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I am going through a PID in which the line size was increased from 2 inch to 4 inch for temperature measurement and then decreased to 2 inch using two reduces. What is the need for reducers before temperature measurement?

Navinmm
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  • There shouldn't be any need. What kind of sensor was used? External or internal probe? A constriction might be used to create a pressure differential for flow measurement. – Transistor Oct 04 '22 at 06:18
  • Two reducers? a taper is usually better with available space. – Solar Mike Oct 04 '22 at 06:50
  • @SolarMike found this online https://www.pipingengineer.org/process-instrumentation-temperature-measurement/#:~:text=Minimum%20pipe%20size%20usually%20required%20is%204%E2%80%B3.%20If%20pipe%20is%20of%20smaller%20size%2C%20it%20is%20locally%20increased%20to%204%E2%80%B3%20NPD%20with%20the%20use%20of%20two%20reducers. – Navinmm Oct 04 '22 at 07:01

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You do not need larger pipes to measure fluid temperatures.

The linked article from your question comments wants a larger diameter to fit "standard" attachment methods. You can't drill a 1 inch hole into a 1 inch pipe, but a T would work fine. You can get into whether or not a thermo well is required. The learning here is don't just trust randomly sourced information about engineering on the internet. I promise you can measure temperature in a 2 inch pipe without making the pipe bigger, and that you can increase the diameter of a pipe with or without multiple reducers.

Maybe the article was written by a pipefitter instead of a welder so they only think in terms of reducers. Maybe your site had a supply of thermo wells and needed to use them, or maybe the fluid requires it. Maybe your original installer and designer was working cost-plus. Certainly why engineers did things the way they did in the past has baffled most of us at one time or another. Looking at the pipe instead of the diagram might help (remember that the map is not the territory).

https://www.bapihvac.com/application_note/using-thermowells-in-small-pipes/

Tiger Guy
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  • Thanks for your answer. Just curious to know if thermowell are not an option and an internal temperature probe is required, then should be pipe diameter be increased to minimum 4 inch. And if so what is the reason? – Navinmm Oct 07 '22 at 06:23
  • @Navinmm the only reason to increase pipe diameter is to be able to weld a thermowell to it. – Tiger Guy Oct 07 '22 at 13:43