Our weld neck flanges are fully machined from A105 Forged Carbon Steel and A182 & 304/316 Stainless Steel and meet ANSI standards. They are available upon request.
Weld neck flanges are the most popular type of flange connection, recognized by their extended neck and beveled end designed for butt welding directly to pipe. This creates a strong, continuous joint that handles high stress and flow more naturally than other flange styles. In larger sizes and higher pressure classes, weld neck flanges are almost always the preferred choice. They are often becoming the only type specified for critical applications.
Their tapered hub reduces stress concentration at the base and ensures long-term reliability in high-pressure and high-temperature systems. Whether used as standard or reducing flanges to join pipes of different sizes, weld neck flanges maintain system integrity and flow efficiency.
Weld neck flanges are manufactured according to the ASME B16.5 standard, which covers pipe flanges and flanged fittings up to 24 inches in diameter. For larger sizes, they follow ASME B16.47, which covers flanges from 26 inches up to 60 inches.
| Pressure Class | OD (inches) | Flange Thickness T (inches) | Hub Dia. H (inches) |
|---|---|---|---|
| 150# | 3.5 – 48 | 0.44 – 2.12 | 1.9 – 23.6 |
| 300# | 3.9 – 51 | 0.62 – 2.75 | 2.1 – 25.6 |
| 600# | 4.3 – 55 | 0.81 – 3.62 | 2.3 – 27.5 |
| 900# | 5.0 – 57 | 1.12 – 4.62 | 2.8 – 29.5 |
| 1500# | 5.6 – 61 | 1.44 – 5.62 | 3.1 – 31.4 |
| 2500# | 6.5 – 66 | 2.06 – 7.25 | 3.5 – 33.3 |
* Exact dimensions depend on ASME/ANSI B16.5 or B16.47 standards and the specific pipe size.
Below is a typical diagram of a weld neck flange, showing its tapered hub, butt weld connection, and how it matches with the pipe or fitting.
Used in oil, gas, and chemical lines where pressure spikes demand a strong, leak-resistant joint. The tapered neck helps distribute stress evenly.
Ideal for boilers and steam lines because the butt weld connection handles thermal expansion without warping or leaking.
Preferred in harsh marine environments due to their robust weld design, which withstands vibration, shifting loads, and corrosive conditions.
Common in municipal and industrial water systems where large pipes require secure, aligned connections that minimize flow disruption.
Widely used in chemical plants and refineries for critical lines where safety and long-term reliability are essential.
A weld neck flange has a long tapered hub that’s butt welded to the pipe. This design spreads stress evenly and ensures a strong, leak-resistant connection.
Slip-on flanges are simpler and cheaper, which makes them suitable for low-pressure lines. Weld neck flanges are stronger and leak-resistant, preferred for high-pressure, high-temperature applications.
They reduce stress concentration, handle high pressure and temperature, and create a seamless, leak-proof joint that’s perfect for demanding or hazardous systems.
A weld neck flange is butt welded to the pipe. You bevel and align the pipe and flange, tack them in place, then perform a full penetration weld to secure the joint.
Use weld neck flanges for high-pressure pipelines, steam systems, and areas with heavy vibration or thermal expansion where a secure, lasting connection is needed.
Capabilities:
• Custom Bolt Holes, Overbore, Counterbore, Tapped, Welds, O-ring Grooves, Threads, Special Serrations, Bevels, Chamfers
Thread Style:
• Metric Parallel, Metric Tapered, Parallel (BSPP), Taper Thread (BSPT), UN/UNF/UNC Thread,
NPT (National Pipe Thread)
Serrations:
• MWD
Tolerances:
• Contact API’s engineering department for exact specifications and tolerances.
