High Bearing Vibration on MS5002C GT after Major Inspection


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Dear All
When the Major Inspection achieved on the Double shaft FrameV HDGT, the vibration level on bearing #1 seems higher than it should be and is running at about half the trip level. This MS5002C is one of 4 machines used on TCF (Turbo Compression Facilities) driving 3 BCL CC compressors of an Oil Recovery Plant.

After the MI; the first starts were very hard with TRIP (high high Vibration). At the end, the turbine is running with about 10mm/s on bearing1.

As I said, we've got 4 Frame V turbines and the seismic vibration level on the 3 others never exceeds 5mm/s.

Right Now and couple months after this MI, Here is the situation: 1) Bearing#1 BB1 still 10,5 mm/S (before the MI Vib max was about 7mm/s). 2) Hard Startup, during the startup the BB1 reaches 18,5 mm/s and after 3 running hours, it stabilizes at 10mm/s. 3) The metal bearing#1 Temperature is higher than the bearings 3 and 4.

The bearings are fitted with radial vibration probes and Keyphaser. Using a SKF Microlog on bearing 1, the spectrum is high vibration amplitude in radial direction at the rotational component 1X and the values are below:

Probe VI-6132: Overall value = 144,4 microns pick-to-pick and PHASE=101° with 1X = 134,9 microns, 2X=14,2 and 3X= 4,9

Probe VI-6133: Overall value = 29,8 microns pick-to-pick and PHASE= 184,7° with 1X =16,5 microns, 2X=11,6 and 3X= 2,4

And the phase difference between the two probe measurements is 83,7°

One more thing; During the MI, all parts used are OEM spare parts, all bearings changed, 1st and 2nd stages nozzle replaced and the HP rotor send to the contractor shop (who did the MI) for inspection and shop balancing.

My question ares: What’s going wrong on this machine? How to explain this vibration level? Does trim balancing correct the actual situation?

Many thanks in advance