Weld Neck Flange

What is Weld Neck Flange

Weld neck flange have a piece of long tapered hub used for welded to the pipes. Manufacturers produce weld neck flanges with high integrity and can fabricate them in all sizes, many types, and different pressure classes. Moreover, it also has the ability to relocate stress to pipes, which means a WN flange can decrease high pressure at the bottom of it. Due to the specialty of strength and construction, weld neck flanges are suitable to elevate temperature and pressure when applied.

Key Features of a Weld Neck Flange:

Tapered Neck (Hub): Matches the dimensions of the connecting pipe for smooth flow and stress distribution.

Butt Weld Connection: Welded to the pipe using a butt weld, which provides strong, leak-proof joints.

Raised Face (RF) or RTJ Options: Typically available with raised face or ring-type joint (RTJ) sealing surfaces.

ASME B16.5 / B16.47 Compliant: Manufactured under standard dimensions for compatibility.

Standard Specification of Weld Neck Flange

ASME B16.5

Size：1/2″ ~ 24″

Pressure: 150#, 300#, 600#, 900#, 1500#, 2500#

ASME B16.5 is a widely recognized and used standard published by the American Society of Mechanical Engineers (ASME).This standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fittings.

ASME B16.47A

Size: 26″ ~ 60″

Pressure: 150#, 300#, 400#, 600#, 900#

ASME B16.47 A standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing for large-diameter steel1 pipe flanges in sizes ranging from NPS 26 through NPS 60.  They tend to be thicker, heavier, and have larger bolt circles and bolt sizes compared to Series B. They are often considered stronger and able to handle more external loading.

ASME B16.47B

Size: 26″ ~ 60″

Pressure:75#, 150#, 300#, 400#, 600#, 900#

The ASME B16.47 standard covers two series of large-diameter steel flanges, one of which is ASME B16.47B, titled “Large Diameter Steel Flanges: NPS 26 Through NPS 60 Metric/Inch Standard.” They are generally lighter and thinner with smaller bolt circles and bolt sizes, requiring more but smaller fasteners.

EN 1092-1

Size: DN 10 ~ DN 4000

Pressure: PN 2.5, 6, 10, 16, 25, 40, 63, 100, 160, 250, 400

EN 1092-1 is the European standard for circular flanges made from steel, used to connect piping systems and equipment. It applies to flanges for pipes, valves, fittings, and other pipeline components — and is widely adopted across Europe and internationally.

JIS B2220

Size：10A ~ 1500A

Pressure: 5K, 10K, 16K, 20K, 30K, 40K

JIS B2220 is a Japanese Industrial Standard (JIS) that specifies steel pipe flanges. It is published by the Japanese Standards Association (JSA).

DIN 2631 to DIN 2635

Size: DN 10 ~ DN 1000+

Pressure:

DIN 2631	DIN 2632	DIN 2633	DIN 2634	DIN 2635
PN 6	PN 10	PN 16	PN 25	PN 40

They are German Industrial Standard (DIN) that specifies welding neck flanges (Vorschweißflansche). This type of flange attaches to a piping system by butt welding the pipe directly to the flange neck. This design provides excellent stress distribution and is suitable for higher pressure and temperature applications.

Sealing Face of Steel Flange

There are several different types of sealing face when it comes to steel flange. They are FF for flat face, RF for raised face, and RTJ for ring joint face.

If FF flange is applied, it demonstrates that the related gasket can have full contact with this flange.

RF (raised face) flange is always chosen to decrease the surface of the seal, which in turn can concentrate surface pressure.

RTJ (ring joint face) flange is more suitable to be used under high-pressure and high-temperature circumstances.

What are the Different Types of Weld Neck Flanges?

Standard Weld Neck Flange

Engineers and designers commonly specify this flange type in high-pressure and high-temperature piping systems. Its defining feature is a long, tapered neck that transitions smoothly into the connected pipe, offering superior strength and stress distribution.

Long Weld Neck Flanges

These have an elongated hub or neck. They are often used as a nozzle for pressure vessels, tanks, or columns, providing extra reinforcement and welding room.  

Reducing Weld Neck Flanges

These are designed to connect pipes of dissimilar diameters. One end has a bore size to match the larger pipe, and the other end has a smaller bore size for the smaller pipe.  

NW Long Weld Neck Flanges

NW Long Weld Neck Flanges (also sometimes called Nozzle Weld Long Weld Neck Flanges) are a special type of long weld neck flange designed primarily for nozzle connections in pressure vessels, columns, tanks, and heat exchangers.

