Posted on behalf of Umar Ali Khan

At one of our Gas processing plants we have a centrifugal compressor. It has a LP casing and a HP casing. The HP rotor has 8 impellers. On the HP rotor we faced a rotor rub with the labyrinth seals. The rub was however partial on the circumference, that is, at 0 to 90 degrees circumferentially. This rub occurred on all the interstage labyrinths, balance piston labyrinths and shaft end labyrinths. The tilt pad journal and thrust bearings however came out to be perfectly OK. We suspect that this is because of a temporary rotor bow. However we cannot exactly identify the cause of this temporary rotor bow.

Umar Ali Khan Mechanical Engineer
OMV Pakistan

Mr. Khan,

When you say temporary, you imply that
1. When you checked the runout of the rotor, it was within acceptable limits
2. After cleaning out the labyrinth 'rubs', you were able to restart the machine and it ran without excessive vibrations

Can you please advise if the gas carries any particulates, and if so their size distribution and quantity (in ppm) ?

What are the radial labyrinth clearances?

Were all the 'rubs' in the same angular alignment 0-90 deg., with 0 being the 12 o'clock poition?

Were there any rust marks or stains in the casing or rotor?

Were there any heat marks (blueing)of the labyrinths or shaft areas near the labyrinths? If so, what did you do with the blue marks?

The additional data may help us understand the case better. Thanks.

V.Narayan.