Comparison of corrosion performance of grade 316 and grade 347H stainless steels in molten nitrate salt

Abstract

Thermophysical properties and corrosion characterization of low cost lithium containing nitrate salts produced in northern Chile for thermal energy storage AIP Conference Proceedings 1734, 050014 (2016) Abstract. Stainless steel samples machined from SA-312 TP316 and SA-213 TP347H pipe were exposed to a molten nitrate salt environment at 600°C (1112°F) for up to 3000 hours in order to generate corrosion rates for use in concentrated solar power (CSP) facilities. Descaled weight loss measurements were made at 1000, 2000, and 3000 hours, with optical and scanning electron microscopy being performed on samples at the longest exposure time. The 316 and 347H alloys exhibited metal losses of 4.4 and 4.8 um respectively at 3000 hours. A linear fit to the data sets yielded annualized metal loss rates of 8.4 and 8.8 um/yr. The oxides were relatively uniform in thickness and multilayered. The inner layer consisted of a (Fe, Cr)-spinel with appreciable amounts of Mn while the outer layer was an oxide composed of only Fe. No pitting, intergranular attack, or other localized attack was found, despite the presence of a sensitized microstructure in both alloys and chloride impurity in the salt mixture. The observations presented here indicate that the two alloys perform quite comparably with respect to molten salt-induced corrosion and in that regard; either would be expected to perform satisfactorily in the intended application.

The corrosion behaviour of stainless steels and Ni-based alloys in nitrate salts under thermal cycling conditions in concentrated solar power plants

“…The spallation behaviour of corrosion products on stainless-steel surfaces has been reported by several researchers (Bradshaw and Goods, 2001b;Gomes et al, 2019;Stott and Wei, 1989;Trent et al, 2016), and attributed to the stress due to the mismatch of thermal expansions and Young's modulus between the bulk steel and corrosion scales. Referring to Ni-based alloys, the corrosion products formed are more uniform with a consistent distribution of elements across the corrosion surface (see Table 5) for samples from isothermal and thermal cycling experiments.…”

Bibliometric Map on Corrosion in Concentrating Solar Power Plants

“…The blue cluster is related to thermal energy storage materials. In the green cluster, different keywords related to different types of steel ("martensitic steel" and "ferritic steel") [68][69][70][71][72], and "alloy" [18,[73][74][75][76][77][78][79][80] can be noted. However, "stainless steel" belongs to the second cluster because it is the most common material used for storage structures and relates to the evaluation of corrosion effects by molten salts [18,19,64,67,75,[81][82][83][84][85][86][87][88].…”

Suppression of molten salt corrosion by plasma sprayed Ni3Al coatings

“…Both distinctive trends need to be considered to fully capture the critical information on time dependent corrosion behaviour. As an illustration, the corrosion rate of Ni 3 Al/SS347 would have been mistakenly reported as ~ 0.5 µm/year had it been calculated solely based on the final ΔM/A value measured at 3000 h. This is incorrect for both regimes as it does not capture the change in the O uptake that occurs at 500 h. Furthermore, there is currently no consensus in literature whether pre-descaling is required [21,25,30,31,43] or not [15,22,28,34,37,38] in the measurement of ΔM/A. Descaling is not performed in this study to capture the full evolution of the oxide layers without damaging the substrate.…”

“…Cr-based material forms a slow growing protective CrO x under an oxidising environment. However, it is unsuitable for use in molten nitrate salts due to its high solubility [15,17,19,25,[29][30][31][32]. Ni-based coating is preferred over Fe-based because of its ability to form a protective oxide layer, whilst Fe oxide is non-passivating [21].…”