Chapter 3 - Machinery Component Failure Analysis

Abstract

The bearings in a machine are among its most vital components and the ability to draw the correct inferences from bearing failures is of the utmost importance. The different causes of rolling-element bearing failures are considered. These include defective bearing seats on shafts and in housings; misalignment; faulty mounting practice; improper fits; inadequate or unsuitable lubrication; ineffective sealing; vibration; and passage of electric current through the bearing, Methods for bearing troubleshooting and practical solutions are outlined. The most probable causes of damage of journal and tilt-pad thrust bearings, and potential corrective actions, are summarized. The principal gear failure modes and a universally applicable approach to gear failure analysis are outlined. The analysis includes visual inspection; metallurgical inspection; system dynamic analysis; design review of the casings; bearings, shafts and seals; and detailed analysis of the individual gears. Gear tooth wear, scoring, surface fatigue, failures from the manufacturing process and breakage are all described. Gear-coupling failure analysis and gear-coupling failure mechanisms are outlined and an example of a failure analysis report for a high-speed coupling is given. Troubleshooting seals and seal-failure analysis are discussed, including a description of the main failure modes and remedial actions. The importance of lubrication analysis as a vital part of the root-cause assessment of lubricated machinery component failures is discussed. The different forms of water contamination of oils, methods to remove water and oil analysis methods are summarized. Component damage caused by magnetism in turbomachinery is considered.