Gas Turbine frame V high exhaust temperature


Thread Starter

Ayman Elsebaii

We have GE Frame V gas turbine 5002B with 41900 running hours. during running the turbine sparks came out from exhaust at steady state. turbine was shut down normally (No trip).

Examining turbine's parameters the following was found:

1) Exhaust temperature starts normally at average 420 deg C then it rises to 480 then to 540 at the moment where sparks came out.

2) Compressor discharge pressure starts normal at 5.81 bar then it starts degrading to 5.1 bars

3) Bearing one vibration rose to about 0.48 inch/sec then degrades to 0.1 inch/sec and during sparks it rose to 0.4 inch/sec (alarm set point 0.5 inch/sec)

4) TNH remained at 100% then it showed instantaneous increase to 101.25 % then to normal

5) during TNH notch, FSR showed revers notch from 40% to 35% then back to 42%

6) Gas Nozzles were disassembled and examined as well as linears. they found to be normal

what could be the possible cause for the described problem plus what further examination shall be done?

did you check your combustion fuel system, the pressure, and the flow and even the fuel valve.

good luck,
Is this a Gas Fuel machine? Are you sure you have no fuel gas problems which could cause a possible liquid carry over in the gas system? Was fuel gas supply temperature OK Is there any chance that you are operating near the gas dew point? Was there any evidence of unusual levels in your Fuel Gas Scubbers?

Most of your data looks like some kind of uncontrolled fuel problem.
To be honest, anything that causes sparks to come out of the exhaust stack needs to be investigated immediately and probably requires a machine shut-down until the cause is established as you could be heading towards major damage, if you are not already there. Sorry to be gloomy but this looks like a pretty serious problem.

Ayman Elsebaii

Thanks for your replies,

I have checked the gas parameters and was found to be in normal range, the gas temperature is far apart from gas critical temperature. Moreover, the gas valves behaviour is normal (Gas Control Valve and Speed Ratio Valve) with exception of the notch described above.

What is strange is the abnormal behaviour (Sparks) occurred with one single alarm (low air inlet trouble). I think with that severity there must have been dozens of alarms at Mark V log.
Ayman Elsebaii,

I've been following this thread with interest. And this comment has me very curious:

> I think with that severity there must have
> been dozens of alarms at Mark V log.

This being a two-shaft machine, the high vibration seems to have been experienced only on the HP shaft. Certainly it's possible that something happened to cause a momentary excess of fuel which caused the HP shaft speed to increase, which may be a reason for FSR to decrease to try to limit the HP shaft speed increase.

But, am I don't have any experience with 5002B machines, but if the unit has variable second-stage nozzles they are usually used to control HP speed, and FSR is usually used to control LP speed. If this is a compressor drive, what happened to LP speed when the HP speed was higher than normal? If the unit has variable second-stage nozzles, what were the nozzles doing during the event?

The sparks are what really have us all wondering, though. I have seen older machines with very rusted exhaust ducts emit "sparks" (glowing bits of rusted exhaust ductwork, actually) when there was too much liquid fuel admitted during start-up, causing a low "boom." The sudden pressure increase caused rusted bits of the perforated sheet metal which were wet with liquid fuel and had ignited to be "blown" out of the top of the stack, which wasn't very tall (the units were older simple-cycle units with short exhaust stacks). In the night sky it looked like sparks, until the larger pieces started striking hardhats as they fell back to the ground. It was quite a sight, actually.

I would hope the unit was shut down and borescoped to see if there was any damage to the HP section, in particular. Because the machine is a two-shaft unit, though, anything "liberated" from the HP shaft would have to travel through the LP turbine and into the exhaust, so that would not bode well for the LP turbine nozzles and buckets.

Please write back to tell us how this progresses. If the unit was re-started with no after-effects, then it would seem that something may have ignited in the exhaust similar to what was described above, though that doesn't explain the HP shaft speed deviation and increased vibration.

As for the comment about more alarms in the Alarm Log, I'm always surprised about how many people think gas turbines have so much instrumentation and should be capable of monitoring and recording so many parameters. They expect the control system to alarm on most every abnormal condition--and yet these same people complain about how many alarms are annunciated by the turbine control system, and that with only the typical, almost "bare-bones" instrumentation most turbines operate with.

