Corrosion evaluation by electrochemical real-time tracking of VM12 martensitic steel in a ternary molten salt mixture with lithium nitrates for CSP plants

Abstract

In the context of Concentrated Solar Power (CSP), the metallic materials employed to build the critical components of the plant are exposed to severe conditions, Carbon and stainless steel have been used for this application. However, the technology CSP will evolve, so these materials will probably be replaced by superior performing and economically competitive ones. Likewise, the investigation of molten salts with better thermophysical properties but no more corrosive than the actual benchmark has become a complex challenge. Thus, the research motivation was to study the performance of a martensitic steel exposed to a promising ternary molten salt with lithium nitrate at 550 °C by its corrosion behavior and mechanical properties. The corrosion process was monitored through electrochemical impedance spectroscopy (EIS). The mechanical properties in molten salt at high temperature were determined by slow strain rate testing (SSRT), complementing with the characterization of corrosion products to propose the corrosion mechanism in one scheme. The results showed that the steel is less robust but more ductile in the presence of molten salts at high temperatures; besides the material develop a multi-layer non-porous corrosion product that, despite deteriorating, confers corrosion rates within the recommended ranges for the application. • The corrosion process of steel in molten salts can be monitored in real-time by EIS. • VM12 steel and lithium-containing molten salt showed high compatibility for CSP. • The outer layer of corrosion products is spalled due to its thickness increasing.