Very high stress corrosion cracking susceptibility of Types 304 and 310 austenitic stainless steels (SS) occurred at 60 °C upon exposure to a concentrated FeCI2-CrC13- NiCI2 solutions (abbreviated as MClz), which is representative of the anolyte formed in occluded regions during localized corrosion in C1- solutions. Stress corrosion cracking of 304 SS occurred in the absence of applied stress for tests between 60 and 200 °C. Crack initiation in MClz occurred only under conditions of active corrosion, and was accompanied by significant hydrogen absorption. Additional studies evaluated solution acidity and corrosion kinetics in concentrated MCIz solutions. Test results support a hydrogen-assisted active corrosion model for both crack initiation and crack growth. Obvious challenges to such a model have been presented and then addressed in relation to current and published test results.
Keywords: austenitic stainless steels, stress corrosion cracking, anolyte, ferrous chloride, chromic chloride, absorbed hydrogen