Orifice Flanges are used with orifice meters for the purpose of measuring the flow rate of either liquids or gases in the respective pipeline. Pairs of pressure "Tappings", mostly on 2 sides, directly opposite each other, are machined into the orifice flange. This makes separate orifice carriers or tappings in the pipe wall unnecessary.
Orifice Flanges generally come with either Raised Faces or RTJ (Ring Type Joint) facings. They are, for all intensive purposes, the same as weld neck and slip-on flanges with extra machining.
The image on the right shows a set Orifice Flanges, where a Orifice Plate is mounted and a jack screw is machined. This jack screw is used to facilitate separating the flanges for inspection or replacement of the Orifice Plate and gaskets.
The range of orifice flanges covers all standard sizes and ranges, and all common flange materials. Flanges are available in Welding Neck, Slip On, and Threaded form, and are typically supplied with two 1/2" NPT tappings in each flange.
The American National Pipe Thread Tapered
NPT is the best known and most widely used connection where the pipe thread provides both the mechanical joint and the hydraulic seal. NPT has a tapered male and female thread which seals with Teflon® tape or jointing compound.
ASME B1.20.1 covers dimensions and gaging of NPT pipe threads for general purpose applications.
ASME B16.36 covers Dimensions and dimensional tolerances from orifice flanges (similar to those covered in ASME B16.5) that have orifice pressure differential connections. Coverage is limited to the following flanges:
- Welding Neck Classes 300, 400, 600, 900, 1500, 2500
- Slip On Class 300
- Threaded Class 300