We have a Frame 5 Gas Turbine driving a Centrifugal Compressor thorugh a gearbox. Since approx 2 months, Gas Turbine exhaust end bearing (Bearing# 2) has been experiencing intermittent vibration peaks as high as 2.0 to 2.7 mils. Normal running vibration is 0.8 to 1 mil. The vibration peaks appear after 18 to 24 hours gap. The vibration increase and decreases over a period of 10 to 20 minutes. When these vibration peaks appear, the Gas Turbine inlet end beraing( Bearing# 1) also shows vibration peaks but with a lot lesser amplitutde. This means that the problem is at the Bearing # 2 area. Machine is fitted with proximity probes and data has been collected using ADRE. Unfortunately, one out of the 2 probes installed at Bearing # 2 is not functional, so the vibration data collected from Bearing # 2 is limited. However from the one working probe, the spectrum shows that it is primarily the 1X component that increases and results in an overall amplitude increase. During the vibration increase period, the phase angle changes by about 30 degrees or so. The vibration peak events are not linked with any RPM or load change. Also these are correlation with ambient temperature change in day or night. The lube oil pressure or temperature is constant.
When the vibration is running normal, the spectrum shows following peaks:
Overall amplitude = 0.98 mils
1X = 0.37 mils
2X = 0.23 mils
3X = 0.2 mils
4X = 0.11 mils
5X = 0.15 mils and so on.
During the high vibration event, only the 1X increases, while the other times speed peaks have negliginle rise.