Temp. Transmitter Head Residue
Temp. Transmitter Head Residue
(OP)
Hello All,
I'm not 100% sure this is the right forum to post this, but it seems like the best place to start.
I'm on-site commissioning a boiler and I have a number of thermocouples/transmitters throughout the unit and piping. Two of these are installed on the bottom of two different outlet pipes - so that the head is directly below the probe. These two pipe circuits are completely independent.
So far we've only commissioned one of these circuits in the boiler, and only one of these TT's is in service. This TT is providing curious data, so today I went to check the wiring in the head and it had quite a bit of white residue build-up or "gunk" inside it. This residue is like a grainy, white paste. It is on the cover, and the wires not being used. I've never seen this before, so, I checked a few other TT's on the same circuit nearby and there was no evidence in any of them of any of this white residue. They were all clean.
Then I decided to check the other TT that is in the bottom of the other circuit, and it had the same build-up. This time some water even dropped out. IT was a small amount, probably just enough to fill the cover, but it definitely caught me by surprise.
Can anyone tell me what this is? I have never seen this build-up up before and I asked the (new) controls tech on-site and he has never seen it before either. The build-up is not on the transmitter part itself.
Thanks in advance for any feedback.
I'm not 100% sure this is the right forum to post this, but it seems like the best place to start.
I'm on-site commissioning a boiler and I have a number of thermocouples/transmitters throughout the unit and piping. Two of these are installed on the bottom of two different outlet pipes - so that the head is directly below the probe. These two pipe circuits are completely independent.
So far we've only commissioned one of these circuits in the boiler, and only one of these TT's is in service. This TT is providing curious data, so today I went to check the wiring in the head and it had quite a bit of white residue build-up or "gunk" inside it. This residue is like a grainy, white paste. It is on the cover, and the wires not being used. I've never seen this before, so, I checked a few other TT's on the same circuit nearby and there was no evidence in any of them of any of this white residue. They were all clean.
Then I decided to check the other TT that is in the bottom of the other circuit, and it had the same build-up. This time some water even dropped out. IT was a small amount, probably just enough to fill the cover, but it definitely caught me by surprise.
Can anyone tell me what this is? I have never seen this build-up up before and I asked the (new) controls tech on-site and he has never seen it before either. The build-up is not on the transmitter part itself.
Thanks in advance for any feedback.





RE: Temp. Transmitter Head Residue
If the insertion is "upside down", then gravity will pull any residual thermal paste down along the thermocouple sheath and it could accumulating in the head?
The water is a real concern.
There's always the possibility of condensed humidity, but I would think that the ambient temperatures in a boiler room are not likely to drop below ambient dewpoint, but could that be the case somehow? Some source of cold air hitting the head and condensing air humidity?
The other option is a leak. I can't ever recall a thermowell leaking internally, but on occasion a threaded thermowell doesn't get tightened and will leak at the threads, and this is a commissioning, could that might be the case? Being upside-down, the cover/cap on the T/C head might catch any leakage depending on the style of the head and let it collect.
And I have seen installations where the T/C was held into a pipe by a threaded compression fitting which could leak.
RE: Temp. Transmitter Head Residue
In terms of water, I'm not really sure where it came from. I think if it was a leak through the TW there would have been more of it. This seemed like the cap had somehow just filled up and it dumped out when it was inverted.
This unit is outside and it is currently extremely hot outside, but when the units were wired it was cooler.
RE: Temp. Transmitter Head Residue
Pamela K. Quillin, P.E.
Quillin Engineering, LLC
RE: Temp. Transmitter Head Residue
But spring loaded assemblies are loosey-goosey because the element sheath has be able to be moved by the spring.
The space at the top of the well and bottom of head (upright orientation) is common to both components. The head would only be sealed from the well if the element sheath were brazed to the bushing. Thermal goop could easily move from the well to head in a spring loaded assembly.
RE: Temp. Transmitter Head Residue
Pamela K. Quillin, P.E.
Quillin Engineering, LLC
RE: Temp. Transmitter Head Residue
Nothing wrong with your reading; spring-loading wasn't mentioned.
I'm just assuming spring loaded because that means the well is 'open' to the head and spring loaded assemblies are commonly used with thermowells.
RE: Temp. Transmitter Head Residue
It is indeed spring loaded. I have some pictures too which I will upload tomorrow. The TT is working alright, but I'm still curiuos to what gunk is.
Thanks for all the feedback so far.
RE: Temp. Transmitter Head Residue
Please see attached photos of the heads in question. Like I said, they both work, but I'm curious about what this stuff is.
Cheers
RE: Temp. Transmitter Head Residue
Please see the other photo in this posting.
I think they're pretty self explanatory, but let me know if you have any questions.
RE: Temp. Transmitter Head Residue
Note what Omega says about their thermal paste:
in their spec sheet here:
www.omega.com/manuals/manualpdf/m0066.pdf
It appears that the installer came from the school of "if a little bit is good, lots is better".
Although The spec sheet omits mention of vertical 'upright', I suspect that's what they mean and they're aware of the effects of process heat and gravity on the paste and where it ends up in horizontal or upside down vertical installations. I think the stuff is thermal goop and just requires paper towel clean-up.
Could the "water" you mentioned be the oil base from the thermal compound? I doubt that there are water based compounds given the use of thermowells at elevated temperatures.
If it was real water, that's still an issue.
RE: Temp. Transmitter Head Residue
I checked the one that dumped the water today after running yesterday and there was no water in it. I don't think it could be from the steam itself. Must have got in there during installation, whether it was water, or the oil base of thermal compound.
RE: Temp. Transmitter Head Residue
RE: Temp. Transmitter Head Residue
RE: Temp. Transmitter Head Residue
beyond that the material you describe is similar to the soap used to pull wire and cables in long runs