Orifice Flanges Explained: Flow Measurement and ASME B16.36
Orifice Flanges Explained: Complete Guide to Flow Measurement
Published: April 10, 2026 | Category: Technical Guide
Introduction
If you’ve ever needed to measure flow in a pressurized piping system, chances are someone pointed you toward an orifice flange. These flanges are purpose-built for flow measurement, giving you clean access to differential pressure readings.
How an Orifice Flange Works
An orifice flange has tapped holes (pressure taps) drilled radially through the base, positioned on either side of a thin orifice plate. The orifice plate restricts flow, creating a measurable pressure differential that lets instrumentation calculate flow rate using Bernoulli’s equation.
Governing Standards
- ASME B16.36 – Orifice Flanges
- API 2530 / AGA Report No. 3 – Flow measurement
- ISO 5167 – International standard
Types of Orifice Flange Assemblies
Weld Neck (Most Common): Two flanges welded into pipeline with jack screws for plate removal.
Slip-On/Threaded: For lower-pressure applications (Class 150-300).
Pressure Tapping Locations
- Flange Taps: 1 inch from plate face (ASME B16.36, North America)
- Corner Taps: Adjacent to plate (ISO 5167, European)
- D and D/2 Taps: Pipe taps for special applications
Specifications
- Size Range: 1″ to 24″
- Pressure Classes: 300# to 2500# (no 150#)
- Materials: A105, F304/L, F316/L, LF2
- Tap Size: 1/2″, 3/4″, or 1″ NPT
- Key Feature: Jack screws for plate removal
When to Specify Orifice Flanges
- Custody transfer metering in oil/gas
- Refinery process control
- Boiler feedwater measurement
- Water/wastewater treatment
Common Mistakes to Avoid
- Wrong tap orientation (horizontal for liquids, top for gas)
- Forgetting jack screws
- Wrong tap size
- Incorrect beta ratio (should be 0.3-0.7)
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