AWWA C228 is the modern standard governing stainless steel pipe flanges for water service, providing rigorous guidelines for design, materials, and dimensions in both potable and non-potable systems. By utilizing high-grade, corrosion-resistant alloys—primarily 304/304L and 316/316L—these flanges offer superior durability in chemically aggressive, high-salinity, or high-humidity environments.
| NPS | OD (in) | ID (in) | THK (in) | Bolt circle (in) | # Holes | Hole Ø (in) |
|---|---|---|---|---|---|---|
| 4 | 10.00 | 4.57 | 1.130 | 7.88 | 8 | 0.875 |
| 5 | 11.00 | 5.66 | 1.210 | 9.25 | 8 | 0.875 |
| 6 | 12.50 | 6.72 | 1.310 | 10.62 | 12 | 0.875 |
| 8 | 15.00 | 8.72 | 1.310 | 13.00 | 12 | 1.000 |
| 10 | 17.50 | 10.88 | 1.500 | 15.25 | 16 | 1.125 |
| 12 | 20.50 | 12.88 | 1.630 | 17.75 | 16 | 1.250 |
| 14 | 23.00 | 14.19 | 1.940 | 20.25 | 20 | 1.250 |
| 16 | 25.50 | 16.19 | 2.140 | 22.50 | 20 | 1.375 |
| 20 | 30.50 | 20.19 | 2.330 | 27.00 | 24 | 1.375 |
| 24 | 36.00 | 24.19 | 2.690 | 32.00 | 24 | 1.625 |
| 32 | 45.25 | 32.25 | 3.250 | 41.50 | 28 | 1.875 |
| 40 | 54.25 | 40.25 | 3.630 | 50.25 | 36 | 2.125 |
| 48 | 65.00 | 48.25 | 4.500 | 60.75 | 40 | 2.125 |
* Class SF dimensions shown follow AWWA C228 stainless steel-ring flange standards.
| NPS | OD (in) | Bolt Circle (in) | Bolt Hole (Qty x Size) |
|---|---|---|---|
| 4 | 10.00 | 7.88 | 8 × 0.875 |
| 5 | 11.00 | 9.25 | 8 × 0.875 |
| 6 | 12.50 | 10.62 | 12 × 0.875 |
| 8 | 15.00 | 13.00 | 12 × 1.000 |
| 10 | 17.50 | 15.25 | 16 × 1.125 |
| 12 | 20.50 | 17.75 | 16 × 1.250 |
| 14 | 23.00 | 20.25 | 20 × 1.250 |
| 16 | 25.50 | 22.50 | 20 × 1.375 |
| 20 | 30.50 | 27.00 | 24 × 1.375 |
| 24 | 36.00 | 32.00 | 24 × 1.625 |
| 32 | 45.25 | 41.50 | 28 × 1.875 |
| 40 | 54.25 | 50.25 | 36 × 2.125 |
| 48 | 65.00 | 60.75 | 40 × 2.125 |
* Class SF dimensions shown follow AWWA C228 stainless steel-ring flange standards.
See the full size range and specs:
A Slip On Flange is a type of pipe flange that is slipped over the end of a pipe and welded in place.
A Blind Flange is a detachable sealing device used to block off a pipeline or to create a stop.
AWWA C228 Class SF flange dimensions are defined by nominal pipe size (NPS) and include outside diameter (OD), bolt circle (BC), number of bolt holes, hole diameter, and thickness.
Class SF flanges are typically available in sizes from 4” to 48” and follow drilling patterns compatible with ANSI/ASME Class 300. Exact dimensions vary by size and must be referenced from AWWA C228 standard tables.
AWWA C207 and AWWA C228 may share similar dimensional patterns in some sizes and classes, but they are different standards with different material specifications. C207 covers carbon steel flanges, while C228 covers stainless steel flanges, so interchangeability should always be confirmed by checking the exact dimensions, pressure class, and service requirements.
AWWA C207 covers carbon steel flanges, while AWWA C228 covers stainless steel flanges for the same applications. Both define dimensions, pressure classes, and material requirements.
API International stocks the pipe sizes, pressure classes, and materials you need for your project. Our machine shop can also modify stock products to accommodate any special project requirements. Contact API International’s experienced sales team, and we will help you select the right flange for your application.
API International is a premier manufacturer and engineering solutions provider that specializes in flanges, expansion joints, valve accessories, and precision-engineered piping components. By offering a wide variety of both AIS/BABA-compliant (Domestic) and imported products, we provide the flexibility and speed the industry demands. Our customers rely on us for more than just parts; they choose us for our superior technical support, rapid national distribution, and commitment to project-critical deadlines. Contact our expert sales team at 503.692.3800 to discuss your next project’s specifications or to request a quote.
• Custom Bolt Holes, Overbore, Counterbore, Tapped, Welds, O-ring Grooves, Threads, Special Serrations, Bevels, Chamfers
• Metric Parallel, Metric Tapered, Parallel (BSPP), Taper Thread (BSPT), UN/UNF/UNC Thread, NPT (National Pipe Thread)
• MWD
• 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
• Forged:
- Ring Rolling:
• Materials: Carbon Steel, Stainless Steel, Duplex
• Size: 2–202”
• Cast:
- Centrifugal Casting (Industrial):
• Material: Stainless Steel
- Continuous Casting:
• Stainless Steel
- Sand Casting:
• Material: A536, Stainless Steel, Ductile Iron
- Investment/Lost-Wax/Precision Casting
• Stainless Steel
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 | Stainless Steel, Carbon 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 engineering solutions provider that specializes in flanges, expansion joints, valve accessories, other pipe fittings, and custom-fabricated parts. We offer a wide variety of AIS & imported flanges along with other industrial pipe fittings 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.
