Diagnosis of Bearings Condition – non-synchronous peaks in FFT

Realy only on bearing defect frequency is a mistake that can lead to failure in indicating the condition of bearings.
Described in this case el. the motor has a revolution speed of 1770 and bearings 6308 with the following bearings frequency:

The el. motor and screw pump is positioned vertically.


During analysis, it was indicated high bearing envelope.

There weren’t any bearing frequency seen on FFT velocity or envelope:

It was decided to replace both bearings.
Next measurements and feedback from the Crew confirm our diagnosis.

It is important to know that not always bearing defect frequencies are visible when the bearing has defects. If we have only a number of the bearings and don’t have an exact producer then the bearing defect frequency can be different than we assume. Bearing with significant defect during its last worn down stage may have only rise floor and haystack shown in velocity/envelope.