Wheel Space thermocouples problems

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Thread Starter

Controman

Hi every control forum member

9E gas turbine with mark6e control system.:

I'm working on HGP for one of our gas turbines and before lifting the upper casing we removed all wheel space thermocouples (for upper and lower casing), but two of them was difficult to pull, so they was sheared.

I observed that for the last HGP (about 3 years), the same of one of them was shearing (it's the 2AO2).

Near these thermocouples there's a number and a name incised (for example: 3FO1 985).

Questions: What can be the reasons of this difficulty?
What are the numbers incised near every thermocouple? and if they mean the distance, it will be between what and what?

I read the last topic about these thermocouples but I didn't find this information (thread 1431791163#1431791163).

Best Regards
 
Controman,
Without being able to see how and where the T/Cs are separating, it's pretty difficult to say what the reason is for the damage. The guide tubes for the T/Cs are subjected to some very high temperatures, and if there are leaks of joints allowing hot combustion gases to impinge on the guide tubes that could result in some problems with removal.

Also, sometimes if the nozzle segments shift/rotate slightly during operation this can cause difficulty with insertion/removal. I think sometimes this is called "nozzle creep" and is more pronounced on some machines than others. Check with your service provider's engineer for more details about that.

If the rotor is removed, you should inspect the guide tubes to make sure they are not damaged and are properly aligned. Some guide tubes are made up of more than one section and they can be misaligned and or damaged by the wonderful, caring and sensitive mechanical workers performing the mechanical service on the turbine.

The stamped numbers on the casing near each wheelspace penetration should indicate the thermocouple placement, so your example 3FO1 would be Third Stage, Forward Outer Wheelspace T/C #1 (on the left side of the machine).

I've not seen any additional information stamped on the casings, but the Belfort Bunch are known for changing things. Your guess about the second group of stamped characters being the insertion depth/length is very good; have you measured any of the wheelspace T/Cs you've removed that were NOT damaged and compared the length to the second group of stamped numbers? Please write back to let us know what you find.
 
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