Yes; the turbines are protected as best as possible by the control systems against the most common and most destructive problems. But, the control systems are not as instrumented or as "smart" as many people would think them to be. (And, again, these same people decry the amount of alarms annunciated by the control systems, as being excessive as well as cryptic.)

I don't know of any turbine, though, that has "spark detectors" or will alarm when sparks are being emitted from the exhaust. Spark plugs; flame detectors; yes. Spark detectors, no.

Please tell us more about the results of the investigation as they become known. And, please correct any false assumptions I made about the configuration of the 5002B machine at your site.
All MS3002, MS5002A, MS5002B, MS5002C and MS5002D GE gas turbines have variable 2nd stage nozzles, which do control the speed of the HP shaft. Physically, they are controlling the energy split between the HP and LP shafts, but HP speed is what is used to control the position of the nozzles.

I can't add anything to the discussion on the sparks, unfortunately - I'm scratching my head, too.
before restart again you should do the following:

*check the Y fuel gas Strainer;and also all the thermocouples inside Exhaust compartiment.

*check inside inlet admission with borescope the axial compressor blades and you should change your ""air filter""

please let me know if the pb was resolved
before restart you need to check:

1-exhaust thermocouple "inside" exhaust compartiment

2-borescope inspection for axial compressor blades from inlet

3-should be changed the air filter

Hi there,

Perhaps you can clarify the followings :-

1. Was it a spark or fire-ball came out through the exhaust stack?

2. The MS-5002B, is it gas fuel or liquid fuel or dual-fuel combustors?

3. Any internal inspection being carried out at the exhaust section? My suspect, maybe some flying object (non rotating blades) being broken and flew with exhaust gas stream and hit/in-contact with the exhaust stack inner wall...

4. Can you also share with us either you have the Power Turbine Nozzle Guide Vane or not? I am more familiar about MS-5002D two-shaft, the Nozzle guide vane is applicable for this machine for its power turbine.

5. Please share with us what were the follow-ups findings that you observed and problem status...

I agree with Samy there. This is a gradual unloading shutdown of the gas turbine & not a trip caused typically by high inlet air filter DP or low inlet air flow, which could cause an excessive fuel/air mass ratio, which I think explains the rise in exhaust temperature & lowering of compressor discharge pressure. As for the temporary spike in bearing vibration, I think it might have been due to a sudden surge in your bearing metal/lube oil temperature, though I am not certain. I am also unable to explain the sparks. What I recommend is the following:-

1) Check your air inlet filers. If they are choked, replace them.

2) Check your air inlet filter DP pressure transmitter & unloading pressure switch. If there was any fog/misty conditions/hail/snow/rain fall, when this phenomenon occurred, it would also do well to check your duct dp Vs time & inlet air filer dp Vs time trends. Typically, these trends should be similar. If they are different, then drain & purge the lines from the filter house to the pressure transmitter & unloading switch.

3) What was your IGV position before shutdown? Had you given a load raise command just before the shutdown? The possiblities in this regard are:-

a) Check your hydraulic system -- main & auxiliary hydraulic oil pumps, hydraulic oil filters for choking, IGV filters for choking, oil lines for clogging or leakages. Even an oil hydraulic test would be good.

b) Check your IGV actuator, mechanical linkages [turnbuckle] & your rack & pinion arrangement. Going for an IGV calibration would be good.

c) Check your fuel servo control valve & whether the command from Mark 4/5/6 is getting extended to your IGV. Also check the LVDTs. I would recommend an FCV calibration.

Hope this helps.
P.S. :- I am not experienced with twin shaft GTs & this is based on my experience with frame 9E single shaft GTs alone. Any errors may please be notified.
This thread is old i wonder has the original poster found what went wrong?

I am thinking the spark could be due to rubbing of parts in turbine section. This explains why the surge in vibration, reduction in compressor discharge pressure and thus increment in exhaust temperature.

I think the turbine initially slowed down due to the rub, then the droop caused the TNH to surge when the friction was suddenly lifted.

Just a wild guess. Hopefully the original poster is willing to share what the real root cause is.