High-Temperature Drive Shaft Failure with a Twist

An unusual high-temperature failure is presented involving the bearings and drive shaft of a centrifugal slurry pump. The unique characteristics of the failure are explored including localized heating and interactions between the ductile iron bearing collar and the shaft material. Maximum surface temperature of the shaft at the time of failure is estimated to be 2100-2300 degrees F. Partial melting of the ductile iron bearing collar and softening of the shaft appears to have resulted in both the inclusion of ductile iron in the shaft material in the molten state and a form of friction stir welding which joined the two components. Hardness values in excess of 900 Vickers were recorded around the material interface. It is theorized that rapid diffusion of carbon into the shaft material occurred during failure facilitated by mechanical mixing due to severe high-temperature deformation. Graphite nodularity and phase analysis of the ductile iron collar and an embedded ductile iron fragment were conducted by means of microscopy and image analysis.