China Nonferrous Metallurgy

In this paper, the form and reason of S31608 stainless steel elbow’s failure in silicon tetrachloride cold hydrogenation process are studied. The chemical composition, microstructure and corrosion product composition of the elbow failure location are analyzed by metallographic analysis, ESD and SEM method. The results show that the main failure mode of elbow is stress corrosion cracking with the inner wall extends to the outer wall. The external cause of cracking is the combination of Cl^- ontaining corrosive medium in contact with the inner wall of the elbow, residual stress produced by fabrication and stress superposition under the action of internal pressure. The internal reason is the precipitation and deformation structure on grain boundary of elbow. The main reason for S31608 stainless steel failure is the presence of Cl^- Pand other corrosion components in the medium and stress. With a decline in corrosion resistance caused by the precipitation and deformation structure on the grain boundary of the elbow, the Cl^- contained in the corrosive medium on the elbow fracture, which poses a extremely strong penetration and erosion effect on the Austenitic stainless steel surface film, is able to dissolve the protective film and causes the failure of the elbow due to stress corrosion under the action ofresidual stress and working stress.