thermocouple & thermowell configurations

[someguy79]

Can someone provide some examples of reliable and accurate thermocouple and thermowell configurations applied to piping? I am most interested in the mechanical layout and sizing as opposed to the interaction of the sensor and electronics.

I am aiming to minimize heat leak to the process fluid (LNG in this case) and to decrease thermal resistance between the sensor and process fluid. One requirement that makes this difficult is the need for serviceable sensors. Currently T-type 1/4" DIA insertion probes are being used in thermowells similar to those on the site listed below.

http://www.omega.com/pptst/SERIES_260W.html

http://www.omega.com/pptst/NB1-ICIN_INDUST_TC.html

In the extreme case of improved performance, a bare sensor could be put in the process stream, but that would be very risky. (reliability, serviceability, damage to downstream equip if it fails, etc.)

 

[dcasto]

I've thought about skin temperature probes epoxied to line and then armoured wire out through the insulation. I've done this with pipelines where there can be not thermowells.

 

[EdStainless]

For good response you need a few things.
You can make a thermowell that has a high TC material as the plug (tip) (Cu or brass) and lower TC material for the body (SS).
You can also use a bare element thermocouple in it. I have even used ones that were spring loaded to maintain contact. Use as thin of wire as practical.
You can take it one more step and put a small amount of Mg oxide slurry in the bottom of the thermowell. This will further improve response.

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