Development of flow-accelerated corrosion prediction method (1) Acquisition of basic experimental data including low temperature condition

Abstract

A series of study is presented to develop a prediction method for pipe wall thinning in power plants in order to improve the maintenance management for piping system. As the first report, experiments for flow-accelerated corrosion (FAC) of carbon steel specimens were conducted and basic data were obtained, focusing on relatively low temperature condition. FAC rate is seen to decrease by lowering temperature and the trend curve tends to remains to keep considerable level in lower temperature around 50 °C. Obtained data would mean that FAC susceptibility of pipeline in condensate demineralizer downstream and deaerator upstream in PWR plants is comparable. In terms of pH, a large drop in FAC rate is seen around pH 9.0 as in previous studies, and its ratio of pH 9.2 to pH 7.0 is approximately 1/10. This ratio fairly agrees with iron solubility in each pH condition at 150 °C while it is smaller in lower temperature condition, which may require additional effect related to pH and temperature to be considered to evaluate the FAC rate. The effect of iron contents on FAC rate is confirmed by referring to saturation solubility of iron. It is suggested that FAC may occur even when the iron concentration in the bulk water is in saturation level, which should be considered in the modelling process for FAC prediction.