Accurate diagnosis of radial, torsional and axial phenomena often requires on-site measurements using existing or specially installed instrumentation. High speed, simultaneous acquisition of vibration signals as well as process and other machine instrumentation may be necessary. Baseline measurements for future reference can be recorded for transient operating conditions such as startup and shutdown.

Such testing may be necessary to identify and correct resonance situations within casings, baseplates and piping as well as rotor lateral and torsional critical speeds. External excitation is applied for measurement of the specific natural frequencies and mode shapes. To avoid self-excited vibrations such as shaft whip, advanced stability verification tests measure a particular rotor mode’s log decrement under various machine operating conditions.

Modeling complements field measurements for accurate diagnosis and resolution of vibration problems. To mitigate risk, such analysis permits evaluating design modifications before field implementation. Measurement and test condition limitations often necessitate FEA when dealing with various machinery components, in particular, turbine blades and impellers.

A high quality shop balance is necessary to achieve reliable vibration performance of critical machinery. To help ensure successful commissioning, witnessing of shop low speed and/or high speed balancing is recommended. If balance degradation occurs during operation, in situ or field balancing may be an option to minimize vibration at the speed(s) of concern. Single or multiple plane corrections are accomplished using influence coefficient or modal balancing methods.