Failure analysis of 316L stainless steel crucible by molten fluoride salt interaction with clay bonded silicon carbide

•We present analysis of a failed stainless steel molten salt corrosion experiment.•We examine corrosive gas evolution between molten salt and insulation.•Corrosive gas leads to the structural failure of the high temperature system.•Stainless steel shows heavy attack through vapor fluorination.

Detailed investigation of a recently failed static corrosion test involving molten eutectic LiF–NaF–KF salt at 850 °C contained in 316L stainless steel crucibles shows that a single sealed crucible leaked molten salt into the electric furnace due to mechanical failure, causing a chemical reaction between the molten salt and the clay bonded silicon carbide insulation used in the furnace. As a result, corrosive vapors of Na2SiF6, K2SiF6, SiF3, and F2, were formed. These vapors reacted with the stainless steel crucibles and lead to the formation of a porous corrosion crust and the eventual catastrophic structural failure of all nine sealed 316L stainless steel crucibles.