Corrosion properties were investigated on stainless steels and Ni-base alloys in supercritical water containing 0.01mol/kg-H2SO4 at 400°C/30MPa and 400°C/60MPa as a function of oxygen concentration ranging from 3ppb to 800ppm. Corrosion rates and compositions of oxide scales indicated that Cr was basically the key element for corrosion resistance of the alloys in the testing environments. However, Fe became another major contributor to corrosion resistance when oxygen
concentration of the environment was increased up to 800ppm. Oxide stability of Cr, Fe, and Ni estimated as potential-pH diagram is in good agreement with the experimental results.
Keywords: supercritical water, oxygen concentration, Ni-base alloy, austenitic stainless steel, sulfuric acid, oxide scale, phase stability