Dynamic corrosion behavior of 316L stainless steel in quaternary nitrate-nitrite salts under different flow rates

Nitrate salts have been applied as heat transfer and heat storage medium in the Concentrating Solar Power (CSP) plants. Corrosion is critical to the long-time safe operation of the CSP system. This experimental study was conducted to research the dynamic corrosion behaviors of 316 L stainless steel in high-temperature quaternary nitrate nitrite mixture. The effects of corrosion on 316 L stainless steel were investigated under the varied flow rates of 0.6 m/s, 1.3 m/s and 2 m/s with 565 °C constant temperature for 1000 h. The results showed that oxidation corrosion occurred in 316 L stainless steel at all working conditions. The dynamic corrosion curves were parabolic, and the value corrosion weight loss (mmass) increased with the increase of the flow rate. Meantime, when the products flow rates were 0.6 m/s, 1.3 m/s and 2 m/s, the values of mmass were 3.6 mg cm−2, 3.77 mg cm−2 and 4.36 mg cm−2. The values of corrosion depth (Rdepths) were 0.039 mm/a, 0.041 mm/a and 0.048 mm/a, respectively. Besides, the corrosion products were consisted of hematite (Fe2O3), magnetite (Fe3O4), trace amounts of MgFe2O4 and NaFeO2 with the structure of lamellar. Furthermore, the corrosion products gradually transformed into FeCr2O4 with structures of dense and massive, and the increase of the flow rate deepened the degree of corrosion, but it had little effect on the types of corrosion products.