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Thermocouple drilling/extraction

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
No I stole it from my neighbour Not all good ideas are yours :stirthepot::stirthepot:

Peter
I like the idea of adding a seal or o-ring. Never heard of that addition. And it is just some rubber so easy enough to drill out if it does not work. If you had to you could make one by shooting some silicone caulk into the hole and let it cure. Oil the metal first so it does not stick
You might look into "hot tapping" methods used for plumbing. Special tools and methods to drill into pressurized pipes. to add a connection.
BilLD
 

herthbn

Plastic
Joined
Jun 5, 2023
Peter has the best idea. I think he stole it from me. What PSI is this well sitting inside? If it is much the hydralic method should not do any harm to the well. If it does not work it will help lube any drilling.
Use a piece of welding rod to measure the depth to check if it is moving. You need to push it out far enough it moves out 8+ inches so you can grab it.
They make needle tips for grease guns. Solder on a 48" long piece of small copper tube to the needle. Use that to get the grease in deep.


Bill D
The well is actually inside of the steel turbine shell. It shouldn’t ever see any sort of pressure but if it was ever to come in contact with it, it would be 2400psi at 1000 deg F. steam. It’s a pretty thick walled thermowell so I don’t think I would have any concern to its integrity with this method.
 

EPAIII

Diamond
Joined
Nov 23, 2003
Location
Beaumont, TX, USA
Yes, damage to that SS tube is going to be your biggest problem. Whatever you use should have the best possible guidance. A gun drill (D bit) will have the largest area in contact with that tube and would be highly resistant to cutting sideways.

Do use a cutting OIL with good lubrication properties to prevent any galling. And pull the bit out of the hole often and clean off ALL the chips and re-lube it before inserting it again.

You need a plan and probably better information to detect and not drill past that reduction in diameter.

When you reach that point or slightly before it, you will need a smaller bit (1/4"?) with a full sized (1/2") shank, again for guidance. If this is a two piece assembly you can start with a short 1/4" gun drill, keeping the 1/2" shank close for good guidance while entering the size transition. Perhaps only 1/2 or 1/4" of the smaller bit being exposed. Then, as the drilling progresses and you enter the 1/4" bore, progressively longer bits can be used.

I am wondering how difficult it would be to just cut the existing tube out and weld in a new one. It may come to that in any case.



Get a gun drill of a diameter to fit the thermowell and use compressed air to blow out the chips. It'll need a carbide tip (most have that as standard) because the thermocouple insulators will be ceramic, not epoxy. The station workshop, or an outside supplier will need to make the air feed fitting and adaptor to whatever drill motor you use.
The gun drill will be self piloting and shouldn't damage the thermowell, but it'll need feeding gently so it doesn't grab on the sheath/insulator/wire nonhomogeneous mixture.

Spent 7 years putting thermocouples into thermowells as part of the job when doing power station turbine performance tests, but luckily didn't get one stuck :)
 

herthbn

Plastic
Joined
Jun 5, 2023
Yes, damage to that SS tube is going to be your biggest problem. Whatever you use should have the best possible guidance. A gun drill (D bit) will have the largest area in contact with that tube and would be highly resistant to cutting sideways.

Do use a cutting OIL with good lubrication properties to prevent any galling. And pull the bit out of the hole often and clean off ALL the chips and re-lube it before inserting it again.

You need a plan and probably better information to detect and not drill past that reduction in diameter.

When you reach that point or slightly before it, you will need a smaller bit (1/4"?) with a full sized (1/2") shank, again for guidance. If this is a two piece assembly you can start with a short 1/4" gun drill, keeping the 1/2" shank close for good guidance while entering the size transition. Perhaps only 1/2 or 1/4" of the smaller bit being exposed. Then, as the drilling progresses and you enter the 1/4" bore, progressively longer bits can be used.

I am wondering how difficult it would be to just cut the existing tube out and weld in a new one. It may come to that in any case.
Tomorrow will tell how accessible this thing is really going to be. If it’s a straight shot in, I plan to do just like you mentioned above if I go the drill route. My first attack will be trying to put a sleeve over the probe and try the hydraulic method like mentioned before. That will be the least damaging. If that doesn’t work, the final attempt will be drilling.

