Orifice flanges are used in conjunction with orifice meters to measure the flow of liquids or gases in the respective pipeline. Paired “pressure taps” are incorporated into the orifice flange, usually on 2 sides, directly opposite each other. This makes separate orifice supports or tapping points in the pipe wall superfluous.

Orifice flanges are usually supplied with either raised faces or RTJ (Ring Type Joint) faces. They are in all respects the same as weld neck flanges and slip-on flanges with additional machining.

The illustration on the right shows a series of orifice flanges with an orifice plate attached and a jack screw machined. This jack screw is used to facilitate the separation of the flanges for inspection or replacement of the orifice and gaskets.

The range of orifice flanges covers all standard sizes and ranges as well as all common flange materials. The flanges are available as weld neck flanges, slip-on flanges and threaded flanges and are generally supplied with 2 1/2″ NPT connections in each flange.

The American National Pipe Thread Tapered

NPT is the best known and most commonly used connection where the pipe thread provides both the mechanical connection and the hydraulic seal. NPT has a tapered male and female thread that is sealed with Teflon® tape or a sealant.

ASME B1.20.1 covers the dimensions and sizing of NPT pipe threads for general applications.

ASME B16.36 covers the dimensions and dimensional tolerances of orifice flanges (similar to those coated in ASME B16.5) with orifice differential pressure ports. The scope is limited to the following flanges:

• Welding Neck Classes 300, 400, 600, 900, 1500, 2500
• Slip-On Class 300
• Threaded Class 300