Importance

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Abstract

In the test of a casing enclosed shaft and impeller for structural integrity against defects such as loose bolts or cracks, an apparatus and process is disclosed which enables in-situ testing to occur within a casing. A model of the shaft and impeller, such as a spare part, is suspended so as to simulate the in casing boundary conditions and is then vibrated. Vibration or 'ringing' occurs through a normally exposed end of the shaft far removed from suspected defects. A cap can be used to suspend the shaft and impeller or rotor. Vibration is imparted to the remote end of the shaft, sometimes on the cap, with an instrumented hammer blow of specific duration and known energy. Measurement and resolution of the resultant vibrations and energy dissipating damping occurs by mounting accelerometers to the remote normally exposed shaft end and recording and playing back the vibrations from the mounted accelerometers through a spectrum analyzer. Defects are created on the suspended model and the vibration signatures recorded. Thereafter, the same test is conducted on the casing enclosed suspect shaft and impeller or rotor and the vibrational signature obtained in the rotor matched to the model generated vibrational signature. Prediction of either intact structural integrity or defect is made on the basis of the comparison of measured vibrations. A simultaneous technique of computer modeling the vibrations is disclosed which enables expansion of actual test results to defects outside those specific signatures obtained from the model testing.

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First Claim