There is no way to replace this thermowell without complete turbine disassembly. Then it’s a huge chore to replace it after disassembly. That option will NEVER take place considering we literally just did a full turbine overhaul one month ago. We were already reassembled when this probe broke. If this extraction doesn’t work, we basically will have to fly blind without this temperature measurement. People won’t like it but it’s about all we will have left.
 

jim rozen

Diamond
Joined
Feb 26, 2004
Location
peekskill, NY
The only thing harder to get out of there, aside from a busted thermocouple, is a busted off carbide drill in there. If the item in the center shifts a bit the drill could fetch up and grab in there.
 

tdmidget

Diamond
Joined
Aug 13, 2005
Location
Tucson AZ
The only thing harder to get out of there, aside from a busted thermocouple, is a busted off carbide drill in there. If the item in the center shifts a bit the drill could fetch up and grab in there.
No way it should take 45 days to open that H.P. for just that. What is the output of this unit? Who built it? How old?
 

herthbn

Plastic
Joined
Jun 5, 2023
No way it should take 45 days to open that H.P. for just that. What is the output of this unit? Who built it? How old?
It’s a GE 550mw coal unit built in the early 70’s. We just got done with an overhaul on it where we had to pull the rotor and replace a row of blades. That outage was 44 days. If we ran into no issues pulling the lower half of the inner shell where this thermocouple is located, it would take no less than 3 weeks, and that would be pushing it. But a project like that would cost a substantial amount of money. So much so that we would formulate a plan to run without this temperature indication. Given we only have four more years of run time left before the unit is retired, we won’t be getting many more big projects with spending approved.
 

tdmidget

Diamond
Joined
Aug 13, 2005
Location
Tucson AZ
It’s a GE 550mw coal unit built in the early 70’s. We just got done with an overhaul on it where we had to pull the rotor and replace a row of blades. That outage was 44 days. If we ran into no issues pulling the lower half of the inner shell where this thermocouple is located, it would take no less than 3 weeks, and that would be pushing it. But a project like that would cost a substantial amount of money. So much so that we would formulate a plan to run without this temperature indication. Given we only have four more years of run time left before the unit is retired, we won’t be getting many more big projects with spending approved.
So you are doing this in house, that is, not APM or Siemens or other contractor? Do you have the replacement thermocouple?
 
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herthbn

Plastic
Joined
Jun 5, 2023
Yes. We are doing this in house with some local millwrights. I have the spare probe ready to go ones it’s clear. We found out today that the spare well thst is right next to this one also has a broken probe in it, but it looks like it’s been there for many many years.
 

tdmidget

Diamond
Joined
Aug 13, 2005
Location
Tucson AZ
Yes. We are doing this in house with some local millwrights. I have the spare probe ready to go ones it’s clear. We found out today that the spare well thst is right next to this one also has a broken probe in it, but it looks like it’s been there for many many years.
I'm thinking just weld in another thermowell, maybe upstream. I would get an engineer to spec that. Could you post a pic of the thermocouple?
 
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herthbn

Plastic
Joined
Jun 5, 2023
Easier said than done. That would require some really serious engineering from GE for proper placement. They arent always the easiest group to get ahold of, let alone thier engineering department. It’s not as simple as moving it in a pipe. It would need extreme precision to place it directly where it needs to go without going too far and puncturing into the flow path.

The t/c is quite literally 1/4” o.d. By 47.4” long with 4 wires hanging out the end.
 

NRDock

Cast Iron
Joined
Jan 24, 2015
Location
Central Pennsylvania
We found out today that the spare well thst is right next to this one also has a broken probe in it, but it looks like it’s been there for many many years.
So, the designer had a good plan and cheap lazy maintenance ignored the fucked spare till the last option was also fucked. I have no advice or sympathy.
 

tdmidget

Diamond
Joined
Aug 13, 2005
Location
Tucson AZ
NR, I wouldn't go that far. There's a story here but I don't know what it is. I do know that GE is on the rocks. Scumbag Jack Welsh turned a great American manufacturing company into a finance company and used the service arm to sell it. When the finance shit went South those losing service contracts were a liability. If GE isn't making a shit ton of money off you now they do not want to hear from you. Relocating the thermowell MUST be engineered and done well. It does seem strange that this has happened twice. The first time some one should have demanded to know why.
 

