Flanges are forged or cast steel rings used to connect pipes, valves and pumps, forming a piping system that allows for easy cleaning, inspection or modification. They are attached via welding, threading or bolting, often using gaskets to ensure a tight seal. Key standards include ASME B16.5, with common types being weld neck, slip-on and blind. 

Key Types of Flanges:

Weld Neck Flange: Features a long-tapered hub designed for high-pressure and high-temperature applications.

Slip-On Flange: Slips over the pipe, allowing for easier alignment and lower cost.

Blind Flange: A solid disc with no bore used to blank off pipeline ends or openings.

Socket Weld Flange: Used for Small-Diameter, High-Pressure Piping.

Threaded Flange: Assembled without welding, suitable for specialised low-pressure applications.

Lap Joint Flange: Used with a stub end, ideal for systems requiring frequent dismantling. 

Flange Facing Types:

Raised Face (RF): Features a small raised section around the bore common for higher pressure applications.

Flat Face (FF): Used when mating materials are brittle.

Ring Type Joint (RTJ): Features a metal ring gasket to maintain a seal under high-pressure and high-temperature conditions.

Tongue & Groove (T&G): Self-aligning and provides a secure seal. 

Pressure-Temperature Ratings:

Flanges are classified by pressure-temperature ratings (ASME B16.5) and are commonly rated in pressure classes such as 150 lb, 300 lb, 600 lb, 900 lb, 1500 lb and 2500 lb.

Common Materials and Sizes:

Materials: Forged Carbon Steel (ASTM A105), Low-Alloy Steel (ASTM A350), Stainless Steel (ASTM A182) and Duplex Steel.

Sizes: Typically range from 1/2 inch to 24 inches (nominal pipe size).

Dimensions: Include the Pitch Circle Diameter (PCD), Bolt Size, Hub Diameter and Outer Diameter. 

Flange Marking:

Flanges are marked to identify their specifications, including: 

Nominal Size

Pressure Class

Material Grade

Manufacturer’s Mark

Batch Number