We have a gas turbine of 127 MW (GE) frame 9E. The GT has conventional combustors and can run on both Gas and HSD. All the parameters including spreads were normal before the planned outage. During last CI, major Liner damage was observed with complete cap cowl assembly damage. Fuel Nozzles locking strips melting and erosion on fuel tip was also discovered upon disassembly. The OEM had changed the part number of these fuel nozzles. The minor update by OEM was due to change in dimensions of C-seal and C-seal groove. The new C-seal thickness and height was increased. The Recess depth and ID of C-seal grove was also increased. The question is, can this update in design of C-seal lead to the damage that was reported down in liners or has any one experienced same type of damage at their plants due to any other issue. moreover, is anyone using such fuel nozzles in which OEM had changed the C-seal design and what is their experience with respect to that.
Furthermore, also please share that how much is the probability of Liners damage in case if there is leakage from the Fuel Nozzles C-seal.

 

@ALesix,

This topic of this thread is a little off-topic for a controls-related forum.

You might get some anectodal information from people who have implemented the new fuel nozzles, but the likelihood of getting answers to your other questions is low. (I hope I'm wrong, though!)

Did you find this damage on all fourteen liners/fuel nozzles/caps & cowls?

You also didn't say if the machine runs primarily on natural gas or HSD. It does sound as though there was some kind of fuel leaking from nozzle threaded connections, but without photos it's impossible to say with any degree of certainty. Is it possible that the fuel nozzles were not properly assembled (torque specifications followed; crimps seals/strips)?

I have seen some damage like you seem to be describing but in one instance it was because the fuel purge systems weren't working correctly, and in another instance the proper seals (thickness) weren't used and torque specifications weren't followed/documented. Or the increased dimensions of the seals caused them not to fit properly in the grooves?

Was there any increase in exhaust temperature spreads on either fuel?

If there was extensive damage to the cap and cowl it would seem like there was fuel flowing where it shouldn't have been, and in turn that could have caused a mis-shapen flame ball inside the combustor to impinge on the liner. But the lack of high spreads is unusual for this type of problem.

And, this is most likely not the result of a turbine control system problem.

 

The damage was found on all 14 liners and cap & cowls.
The machine primarily runs on Natural gas.
The FNs flow inspection was carried out by conducting the air flow test.

1. 04 FNs passed the flow test & no leakage was observed
2. 05 FNs passed the flow test, however, leakage was observed from bolts
3. 05 FNs failed to pass the flow test as well as leakage was observed from bolts

There was no increase in exhaust temperature spreads observed during operations before CI.
We are also skeptical about the exhaust spreads not going high as upon CI, the damage was a surprise. Not to mention that after CI was completed with refurbished parts, GT did trip once on high exhaust spread and combustion trouble alarm during startup.