Corrosion investigation of stainless steel water pump components

Two components of a water pump installed in a casting shop for recirculation of cooling water experienced severe and accelerated corrosion after two months in service. The received pieces of the water pump assembly were a shaft and a conical tube, which was used as connector with the impeller. The shaft exhibited circumferential pitting corrosion behavior in specific areas where it was in contact with another pump component. Light optical microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy were mainly used as analytical techniques for corrosion process evaluation and for the identification of the morphology and chemical composition of corrosion products, in order to draw safe conclusions concerning the type of the corrosion and the respective root-source. The main findings of the investigation indicated that pitting corrosion was the dominant failure mechanism for both water pump components influenced by the presence of aggressive environmental conditions, characterized by the presence of chlorides and sulfates that accelerate corrosion process above a certain temperature range (T > 50-55 °C).