Characterization of oxide scales grown on alloy 310S stainless steel after long term exposure to supercritical water at 500°C

The oxide scale grown of static capsules made of alloy 310S stainless steel was investigated by exposure to the supercritical water at 500°C 25MPa for various exposure times up to 20,000h. Characterization techniques such as X-ray diffraction, scanning/transmission electron microscopy, energy dispersive spectroscopy, and fast Fourier transformation were employed on the oxide scales. The elemental and phase analyses indicated that long term exposure to the SCW resulted in the formation of scales identified as Fe3O4 (outer layer), Fe-Cr spinel (inner layer), Cr2O3 (transition layer) on the substrate, and Ni-enrichment (chrome depleted region) in the alloy 310S. It was found that the layer thickness and weight gain vs. exposure time followed parabolic law. The oxidation mechanism and scales grown on the alloy 310S stainless steel exposed to SCW are discussed.