A Systematic Study of Fracture of an Impeller Used in a Sewage Plant

In this work, the procedures for assessing the damage that has already been occurred on the fracture impeller used in the sewage plant during the working have been applied. Failure quickly happens during the service of the impeller. First, cracks in various places are mentioned in this paper. The mechanism of the drive failure was studied. To characterize failure modes and fracture surfaces, light microscopy, scanning electron microscopy and vibration techniques were used. The fundamental impeller failure modes are summarized. The results revealed that the failure seems to be due to mainly the existence of cracks in the concrete ceiling that the aerator hanged in. These cracks made a misalignment in the shaft rotation and then some cracks formed in the holes used for fixation and finally failure occurred under fatigue loading. Moreover, these cracks can be formed inside the metal (just below the surface) or started just on the surface of the holes and then extended to the core of the impeller material. Both mechanisms are dangerous and cause failure during service. On the other hand, a high concentration of tension is caused by the fact that sharp edges close to the welding region occur between the roller body and the blades.