Investigation of Failed Pin Carrier Plate for the Anti-Rotation Device in a Motor
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Parts of the anti-rotation device expelled from a power plant motor were analyzed. The “anti-rotation” device prevents the pump from rotating backwards when there is pressure in the discharge line and the motor is off. Parts that were recovered include about 2/3 of the spring compression ring and an “ear” that apparently came from the missing segment of the spring compression ring. Results of this investigation revealed that a nearly simultaneous overloading occurred on both sides of the pin carrier plate as indicated by almost equal size fracture. At least two crack initiation sites were identified on both sides of the pin carrier plate. Under tensile loads, surface irregularities can lead to surface cracks resulting in the fracture of the plate. Areas rich in aluminum were identified (using energy dispersive spectroscopy) in the vicinity of surface irregularities. A number of suggestions on avoiding such failure are proposed.
KeywordsFailure Fatigue Fracture
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