Effect of chloride content of molten nitrate salt on corrosion of A516 carbon steel.

Abstract

The corrosion behavior of A516 carbon steel was evaluated to determine the effect of the dissolved chloride content in molten binary Solar Salt. Corrosion tests were conducted in a molten salt consisting of a 60-40 weight ratio of NaNO 3 and KNO 3 at 400°C and 450°C for up to 800 hours. Chloride concentrations of 0, 0.5 and 1.0 wt.% were investigated to determine the effect on corrosion of this impurity, which can be present in comparable amounts in commercial grades of the constituent salts. Corrosion rates were determined by descaled weight losses, corrosion morphology was examined by metallographic sectioning, and the types of corrosion products were determined by x-ray diffraction. Corrosion proceeded by uniform surface scaling and no pitting or intergranular corrosion was observed. Corrosion rates increased significantly as the concentration of dissolved chloride in the molten salt increased. The adherence of surface scales, and thus their protective properties, was degraded by dissolved chloride, fostering more rapid corrosion. Magnetite was the only corrosion product formed on the carbon steel specimens, regardless of chloride content or temperature. 4 ACKNOWLEDGEMENTS

Study of corrosion by Dynamic Gravimetric Analysis (DGA) methodology. Influence of chloride content in solar salt

“…These results are in agreement with previous studies of corrosion tests reported by Bradshaw et al. [19].…”

High temperature corrosion in molten solar salt: The role of chloride impurities

“…Commercial salts of different sources may contain various levels of impurities such as carbonates, chlorides, and sulfides. Among these impurities, chlorides can significantly increase the corrosivity of the salts . The influence of chloride impurities on the corrosion behavior of solar salt containment materials has only been studied in very few cases and the mechanism is still under debate.…”

Materials selection for thermal energy storage systems in parabolic trough collector solar facilities using high chloride content nitrate salts

“…Several authors reported interesting results about the influence of chloride content in the corrosion performance of carbon steel showing a dependency between corrosion rates and chlorides content [21][22][23][24]. However, these results are associated to short corrosion tests which would be insufficient for a detailed evaluation of corrosion mechanism or longer thermalcorrosive treatments analyzing the effect of chloride content up to 1% by weight.…”