Effects of Piping in Vibration Analysis

Carlos E. Torres

CEO, Power-MI

eventNovember 30, 2020

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Vibration analysts may consider the effect of piping when analyzing pumps, compressors or any other asset type connected to a pipe. The mass of the machine is usually small compared to the mass of the piping and its fluid. Some issues can be caused by piping, not by machinery failures. The two typical issues caused by piping are misalignment and resonance. Ideally, disconnecting piping while running the machine should be enough to discard a problem caused by piping if the vibration level changes significantly. 

When the piping is improperly supported, it can cause either shaft misalignment or a shift in the system's natural frequency (e.g., motor-pump-base-piping) can cause resonance. A solution to that is to use flexible pipe connections to change the stiffness of the system. 

If the piping is causing misalignment, a flexible coupling can be used. However, a detailed study of the working conditions of the coupling should be done in advance. Maintenance departments must also consider the thermal expansion effect in the piping. An accurate check of the alignment condition can be done using laser shaft alignment equipment. Soft foot and base conditions must also be checked.

Vibration transmission of other machines connected to the pipe can cause abnormal vibration in other machines connected to the same pipe. A detailed analysis should be done, taking background readings and synchronous time averaging with the vibration analyzer.

Flow issues, such as water hammer, vortex shedding, turbulence, or cavitation, can create abnormal vibrations in the machine. A simple test is to check these abnormal signals putting the accelerometer along the pipe to detect the point of highest levels. The cause could be a hole or a valve. Nevertheless, the reality is not that simple, and analysts should also check a possible system's resonating condition. In most cases, analysts must work together with process engineers and machine manufacturers to find the cause of the abnormal vibration.