Overview
A weld neck orifice flange is a weld-neck flange arrangement with pressure-tap connections used with an orifice plate for differential-pressure measurement. ASME B16.36 is an important product standard for orifice flanges within its scope. The complete assembly includes two flanges, tap holes, plugs, gasket arrangement, bolting, and often jack screws or plate-handling features depending on the specified design.
The flange set must match the meter-run design, orifice plate, flow direction, tap orientation, pipe bore, class, material, and facing.
Why It Matters for Pipe Components
An ordinary weld-neck flange cannot be treated as an orifice flange by drilling unreviewed holes. Tap diameter, location, thread, orientation, and internal passage quality affect pressure measurement and leak integrity.
Bore mismatch, weld protrusion, roughness, or misalignment near the plate can disturb flow and measurement. Metering requirements can therefore be more restrictive than ordinary piping fit-up.
Plugs and tap connections are pressure-boundary items. Their material, thread, sealant, rating, accessibility, and protection should be specified.
Methods, Parameters, or Process
Coordinate piping, flange, instrumentation, and metering requirements in one datasheet.
| Parameter | Required decision | Inspection focus |
|---|---|---|
| Flange standard | ASME B16.36 or project design | Scope, dimensions, marking |
| Meter size/class | NPS/DN and class | Flange set and bolting |
| Bore and bevel | Pipe wall and meter-run bore | Internal transition and weld |
| Tap arrangement | Type, orientation, thread, plugs | Location, cleanliness, accessibility |
| Facing and plate | Face, gasket, plate thickness and bore | Assembly stack and sealing |
| Documentation | Drawing, material certificate, dimensional report | Configuration and traceability |
Supplier and Inspection Checklist
- Order the flanges as a matched set where required.
- Confirm flow direction and pressure-tap orientation.
- State tap thread, plug material, and sealing method.
- Verify bore and weld transition against the meter run.
- Inspect tap passages for burrs, blockage, and contamination.
- Check facing, plate, gasket, and stud-length compatibility.
- Maintain orientation marks through coating and packing.
- Protect taps with suitable plugs or caps.
- Use a controlled dimensional drawing for release.
Application to Pipe Fittings, Valves, and Flanges
Orifice flange sets are used in process, steam, gas, and liquid flow measurement. They connect the mechanical piping joint to impulse lines or transmitters. Installation must consider condensate, gas pockets, accessibility, heat tracing, and instrument isolation.
For severe service, the tap material, root valves, tubing, manifolds, and seals require the same pressure-temperature and compatibility review as the main line.
FAQ
Is an orifice flange the same as a standard weld neck flange?
No. It includes specified pressure-tap features and is coordinated with an orifice measurement assembly.
Which standard covers orifice flanges?
ASME B16.36 is an important standard within its defined scope. Confirm the project edition and meter specification.
Can taps be drilled after flange installation?
Only under an approved engineering and machining procedure. Uncontrolled drilling can damage the pressure boundary and measurement geometry.
Why should the pair be matched?
The two flanges, taps, faces, plate, gasket, and bolting must assemble with the intended geometry and orientation.
Is the orifice plate included with the flange?
It depends on the purchase scope. State plate material, thickness, bore, edge, tag, and certification separately.
Next Steps
Issue a meter-run or orifice-flange datasheet that defines size, class, bore, facing, taps, orientation, plugs, plate, gaskets, bolting, material, and inspection.
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