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.