Corrosion evaluation of eutectic chloride molten salt for new generation of CSP plants. Part 2: Materials screening performance

Abstract

The operating temperature of a steam turbine is limited to 565 °C by the molten nitrate heat-transfer fluid; therefore, molten-salt CSP technologies require alternative salt chemistries such as chloride. The prevention of high-temperature corrosion on containment materials plays a critical role, and a corrosion mitigation plan is needed to achieve the target plant lifetime of 30 years. This paper performed a materials screening test, using a eutectic ternary chloride molten salt, composed by 20.4 wt. % KCl + 55.1 wt. % MgCl2 + 24.5 wt. % NaCl, in stainless steel (AISI 304) and two Ni base materials (Inconel 702 and Haynes 224). The corrosion mechanism and corrosion rates were obtained through electrochemical impedance spectroscopy (EIS). Ni base alloys showed a protective scale layer during 8 hours of immersion with a corrosion rate of 6.34 mm/year (In702) and 3.12 mm/year (HR224). Monitoring corrosion results were confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), obtaining alumina and chromia protective layers.