Hub flanges are slip-on or weld-neck style flanges with a reinforcing hub (collar) between the flange ring and the pipe connection. The hub provides added strength, improves stress distribution at the weld, and helps with pipe alignment. In ANSI/ASME standards, hub geometry is specified by dimensions such as hub diameter and length through hub, and is used across threaded, slip-on, socket-weld, lapped, and weld-neck flanges.
A hub is the raised, collar-like section on a flange that connects the flat face to the pipe bore.
Looks like a short, tapered cylinder behind the flange ring.
Found on weld-neck, slip-on hub, and some AWWA hub-type flanges.
Reinforcement – Distributes stress more evenly.
Alignment – Centers pipe and bolt holes.
Weld Strength – Supports full-penetration welds.
Durability – Reduces fatigue and extends service life.
Non-Hub (Ring or Plate) Flange: Just a flat disc with bolt holes; lighter and cheaper, but less strong.
Hub Flange: Has the extra collar for strength and proper stress transfer — preferred in higher-pressure, larger-diameter, or critical applications.
1. AWWA C207 — Appendix B – 4″ to 96″, waterworks service.
2. ASME B16.5 — ½″ to 24″, hub dimensions defined for weld-neck and other hubbed flanges.
3. ASME B16.47 (Series A/B) / MSS SP-44 — 26″ to 60″, large-diameter hubbed flanges for pipelines.
1. Class D hub flange: 150–175 psi (depending on size)
2. Class E hub flange: 275 psi
The following table shows dimensional ranges for AWWA C207 hub-type flanges (Classes D & E)
| NPS Range (in.) | Outside Diameter (OD) | Hub Bore ID | Flange Thickness |
|---|---|---|---|
| 4″ – 6″ | 9.0″ – 11.0″ | 4.5″ – 6.7″ | 0.94″ – 1.00″ |
| 8″ – 12″ | 13.5″ – 19.0″ | 8.6″ – 12.9″ | 1.00″ – 1.25″ |
| 14″ – 20″ | 21.0″ – 27.5″ | 14.2″ – 20.2″ | 0.75″ – 1.00″ |
| 24″ – 30″ | 32.0″ – 38.8″ | 24.2″ – 30.2″ | 1.00″ – 1.75″ |
| 36″ – 48″ | 44.5″ – 61.0″ | 36.2″ – 48.3″ | 1.25″ – 2.00″ |
| 54″ – 72″ | 68.0″ – 87.0″ | 54.3″ – 72.2″ | 1.50″ – 2.25″ |
| 78″ – 144″ | 94.0″ – 176.0″ | 78.3″ – 144.3″ | 1.75″ – 3.00″ |
Used in medium-pressure oil, gas, and steam pipelines where extra reinforcement is required.
Applied in welded pipe systems carrying high-temperature steam or fluids.
Provide secure, reinforced joints for high-stress hydraulic and gas systems.
Still manufactured for compatibility with legacy installations, even though removed from the AWWA C207 scope in 2013.
Flat face design used mainly in waterworks and municipal piping. Easy to install and widely used in replacement projects.
Tapered hub with raised face or RTJ (Ring Type Joint). Provides maximum strength and reliability in high-pressure, high-temperature applications.
Solid flanges used to seal the ends of pipelines or equipment. Common in systems where access or expansion may be needed later.
Standard hub or weld-neck flanges have a longer neck for welding strength, while standard slip-on flanges have a low hub and no extended neck, making them easier to install but less rigid under high pressure.
A hub blind flange is designed to seal the end of a pipe or valve connection. It is a solid plate with a hub or collar that allows secure bolting, commonly used when a line needs to be closed but may later be reopened or extended.
To order hub flanges from API International, determine your required pipe size, pressure class, material, and any special standards (such as ASME B16.5). Contact API International’s experienced team, who will help you select the right flange for your application.
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
