Sensing Temperature in buried pipe?

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Thread Starter

Tim Greif

I have a sludge recirculation line that's 6-feet below grade that I need to measure the temperature of its contents. I'm figuring on using a stainless thermowell into the top of the pipe and a stainless lagging extension (with union in middle) extending above the ground surface. The connector head will be accessible and I'll be using a spring loaded long RTD probe. Anybody see anything that might go wrong here?

It's either this or just bury the connector head near the pipe like a normal installation and paint the whole assembly with tar or something and hope I never have to dig it up.
 
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Paul Dackermann

Greetings:
In reviewing your question, I am not sure whether this new construction or a retro-fit. My reasons for mentioning this is focused on approach and options.
If the design is new, where is the manhole and or handhole arrangement?
How long is the pipe run? Is it feasible to acquire the temperature reading elsewhere?
Let us say for example: you have a 50' to 100' run from one building to another, or vessel to another. Is it possible to tap in at another point?
I do not believe you should have a great variance in temperature from origination to destination, suction to discharge. It may be worthwhile to consider an alternative.
Concerning you design thoughts. I would avoid outright burial and tar scenario. Could come back to haunt you.
I believe your initial thought is going down the right path. The placement of the union and as well the inclusion of the union in the design is an area of concern if it is not accessible or protected.
I will assume you are able to have a reasonable size handhole for securing the extension. With this said go with the union in the handhole.
Might want to consider a double pipe with a slip fit in the outer pipe for any shifting and settling issues. Hopefully you will have none.
Place a bushing and seal around the pipe at the entry to the handhole. If the handhole is deep enough you will have only 3 to 4' buried.
Send back with more info if necessary.
Good Luck!
Regards,
Paul
 
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I would think about the following issues. First be sure that you are locating the tip at the point you want to measure. If it is too close to the pipe wall, your measurement will be biased by the outside temperature.
Depending on the temperatures involved, over a period of time, water, by way of condensation, will start to eat away at the RTD and it will have to be replaced. Burying it won't help. Sometimes a dual element is used. One element is "stand by". It is also possible to fill the thermowell with oil to keep the moisture out. I'm assuming that the measurement is remote so
the implication is that you will need a transmitter at the head. My vote would be to keep it accessible.

Regards
Erich Mertz
[email protected]
 
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S. ELAVAZHAGAN.

Hi,
Well, What about RTD removal?? or replacement?

Even though you have provided Lagging , this will help as long as installed RTD functions well. But in both the cases When u need to replace or remove RTD I think you have to completely dig..... I think you have to go for RTD with lagging for 8 feet considering Rain water stagnation too. I never seen RTD with lagging of 8 feet. I would like to know Immersion length of RTD.

with best regards,
S. ELAVAZHAGAN.
Engineer - I & C.
TCE Consulting Engineers Ltd.
 
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Our sister company is a manufacturer of RTD's and thermocouples. You are on the right track with the spring loading of the RTD and the lagging. You can save yourself a lot of money on the lagging of the well if you just put a 1/2" stainless pipe extenstion up to above ground. I would make sure the tip of the thermowell is in the proper place for your temperature measurement in your sludge line. The spring loading of the RTD can be up at the above ground end of the 1/2" extension pipe using a unior or coupling. We have made RTD's over 20 feet long and there is no problem with the measurement. The temperature is sensed at the tip of the RTD and the rest of the length is just a holder and doesn't contribute to the temperature measurement, uless there is a fault in the wire. If you need any help, don't hesitate to contact me.

Regards,
Carl Causey
Thermotech USA, INC.
Flow-Temp, Inc.
 
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