Materials of Weld Neck Flanges

Carcon Steel: ASTM A105 / A105N,ASTM A350 LF2 / LF3, A694 F42 / 46 / 52 / 56 / 65 / 70

Carbon steel is a fundamental engineering material composed primarily of iron and carbon. The carbon content in the steel largely dictates its properties. Generally, carbon steel contains up to 2% carbon by weight, with smaller amounts of other elements like manganese, silicon, and trace impurities such as sulfur and phosphorus.

Alloy Steel: ASTM A182 F5 / F9 / F11 / F12 / F22 / F91 / F92

Alloy steel material is a type of steel where other alloying elements are intentionally added to carbon steel to enhance its properties. These elements, such as manganese, silicon, nickel, chromium, molybdenum, vanadium, boron, and copper, are added in varying proportions to achieve specific characteristics that are not inherent in plain carbon steel.

Stainless Steel: A182 F304/304L/304H – F316/316L – F317 – F310S – F321 – F347 – F904L

Stainless steel is a versatile and widely used material prized for its corrosion resistance and aesthetic appeal. Unlike carbon steel, stainless steel contains a minimum of 10.5% chromium by mass. This chromium reacts with oxygen in the air to form a thin, stable, and invisible passive layer of chromium oxide on the steel’s surface, which prevents rust and protects the underlying material from further corrosion.

Duplex Stainless Steel: A182 F51/53/55/60

Duplex stainless steel is a type of stainless steel that has a mixed microstructure of austenite and ferrite, approximately in equal proportions. As a result, this combination provides a unique blend of properties that are often superior to single-phase (austenitic or ferritic) stainless steels.

Common Types of Flange Gasket Faces

1.Flat Face (FF)

Entire face is flat and smooth.

Used with full-face gaskets.

Common in low-pressure, low-temperature systems (e.g., cast iron equipment).

Requires even bolt tension to prevent leakage.

2.Raised Face (RF)

Most common type in process piping.

Concentrates pressure on the gasket area for better sealing.

Works with a variety of gaskets (spiral wound, ring, etc.).

Standard in ASME B16.5 flanges.

3.Ring Type Joint (RTJ)

Features a precision-machined groove for a metal ring gasket.

Designed for high-pressure, high-temperature applications.

Common in oil & gas and petrochemical industries.

Provides a metal-to-metal seal.

4.Tongue and Groove (T&G)

One flange has a raised tongue, the other a matching groove.

Requires matched pairs and usually soft gaskets.

Often used in high-integrity joints, including heat exchangers.

5.Male and Female (M&F)

Similar to T&G, but the sealing surfaces are flat.

Male flange fits into a recessed female flange.

Typically used in specialized or custom systems.

 Advantages of Weld Neck Flange

Advantage	Description
High Strength and Pressure Rating	Suitable for high-pressure, high-temperature applications due to robust design.
Excellent Stress Distribution	Tapered hub evenly distributes stress to the pipe, reducing risk of failure.
Superior Sealing Performance	Butt-welded connection ensures leak-proof, secure joints.
Corrosion and Fatigue Resistance	Ideal for corrosive environments and systems with temperature/pressure cycles.
Smooth Flow and Pipe Matching	Matches well with seamless pipes, reducing turbulence and erosion.
Industry Standard Compliance	Manufactured to standards like ASME B16.5/B16.47 for wide industrial use.

Key Applications of Weld Neck Flanges

Oil & Gas Industry

Petrochemical & Chemical Processing

Power Plants

Shipbuilding & Marine Applications

Water Treatment Plants

Pharmaceutical & Food Processing

High-Integrity Piping Systems

Frequently Asked Questions (FAQs)

1.Why Choose Weld Neck Flanges?

High structural strength.

Excellent under repeated bending, stress, and pressure.

Reliable and long-lasting seal when properly welded.

2.How Are Weld Neck Flanges Tested for Quality?

Quality testing of weld neck flanges involves a combination of methods before installation to ensure they meet industry standards and performance requirements. Manufacturers and quality control personnel perform visual inspections and dimensional checks to verify physical attributes. They also employ non-destructive testing (NDT) methods like ultrasonic testing (UT), radiographic testing (RT), or dye penetrant testing (PT) to detect internal or surface defects. In some cases, they conduct hydrostatic or pressure testing to verify the flange’s integrity under pressure. This comprehensive testing process ensures the weld neck flange’s fitness for service.

3.What is the difference between weld neck flange and slip on flange?

The main difference between a weld neck flange and a slip-on flange lies in their design and strength. Specifically, a weld neck flange’s long tapered hub is butt-welded to the pipe, thereby providing excellent stress distribution and making it ideal for high-pressure, high-temperature applications. In contrast, installers slide a slip-on flange over the pipe and fillet-weld it on both sides, which is easier to install and more cost-effective but less robust, typically used in lower-pressure systems.