ON GAS TURBINE FRAME 6B WE HEARING STRANGE SOUND. DURING START UP ON FIRING AND THE UNIT OPERATE ON GAS FUEL (NOT DISTILLATION FUEL), WE HEARING A BIG EXPLOSION,

 

This would scare the sh.t out of me...!! More information required

 

> This would scare the sh.t out of me...!! More information required

+1

cww

 

> This would scare the sh.t out of me...!! More information required

I couldn't have said it better! And my bet is that it (the explosions) have happened more than once, because just once would have been dismissed as a one-off event.

And for someone to post this without providing any more information than was provided just proves my thoughts.

No information like they just came off a maintenance outage, or the unit had experienced multiple trips and was being re-started, and no mention of any alarms (Process or Diagnostic) because apparently the unit didn't trip on high exhaust temperature and made it up to load (or not!); we weren't told ANYTHING!.

So, about the best response that can be given is just what you said so eloquently, Bob!

 

HELLO

WE HEARING AN EXPLOSION WHEN WE STARTING THE UNIT ON GAS FUEL (GAS TURBINE F6B MK5) ON FIRING. AND AFTER THIS THE UNIT RUNNING NORMALACC, FULL SPEED, LOUD)

WE CHECKED AND CALIBRATE LVDT FOR SRV AND GCV.

REGARDS;
KHALID
[email protected]

 

Give it a master reset and try again.

Chance are it wont go boom twice.

 

HELLO FOR ALL,

I WANT TO EXPLAIN SOME INFORMATION.

THERE ARE TWO UNIT F6B,AND THE OPERATOR MAKING LOGIC FORCE (L86FPG2HT=0) FOR TWO UNIT TO ESCAPE FROM TRIP. ONE OF THESE UNIT MAKES THIS PROBLEM AT THIS MOMENT (FIRING@FSR=17%, @TNH=21%). AND GO ON CONTINUE SEQUENCE TO FULL SPEED AND LOUD.

WE CALIBRATE SRV AND GCV ,RESTART <R><S><T>.

BUT THE PROBLEM IS STILL AT THIS UNIT. THE OTHER UNIT IS GOOD.
IS P2 CAUSES THIS PROBLEM? IF THAT WHAT WE CAN DO?
I HOPE THIS INFORMATION GOOD.

REGARDS:
KHALID
[email protected]

 

In our frame 6B, Mark V, with DLN 1 once we faced a similar abnormal sound in start up. On verification we observed that IBH valve malfunctioned, which was 100% open. In startup make sure IBH is kept off and verify physically. We open the IBH manual drain open and ensure air is dry before opening the IBH after machine attains FSNL. In startup mode you can see some humid air. This can create abnormal sound at firing speed.

 

I'd sure try not to make it a repetitive event. I'd chicken switch and see what's wrong. And though this is an illustrious group, I'd probably do that before I got on the mailing list. For machine, if not personnel safety.

Regards
cww

 

>>"THERE ARE TWO UNIT F6B,AND THE OPERATOR
>MAKING LOGIC FORCE (L86FPG2HT=0"

Wow!! I can't believe this was allowed, especially without knowing the cause.

 

>THE OPERATOR MAKING LOGIC FORCE (L86FPG2HT=0) >FOR TWO UNIT TO ESCAPE FROM TRIP.

Unbelievable ... Seem like you have a leaking SRV valve and you are passing way to much gas at startup. Typically fpg2 is about 4-6 bar (someone correct me if im wrong) at light off. I would guess fpg2 is at full line pressure, probably 23 bar or more. Way too much gas at light off. This is the scenario L86FPG2HT is to protect against, but it wont do much good with it forced off.

What is fpg2 at zero speed ? Does this unit perform a gas leak test at start up ? Is this forced as well ? Is there a HRSG on the back or is it open cycle ? What is your purge time, has this been "customized" by site operators ? What vintage turbine is this ? MK IV, V or VI ? What type of gas valves are used, combined SRV/GCV assembly located in a cabinet inside the auxiliaries compartment, or individual gas valves located in a separate module.

Does the GCV leak as well ? This is scariest scenario, if both both SRV and GCV are leaking gas is collecting in the turbine/hrsg waiting to go boom.

Trouble shooting steps I would take would be

1) remove and dispose of the operator

2) focus your efforts on determining if the SRV is leaking. A calibration will often not help determine if there is a leaking seat. I would suggest de-energizing 20FG-1 and run the QA and HQ oil pumps. This will de-energize the trip relay and drive the valve hard into the seat.

 

I cannot believe this......

You are forcing protection logic without fully understanding the consequence. If you don't force the point, then the machine trips correct? If so, then the MK5 is doing what it should, it's protecting your machine. This means that there is a fault in the field and this should be investigated.

A simple calibration of the SRV / GCV may not identify the issue. We have experienced a number of similar issues, however, none have been the same. The most similar occurance we had, was when the stroke length of the GCV was excessive and the full travel had been calibrated for 100%. Hence requesting a % position, the valve was actually opening further than required. You should understand that during light off the GCV is effectively open loop control.

You will only know this is wrong if you;

1) Know what the GCV stroke length should be. Ours is 45mm
2) Know what the calibration figures are, in particular autocal.
3) You physically measure the stroke length.

I would suggest that this machine is not run and that a full calibration, including stroke measurements and an inspection of the valve internals is performed. You should do both the GCV and SRV.

You should not be forcing the logic or performing a master reset simply to carry on running!

As HRSG_Boom states "Chances are it wont go boom twice."

 

cww,

For those of who are not familiar with chicken switching, can you please explain?

Thanks in advance!

 

Chicken Switching is when you hit the big red button. Probably would have to sequence down on a turbine. Could be replaced by Emergency Stop if you can't find Chicken Switch name plates. First heard I think, when spinning up 24" grinding wheels. If they vibrate, you have to make a judgment call whether it will smooth out or come apart. It's best to make the right call and soon enough. See "Pucker Factor"

Regards
cww

 

Firstly, the SRV leakage when it is closed, has to be addressed. What P2 (Interstage) pressure do you have at standstill? If the SRV is leaking across the seat when the Interstage vent is open (20VG), you usually can hear it hissing over the seat and up the vent. The other problem which can cause a "boom" at light off, is firing at too high a speed. How long is your purge time (K2TV)? Normal sequence is turbine cranks to 14HM (firing speed) which starts the purge timer then turbine fires. You say firing at 21% speed, that seems a bit high, usually 14HM is set at 18% on a Frame 6. if your starting means is allowing the shaft speed to drift from 14HM up to 21% before firing, you could be getting a bit too much gas at light off, hence the "boom". Check your P&ID for the torque converter and adjust the max. cranking speed to about 1% above 14HM.

Firstly I would open your SRV & GCV and check the seats etc. then re-cal both valves.

 

I have experience such incidents as well (thank god I'm still alive to share it here )

However the root cause for my problem was due found to be because of the passing of GCV and SRV (yes both of them)!

Nevertheless, the unit was taken down and inspected. Lady Luck was definitely on my side at that time as no abnormalities were observed.
As a precaution (after the incidents), although purge cycle is done during every start up, its always advised that cranking is done for several minutes prior to start up especially if the unit is on standby for long period.