At API International, we stock ASME B16.5 Class 300 flanges in the most common styles, including slip-on, weld-neck, and blind, with raised face and flat face options. Our flanges are forged from carbon steel or stainless steel to support long-term durability and corrosion resistance. We offer a comprehensive range of dimensions in both domestic (AIS) and import materials, with the added capability to provide custom-machined solutions for unique project requirements.
Class 300 is a higher pressure class within the ASME B16.5 system. The class designation does not represent a fixed pressure value. Instead, it represents a pressure-temperature rating system defined by the material group. For example, a carbon steel Class 300 flange has a pressure rating of approximately:
This rating system allows flange assemblies to operate safely in more demanding pressure and temperature conditions than B16.5 Class 150.
| NPS | Outside Diameter (OD) | Bolt Circle | Bolt Hole (Qty x Size) |
|---|---|---|---|
| 2 | 6.50 in | 5.00 in | 8 × 0.750 |
| 3 | 8.25 in | 6.63 in | 8 × 0.875 |
| 4 | 10.00 in | 7.88 in | 8 × 0.875 |
| 6 | 12.50 in | 10.63 in | 12 × 0.875 |
| 8 | 15.00 in | 13.00 in | 12 × 1.000 |
| 10 | 17.50 in | 15.25 in | 16 × 1.125 |
| 12 | 20.50 in | 17.75 in | 16 × 1.250 |
| 16 | 25.50 in | 22.50 in | 20 × 1.375 |
| 20 | 30.50 in | 27.00 in | 24 × 1.375 |
| 24 | 36.00 in | 32.00 in | 24 × 1.625 |
* Dimensions follow ANSI / ASME B16.5 Class 300 flange standards. Actual flange dimensions may vary depending on flange type, facing style, and material specification.
Slip-on flanges are a cost-effective alternative to weld necks, favored for their ease of alignment and simplified installation.
Blind flanges serve as the definitive endpoint for a piping system, used to terminate lines or isolate specific process equipment.
Weld neck flanges are a premier choice for high-pressure systems and remain one of the most commonly used flange types.
ANSI/ASME B16.5 defines seven standard pressure classes: 150, 300, 400, 600, 900, 1500, and 2500. These classes establish the pressure-temperature ratings for flanges, which dictate the maximum allowable working pressure based on the material type and operating temperature of the system.
ANSI/ASME Class 300 refers to a flange pressure class used in piping systems under the ASME B16.5 standard. For example, a Class 300 flange made from ASTM A105 carbon steel is typically rated for about 740 psi at 100°F, though the actual pressure rating decreases as temperature increases.
Class 150 flanges are engineered for moderate pressure and temperature applications, while Class 300 flanges are built for more demanding service. Because Class 300 flanges require different dimensions and bolt patterns, they are not interchangeable with Class 150 components; these differences are critical for ensuring a reliable seal in high-stress industrial applications.
Class 300 flanges are not interchangeable with Class 150 flanges because the bolt circle diameter, bolt quantity, and thickness are different.
Contact API International’s experienced sales team, and we will help you select the right flange for your application. You can also explore our full range of ANSI and ASME flanges in our online product catalog, or contact us for custom flange options designed to meet your project specifications. Get connected with a dedicated sales representative today, or call us at 503.692.3800
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.
