Impact of NaCl impurity on corrosion of 316 L steel in molten nitrate salts for thermal energy storage: An electrochemical study

The impact of NaCl impurity on corrosion of stainless steel (SS) 316 L in binary nitrate salts (60 wt% NaNO₃ + 40 wt% KNO₃) was systematically investigated at 565°C via electrochemical measurements. SS 316 L exhibits active dissolution behavior in salts containing 0–1.4 wt% NaCl. The influence of NaCl impurity shows a strong time dependence according to the negligibly affected corrosion current density obtained from a short-time potentiodynamic polarization sweep. The corrosion process of 316L in salts with NaCl-free is controlled by ions transport through the oxide layer. With the presence of NaCl impurity, it is controlled by higher rate of ions transport and the diffusion of metal chlorides. The alternation in basicity in the corrosion front caused by chloride ions increases the solubility of chromium oxide and hence the dissolution of chromium oxide, which can lead to the formation of a less protective oxide layer.