What is the benefit of FNI and what will trigger FNI?

What is the benefit of Fuel Nozzle Inspection and what will trigger fuel nozzle inspection?
Is there the need to do combustion inspection before fuel nozzle inspection or it could be combined

I can only answer this question specifically for GE-design heavy duty gas turbines and generally for other gas turbines that use exhaust gas temperature sensors to monitor for combustion problems. Fuel nozzle inspections are warranted when there are higher than normal exhaust gas temperature spreads, which are quite often the result of worn, plugged (choked) or damaged fuel nozzles. A fuel nozzle inspection can find or eliminate fuel nozzle issued as a cause of the high exhaust temperature spreads (which can be caused by many other issues which require much more disassembly and inspection). While the fuel nozzles are removed, though, a visual and/or borescope inspection of combustion liners and transition pieces and first stage nozzles can also be performed to find other issues which may be possible to see with the fuel nozzles removed.

Fuel nozzle inspections and rebuilds are almost done when combustion inspections are done--at least a visual inspection of the outside of the fuel nozzles if not a disassembly and reassembly.

The type of fuel and the condition of the fuel (contaminants which may not be caught or removed by strainers or filters used at the site (including gas compressor lubricating/seal oil) need to be taken into account when deciding to perform a fuel nozzle inspection between or before another mechanical inspection such as a combustion inspection.

This really isn't a controls-related question, but we do--from time to time--answer or make comments on non controls-related questions.

Hope this helps!
Gas Turbine combustion systems are sensitive to Fuel Flow variations from Fuel Nozzle to Fuel Nozzle and combustion chamber to chamber.
Unbalanced fuel flow causes variations in emissions, dynamics, exhaust temperatures and combustor metal temperatures.
Therefore, it is very important that the Fuel nozzle Assembly has to be periodically inspected, cleaned, checked and Tested.
As a requirement of a maintenance inspection, fuel nozzle refurbishment is a mandatory requirement and should be scheduled and performed at an experienced Service Centre who knows the "OEM Defined" flow mean values and its allowed flow tolerances.
Clients opting to do the cleaning of fuel nozzles manually at site and deciding not to send to a specialized and experienced service centre, invites more risks of damaging expensive and critical HGP components.
Periodic & meticulous Clean, Check, Test & Calibration of Fuel Nozzles and its related accessories in the fuel system compartment is of paramount importance during each scheduled Inspections.

Jais John
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