Weld neck flanges — overview

Weld neck flanges are flanged fittings with a tapered hub that is butt‑welded to the pipe. The hub provides a smooth transition from flange to pipe wall, reducing stress concentrations and making these flanges especially suitable for high‑pressure and high‑temperature applications. In plain terms: they are robust, long‑lasting pipe flanges that are welded on rather than slipped over.

What a weld neck flange looks like and how it works

A typical weld neck flange has a flat bolting face and a protruding neck (hub). The neck is welded to the pipe by a butt weld, producing a continuous, smooth bore across the connection. This construction improves strength and alignment and helps avoid turbulence and corrosion points where fluid meets the flange.

Where weld neck flanges are used

Weld neck flanges are used across many industries where reliability and safety matter. Typical applications include:

• Oil & gas and petrochemical plants
• Power generation (including boilers and steam lines)
• Offshore and marine systems
• Chemical processing and tank farms
• Pharmaceutical and food processing (where sanitary stainless steel is required)
• Water and wastewater treatment
• Automotive and construction projects
• Maintenance and small workshop/garage pipework where a robust welded connection is needed

Who buys weld neck flanges

Customers include design engineers, plant maintenance teams, fabricators, mechanical contractors and procurement departments. They are suitable both for professional industrial installations and for skilled workshop projects that require a strong welded flange connection.

Materials: stainless, heat‑resistant and acid‑resistant steels

Our store specialises exclusively in flanges made from stainless and specialised stainless alloys — no aluminium or plain carbon steel. You will commonly find weld neck flanges in these steels:

• Austenitic stainless steel 304 — (Europe EN 1.4301, also referred to as AISI 304 / UNS S30400). General‑purpose stainless with good corrosion resistance and formability.
• Austenitic stainless steel 316L — (Europe EN 1.4404, equivalents AISI 316L / UNS S31603). Better resistance to chlorides and many chemicals; widely used in chemical, marine and food industries.
• Duplex and super‑duplex — for improved strength and resistance to chloride stress corrosion cracking (e.g. duplex grades commonly referenced as EN 1.4462 / UNS S32205). These are often used in aggressive environments such as offshore and desalination plants.
• Heat‑resistant stainless — grades such as 310S (EN 1.4845 / UNS S31008) are available where elevated temperature resistance is required.

When choosing material, consider the fluid, temperature, and environment (chlorides, acids, salt spray, etc.). If in doubt, consult a materials engineer or contact us with your service conditions.

Standards and flange faces

Weld neck flanges are manufactured to common international standards. In Europe you will see flanges to EN standards (often quoted with a PN or pressure rating), while in the US specifications such as ASME/ANSI (for example ASME B16.5 for many pipe flanges) are common. When ordering, check the required standard, pressure class and dimensions to match your piping system.

Common flange faces include raised face (RF), flat face (FF) and ring‑type joint (RTJ). The face type affects gasket selection and sealing performance — for example, RTJ is used for very high pressure applications, while RF is the most common for general services.

Practical guidance when choosing weld neck flanges

• Match standards and dimensions: ensure flange standard (EN or ASME), nominal pipe size and bolt pattern match the mating components.
• Select the correct material grade: choose based on corrosion resistance and temperature requirements (e.g. 316L for chloride exposure; duplex for very aggressive environments).
• Face type and gasket: choose RF, FF or RTJ depending on pressure and sealing needs and use the correct gasket type.
• Welding considerations: weld neck flanges require butt welding by qualified welders; pre‑ and post‑weld procedures depend on material (e.g. some stainless steels need controlled heat input or post‑weld cleaning/passivation).
• Inspection and traceability: for critical systems, request material certificates (e.g. EN 10204) and any required non‑destructive testing (NDT) or mill test reports.

Short glossary (simple explanations)

Butt weld — a weld where the pipe and flange edges are joined end‑to‑end so the bore is continuous.
PN — pressure nominal used in European standards to express pressure capability.
ASME/ANSI — common US standards for dimensions and pressure ratings of flanges.
RF / FF / RTJ — types of flange faces that influence how the joint seals.

Buyers from the UK — what to check

If you are ordering from the UK, make sure to specify the standard you need (EN or ASME), the exact material grade (for example 316L / EN 1.4404), the flange face type and any certification required by your project (material certificates, heat treatment or NDT). If you need help matching flanges to existing pipework, provide the pipe nominal bore, wall thickness or pipe schedule and the mate flange details.

Need help?

If you would like advice choosing the correct weld neck flanges for your application — including material selection, flange standard or face type — contact our technical team with details of the fluid, temperature, pressure and environment. We can recommend suitable stainless or acid/heat‑resistant materials and the correct flange specification for safe, reliable service.