Corrosion evaluation of alumina-forming alloys in carbonate molten salt for CSP plants

Abstract

The use of carbonate molten salts for the new generation of concentrated solar power (CSP) plants have been considered and analysed during the last years to improve the efficiency of energy generation. However, the high temperature and corrosivity of the salts pose a risk on safety and profitability of the technology requiring more resistant materials. In this study, two alumina-forming austenitic (AFA) alloys corresponding to modified OC4 and HR224 grades, were exposed to the eutectic ternary Li2CO3-K-2-CO3-Na2CO3 (32.1-34.5-33.4 wt%) salt mixture at 650 degrees C for 1000 h. The evolution of weight change along the exposure time and analysis of the resulting scales by means of scanning electron microscopy (SEM), X-Ray diffraction (XRD), and glow discharge optical emission spectroscopy (GDOES) revealed a good performance of both steel grades associated with the formation of multi-layered corrosion products. Whereas both alloys undergo external oxidation with the formation of NiO, internal oxidation with the formation of two spinels is the case of HR224. The rate of corrosion is significantly lower than those reported in molten carbonated in non-AFA alloys, allowing to recommend OC4 and HR224 for use in the carbonate-based CSP. (C) 2019 Elsevier Ltd. All rights reserved.