TES-PS10 postmortem tests: Carbon steel corrosion performance exposed to molten salts under relevant operation conditions and lessons learnt for commercial scale-up

Abstract

Postmortem tests were performed over components removed from the TES-PS10 pilot plant after almost four years of continuous operation being exposed to solar salts under representative commercial operation conditions. Accordingly, corrosion performance of plates sections extracted from both storage tanks and samples cut from the hot molten salts pump were evaluated. Corrosion damage extension, oxides layers morphology, and corrosion products chemistry were analyzed by X-ray diffraction, energy dispersive X-ray spectrometry, optical microscopy, and SEM. In addition to materials compatibility with molten salts, mechanical tests were carried out over the storage tanks plates sections. Although the corrosion damage extension over the plates extracted from storage tanks was low and the mechanical properties were according to the standard, some interesting observations were seen. For example, a sample extracted from the hot storage tank and exposed to intermittent contact with molten salts showed some areas characterized by the growth of a non-protective oxide scale. Moreover, localized corrosion with slight penetration through the base material was identified for all storage plates samples under evaluation. On the other hand, the molten salt pump parts under study showed adherent and uniform oxides layers without detecting corrosion-erosion phenomena. Some cavities were found in the discharge elbow, and these imperfections were associated to a bad metallurgical quality during casting. Summarizing, corrosion phenomena suffered by the components under evaluation could be corrected in future plants by applying the lessons learned discussed in this study. As conclusion, materials selection analyzed within this postmortem evaluation is valid from the corrosion point of view to be used in the design of commercial TES systems in PTC plants.