ASME B16.36

Covers — flanges modified for flow measurement:

• Sizes from NPS 1 to NPS 24.
• Pressure classes: 300, 400, 600, 900, 1500, and 2500.
• Flange types: Weld Neck, Slip-On, and Threaded.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Standard non-metering flanges → ASME B16.5.
• Class 150 orifice flanges (rarely used because they are too thin to accommodate the radial pressure taps properly).

B16.36 is identical to B16.5 in pressure ratings and basic dimensions, but adds metering features:

• Pressure Taps — requires radial holes drilled through the flange ring to connect instrumentation tubing.
• Jack Screws — mandates drilled and tapped holes for jack screws, allowing operators to mechanically spread the flanges apart to insert or remove the orifice plate without dismantling the piping.

Orifice flanges are the physical boundary between the primary piping process (B31.3) and the instrumentation system. The differential pressure measured across the orifice plate installed between these flanges provides a reliable calculation of flow rate.

The standard mostly aligns with B16.5, meaning an orifice flange will bolt perfectly to a standard B16.5 flange, but orifice flanges are almost always sold and installed as matched pairs.