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.