herthbn

Plastic
Joined
Jun 5, 2023
NR, I wouldn't go that far. There's a story here but I don't know what it is. I do know that GE is on the rocks. Scumbag Jack Welsh turned a great American manufacturing company into a finance company and used the service arm to sell it. When the finance shit went South those losing service contracts were a liability. If GE isn't making a shit ton of money off you now they do not want to hear from you. Relocating the thermowell MUST be engineered and done well. It does seem strange that this has happened twice. The first time some one should have demanded to know why.


The designer had a good idea up until the junction box location and insertion point. Nothing is maintenance friendly about these. These things are mounted on the under side of the turbine shell 30’ in the air, the wells are straight inside of the turbine shell (or at least I think they are) but the insertion point where the junction box mounts to are welded in at an angle. So that means these probes start off straight for the first 11”, then they need to get past a 15-20 deg bend before finally going straight for another 36” to its final end point. Looking at these, it’s makes complete sense why they just break off when trying to perform maintenance on them. And that’s exactly how we broke this one, doing our due diligence and performing maintenance.

I would understand if everything stayed cold or a consistent temperature, these probes would definitely come out easier. But when we are cycling these units and having so many thermal changes, things move and don’t go back where they were when they started. I mean we are taking these from ambient temperatures all the way up to 1005 deg., then a week later back to ambient. My point is, these are not maintenance friendly.
 

NRDock

Cast Iron
Joined
Jan 24, 2015
Location
Central Pennsylvania
All I can suggest here is fix per OEM design unless you can prove a change is better.
In general, I suggest a significant interviewing skill is determining where a company is in the bonus/fucked cycle.
 

EmGo

Diamond
Joined
Apr 14, 2018
Location
Over the River and Through the Woods
The designer had a good idea up until the junction box location and insertion point. Nothing is maintenance friendly about these.

Not to be mean or anything but when the subject of the spare came up, the remark "we just finished a rebuild" popped into my mind.

Sure, the #1 was trashed years ago and you guys can be excused for not knowing about it ... but it wasn't detected during a rebuild ? You don't do an inspection ? Wouldn't it have been a lot easier to extract the broken one when the whole unit was undergoing maintenance ?
 

herthbn

Plastic
Joined
Jun 5, 2023
Not to be mean or anything but when the subject of the spare came up, the remark "we just finished a rebuild" popped into my mind.

Sure, the #1 was trashed years ago and you guys can be excused for not knowing about it ... but it wasn't detected during a rebuild ? You don't do an inspection ? Wouldn't it have been a lot easier to extract the broken one when the whole unit was undergoing maintenance ?
You are most definitely correct in saying it would have been easier to extract the broken spare. With one exception, we didn’t know the spare slot had a broken probe in it prior to the start of the outage. We have had such a large turnover in plant personnel in the last 5-10 years that any one who might have known it was broken would have retired many years ago. The knowledge and history of these units is gone.

Had we known it was broken before we started and had we broken the active one before reassembly was underway, we would have definitely gone after replacing both. But at the time, we had no reason to go any further into the turbine disassembly where these are located so we stopped with our proposed work scope. These aren’t on a normal inspection list either.
 
Joined
Apr 19, 2006
Location
Manchester, England
You are most definitely correct in saying it would have been easier to extract the broken spare. With one exception, we didn’t know the spare slot had a broken probe in it prior to the start of the outage. We have had such a large turnover in plant personnel in the last 5-10 years that any one who might have known it was broken would have retired many years ago. The knowledge and history of these units is gone.

Had we known it was broken before we started and had we broken the active one before reassembly was underway, we would have definitely gone after replacing both. But at the time, we had no reason to go any further into the turbine disassembly where these are located so we stopped with our proposed work scope. These aren’t on a normal inspection list either.
You have my sympathy. When the music stopped you’ve been left holding the baby. Just don’t do anything rash.

Regards Tyrone
 








 
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