High frequency pulsation generated by centrifugal compressors can cause fatigue failures of the compressor internals, impair compressor performance, and damage the attached compressor piping. There are a number of sources producing pulsation in such a complex machine. The main origin of pulsation are turbulences, blade-stator interaction phenomena, secondary flows resulting in boundary layer separation, fluid solid interactions, and compressor piping interactions. Some of them are discussed in literature at large (Japikse, 1995).
This paper describes severe pulsation conditions, in certain type of radial inlet compressors, which resulted in unacceptable piping vibration, compressor impeller failures, and other compressor component failures. From the information gathered during several failure investigations and field tests, the following concepts of failure origin were considered: flow in the diffuser, impeller blade vibration, shroud geometry, impeller radial clearance, housing effects, volute cut-off design, flow through the inlet guide vanes, flow turbulence. The investigation was carried out using modal analysis tests, finite element modeling, field measurements, and compressor internal inspections. As the process of investigation followed, the predominant pulsation/vibration sources were diagnosed as high unsteady gas velocities in the diffuser and resonances in the compressor.
The results presented in this work are based on five investigated compressors, two 16 MW and three 25 MW machines. The discharge piping vibration levels constitute a benchmark for evaluation of some of the implemented modifications.