vibrations problem

1. VIBRATIONS PROBLEM ON
COMPRESSOR TRAIN
Strange changes in vibration behavior
Igor Vondrak, Petrokemija

2. INTRODUCTION
• During steady state operation of the Ammonia plant the changes in
the vibration condition of turbine TC 21105 and ammonia compressor
TC 21105HP in the direction of 21XE174-1 and 21XE2174-2 probes of
the turbine and in direction of 21XE21175-1 and 21XE21175-2 probes
on the compressor was observed.
• The levels of vibrations are not so intensive and below the alarm limit,
but they require attention because there were no any changes in the
process conditions and operation of the machine.

3. SHEME OF COMPRESSORS TRAIN

4. ANALYSIS
• Overall vibration level trending where done and it can be seen on the
next picture (21XE174-2-turbine)

5. VIBRATION TREND ON HP COMPRESSOR
• Trend vibration on the HP compressor in the direction of probe
21XE175-2:

6. SPECTRUM
The observed changes are happening at the
turbine outlet and HP compressor.
Frequency analysis indicates that the
dominant harmonic of 1X is same on the
turbine and the compressor.

7. APHT DIAGRAM
The 1X vibration analysis were performed
(APHT diagram or AccRegion diagram). There
is an extreme phase shift with changes in
amplitude of 1X frequency.

8. POLAR PLOT (ACCEPTANCE REGION)
Display shows changes of 1X vibration
component in polar diagram for a short
period of time (1day).

9. ORBIT PLOT
Orbit display indicates that the precession is
positive and can be seen from the spectrum
also.

10. CONCLUSION
• The observed increase of vibration level is not such that would cause machine trip, but it is certainly a change that is not desirable in steady work
operation.
• The trend of overall vibration indicates that in a specific period of time the disappearance and reappearance of vibrating state occurs without any
change in machine operation mode.
• The dominant frequency of vibration is 1X, with small amount of sub-harmonic components. 1X component changes (APHT diagram) are very
uncommon and occur on both machines (more changes on the turbine). Phase shift is also very intense which corresponds with intense and rapid
changes of 1X amplitude component. This change is evident in the polar diagram also.
• Developments of other components (not 1x) are very small and insignificant (the size of 3 μm).
• Orbit has a positive precession indicating certain preload form, but not essential.
• Regarding to the collected data it is very hard to uniquely determine what exactly cause the vibration change.
• The HP turbine and the compressor are connected with a gear coupling, so that the vibration occurred on one of the machines should not be
transferred to another machine unless the cause is on the coupling.
• One possibility is that the lubricating oil nozzle connected to the coupling comes into contact with it and thereby causes these vibration changes. The
intense changes of 1X component in the amount and phase angle at the same time can be characteristic of thermal rub where there is a local
overheating and the rotor bowing.
•
• The thermal hub can occur in the steam turbine and / or oil seals and in compressor on labyrinths and / or sealing system where the minimum
clearances are.
• The deviation from normal values (reference pressures, oil levels, ...) of the compressor sealing system are not observed.