Vibrations analysis of rotating machinery offers abundant information about failure root-causes and asset condition, as well as aiding early failure detection and prognosis. Vibration based condition monitoring normally focuses on lateral vibrations, as measurement techniques and technologies are highly developed and standardized, in comparison with torsional vibration measurement. However, the later describes the effects of the main forces acting on rotating machines and the primary shaft function, i.e. transmitting torque. The present work focuses on torsional vibration measurement and analysis of a 110 kW primary coolant circuit centrifugal pump of a Nuclear Research Reactor (comprising impeller, flywheel and motor shafts, linked by flexible couplings) during start-up and operation. A measurement technique and a methodology for condition monitoring based on torsional vibration analysis are presented. A modal analysis based on a Finite Element Model is presented as support tool for this kind of technology, showing high dependence of the shaft torsional behaviour with the shaft flexible coupling stiffness. Experimental results during the pump start up and steady state operation at different loads are presented, showing torsional vibrations of the pump shaft close to rotor's first torsional mode. This kind of analysis yields vital information about the asset's condition that doesn't show up in lateral vibration data.
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