Abstract
A number of metallic and ceramic materials were exposed in both supercritical and subcritical zones of the effluent path in a pilot supercritical water oxidation (SCWO) unit which had been developed for treatment of hazardous wastes. The test coupons as well as several components removed from the reactor and from effluent sections of the plant were evaluated during and upon completion of a recent process demonstration program. This paper summarizes results of the materials performance evaluation. Typical materials evaluated after exposure in the SCWO environment (T>374°C) included high-nickel alloys such as Alloys 625, 718, C-276, and 750, titanium and its alloys, platinum and its alloys, and a few ceramics. Some of these materials as well as titanium were also exposed in the subcritical environment (T<374°C). Incidence of corrosion experienced during the SCWO demonstration program are illustrated in terms of metal loss, incidence of localized corrosion such as pitting and crevice corrosion, and examples of severe stress-corrosion cracking in the high-nickel alloys. The results provide a basis for future design, retrofit, and replacement decisions.
