Corrosion Properties of Type 304 Stainless Steel in NaOH Solution

Yoshida, Eiichi; Yaguchi, Katsumi*; Aoto, Kazumi 

In sodium cooled fast reactors, when a very small-scale sodium leakage occurs to an air atmosphere through a fine crack of component or piping in the sodium systems, sodium may produce corrosive compounds by the chemical reactions with the air atmosphere, and corrosion damage of component materials may be induced. Therefore, evaluation of the corrosion behavior and the amount of damages of the component materials by the corrosive compound is important from the viewpoint of a design of a plant and maintenance management. The corrosion tests were conducted with the parameters NaOH concentration [55-100mass.% NaOH] and NaOH solution temperature [348-1027K] for the SUS304 stainless steel which is a typical structure material. The corrosion rate and corrosion crack susceptibility were examined. As the results, the corrosion rate of SUS304 was dependent on the temperature of NaOH solution, though the influence of NaOH concentration in solution was small. The different temperature dependency was shown in 55-85% NaOH solution and 100% NaOH. The activation energy was about 30kcal/mol in 55-85% NaOH solution and was about 9kcal/mol in 100% NaOH, respectively. The corrosion rate of this experiment was roughly in agreement with the reference values in NaOH solution obtained by the past experiments. The morphology of corrosion was general corrosion under all conditions. In the SCC experiment using the U-bend test specimen, TGSCC was observed under a part of condition. However, the observed region in this study was within the limits of the SCC boundary region of SUS304 in sodium-hydroxide solution.