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RTD + Thermowell Connection in Small Diameter Line
Which is the best way to connect an RTD thermowell in a 20mm OD pipe?

Hi,

I've an application which requires the use of an RTD to measure temperature.

Process medium is superheated steam at 300 degC and 40 bar. Steam velocity varies from 1 to 4 m/s. The pipe where the thermowell is to be connected has 19/20mm ID/OD.

Can you please suggest the best possible way to mount the thermowell?

Thanks in advance.

First of all I'm having trouble thinking the wall thickness is only 0.5mm at 40 bar, ignoring that.

The usual method of installing a thermowell in a small line is to have it orientated along rather than across, usually a tee with the process coming or leaving the branch. For that size you would have to increase the line size to accommodate the well. You should have a pipe spec and installation details to follow.

Consider using a bare 1/4" RTD strapped to the outside of the pipe then well insulated, this avoids the need to deal with high pressure, an inside out thermowell so to speak.

you need to get piping design or your shop involved. Typically increase
a section of line to 2" and install a tee mounted thermowell and sensor, then take the line size back to 1".


By the way you are dealing with condensate not superheated steam!

you need to get someone else involved, you are dealing with dangerous setup there.

I stand corrected, you are dealing with 50DegC superheat...

if you use the outside tube temperature, you can get a good reading if you insulate to reduce measurement error.

I agree you'll minimize the problems with an external measurement.