Failure Analysis on Fracture of an Oil-well Pump Valve Cover

The valve cover of a oil-well pump plunger fractured after use for less than two months in an oil field. The macro and micro fracture appearance characteristic, microstructure, hardness and chemical compositions of the valve cover were analyzed by optical microscope, scanning electron microscope, microhardness tester, etc. The results show that the unreasonable structure design and poor surface machining quality of the valve cover caused its surface stress concentration and premature appearance of fatigue crack source. At the same time, the existence of lots of inclusions containing silicon in the material resulted in rapid propagation of the intergranular cracks, which led to the final fatigue fracture of the valve cover.