Reducing flanges connect pipes of different diameters, creating a smooth transition in size within a piping system. They maintain steady flow and pressure with minimal disruption, moving from larger to smaller pipes or from smaller to larger. These flanges join pipe sections precisely to reduce turbulence and avoid pressure drops.
Using the right reducing flange improves system efficiency and reliability without compromising design standards or safety. Their compact shape also makes them a smart choice for tight spaces where separate reducers are not practical.
At API, we offer reducing flanges in a wide range of sizes, materials, and pressure classes to fit everything from general water systems to demanding industrial applications.
Reducing flanges follow international standards that keep pipe systems compatible, safe, and dependable across many applications. These standards lay out the flange dimensions, pressure ratings, facing types, and bolt patterns, along with requirements for materials, testing, and marking. This helps ensure that reducing flanges fit properly and perform as expected in any pipeline system.
| Standard | Size Range | Pressure Classes | Typical Use |
|---|---|---|---|
| ASME B16.5 | ½” – 24” | 150, 300, 400, 600, 900, 1500, 2500 | Industrial piping systems |
| ASME B16.47 | 26” – 60” | Series A & B (≈ 150–900) | Large diameter pipelines |
| AWWA C207 | 4” – 144” (often) | B, D, E, F classes | Waterworks, low-pressure lines |
Typical reducing flange dimensions are shown across common sizes and pressure classes.
| Size (Large x Small) | Class | Bolt Circle (BC) | Thickness (T) |
|---|---|---|---|
| 6” x 4” | 150 | 9.50” | 0.75” |
| 6” x 4” | 300 | 9.75” | 0.94” |
| 8” x 6” | 150 | 11.75” | 0.87” |
| 8” x 6” | 300 | 12.00” | 1.06” |
| 10” x 8” | 150 | 14.25” | 1.00” |
| 12” x 10” | 150 | 17.00” | 1.12” |
Used across processing, refining, and transport to handle changes in pipe sizes, maintain pressure and flow, and reduce leaks.
Connects pipes of different diameters through collection, processing, and distribution, smoothing transitions and balancing pressure.
Helps move air efficiently through complex building systems, keeping flow steady and minimizing clogs or leaks.
Joins pipes of various sizes in multi-floor or large facilities to maintain consistent water flow and reduce turbulence.
Slip-on reducing flanges slide over the pipe and are then welded in place. They’re cost-effective, easy to install, and ideal for low to medium-pressure systems.
Weld neck reducing flanges have a tapered hub that handles high pressure and stress. They’re often used in power plants and refineries for secure, leak-free connections.
Threaded reducing flanges screw onto matching pipe threads without welding. They’re simple to install, reliable at low pressures, and easy to remove or reuse.
A reducing flange connects pipes of different sizes while maintaining the same bolt circle and face dimensions, allowing for smooth changes in diameter without extra fittings.
They save space and cost by avoiding separate reducers, improve flow and pressure control by smoothing transitions, and increase safety by reducing leaks and stress points.
Select a flange that matches your large and small pipe diameters, then confirm the required pressure class, bolt circle, and thickness to meet your system specs. For more information, contact us and we will help you select the right size.
They’re widely used in oil & gas, water treatment, HVAC, plumbing, and general process systems wherever pipe sizes vary.
API-certified reducing flanges meet rigorous standards for quality, durability, and pressure ratings, ensuring reliable long-term performance. Learn more about us.
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.
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