Premature Fractures of the Pump Shaft of a Refinery Wastewater Unit Due to Biological Corrosion and Corrosion Fatigue

The pump shaft of a wastewater unit experienced three failures during nine-month service. The conditions of exposed wastewater and characteristics of the failed shafts were investigated. The results showed sufficient opportunity was provided for SRB microorganisms to effectively activate on the shaft surface in water-stagnant areas despite performing chemical and biological treatments on the wastewater. SRBs induced deep pits with tunneling-like structure, which created favorable conditions for stress concentration and initiation of corrosion fatigue. The morphological and characteristic features of related crack propagation on the fracture surface have been discussed.