Welding Neck Flange

A welding neck flange is a type of flange that is butt-welded to a pipe through a tapered neck structure. It has high connection strength and stress resistance, making it suitable for medium and high-pressure piping systems (nominal pressure 1.0-25.0MPa), especially for harsh conditions with high temperature, high pressure, low temperature, or drastic pressure and temperature fluctuations. The following is a detailed overview of welding neck flanges:

Structure and Features

Structure: It is integrally forged from a flange disc and a tapered neck. The outer slope of the neck is ≤7°, and it is butt-welded to the pipe through a circular pipe transition section. The height of the neck increases with the nominal pressure, and the structural rigidity is about 50% higher than that of a slip-on flange.

Advantages:

High Strength: The tapered neck design reduces stress concentration and improves sealing performance and load-bearing capacity, making it suitable for high-pressure pipelines (PN>2.5MPa).

Good Sealing: It is not easily deformed, and the weld is far away from the joint surface, avoiding the influence of welding temperature.

Suitable for Harsh Conditions: Widely used in pipelines transporting flammable, explosive, or high-value media, such as in the petrochemical and natural gas industries.

Disadvantages:

Larger volume, heavier weight, and more difficult to install and position.

Higher manufacturing and installation costs, and prone to bumps during transportation.

Differences from Slip-On Flanges

Welding Method: Welding neck flanges use butt welding (circular weld, Class B weld, can be radiographically tested), while slip-on flanges use fillet welds (Class C weld, cannot be radiographically tested).

Pressure Rating: Welding neck flanges are suitable for high-pressure scenarios of 1.0-25.0MPa, while slip-on flanges are suitable for lower pressure scenarios of 0.6-4.0MPa.

Material and Processing: Welding neck flanges are usually machined from forged steel parts, while slip-on flanges are mostly processed from steel plates, resulting in lower costs.

Specifications and Standards

Size Range: DN15~DN4000.

Pressure Rating: PN2.5~PN400, Class150~Class2500.

Sealing Surface Forms: Raised Face (RF), Female Face (FM), Male Face (M), Tongue Face (T), Groove Face (G), Flat Face (FF), Ring Joint Face (RJ).

Common Standards: GB/T9115, HG/T20592, ASME B16.5, ISO7005-1, etc.

Material

Carbon Steel: ASTM A105, Q235, 16Mn, etc.

Stainless Steel: 304, 316, 304L, 316L, 321, etc.

Alloy Steel: 15CrMo, 12Cr1MoV, etc.

Application Fields

Petrochemical: Used in pipelines transporting flammable, explosive, or high-value media.

Natural Gas, Power, Heating: Suitable for pipelines with large pressure or temperature fluctuations.

Chemical Industry, Shipbuilding, Pharmaceutical, etc.: Meeting the connection needs of harsh working conditions.

Precautions

Installation: Ensure that the outer diameter of the pipe matches the welding port of the flange to avoid deviations.

Inspection: The weld must undergo strict non-destructive testing (such as radiographic testing) to ensure the quality of the connection.

Selection: Select the appropriate sealing surface and material according to the pipe medium, pressure, and temperature.