Characterisation of corrosion films on steels after long-term exposure to simulated supercritical water conditions

The goal of this paper is to present results of oxidation kinetics and morphologies for steels exposed under supercritical water conditions. The steels have been chosen to be appropriate for high temperature uses in power plants, tubes or waterwall components. The exposure conditions have been selected as relevant for advanced supercritical boilers or new supercritical nuclear power plant concepts, the temperature being chosen from the upper limit of potential service conditions. The test matrix has been agreed with the European HPLWR consortium and its material experts. For the purpose, corrosion products, oxide layers and films, were grown on a range of ferritic and stainless steels exposed to pure water (inlet dissolved oxygen content 1 ppm, inlet conductivity 0.07 ìS cm-1) in a supercritical condition, i.e. at a temperature of 650°C and pressure of 30 MPa, up to 900 h. Results from the characterisation of the corrosion products with optical and scanning electron microscopy, including a linescan EDS analysis of metallographic cross-sections, are presented and discussed. In order to evaluate the possibilities of the analytical techniques employed, the obtained results for the thickness and indepth composition of the formed scales are compared to results of the indepth analysis of similar samples with Glow Discharge Optical Emission Spectroscopy (GDOES). Some implications of the obtained results on the corrosion performance of the studied materials are also discussed.