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A Note On Orifice Flanges – ASME/ANSI B16.36

A Note On Orifice Unions - ASMEANSI B16.36

Orifice Flanges are primarily used for measuring the flow rate of liquids or gases in a pipeline. Pairs of pressure taps, mostly on 2 sides and directly opposite from each other, are machined into the orifice flange. Additional instrumentation can be provided as required by your application.

Orifice Flanges generally can come with Raised Faces or Ring Type Joint (known commonly as RTJ) facings. Structurally they are very similar to standard B16.5 weld neck, slip-on, and threaded flanges with some extra machining.

A set of two Orifice Flanges is often called an Orifice Set Union or an Orifice Pair, and an Orifice Plate (the type of orifice plate will differ based on the needs of the project) is mounted between both flanges.

A jack screw is machined and installed as well. This jack screw is used to facilitate separating the flanges for inspection or replacement of the Orifice Plate and gaskets.

When installing the orifice plate flange the pressure taps need to be at the same elevation. The assumption when making the calculation for the orifice plate is that the pressure head of the tubes is the exact same on each side of the orifice plate.

Pressure taps should not be installed facing down as it creates the risk of the taps becoming plugged with debris.

As a reminder, orifice unions begin at the 300# class and increase from there. We have had several previous requests for orifice flanges in the 150# pressure class, and we have to offer the 300# class or greater as an alternative.

The reason for this is 1) ASME has not provided dimensions for a 150# orifice set under B16.36 specifications and 2) the aforementioned is so because 150# class flanges are generally not thick enough at the base of the flange to provide you with the material necessary to drill and tap your desired instrumentation for your application.

If you have any further questions about Orifice Flanges, Orifice Set Unions, or Orifice Plates feel free to call or e-mail Texas Flange at 281-484-8325 or [email protected].

Don’t forget to check out our other free online resources!

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