We have a GE Frame 5 rotor that was damaged 5 years ago. It was sent to GE for re-built. Only low speed balancing and running speed test (casing vibration reading < 2mm/s, no displacement reading taken) was performed after the re-built. The rotor was stored vertically since then.

This year, we installed this rotor and it is now running with high 1x vibration (140 um pp on both #1 and #2 bearing) at 5100 rpm. We think this is due to residual unbalance in the rotor. Misalignment was ruled out as we stopped to check it last week.

My question is: Is high speed balancing required for the frame 5 rotor since it is running above 2nd critical speed?

Any info or ideas will be appreciated.