Stress Corrosion Cracking Behavior of Welded Joints in 304 Stainless Steel Flange Neck on a Tandem Mixer.

During the major overhaul of a chemical plant, the pipelines were disassembled and cleaned. Upon reinstallation, an air-tightness test discovered that the flange of the tandem mixer had cracked at the 304 stainless steel (SS) welding joint, affecting normal production. In the present paper, the microstructure of the weld joint was analyzed using SEM equipped with an EDS detector, to explore the corresponding cracking mechanism. The results show that the cracks start on the inner surface of the flange and extend outside. The microstructure in the welding heat affected zone (HAZ) is coarse and carbides are occurring at the grain boundaries, which reduces the strength. The precipitation of carbides at grain boundaries also reduced the Cr content in the crystal, resulting in a decrease in the corrosion resistance of the passivation film on 304 SS. The HAZ showed lower elongation compared to the 304 SS substrate and the fused zone. Under the combined action of stress and corrosive media, the HAZ undergoes stress corrosion cracking. [ABSTRACT FROM AUTHOR]