BY AMIN ALMASI. There are many reasons for turbomachinery problems and failures. Resonance, for example, is often overlooked. Rotating parts and components such as impellers and blade rows could be in resonance with any excitations generated by turbomachinery. Resonances for the first and second natural frequencies can be dangerous. Generally, there could be numerous cases of resonance. The second natural frequency of a rotating component, in one example, proved to be almost exactly an integer multiple of the first natural frequency. This led to excitation and operational problems. Fluid-induced vibration, oscillatory changes of fluid pressure, and turbulent flow (vortex formation) might also cause high vibration or even failure. Fatigue, too, is often a root cause in failures of rotating parts. Individual stress amplitudes should be analyzed to ensure associated components will not fail due to different forms of fatigue such as high-cycle fatigue (HCF) and low-cycle fatigue (LCF).
Reliability and Maintenance Management Consultants