidation productions such as NiS and Ni₃S₂) for outward transport of metal cations. This phenomenon can be attributed to the emulative oxidation-sulfidation of alloy 600 because the supercritical water containing organic sulfides system may become a mixture of dominant SCW and H₂S due to the gasification reaction of organic sulfides. The formation and growth processes of corrosion scales was also discussed.