What Is a Weld Neck Flange?

A Weld Neck Flange (WN flange) is designed with a long tapered hub that provides reinforcement and smooth stress transition to the pipe. The neck helps reduce stress concentration at the flange base, making it ideal for high-pressure, high-temperature and low-temperature applications.

Weld neck flanges are commonly used in critical pipeline systems where the pressure rating exceeds PN 2.5 MPa or where severe operating conditions require maximum strength and reliability.

They are widely applied in oil & gas, petrochemical, power plant and industrial piping systems.

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Our Supply Range

Materials

• Carbon Steel

• Stainless Steel

• Alloy Steel

Material Grades

• ASTM A105 / A105N

• ASTM A182 F11, F22

• ASTM A182 F304 / F304L

• ASTM A182 F316 / F316L

Size Range

• 1/2” to 24” standard

• Customized production up to 48”

Wall Thickness

• SCH 10(S) to SCH 160

Pressure Ratings

• Class 150 to Class 2500

Face Types

• RF (Raised Face)

• RTJ (Ring Type Joint)

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Types of Weld Neck Flanges

1. Standard Weld Neck Flange

Designed with a tapered hub that matches the pipe wall thickness, providing smooth flow transition and high mechanical strength.

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2. Reducing Weld Neck Flange

A reducing weld neck flange combines the function of a reducer and a flange. It allows direct welding to smaller diameter pipes, eliminating the need for a separate reducer fitting.

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3. Long Weld Neck Flange (LWN)

Also called Long Welding Neck Flange, this type has an extended hub that resembles a pipe section. It is commonly used as a nozzle connection in pressure vessels, columns and barrels.

Available options:

• Standard thickness LWN

• Heavy LWN flange (thicker wall for higher pressure service)

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Face Types

Raised Face (RF)

Raised Face weld neck flanges feature a small raised portion around the bore where the gasket is seated.

Raised face height:

• Class 150 & 300 → 1/16”

• Class 400 and above → 1/4”

RF flanges are widely used in medium to high pressure applications.

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Ring Type Joint (RTJ)

RTJ weld neck flanges have a precision-machined groove designed to hold a metal ring gasket.

This type provides superior sealing performance and is suitable for:

• High pressure systems

• High temperature services

• Oil & gas transmission pipelines

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Standards for Weld Neck Flanges

Material Standards

• ASTM A105 / A105N (Carbon Steel)

• ASTM A182 F11 / F22 (Alloy Steel)

• ASTM A182 F304 / F316 (Stainless Steel)

Manufacturing Standards

• ASME B16.5

• ASME B16.47

• BS 3293

• DIN 2630 – 2635

• GOST (Available for Russia & CIS market)

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Applications & Features

Weld neck flanges are primarily used in medium and high-pressure piping systems. Due to their tapered hub and full-penetration butt weld connection, they provide:

• Excellent stress distribution

• High structural strength

• Superior sealing performance

• Long service life in harsh environments

They are especially recommended for critical services such as oil & gas pipelines, refinery systems and power plants.

Our flange product range includes weld neck flanges, slip on flanges, blind flanges, socket weld flanges, threaded flanges and lap joint flanges for industrial piping systems.