STRESS CORROSION CRACKING OF AUSTENITIC STAINLESS STEELS IN CONCENTRATED FeCl_2-CrCl_3-NiCl_2 SOLUTIONS

摘要

Very high stress corrosion cracking susceptibility of Types 304 and 310 austenitic stainless steels (SS) occurred at 60°C upon exposure to a concentrated FeCl_2-CrCl_3-NiCl_2 solutions (abbreviated as MC1_z), which is representative of the anolyte formed in occluded regions during localized corrosion in Cl~- solutions. Stress corrosion cracking of 304 SS occurred in the absence of applied stress for tests between 60 and 200°C. Crack initiation in MC1_z occurred only under conditions of active corrosion, and was accompanied by significant hydrogen absorption. Additional studies evaluated solution acidity and corrosion kinetics in concentrated MC1_z 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.