FAILURE ANALYSIS Root Cause Failure Analysis of a Boiler Feed Pump Main Oil Pump Gear

The results of an investigation concerning the failure of a gear from a boiler feed pump main oil pump in a power cogeneration plant are presented. The pinion (driven gear) was visually examined. Most of the teeth of the pinion were damaged. No crack was visible. The stereomicroscopic examination of the surface of the fracture exhibited fracture marks extending along almost the entire root of the tooth. Emanation of cracks at the fracture surface can be seen. The optical micrograph of the cross-section of the metal, taken from the root of the tooth, shows initiation of a single crack from the surface that propagated inside the metal and reached the opposite side of the surface. The chemical composition of the gear material was determined by the inductively coupled plasma (ICP) technique and energy dispersive x-ray (EDX) analysis. Mechanical misalignment of the pinion led to cyclic shock loading or stress concentration at the end of the tooth, which formed a crack and caused the gear tooth to break off.