When you need an orifice flange for flow measurement, the RFQ is not a standard flange request. ASME B16.36 defines the pressure-temperature ratings, materials, dimensions, tolerances, testing, and marking for flanges with orifice pressure-differential connections. But the standard leaves several critical details to the buyer's metering design. This guide gives EPC engineers, procurement managers, and inspectors a practical checklist to avoid costly mismatches.
Understand the ASME B16.36 Scope First
ASME B16.36 covers flanges similar to those in ASME B16.5 but with orifice pressure-differential connections. The standard explicitly limits coverage to:
- Welding neck flanges: Classes 300, 400, 600, 900, 1500, and 2500
- Slip-on and threaded flanges: Class 300 only
This means if your project requires a Class 600 slip-on orifice flange, it is outside the B16.36 scope. You would need to verify with the manufacturer whether they can supply a non-standard design, and you must define all requirements clearly in the RFQ. For welding neck types, the class range is broad, but you still need to confirm the exact class and facing.
