We have a frame 3 GE and we just finished an major overhaul where every thing was replaced (Rotor, Stator, NGV, 1st stg nozzle, liners TPs and fuel nozzel tips) after operating the machine we noticed an air leakage from the top of spark plug on combustion Can no.6 the vertical one and overheating signs on the body of the spark plug and the tightening rods got loose and as we dismantle it the tip of the spark plug is deformed we replaced the spark plug for 3 times with a new and old one and we still face the same problem we opened the CAN cover and checked the liner of can no.6 no signs of overheating inside the liner we noticed two things :
1- the new fuel tips have smaller holes than the old one.
2- there are 2 versions of the spark plugs one with a lockwasher and another type with a lockplate on the tie rods of sparkplugs.
We actually still dont know the reason for the problem and we cant operate the machine. Would any one suggest ideas ?

 

It would seem that the air leak you mentioned allows hot combustion gases to flow through the spark plug assembly and out into the turbine compartment. Without a path for the hot combustion gases to flow through the body of the spark plug assembly there won't be any damage.

Are you buying these spark plug assemblies from GE or one of its affiliates? Or from another source?

Have you considered making some kind of test rig to mount the spark plug in, one that's sealed and into which you can add compressed air to and check to make sure the assembly isn't leaking BEFORE you put it on the machine? (A flange with a suitable piece of pipe, sealed at the end, and with a fitting for the air supply would work fine and be simple enough to put together.)

If I recall correctly, on those types of spark plugs there is a gasket (high temp paper I think) that forms a seal when the plug is forced out of the combustion can by axial compressor discharge pressure. Perhaps that gasket is not present, or is getting burnt before the plug is "retracted" (forced out by compressor discharge pressure)?

A second spark plug is simply for redundancy--in case the other spark plug fails. While you are analyzing the problem you can run with just one spark plug (unless it fails, in which case the machine won't start at all).

But, something is allowing hot combustion gases to flow out of the spark plug assembly, perhaps even some fuel--and if that fuel makes its way into the turbine compartment it could have bad consequences. The end of the spark plug assembly where the electrical lead plugs into the assembly should be able to be pulled in and then GENTLY allowed to return to its normal position. (A LOT of laborers, once they discover the spring inside the spark plug assembly, just love to pull it and then let the spring slam the spark plug back into place--and it's NOT a toy.)

It's possible, too, that the spark plug assembly is not being installed correctly, causing the plug not to be fully forced out of the combustion can, and allowing hot combustion gases to flow into and out of the spark plug assembly.

For that kind of damage, something has to be allowing flow into and through and out of the spark plug assembly. This seems the most likely cause.

Best of luck. Many people will be following this thread; please write back with the results of your troubleshooting.

 

@Mostafa Abdelazim,

I just took another look at the photo you attached to your original post. If that photo was taken with the machine running it appears the flexible lead attached to the spark plug is not allowing the spark plug to be fully pushed out of the combustion chamber--which would probably explain why hot combustion gases are getting into and out of the spark plug assembly. There should be some slack in the flexible lead when the spark plug is fully extended out of the assembly. If there is no slack then the small gasket I mentioned won't be able to prevent hot combustion gases from making their way into and out of the spark plug assembly resulting in damage to the assembly when axial compressor discharge pressure is trying to push the spark plug completely out of the combustion chamber.

 

As a check, the spark plugs should BOTH extend the same distance when pulled out manually and there should be some slack (extra cable not preventing full movement of the spark plug).

And DON'T just release the spark plug when testing, measuring or adjusting and allow the spring to quickly pull the spark plug back into the assembly; that will damage the ceramic insulator inside the spark plug which will prevent proper operation of the spark plug.

By the way, you didn't mention what fuel(s) the machine burns. And do you know why the fuel nozzle orifices are not the same size as before?

 

Good catch on the picture WTF, that has to be the issue with the plug not being allowed to fully retract from the combustor!!