Direct and indirect contact of an austenitic high-temperature alloy to eutectic chloride melts with possible consequences for inhibitor strategies

Abstract

There is an inevitable difference between direct and indirect contact of metals with eutectic chloride melts defined by the gas phase impurity content, here, humidity and oxygen in argon. The impurities-to-salt ratio will always be higher in the gas phase allowing for a more aggressive attack on metal components. This effect has been studied on a decommissioned metal container from an experimental high-temperature setup, which has never been in direct contact with a chloride melt but with its evaporated species; the vessel lasted only a short time, 700 h. It was found that the vessel suffered more severe damage when exposed to evaporated salt species than in direct contact with the salt melt; the estimated metal thickness loss per year is higher by almost three-fold than the direct contact. In contrast to 253MA fully immersed in MgCl2-KCl, magnesium has not been the most-active cationic species causing corrosion in the vessel wall exposed to evaporated salt species; instead, it has been potassium. Consequently, this unexpected observation needs to be carefully considered in the design of a Gen3-CSP storage tank and the applied inhibitor strategy.