Corrosion of 316H Stainless Steel in Flowing FLiBe (LiF-BeF₂)

Abstract

This milestone was originally envisioned for completion in FY21 and was delayed due to the COVID-19 response and difficulties in fabricating/obtaining fluoride salts. A monometallic type 316H stainless steel thermal convection loop (TCL) was operated for 1000 h with flowing LiF-BeF2 (i.e. FLiBe) salt and a peak temperature of 650°C. In general, the attack was minimal. However, classic mass transfer was not clearly observed with mass losses in both the hot and cold legs. There was an issue with cleaning the loop with water and specimens may have oxidized, which was not an issue with the previous FLiNaK TCL.

Corrosion Testing Trade Study on Testing Methods in Molten Salts

“…TCL setups have varied in size from microloops (less than kg salt quantities) [Kelleher 2022] to larger installations from a few to several hundred kilograms [Keiser 1977, Raiman 2022]. Both chloride salts [Susskind 1960, Pint 2019, 2022a, Kelleher 2022] and fluoride salts [Koger 1972, 1973, 1974, Raiman 2022, Pint 2022b] have been evaluated in TCLs.…”

“…Depending on the size of the loop, the material being examined can either be the tubing itself [Kelleher 2022] or individual samples arranged in various locations along the HL and CL sections [Keiser 1977b, Pint 2019, 2022a, 2022b, Raiman 2022. For the latter case, it was recommended that the examined samples be made of the same or similar alloy as the tubing to avoid galvanic corrosion between the two, which has been observed in the past between Inconel 600 tubing and 304 stainless steel (SS) samples [Koger 1970].…”