Failure Analysis of a Reciprocating Pump Valve
An offshore rig septuplex pump was experiencing chronic suction and discharge valve failures. A more robust valve design implemented by the manufacturer did not solve the problem. MSI engineers performed test stand and on-rig pulsation and vibration testing. Structural and acoustic natural frequencies were determined by test, as well as the harmonic content of the pressure waves in the cylinders and manifolds. Tribological and metallurgical tests were also performed on the valves, guides, and seats. It was determined that a firm deposit film which was forming on the valve guides was hanging-up the valves, causing them to close late and slamming shut. Finite element analysis proved that the impact stress waves were strong enough to lead to fatigue of the valve plates. The valve guide clearances and seat angle were changed slightly to discourage hang-up and high closure rate, solving the problem.
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