Effect of Chloride Impurity on Corrosion Kinetics of Stainless Steels in Molten Solar Salt for CSP Application: Experiments and Modeling

Solar salt (60 wt% NaNO₃ + 40 wt% KNO₃) is widely used in the storage system of concentrated solar power plant. However, the chloride within the molten solar salt can affect the corrosion kinetics of stainless steels and hence affect the overall structural integrity. In this work, the corrosion behavior of 304 and 316L stainless steel (SS) in molten solar salt mixtures with different chloride impurities were investigated by immersion tests at 565 °C. Results show that as the content of chloride in the solar salt increases (up to 1.4 wt%), both 304 and 316L SS keep parabolic corrosion kinetics, and the rate constants increase. In comparison with 304 SS, the better corrosion resistance of 316L SS is ascribed to the higher thickness ratio of FeCr₂O₄ spinel to oxide scale. In addition, to quantitatively describe the effect of chloride impurity on corrosion kinetics of stainless steels, a novel theoretical model based on Fick’s first law is proposed and validated by the experiments.