I want to reduce temperature with impulse pipe (filled with process medium). For example I must reduce 1000 degree C to 400 degree C (medium is steam).

Which length and size of pipe reduce temperature and how many times? Have any diagram with it?

 

Impulse tubing for steam is generally filled with water from a condensate pot. The water isolates the instrument from the steam. Instrument is mounted below the steam line.

Rosemount has an app note showing direct mounting a DP transmitter on a coplanar manifold on a steam line. link here:
http://www.control.com/thread/1320456352

Discussion of thermal cooling of impulse lines here:
http://www.control.com/thread/1240831095#1240921577

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