Evaluation of flow accelerated corrosion and mechanical performance of martensitic steel T91 for a ternary mixture of molten salts for CSP plants

Abstract

Thermal energy storage (TES) systems with molten salts involve different operating conditions causing corrosion problems in the materials due to the high operating temperature. In this work, the corrosion behavior was studied by means of flow accelerated corrosion (FAC) and static corrosion tests in contact with the ternary mixture (KLiNa)NO 3 at 550 °C. Both tests were performed by gravimetric tests (mass gain) and subsequently characterized by SEM and XRD. The results showed a substantial increase in mass gain due to the dynamic effect of the FAC test in relation to the stationary test. Consequently, the dynamic effect of the FAC test at high temperatures could cause stress corrosion cracking in the material, leading to a change in the mechanical performance of T91 steel. Therefore, the slow strain rate tensile test (SSRT) on molten salts was performed to evaluate the impact of temperature on the mechanical property performance of the material. A considerable reduction in the mechanical performance of the material was observed compared to testing the material in air under normal conditions. This research shows the real operating conditions under the corrosion effect of T91 steel and its relevance as a material for the solar thermal industry. • Corrosion of T91 steel in (KLiNa)NO 3 under FAC and static conditions are different. • Lithium compound oxides are formed due to oxidation and lithiumization phenomena. • There was a reduction in the mechanical performance of T91 steel under tensile tests.