Stress Corrosion Cracking of a 304 Stainless Steel Elbow

This research was focused on the failure analysis of a cracked SS304 stainless steel elbow from a chemical plant. The service life of the elbow was 2 years and 8 months. The elbow was welded with two straight pipes at two ends. Cracks were located mainly at positions close to the weld joint and the arc where very strong tensile residual stress existed. Corrosion pits were distributed on the inner surface of the elbow. Cracks were initiated from the corrosion pit bottoms. Branching was observed from the cracks. Cl and S elements were detected in corrosion products from the corrosion pits and the cracks by EDS. SEM results reviewed the intergranular and transgranular brittle nature of the fracture. It is concluded that stress corrosion cracking was the main reason for the cracking of the elbow.