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Critical Speed Vibration on 9001E
After major inspection and rotor inspection of gas turbine bearing No. 1 vibration exceeded 25.4 mm/s during start up

Recently after completion of major inspection & rotor inspection (Integration) on GE 9171E gas turbine, during start up bearing #1 vibration exceeded from 25.4 mm/s at about 1200 RPM.

Bearing #1 and #2 have been changed and also two sections of the IGV ring gear. We have checked lube oil temperature and gas control valve calibration.

Would any one help up ASAP? Any solution is a great pleasure to us.

0 out of 1 members thought this post was helpful...

Khaledian,

It sounds as if the rotor wasn't properly balanced, and/or the bearings weren't properly installed or aligned. Presuming someone was near the unit when it was being started and the vibration was real (that is--there is no instrumentation issue), there is nothing controls-related about this problem.

If you are satisfied that the vibration sensors were properly re-installed after the outage work and that the sensors are the same ones which were removed before the outage work--or, if new sensors were installed after the outage work that the new sensors have the same sensitivity rating as the ones that were removed, the problem is mechanical and the contractor who did the outage work (rotor integration, and bearing replacement) should be supporting the resolution of the problem.

You might try selecting FIRE mode when starting the unit, which will keep theFSR from increasing after flame is established (speed will slowly increase) to see if slowly letting the unit warm up at low speed will help reduce the vibration. But, be aware--while in FIRE mode the starting motor is providing near maximum torque to the unit which is usually 150-160% of the starting motor nameplate rating so you can't run indefinitely in FIRE mode without tripping and/or damaging the starting motor.

There is no other method to control speed below 95% of rated during state-up, so that's the only method of keeping speed low with flame in the unit to try to warm the rotor slowly. You mentioned critical speed--GE doesn't typically publish rotor critical speed information for their heavy duty gas turbines.

Finally, many GE-design heavy duty gas turbines also have Bentley-Nevada proximitors to measure vibration. If the machine at your site has them, what do they say the vibration is when the seismic vibration sensors indicate 25.4 mm/sec? And, the B-N sensors can be extremely useful in determining how to resolve the problem. But you'll need to get someone to site with the proper B-N auxiliary equipment and knowledge/training to assist with resolving the issue.

Hope this helps! Please write back to let us know what you find and how you resolve the problem!!!

CSA,

thank for your information. we have real vibration. we try to start unit by trial weight balance right now.

By Amar DAMENE on 16 April, 2017 - 1:07 pm

Dear Khaled,

I read your message and my response is:

You say that after completion of:
* Major inspection &
* Rotor inspection (Integration)............on GE 9171E gas turbine,

And during start up bearing #1 vibration exceeded from 25.4 mm/s at
about 1200 RPM. what are the limits Alarm and Trip?

How this level of vibration appears?
....it Increases with speed of HP rotor? if yes, then really you have problem

....if Appears suddenly at 1200 rpm?.....maybe the problem is sensor and cable.

Before to change Bearing #1 and #2 have what was the level of vibration before inspection.

My experience, that generally before the inspection e start the GT and measure the level of vibration for all sensors.

After Inspection, we see and we compare to the levels of vibration.

Some cases we reopen the bearings for a second inspection
or we do a balancing after to be sure that we cannot do anything

Hope this guide you
My email: dameneamar@gmail.com

Amar,

the alarm limit is about 12.5 mm/s and the trip limit is 25.4 mm/s.

Replace the load shaft

regards,

Dear Khaladian,

It doesn't make a sense to make field balancing without deep vibration analysis! And you are taking a mega risk that can damage your GT capital parts. You need, first, to conduct a DEEP root cause troubleshooting. Field balancing may solve the high vibration level but you may also just hide or reduce the vibration at that specific area where are located seismic sensors.

As you said the high vibration (24,5 mm/s and over) is reached near 1200 rpm which is the harmonic or critical vibration speed. Did you try to keep running your gas turbine over 1200 rpm? Usually, vibration will decrease after 1600 rpm and after 6 to 8 running hours vibration will decrease more. I used to manage similar situations on GE Frame 5 GT, the high vibration at 1200 rpm was about 32mm/s, down to 26mm/S at FSNL and stabilised around 20mm/s after 6 running hours.

This issue has been done under a qualified OEM supervision. Because, by myself, I will never run that huge machine over the trip alarm setting.

Hope this is helpful!
Regards
Karim