Effect of Oxygen and Nitrogen Oxide Gas Concentration on Corrosion of 310N Stainless Steel in Solar Salt at 600°C

Abstract

Concentrated solar power (CSP) systems commonly use solar salt as a high temperature heat transfer and storage medium. This study examines the effect of oxygen (O₂) and nitrogen oxide (NO) gas concentrations on solar salt thermal stability and 310N stainless steel corrosion at 600°C up to 1224 h. The impact of the gas atmosphere (5–80 vol% O₂, 400–600 ppm NO) on salt chemistry, including nitrate, nitrite, oxide, and chromate ions, was analyzed, and corrosion behavior was evaluated through weight change, corrosion rate, and microstructural analysis. The results show that introducing NO gas concentrations ≥ 400 ppm with at least 5 vol% O₂ stabilizes salt decomposition by controlling nitrite and oxide ion formation and promotes the development of a protective corrosion layer on the steel surface. Once this protective layer is formed, variations in oxygen concentration (5–80 vol%) in the presence of ≥ 400 ppm NO gas have a minimal long-term effect on the corrosion behavior of stainless steel in solar salt. These findings underscore the importance of maintaining minimum O₂ and NO levels to optimize salt chemistry that effectively mitigates steel corrosion in solar salt systems.