Molten nitrate corrosion testing and creep data for stainless steels

Abstract

Molten nitrate salts are commonly used for heat transfer and thermal energy storage in current concentrated solar power plants. Compatibility between storage medium and construction material is vital for the long-term performance of the plant. Stainless steels are widely used for hot storage tanks due to their corrosion resistance and mechanical properties at the typical operating temperatures of 550-600°C. Traditionally, stabilized grades such as 347H have been preferred, but several other grades are available as possible alternatives. In this study, corrosion tests have been performed on several different stainless steels in molten nitrate salts at 570°C. Four different test durations, ranging from 200 to 2000 hours, have been used to study both the short-term oxidation behavior and the long-term corrosion resistance of the materials. The results show that the general behavior and trends are similar for all materials, but there are clear differences in terms of oxide composition, adhesion and thickness. Corrosion rates for the different test periods show how the corrosion progresses over time for the tested materials. SEM-EDS analysis has been utilized for further understanding of the materials’ behavior and oxide characteristics. Furthermore, the creep performance of stainless steel 347H has been studied, generating creep data at temperatures ranging from 650 to 800°C.