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Compressor
Rotor Bow Monitoring Application
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by
MachineryWatch.Com, Inc.
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| Situation: |
| Machine: |
Large
Propylene Process Refrigeration Compressor |
| Industry: |
PetroChemical |
| Location: |
Louisiana |
| Equipment: |
Gas
Turbine Driven, 5 Stage Centrifugal Compressor Power
Turbine and Compressor Speed = 5,700 RPM |
| Instrumentation: |
MAARS
Model 5000, factory installed proximity probes |
| Condition: |
Rotor
Bow from Inter-stage Seal Rub |
| Indication: |
Failure
to Achieve Operating Speed, Trip When Passing Critical
Speed, Excessive 1X Amplitudes on all Probes |
| Corrective Action: |
Compressor
Disassembled, All components dynamically balanced above
critical speed, Spacers
between wheels modified to prevent creation and retention of
bow due to rub-induced thermal bow. |
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Description:
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| The
compressor manufacturer requested assistance in data
acquisition and analysis initially due to failure of the
compressor to achieve design performance at installation.
Initial compressor wheel designs were found to be
improper for the installation so a new rotor was provided
with different compressor wheels.
The new compressor initially started, but had
excessive vibration when passing through the critical speed.
The
problem got worse with each successive start of the machine
so that soon even when idling at about 50% of design RPM the
vibration level approached the manufacturer's recommended
alarm levels. The orbits did not indicate on-going rub
conditions.
The
spectral data all indicated that the controlling frequency
at all probes was 1X RPM.
Evidence of the rub of the interstage seal was
discovered as the machine was disassembled
and a careful review of the clearance measurements
made during assembly indicated that a below minimum
clearance was overlooked during assembly.
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After the high speed dynamic balance on a balance stand in
Houston, the unit was reassembled and levels were well
within the compressor manufacturer's recommendations.
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Compressor Rotor Bow
