Gas Turbine Vibration and Compressor Surge


Thread Starter



Our power plant has 5 GTs, frame 6, of 30MW each. On 24th Jan 10 pm, one of the GTs which was running on 27.5 MW, CPD=8.3 bar and other parameters normal, tripped. The alarms that came were (in sequence):

1. Loss of Flame.
2. Loss of CPD bias.
3. Exhaust temperature high trip.
4. High vibration.

CPD dropped fro 8.3 to 1.37 bar suddenly.
MW changed from 27.5 to -7.3 and then to zero.
Highest TTXM was 629 and TTRX was 567 deg C.
Vibration were past trip limit on BB1, 2, 4 and 5. BB4 even got out.
When it tripped, operators say they saw the turbine air filter house shaking.

After that the GT was started twice but both time speed didn't increase beyond 2100rpm and tripped in high vibration. (a very bad decision made by the seniors present in that shift)

On inspection next morning, IGV was found badly damaged and compressor blades were found broken. Filter house was quite dirty which was cleaned. No trace of foreign particle in Inlet plenum was found except one feather on the bird mesh. The GT had returned from HGPI on September 2016, water wash was done before start up. Inlet air filter were replaced on 9 Jan 2017.

Could it be that some foreign material went inside the plenum on 9th Jan and that caused the surge on 24th Jan night?

Could there be some abnormality in Combustion chamber (Loss of flame came first)? our RLNG quality is coming quite bad these days (on going pigging (cleaning) of pipelines upstream). But the fine filter (Last filter in RLNG line) dp before trip was 0.38kg/cm2.

Please share your experiences of the possible causes.
> Please share your experiences of the possible causes.

1. First you might want to check all the tagging on the equipment inside the plenum are still intact. The tagging should be bolted or riveted to the equipment.

2. No corrosion on the wall of the plenum where debris of the corroded wall could be transfered into the engine.

3. Check the 00 to 4th stage of the axial compressor blade for any sign of broken or damaged tips.

4. If possible, perform boro scoping at the combustor and the PT side to determine any damaged at that stages depending on the number of time the unit goes thru start up sequences.

Opening of the IGV and bleed valve history should be checked prior to the incidence including the control part.

Imran K
Firstly, It's pretty certain that the surge was caused by the huge drop in CPD which was later confirmed to be caused by severe compressor damage. Given the IGV damage it for sure looks like an FOD damage. I don't think that it is a coincidence that there was an Inlet Filter change recently. Was there:-

1) A thorough Inlet Inspection after the Filter change before start-up?

2) After the event have the Inlet Filters and Inlet Ductwork been inspected for any missing bits?

Obviously this is going to be a Major Overhaul, with care, the cause of the event should be found.

Generally, for all, after a major trip like this, do not re-start the machine without a complete visual inspection (Inlet, exhaust, boroscope)
Some air filters were changed 16 days before the incident. inspection of the air filter house didnt show any abnormal condition. All the filters were in their place.

> 1) A thorough Inlet Inspection after the Filter change before start-up?
We change the filter in running machine also. This always has been the practice. The last filter change was done in running machine only.

The duct was inspected but nothing looked missing. The complete inspection is still awaited. I will update if we find anything.

The first appearance of Loss of flame and then immediately (less than a second later) CPD loss came. This may be due to sudden loss of air. Could a foreign object cause loss of air so much that the flames could not be sensed all at the same time.

Also, as per the trip log, IGV (which was 60DGA open before incident) opened up 69DGA and then back to 62 DGA. The AFPCS went out of limit for a second and then normalized. IGV might have opened in response to the high exhaust temperature. AFPCS might have increased due to sudden closing of IGV from 69 to 62 DGA.

Apart from FOD, what other causes could be there? If any?
It's kind of hard from the damage found to the IGVs and the sequence of events leading to the trip (Flame out, CPD Bias,High Vibration) to envisage anything other than something passing through the IGVs unless it was some failure in the IGVs themselves, but that is a long shot!
>Are you trying to indicate that there had been some kind of
>fire or combustion in the Bell Mouth?

I believed it is more of the outside environment that cause the build up of soot. Source could be from activities near or surrounding the air inlet filter. Local venting of lube oil piping. Blasting activities. Exhaust of other equipment etc. This could be worsen if there is no fixed or schedule water wash frequency done on the unit.