Effect of dissolved oxygen content on the oxide structure of Alloy 625 in supercritical water environments at 700 °C

• Corrosion tests of Alloy 625 were conducted in supercritical water at 700 °C with different dissolved oxygen content.
• Duplex layers of oxide structure were observed after corrosion test.
• The effect of dissolved oxygen content on the oxide structure of Alloy 625 in supercritical water was discussed.

The corrosive behavior of Alloy 625 in supercritical water at 700 °C and 24.8 MPa with dissolved oxygen contents of 150 ppb, 1 ppm, and 8.3 ppm was studied. The oxides grown on all test samples exhibited a duplex-layer structure. The outer layer was composed of a spinel oxide Ni(Cr, Fe)2O4 and the inner layer was mainly continuous Cr2O3. Ni-containing oxides, such as spinel Ni(Cr, Fe)2O4, did not form on samples exposed to the supercritical water environment containing 150 ppb dissolved oxygen. Oxygen content might considerably affect the composition and structure of oxides grown in supercritical water for Alloy 625.