Corrosion behavior of stainless steels and Ni-based alloys in supercritical water containing ammonium chloride and oxygen

Corrosion test of stainless steel 316 SS is carried out in supercritical water (400 C/24 MPa) with ammonium chloride and oxygen. The corrosion rates were analyzed by measurement of oxide film thickness, and the oxide on the samples surfaces were analyzed with various analytical methods. After 60 hours exposure, 316 SS undergone severe corrosion attack, forming thick oxide films mainly composed of Fe-Cr spinel, which is Cr-rich, and depleted with Fe. Based on the measurement of oxide films, the corrosion rate of 316 SS exposing in SCW containing NH4Cl and containing NH4Cl and O2 was 3.26 mm/a and 6.76 mm/a, respectively, which is extremely high and totally unacceptable.