Thermal diffusion coatings for corrosion protection in power plant environments
University of New Brunswick
The performance of steels and alloys in subcritical and supercritical water environments can be increased by protection of the substrate material with appropriate surface coatings. In this work, low-grade carbon steel and austenitic stainless-steel alloys were treated with Endurance Technologies Inc. (ETI) protective coatings based on borides and aluminides obtained through their proprietary thermal diffusion process technology. In this work, 1018 carbon steel and 316 stainless steel were coated and have been tested using UNB’s SCW test loop under sub-critical and supercritical conditions with a solution pH of ~ 9.5 (adjusted with ammonia) at temperatures between 350-450oC and a system pressure of 24 MPa for durations up to 500 h. The coatings demonstrated promising performance with little observed blistering, minimal crack formation, delamination or breakaway issues. The coatings’ integrity, structure, and thicknesses (~150–200 µm depending on the coating system) remained at their original levels after exposure. Slight surface oxidation of the corrosion resistant borides and aluminides promoted the healing of the coating surfaces without breakaway oxidation. The selected coating systems under the conditions of the study can be made applicable to long lengths of tubing and complex components based upon ETI’s treatment process.