Fracture analysis of a connecting rod for oil pumping unit in China western oilfield

Abstract

The connecting rod of the pumping unit is fracture after 95 days' service in China western oilfield. The failure causes were analyzed by macroscopic fracture morphology, fluorescence magnetic particle detector, impact testing machine, direct-reading spectrometer, optical microscope(OM), scanning electron microscopy(SEM), energy dispersive spectrometer(EDS) in this paper. The direct cause of the fracture of the sample is the fatigue fracture of the connecting rod under the action of cyclic load, and the fundamental cause of the fatigue fracture of the sample is the material quality itself, including the impact energy of sample varies greatly, the substandard chemical composition of the material, the heterogeneity of the microstructure, the coarse grain, the influence of inclusion.The fracture process of the sample was as follows: under cyclic load, the root of the thread formed a fatigue crack source, and then the crack expanded from slow and fast fatigue, and finally under cyclic load, the crack expanded further until brittle fracture.