The Versatile Application of 4-inch A105 B16.36 Carbon Steel Orifice Weld Neck Flange

An orifice flange is a weld neck flange made to hold an orifice plate for flow measurement. The A105 carbon steel version to ASME B16.36 adds jack screws and meter taps so the plate can be changed and the differential pressure read without breaking the line. For the sealing face, see our flange gaskets and flange products.

What an Orifice Flange Is

An orifice meter needs a thin plate with a bored hole set in the pipe; the drop in pressure across the plate gives the flow rate. The orifice flange is the weld neck flange built to carry that plate. A pair is used — one upstream, one downstream — with the plate trapped between them and the two flange faces spaced by the plate thickness. A105 is the standard forged carbon steel for the body, rated by ASME B16.5 pressure-temperature.

Built-In Features

• Jack screws — threaded holes that push the flanges apart to free the plate for service.
• Meter taps — drilled passages (usually corner taps) that carry the pressure signal to the transmitter.
• Weld neck hub — butt-welded to the pipe for a fatigue-resistant, full-bore joint.
• Plate retainer — a carrier ring that locates and protects the orifice plate.

Orifice Flange Versus Plain Weld Neck

Why It Works for Metering

The jack screws mean the plate is swapped during a turnaround without cutting the line, and the meter taps bring a clean differential-pressure signal straight to the transmitter. Because the flange is forged A105 with a full-penetration weld, the bore stays smooth so the flow profile the plate sees is stable and the reading stays repeatable.

Key Benefits

• Accurate, repeatable flow measurement from a stable bore.
• Plate change without cutting or realigning the pipe.
• Differential-pressure taps built into the flange, not added on site.
• Forged carbon steel body that matches the line rating.

Where They Are Used

Orifice flanges sit on custody-transfer and control lines in oil and gas, petrochemical, water, and steam service, wherever a differential-pressure meter sets the flow. The 4-inch size is common on process skids and station metering runs.

In the Joint

The flange pair is welded into the line; the gasket on each face seals the joint, while the flange bodies carry the line into the meter run. Bore the plate to the meter specification and keep the taps unobstructed for a true signal.

Installation and Care

Weld both flanges with qualified procedure, fit the orifice plate in its carrier between the faces with the correct gaskets, and torque evenly. Keep the meter taps clear of blockage and the jack screws lubricated so the plate can be freed at the next service. Verify the plate bore and orientation against the meter data sheet before the line goes live.

Frequently Asked Questions

Orifice flange or a meter run?

The orifice flange holds the plate; a meter run is the straight pipe upstream and downstream that the standard requires for an accurate reading. You need both.

Can I use a plain weld neck with a plate?

No — a plain WN has no jack screws, taps, or carrier, so the plate cannot be seated or read correctly. Use a B16.36 orifice flange pair.

Why A105 carbon steel?

A105 is the standard forged carbon steel for flanges; pick it where the line rating and corrosion margin allow, and step up to alloy or stainless for hotter or wetter service.