Corrosion evaluation of eutectic chloride molten salt for new generation of CSP plants. Part 1: Thermal treatment assessment

The operating temperature of a steam turbine is limited to 565 degrees C by the molten nitrate heat-transfer fluid; therefore, a new molten salt chemistry is needed to increase the maximum operating temperature in the new generation of CSP plants and improve the thermal-to-electrical energy conversion efficiency in the turbine block, such as chloride molten salts. Nevertheless, the prevention of high-temperature corrosion on containment materials using chlorides plays a critical role and a corrosion mitigation plan is needed to achieve the target plant lifetime of 30 years. This paper presents a corrosion mitigation strategy focused on different thermal treatments performed in the eutectic ternary chloride molten salt composed by MgCl2/NaCl/KCl (55.1 wt.%/24.5 wt. %/20.4 wt.%). Corrosion rates were obtained through linear polarization resistance technique in a conventional commercial stainless steel (AISI 304) at 720 degrees C during 5 h of immersion after the different thermal treatments carried out. Scanning electron microscopy and XRD analysis were used to confirm the corrosion rates and corrosion layer proposed by electrochemical techniques, obtaining a minimum corrosion rate of 6.033 mm/year for the best thermal treatment performed.