Bearing damage caused by a complete stagnation

Observation:

After constantly recurring bearing problems of one specific pump, the client decided to have a damaged bearing analyzed by the manufacturer. The manufacturer reported that the initial problem was caused by √ęstagnation damage√≠. Possible causes of stagnation damage can be: assembly mistakes, standstill corrosion, elevated vibrations in the vicinity. ACD was contacted to confirm/dismiss whether vibrations could be the cause of the defect.

Proposition:

Initially, we did not establish any problems with our data collector. This prompted us to, in consultation with the client, install an online vibration monitoring device.

Sensors in two directions will be installed on the pump concerned and the adjacent machines. This way, we will be able to establish a trend of vibration in our absence. Evidently, the pumps are stopped and restarted during that time and the impact of vibrations of a working pump on a stopped pump is measurable.

Bearing damage caused at a complete stagnation

Bearing damage by stagnation

After analysis, we could see that the elevated vibrations could be contributed to the blade frequency. This concerns pulsations in the product flow, which can easily be conveyed through pressure pipes. These vibrations can be reduced dramatically through adaptions in the operation of the device (adjustment of the speed control system in terms of the valve position).

Bearing damage by stagnation

The vibrations and especially the strong impact of stopping the machines, is easily passed on in the equipment. Abrupt changes in vibrations can easily change the resonance frequency and structure of the machines. 

Based on these observations, a proposal was made to change the pipe supports of the joint pressure pipe lines.

Decision:

The measured phenomena are too small to cause a stagnation as a result of vibrations. As vibrations are not the cause, we attribute the failure to an assembly flaw. In any case, the measurements have contributed to corrective measures, which will increase the life span of the machines.