Corrosion Behavior of Stainless Steel Alloys in Molten Solar Salt
Abstract
Molten nitrate salts (NaNO3–KNO3) have been widely used as heat transfer fluids (HTF) and energy storage media in concentrated solar power (CSP) plants. In the present work, the corrosion resistance of two austenitic stainless steels 316SS and 321SS was assessed during long term isothermal immersion in binary nitrate salt mixture, Solar Salt. The experiments were carried out at 550 C under static conditions. The corrosion rates were determined by weight loss methodology, recording the weight changes of the coupons at different time intervals up to 3000 h. The corrosion scale products were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The formation of multiple oxides was verified, being Fe2O3 and Fe3O4 the main products as confirmed by XRD. A stable FeCr2O4 inner layer was formed on the 316SS surface. At t>1000 h, a partial spallation occurred in the corrosion layers at 321SS. The corrosion rates were found to be 7.3 and 9.0 m per year for 316SS and 321SS, respectively.
Keywords
Molten nitrate salt, Heat transfer fluid, Thermal energy storage, Metallic corrosion