Repeated Start-ups of Centrifugal Compressor Operating above Frist Critical Speed

[Amer93]

Greetings,

Would there be significant effects on centrifugal compressors if started multiple times within a short period of time to collect vibration data on them, where these compressors are operating above 1st critical speed?

 

[1503-44]

Isn't your normal operation speed above 1st critical speed?

You should pass through critical speed quickly. Don't spend any time there.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[JJPellin]

What is the bearing design? What is the driver? The amplification passing through critical depends on a number of different factors.

Johnny Pellin

 

[Amer93]

This is a 6 stages centrifugal compressor with hydrodynamic journal bearings and Kingsbury thrust bearing. It's driven by a steam turbine. I've seen this many times were a machine with high vibrations is started 2-3 times to basically see the vibration levels or collect data through ADRE, etc. Is it harmful for the machine? Does it depend on the amplitude? What if the amplitude reaches the trip level, would this be the case were multiple startups is not recommended?

Thank you for the help.

 

[compguy22]

Why one time would not suffice to collect data?
It is acceptable by design to pass through / cross 1st critical speed during start up, otherwise the compressor will never start.
There is not only the critical speed value to look at, but also separation margins, amplification factor which are covered by API 617 if your machine is to this standard.
If the machine does not trip during normal start up then there is no reason why it would be prevented to start during the test procedure you intend to put in place unless you are not operating in "chartered area". Refer also to MRT procedure and vibration readings based on OEM manual as there are incremental steps for ramp up and run down, oil temperature stabilization etc.

 

[compguy22]

By the way, do not look at compressor only, look at steam turbine too.

 

[Wkcoo]

You can consider the seal & past experience of startup behaviour of the machine train as well. Seen a rock solid steam turbine driven centrifugal compressor, the vibration amplitude remain low even when it is surging on startup.

 

[SB1976]

Hi Amer93,

Electrical motors have a limitation on the number of starts per hour for both hot start as well as cold start. So, if compressor is started multiple number of times within a short span of time, it won't be possible for you to start anytime soon beyond certain number of starts. The bearings and windings on part of the motor will be severely impacted on account of the multiple start / stops.

Regards.