High-Temperature Drive Shaft Failure with a Twist
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High-Temperature Drive Shaft Failure with a Twist Paul Taylor . Harry Tian
Submitted: 22 January 2016 / Published online: 11 February 2016 Ó ASM International 2016
Abstract 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 °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. Keywords Failure analysis High temperature Metallurgical investigation Liquid metal embrittlement Friction stir welding Shafts
Introduction In typical water pump applications, thrust and radial bearings may be expected to give many years of trouble-free
service. The pumps are often located in a building or enclosure which limits the possibility of contamination, the service conditions are well known and consistent, and maintenance and monitoring practices make early detection possible so that repairs can be scheduled in advance. Typical slurry pump conditions are much less ideal. The slurries that they transport abrade the pump and the pipeline, resulting in leaks and contamination of the pump and its surroundings. Cooling water supplies are often contaminated with particulate and active chemicals; settling pond water, for example, is often used to meet this need. Variations in the slurry feed material and production demands on the pump also make maintenance schedules difficult to develop and complete. Finally, the pumps are often located in a physically remote or difficult to access areas [1, 2]. All of these factors can contribute to shortened bearing life as well as delayed detection and treatment of bearing maladies. As a result, bearing failures are more common in these conditions and more difficult to predict. At the same time, production demands may not allow for immediate shut down of a pump, so it is not uncommon for a pump to operate for a short time with a failing or failed bearing. Even so, the case reviewed in this paper is fairly unusual, not because it was a failure of a bearing on the drive shaft of a mine dewatering pump but because of the extent of the damage sustained by the shaft, the temperatures reached, and the metallurgical phenomena involved.
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