 Orifice Flange Unions
Orifice Flange Unions (OFU) contain a differential producing Paddle Type Orifice Plate
(PTOP sold separately) within. On either side of the orifice plate are tap holes drilled
into the orifice flanges which measure the difference between the upstream and downstream
pressure. Depending upon the style of orifice plate used, Orifice Flange Unions (OFU) come in two different facings:
Raised Face and Ring Type Joint and come in several different connection styles:
- Weld Neck - Raised Face Weld Neck Orifice Flange Unions are sold as pairs in the flange ratings listed above.
For an ASME compliant dimensional chart of each flange rating, click the corresponding rating above.
Weld Neck flanges have a tapered hub, providing extra reinforcement and resistance to dishing.
The tapered hub provides a smooth transition from flange thickness to pipe-wall thinkness and endures
well under conditions of bending and expansion. Welding neck flanges are recommended for every severe
service condition both externally (temperatures) and internally (loading conditions).
In particular, welding neck orifice flanges are recommended for handling explosive,
flammable or costly liquids. The strength of a welding neck orifice flange equals the strength of a
butt-welded joint between pipes.
- Slip-On - Many believe that Raised Face Slip-On flanges cut corners on cost, and in certain applications this may be true;
they have an initial lower cost and are easier to assemble. However, their calculated strength is two-thirds that of
weld neck flanges and their life one-third. The flanges slip over each adjoining pipe length and are welded to the O.D.
of the pipe.
- Threaded - Threaded orifice flanges provide the ability to assemble a flow metering section without welding.
In high pressure applications at atmospheric temperatures threaded flanges are best suited where alloy steel is
needed for strength and where post-weld heat treatment is impractical.
- Socket-Weld - Socket-Weld Orifice flange unions are only available in sizes 4" and under.
Note: Ring-type joint orifice flanges are most common in weld-neck style.
RTJ orifice flange unions are for high pressure applications. Even though it is not generally recommended, RTJ orifice flanges can
be made in the different styles listed above in the raised face section.
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