Plastic: Delrin, POM, Lexan, Nylon 66, Nylon 6, PEEK, PP, PE, Acetal
Rubber: EPDM, Neoprene, Buna-N, Viton
Aluminum: A2011, A2024, A2017, A5052, A5056, A6061, A6063, A6463, A6082, A7075
Copper: 3600, 3604, 3771
Titanium: 1-28
Steel Series:
• Ductile Iron: ASTM A536
• Carbon/Mild Steel: A105, A36, A516-70, A572-50, etc.
• Stainless Steel:
- 300 Series – 303, 304, 304L, 316, 316L
- 400 Series – 420J2, 430, 434, 442
Special Metals: Hastelloy, Inconel, Incoloy, Duplex 2205, Super Duplex 2507, Chrome Steel, alloys, or their equivalents
Stock Finish, Spiral Serrated (Phonographic), Concentric Serrated, Smooth Finish, Cold Water Finish, MWD, Phonographic
Dipped, Nickel Plating, Zinc Plating (clear, yellow, black, red, blue), Super Agitine, Powder, Painted, Galvanized, Epoxy, Lacquer
Water/Wastewater, Irrigation, Agriculture, HVAC, Marine, Exhaust, Mining, Energy/Power Generation/Oil
Forming:
• Forged:
- Ring Rolling:
• Materials: Carbon Steel, Stainless Steel, Duplex
• Size: 2–202”
• Cast:
- Centrifugal Casting (Industrial):
• Material: Stainless Steel
- Continuous Casting:
• Material: Stainless Steel
- Sand Casting:
• Material: A536, Stainless Steel, Ductile Iron
Machining: Milling, Turning, Facing, Boring, Drilling, Tapping, Counter Sinking, Laser Cutting, Water Jet, Plasma Cutting
| Products | Type | Materials | Size Range |
|---|---|---|---|
| Flanges | Flat-Face, Raised-Face, & Plate: Slip-On/Ring Weld, Neck, Blind, Socket Weld, Orifice, Reducing, Threaded | See Materials List | 5–202″ |
| Gaskets | Molded, Extruded, sheet | EPDM, Buna-N, NBR, Non-Asbestos (GNA), Red Rubber (GRR), Viton | 5–60″ |
| Screens For Filters | Basket Screens and Cone Screens (Perforated, Mesh) | Galv. Carbon Steel, Carbon Steel, Stainless Steel | 6”D x 8’-H |
| Rings | Exhaust Rings (Marmon Flanges for DPF Filters) | Carbon Steel, Stainless Steel, Aluminum | 1–16” |
| Seamless Rolled Rings | Forged | Carbon Steel, Stainless Steel, Aluminum | 1–165” |
| Square Hole Rings | Repair Couplers | Carbon Steel, Stainless Steel, Galvanized, Epoxy Coated | 3–32” |
| Fabricated Assemblies | Weldments, Pipe Spools, Valve Bodies, Silencer Housings | Carbon Steel, Stainless Steel | 2–24” |
| Long/Short Radius Elbows | EN 10253-2–S235, P235GH–P265GH–P265NL and ASTM A234, WPB, WPC/ A420 WPL6, WPL3/ A860 WPHY52/ ASTM A234 WP11, WP22, WP5, WP9–16Mo3 | 304L & 316L Stainless Steel | (45° & 90°): OD: 21.3mm (1/2”)–3048mm (120”) WT: Up to SCH. XXS/160 |
| Miscellaneous | Tubesheets / Diffuser Plates / Baffles / Ferrules / Sleeves / Pins | Carbon Steel, Stainless Steel, Duplex | 5–104” |
Who we are
API International is a manufacturer and wholesale distributor of flanges, expansion joints, valves, other pipe fittings and custom fabricated parts. We offer a wide variety of AIS & imported flanges along with other industrial pipe fitting and accessories. Customers turn to us when they need quick delivery of parts and are looking for a higher level of customer service. Standard parts are stocked in one of our conveniently located warehouses for quick distribution throughout the United States.
Customer Reviews
API International, Inc. | All rights reserved. | Terms & Conditions | Privacy Policy
