Under-deposit corrosion of Ni-based alloy 825 and Fe-Ni based alloy 800 in supercritical water oxidation environment

The under-deposit corrosion behavior of Alloy 800 and Alloy 825 in oxidizing supercritical water (SCW) containing KCl or NaCl were investigated. A novel-designed reactor was used to ensure that the alloys remained covered by salt deposits in the whole immersion test process. Fe oxides, NiCl₂, and spinel structures were detected on the outer layer, Cr₂O₃ formed as the inner layer. The salt deposits block the diffusion of oxygen into the microenvironment between the alloy surface and the salt deposit layer. A detailed under-deposit corrosion mechanism of the alloys after exposure to oxidizing supercritical water is proposed.