Corrosion of engineering materials in a supercritical water cooled reactor: Characterization of oxide scales on Alloy 800H and stainless steel 316

Oxide scales formed on stainless steel SS316 and Alloy 800H in continuous supercritical water flow conditions are examined using SEM and XRD. Duplex oxide layer structures are observed. In deoxygenated water, an outer magnetite layer is formed on both materials, with an inner layer on Alloy 800H containing chromium oxide. In oxygenated water, only magnetite is seen on SS316, while both hematite and magnetite are observed on alloy 800H. Alloy 800H forms a thinner scale, in which the presence of hematite is thought to provide better corrosion protection. Numerous cracks are formed in the oxide layers after oxygenated treatment.