MSI engineers performed a torsional analysis of a reciprocating pump/gear/motor system being designed for a large overseas petroleum drilling venture. Analysis of the initially designed system indicated that there was a possibility of resonant torsional vibration, driven by 50 Hz line frequency.
The customer requested that additional analysis be performed to investigate how coupling options could be modified to provide improved factor of safety relative to the occurrence of torsional resonance. It was discovered that by switching the pump coupling to a double engagement gear coupling from a flexible spring element coupling, the original problem was fixed, but a new resonance problem was created at twice line frequency. By lengthening the coupling hubs on each side to the maximum standard length, a factor of safety of over 15 percent was obtained relative to the closest torsional resonance, consistent with good engineering practice. The manufacturer of the system included the recommended design change, and the pump was placed in service, functioning with no vibration or reliability problems.
