Corrosion Screening Tests With Ni-Base Alloys in Supercritical Water Containing Hydrochloric Acid and Oxygen

Abstract

Abstract Corrosion of reactor material during oxidation of hazardous organic waste containing chloride proceeds very fast and constitutes one major problem in SCWO applications. The following Ni-base alloys were tested within the framework of our experimental program: Inconel 625 and 686, Hastelloy C-276, Nicrofer 5923 and 6025, and Haynes alloy 214. Test tubes were fabricated from these materials and exposed to SCWO conditions, without organics, at temperatures up to 600 °C and pressures up to 34 MPa. Higher concentrated HCl solutions or the combination of oxygen and HCl cause strong surface destruction. The corrosion measured was higher at lower temperatures and at higher pressures, if all other conditions remained constant. The most severe corrosion — general corrosion with SCC and pitting — appeared at temperatures near the critical temperature, i.e. in the preheater and cooling sections of the test tubes. The corrosion products were insoluble in supercritical water and formed thick layers in the supercritical part of the reactor. Under these layers only minor corrosion occurred.