Failure analysis for the welded elbow at the bottom of the rectifying tower in the alcohol evaporation system

Cracking was found on the welded elbow at the bottom of rectifying tower in an alcohol evaporation system. In order to determine the cause of failure, a detailed analysis was conducted. The analysis included macroscopic observation for the failed tube and optical microscopy for the morphology of cracks. The characterization of fracture was analyzed by scanning electron microscopy, and the components subjected to the cracks were analyzed using energy-dispersive x-ray spectroscopy. Results revealed that the welded elbow had suffered damage from external chloride stress corrosion cracking (ECSCC). The environmental factor responsible for ECSCC is the chloride present in the dampish insulation. The stress factor is the result of the welding residual stress induced in the material which was used to fabricate the elbow.