Dynamic pilot plant test comparison between two ferritic-martensitic alloys in ternary eutectic molten salt

Abstract

In this study, pilot plant equipment simulating a real CSP plant was used to evaluate the corrosion behavior of two ferritic-martensitic alloys, ASTM A335 GrP91 and VM12-SHC, when exposed to 3m/s at 550°C in a ternary eutectic salt mixture composed of 15% wt. NaNO₃, 43% wt. KNO₃, and 42% wt. Ca(NO₃)₂. The results indicated corrosion rates of 0.116 mm/year for P91 and 0.059 mm/year for VM12 along with significant spallation of the oxide layers in both materials. A detailed analysis of salt degradation revealed the formation of solid phases, such as calcium oxide and carbonate which could cause operational problems such as fouling, erosion, and obstruction of pipes. These degradations rendered both the alloys and the salt unsuitable for use in CSP plant construction under the conditions studied.