Weld neck flanges

Weld neck flanges

What is a weld neck flange?

Weld neck flanges are flanges designed to be butt‑welded to a pipe. They feature a long, tapered hub that provides a smooth transition between the flange and the pipe wall, which helps distribute stress and reduces turbulence inside the pipeline. Because the flange is welded directly to the pipe, weld neck flanges are commonly specified where a strong, leak‑resistant joint is essential - for example in high‑pressure or high‑temperature systems. The smooth bore also makes them a good choice when non‑intrusive flow or cleanability is important.

Materials and common grades

In this shop we sell weld neck flanges made only from stainless and corrosion‑resistant steels - including heat‑resistant and acid‑resistant grades. Typical materials and their common designations include:

• Austenitic stainless steels - e.g. AISI/EN 304 (EN 1.4301) and 316L (EN 1.4404). Good general corrosion resistance and common in food, pharmaceutical and general process piping.
• Duplex and super‑duplex - e.g. duplex 2205 (EN 1.4462 / UNS S32205) and super‑duplex 2507 (EN 1.4410 / UNS S32750). Higher strength and improved resistance to chloride stress corrosion cracking; often used offshore and in chemical services.
• Acid‑resistant and nickel‑alloy equivalents - e.g. 904L (EN 1.4539 / UNS N08904) for aggressive chemical environments where additional corrosion resistance is required.
• Heat‑resistant stainless steels - e.g. grades such as 310/310S (EN 1.4845) used for higher temperature applications.

Note: When ordering, specify the exact grade and standard you require (EN, AISI/ASTM or UNS), because mechanical properties and weld procedures can vary between grades.

Standards, face types and sizes

Weld neck flanges are manufactured to recognised industry standards. Common standards include EN 1092‑1 (PN system) for Europe and ASME B16.5 / B16.47 (Class/ANSI) for North American sizing. Face types you can choose from include raised face (RF), flat face (FF) and ring joint (RTJ).

Typical ordering information you should provide: flange standard (EN or ASME), nominal size (DN or inches), pressure rating (PN or ANSI class), material grade and pipe schedule or wall thickness so the weld bevel can be prepared correctly. Common production ranges cover small bore pipe (e.g. DN15 / ½") up to large diameters (ASME sizes up to 24" and larger items per ASME B16.47).

Where and how weld neck flanges are used

Weld neck flanges are widely used across many sectors because of their strength and reliability. Examples of applications and industries include:

• Oil & gas and petrochemical - high pressure and corrosive environments onshore and offshore.
• Power generation - steam lines and high‑temperature connections.
• Shipbuilding and marine - seawater systems and structural piping.
• Chemical processing - acidic or aggressive media where corrosion resistance is critical.
• Water and wastewater treatment - process lines and high‑integrity joints.
• Food, beverage and pharmaceuticals - hygienic pipelines where smooth bore and cleanability matter.
• Construction, automotive and small workshop projects - from structural piping to specialised fabrication tasks.

Choosing the right weld neck flange

To select the appropriate weld neck flange, consider these key points:

• Fluid and environment: choose material compatible with the media (chlorides, acids, high temperatures, etc.).
• Pressure and temperature: match the flange rating (PN or ANSI/class) to operating conditions.
• Pipe dimensions and schedule: provide nominal bore and wall thickness so the flange hub can be machined and bevelled correctly for a proper butt weld.
• Standard and face type: confirm whether EN or ASME standards are required and which face type (RF/FF/RTJ) suits your gasket and sealing method.
• Testing and traceability: request material certificates (e.g. EN 10204), NDT (radiography) or heat number traceability if the project requires it.

If you are unsure which grade or standard is right for your project, consult our technical team with details of medium, temperature, pressure and pipe data - we can advise on material selection and suitable flange specification.

Ordering and finishing options

We supply weld neck flanges machined and bevelled ready for butt welding, with options for specific face finishes, reduced or full bore, and with traceable material certificates where required. Custom sizes and special alloys are available on request for bespoke projects.

Contact us with your flange specification (standard, size, PN/ANSI class, material grade and pipe schedule) and we will help you choose the correct weld neck flange for your application.