I had identified a bearing outer race defect in the spectrum in a Desuplh ID fan at our steel making plant and requested for bearing change out.
The maintenance fitters open dismantled the bearings, came back and said that there was nothing wrong with the bearing was unwilling to change it.
I went over and popped out the rollers, cleaned out the raceway and there it was, a big spall.
Unfortunately, sometimes the condition monitoring team is not aware of the maintenance activity, the work orders are closed without history. When asked they simply say there was nothing wrong with the bearing.
We can easily get into the trap where we raise our trigger for maintenance activity on the premise that the bearing was ok at the previous levels.
Sometimes just removing the bearing cap does not reveal the bearing damage as the damage more likely lie at the bottom half which is the load zone.
See powerpoint attachment.