Mechanistic study of LPSCC of stainless steels - temperature dependence of corrosion in hydrogenated water

The temperature dependence of oxide film thicknesses formation rate was studied to elucidate the role of corrosion on crack growth rate. The thickness of oxide films was measured using Auger electron spectroscopy after test under simulated PWR primary water at 250 to 360°C. It was confirmed that the maximum oxide film thickness was formed at approximately 300°C. Cross-sectional observation revealed that both the inner and outer layers decrease with increasing temperature above 300°C. Similar temperature dependence has been reported for the SCC of stainless steels. Although the peak temperature of SCC is slightly higher than that of corrosion, the suppression of corrosion at high temperature seems to mitigate the crack growth rate. The reason for the suppression effect above 300°C is not clear, but surface electro-chemical reaction seems to be the rate limiting process of the corrosion. (author)