Corrosion of stainless steels and low-Cr steel in molten Ca(NO3)2–NaNO3–KNO3 eutectic salt for direct energy storage in CSP plants

• Hitec XL salt improve the corrosion resistance in storage materials.
• Gravimetric study confirms the corrosion reduction in commercial steels.
• Low wt% Cr addition improves the corrosion in carbon steels significantly.

The corrosive effects of a molten nitrate mixture of 48% Ca(NO3)2+7% NaNO3+45% KNO3 were appraised at 390 °C on two different types of stainless steels (AISI 304, 430), a low-Cr alloy steel (T22) and a carbon steel (A1).The corrosion rates were determined using gravimetric tests, which measured the weight gain during 2000 h to identify the corrosion products with scanning electron microscopy (SEM) and X-ray diffraction (XRD).Studies on stainless steel revealed a better behaviour in corrosive environment, which mainly identifies the formation of (K,Na)CrO4 protective spinel.Fe2O3 and Fe3O4 were the other important products that were found in the tests performed at 390 °C; the formation of some stable compounds with salt impurities, such as carbonates and sulphates, was also observed.