GE Frame 5 Rotor high 1x vibration

[Rreach]

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.

 

[TugboatEng]

What was the cause of the original failure?

 

[Rreach]

One of the turbine blades broke and damaged the rest.

 

[Rreach]

I found out from the OEM that the rotor is expected to vibrate in rigid rocking mode at operating speed, thus I think that is the reason high speed balancing is not required as standard.