Corrosion of high temperature alloys in solar salt at 400, 500, and 680ÀC.

Abstract

Corrosion tests at 400, 500, and 680°C were performed using four high temperature alloys; 347SS, 321SS In625, and HA230. Molten salt chemistry was monitored over time through analysis of nitrite, carbonate, and dissolved metals. Metallography was performed on alloys at 500 and 680°C, due to the relatively thin oxide scale observed at 400°C. At 500°C, corrosion of iron based alloys took the form of chromium depletion and iron oxides, while nickel based alloys also had chromium depletion and formation of NiO. Chromium was detected in relatively low concentrations at this temperature. At 680°C, significant surface corrosion occurred with metal losses greater than 450microns/year after 1025hours of exposure. Iron based alloys formed complex iron, sodium, and chromium oxides. Some data suggests grain boundary chromium depletion of 321SS. Nickel alloys formed NiO and metallic nickel corrosion morphologies, with HA230 displaying significant internal oxidation in the form of chromia. Nickel alloys both exhibited worse corrosion than iron based alloys likely due to preferential dissolution of chromium, molybdenum, and tungsten. .

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

“…Therefore, the appropriate material selection and life time estimation requires intensive hot corrosion studies considering different aspects of corrosion environment and material behavior. Recently, corrosion behavior of the common structural materials such as carbon steels, low‐Cr steels, stainless steels, and in some cases Ni‐base alloys have been studied …”

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

“…derived annual metal losses of 6-15 um for 316 stainless steel at 565°C for salts containing various levels of chloride [1] [4]. A recent study by Kruizenga examined 347 stainless steel at 600°C and projected an annual metal loss of 10.4 um [2]. In another study, shorter term exposures of several austenitic stainless grades (including 316 and 347) yielded metal losses estimated to be less than 4 um/yr [3].…”

“…Appreciable amounts of chromium, and manganese were present in the inner layer likely having been substituted for the iron in the spinel structure. The outer iron oxide composed solely of iron and oxygen is likely either Fe 3 O 4 or Fe 2 O 3 , again based on elemental analysis and other research reports [1][2][3][4][5]. Cr would not be expected in the outer layer to any appreciable extent, as it has a high solubility (as complex anions with oxygen) in the molten nitrate salt [5].…”

“…Austenitic stainless steels have been identified as prime candidates for most hot salt (>500°C) handling based on several studies [1][2][3][4][5]. The work presented here was intended to confirm the generally acceptable behavior of these materials, to develop corrosion rates for potential hot salt containment materials and to optimize the material selection from a cost standpoint (that is, to demonstrate the similarities or differences in the molten salt corrosion behavior between stabilized or non-stabilized grades of stainless steel).…”

Improving the performance of finned latent heat thermal storage devices using a Cartesian grid solver and machine-learning optimization techniques

“…The thermal characteristics of solar salts have received significant attention, in their solid form [4,102,103], their molten form [1,[104][105][106][107], and during phase change [3,[108][109][110][111]. However, little experimental work has been done to describe the melting and solidification behavior of solar salts, particularly within a complex, finned geometry.…”