During power plant annual inspection, PdM department gave a recommendation to replace motor bearing and repair bearing housing dimension. The job was done by third party in a week and a acceptance test (no load condition) was conducted . Vibration spectrum and PV from acceptance test is shown in fig 1.
Fig 1. Vibration spectrum and PV from inboard bearing from acceptance test
The data was taken at 7 July. From vibration spectrum, it was noted some activity at high frequency which usually corresponded to bearing defect, but since it’s magnitude was still lower than acceptance limit criteria it was decided to pass and put it into operation.
9 July , operator reported very high noise from this machine. Vibration spectrum and PV is shown in picture 2
Fig 2. Vibration spectrum and PV after two days in service
It was noted increased noise floor at vibration spectrum and PeakVue. BPFO and BPFI also appear on vibration spectrum. Then it was decided to draw it from service and install new bearing. During inboard bearing disassembly, it was found that bearing housing diameter was 0.5 mm smaller than it should be. Heavily marked path pattern was identified in raceways. The probable cause was smaller dimension of bearing housing make bearing internal clearance get to tight and cause high load at he bearing. This is way the bearing only last for 2 days.
