Evaluation of corrosion resistance of steel alloys in ternary molten salt: implications for TES and industrial heat applications

Several steel alloys were evaluated for their corrosion resistance in ternary molten salt (NaNO 3 –KNO 3 –NaNO 2 , 53-40-7 wt%) at 400 °C under an air atmosphere, with a focus on thermal energy storage (TES) and industrial heat applications. Alloys A335-P11, SS321, A213-T11, A516-Gr70, and A387-Gr11 were tested using static immersion in accordance with ASTM G31 over exposure periods of 1000, 2000, and 4000 hours. Corrosion rates derived from mass loss measurements revealed significant differences among the alloys. SS321 demonstrated the best resistance, with stable chromium-rich oxide scales and rates consistently below 4 μm/year. In contrast, A335-P11 exhibited the highest corrosion rate, with an initial rate of 65 μm/year that decreased to 18 μm/year over time, associated with thick, cracked oxide scales and localized internal attack. The remaining alloys showed intermediate corrosion behavior. SEM/EDS analyses confirmed the critical role of chromium enrichment in improving corrosion resistance. In parallel, mechanical integrity assessments showed no evidence of stress corrosion cracking or severe crevice corrosion, underscoring the predominance of generalized oxidation as the governing degradation mode. These results provide critical insights for predictive corrosion modeling and support the selection of durable materials for reliable, long-term operation in molten salt-based industrial thermal systems, thereby contributing to the transition toward more sustainable high-temperature heat applications. • Five steel alloys were evaluated for long-term corrosion in HITEC molten salt at 400 °C. • Carbon steels A516-Gr70 and A387-Gr11 showed stable corrosion behavior over time. • No stress corrosion cracking or localized attack was observed in carbon steel samples. • Uniform, adherent oxide layers formed on carbon steels, ensuring structural integrity. • SS321 showed the lowest corrosion rates (<4 μm/year) with stable Cr-rich oxide layers.