Failure analysis of melt urea pump impeller

A melt urea pump is out of work after only 6 days in service. The failure of the melt urea pump impeller is analysed using different methods including chemical composition analysis, metallographic observation, SEM and energy dispersive spectroscopy analyses, etc. The results show that the material of the impeller is not the reported AISI 321 stainless steel but AISI 316 stainless steel. There are many honeycombed holes on its impeller, which is the typical feature of cavitation damage. Therefore, the main failure reason of the impeller is the cavitation erosion, and the electrochemical corrosion of the medium also accelerated the failure of the impeller. The failure of the impeller is not related with the as casted defects of the material because no obvious as casted defects are found in the material.