Large Diameter Plate Flat Welding Flange for Utility Piping

For large, low-pressure mains—water, air, ventilation—a full forged welding neck is often overkill. The large diameter plate flat welding flange (PL type) offers a simple, economical disc that welds to the pipe and carries modest pressure.

Zhantong produces big plate flanges to GB/T 9119 and equivalents. This article explains when this lightweight flange is the smart choice.

Plate Flange Design

A plate flange is a flat disc (no hub) with bolt holes, slipped over the pipe and fillet-welded. Its simplicity makes it cheap to produce in very large diameters where a forged WN would be costly.

The lack of a hub means lower fatigue resistance, so it is specified for low-pressure, non-cyclic duty.

Standards and Sizes

In China the common reference is GB/T 9119 (flat welding plate flange), with DIN 2576 and EN 1092 also used. Zhantong supplies diameters well beyond DN1000 with RF or FF faces.

Bolt circle and hole pattern follow the specified standard for interchangeability.

Materials and Faces

Plate flanges are usually carbon steel (Q235, A105) but stainless and low-alloy versions are available. Face type is RF or FF; for full-face gaskets FF is used to avoid bridge contact.

Surface finish and flatness are controlled so the gasket seats evenly across the large face.

Advantages and Limits

Benefits are low cost, easy large-diameter supply and simple alignment. Limits are lower pressure/temperature rating and reduced resistance to bending and vibration versus hubbed flanges.

They suit static, low-pressure networks rather than dynamic process lines.

Applications

Use in water supply and drainage, HVAC cooling loops, ventilation duct flanging, low-pressure air and utility headers. They are common at tank nozzles and building service entries.

For large water mains, plate flanges with full-face gaskets are a standard, economical joint.

Selection and Installation

Specify standard, diameter, pressure rating (PN), face type, material and number of bolt holes. Ensure the gasket covers the full face for FF, and use even bolt torque to avoid flange tilt and leakage.

Avoid in services with significant thermal movement or vibration.