How to determine whether we should use a flange or threaded connection for Pressure transmitter??

[Nebu707]

How to determine whether we should use a flange or threaded connection for Pressure Gauge & transmitter?? Is there any rules, advantages, disadvantages that u can help me with???. thanks

 

[austsa]

Please give more information such as pressure, temperature, fluid, etc.

 

[LittleInch]

Normally gauges and transmitters come in 1/2 " size. I've not seen many 1/2" flanges used. My standard is to have a flanged isolation valve ,1" often with a 2" tee off the main line and a reducer for mechanical integrity, with a tapped blank flange. You can screw direct to a blank flange for many applications, especially at low pressure. Very high pressure or dangerous chemical may use socket welded connections.

As with many of these these sort of installation issues there may be guidelines, but in my experience a lot is based on company specs and requirements.

There have been some failures of screwed connections, especially when they have been cross threaded or use of too much ptfe tape and hence some companies ban or discourage screwed gauges.

With transmitters you need to consider the weight of the entire unit on a small connection and often it's better to mount them remotely and pipe to them.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Krausen]

My preference is to use flanged connections, especially in high pressure piping. Flanged connections tend to be more advantageous to operations (no ptfe/pipe dope thread sealant required, no cross threading issues, etc.). I know some of larger pipeline companies have conducted studies on their systems and found that threaded connections statistically are more likely to leak/fail (especially if located near vibration sources - pumps, custody meters, PCVs, etc.)

 

[moltenmetal]

Transmitters come with either NPT connections or 2-bolt instrument flanges or both.

Directly threading a transmitter to piping is not recommended, since you'll have to disconnect the wiring to tighten the threaded joint if it leaks. If you're going to use a union to provide that point of rotation, use the 2-bolt I flange instead.

Transmitters are limited in maximum service temperature to well within the limits of useful, reliable thread sealant compounds. Leakage should not be an issue. However, in some services, even tiny amounts of leakage are potentially catastrophic. In those cases, use the I flange- and weld the I flange to the piping, block valve etc.

Transmitters operating at temperatures above which the transmitter can handle are fitted with either impulse legs or diaphragm seals. Diaphragm seals are flanged to piping. Impulse legs can be made from pipe but are generally made from tubing with compression fittings.

 

[marty007]

Another important consideration in the interaction of thread sealants with the process fluid. In chlorine production for example, EVERYTHING must be grease-free, so flanged instruments are the way to go.

Check your process fluid.