Probing High-Temperature Electrochemical Corrosion of 316 Stainless Steel in Molten Nitrate Salt for Concentrated Solar Power Plants

Abstract

The corrosion resistance of structural materials, particularly in molten salt environments, is of central importance to design concentrated solar power (CSP) plants. In this perspective, the high-temperature electrochemical behavior of passive film on 316SS in solar salt composition (60 pct. NaNO3: 40 pct. KNO3 by wt. pct.) was evaluated using linear resistance polarization, Tafel polarization, and electrochemical impedance spectroscopy techniques in the application range of 400 to 550 °C. An increase in corrosion rate with temperature and severe oxidation at 550 °C was recorded. However, the corrosion potential (Ecorr) does not vary significantly. The critical analysis of the impedance bode phase diagram reveals two well-separated maxima at 400 °C, indicating the role of the passive layer during the corrosion process. At 500 °C, the observed phase angle is close to 45°, attributed to processes controlled by mass transfer limitations. While analyzing the influence of mass transfer, an equivalent circuit model has been proposed to analyze the corrosion of the 316SS, a material used for piping and containment of CSP plants in molten solar salt.