Case history - Grooving failure of tall oil evaporator

One of two alloy 904L (UNS N08904) wiped film evaporators, operating in ser ies on tall oil, failed after tl year. The form of failure was deep circumf erential grooving of the shell and wipers. Mechanical wear and corrosion we re evaluated as causes. Outside engineers were consulted and, after investi gation, concluded that it was a corrosion failure, They recommended upgradi ng materials to an austenitic stainless steel (SS) containing 6% molybdenum . The plant owners believed wear to be the cause, however, and the replacem ent was made mainly from type 317L SS (S31703).