Stainless steel flanges are highly durable, corrosion-resistant, and able to withstand high pressure and temperature. The protective chromium oxide layer makes them self-healing and easy to maintain (through the natural passivation process), ensuring long service life even in demanding environments.
They are widely used in piping systems across industries such as water treatment, chemical processing, marine, and food production. With various grades and manufacturing methods available, stainless steel flanges can also be custom-fabricated to meet specific performance requirements.
Stainless steel flanges must meet strict industry standards to ensure safety, reliability, and compatibility across piping systems. These standards define chemical composition, pressure ratings, and dimensional requirements, giving engineers and end users confidence in performance. Stainless steel flanges are available to meet a variety of standards, including AWWA, DIN or metric, and ANSI-class rated.
AWWA C228 – Sets minimum material and dimensional requirements for stainless steel flanges in piping systems.
ASTM A182 – Covers forged or rolled stainless steel components designed for high-temperature service.
ANSI/ASME B16.5 – Dimensional standard for pipe flanges and fittings.
ANSI/ASME B16.47 – Applies to large-diameter steel and stainless steel flanges.
DIN/Metric Standards – European and international standards commonly used worldwide.
Different grades of stainless steel are available to match specific operating environments and performance needs. The right grade helps prevent corrosion, withstand stress, and extend service life in demanding conditions.
304 Stainless Steel – General-purpose grade with good corrosion resistance and strength.
304L Stainless Steel – Low carbon content for improved weldability and higher corrosion resistance.
316 Stainless Steel – Includes nickel and molybdenum for added protection against chlorides and high-temperature exposure.
316L Stainless Steel – Low carbon version of 316 with enhanced weldability and resistance in aggressive environments.
High Carbon Variants (304H, 316H) – Offer higher tensile strength at elevated temperatures.
Dual Grades (304/304L, 316/316L) – Higher strength grades, with lower Carbon content, meet the material requirements of more than one standard, such as AWWA C228, for broader application use.
Used in everyday plumbing and building systems where strength and reliability are essential.
Handles high-pressure and high-temperature conditions for transporting liquids or gases in factories and processing plants.
Resistant to aggressive chemicals, making them ideal for pipelines carrying acids, solvents, and other corrosive materials.
* For specialized projects, always refer to the applicable standards or contact us to select the correct grade and flange type.
Slides over the pipe and is welded at both the inner and outer diameters. Easier to install and align than weld neck, but suited for moderate pressure systems.
Solid flange with no bore, used to seal the end of a pipe system or pressure vessel. Allows easy access for inspection or future expansion.
Designed with a long tapered hub that is welded to the pipe, providing excellent strength and stress distribution. Ideal for high-pressure and high-temperature applications.
Has a socket to insert the pipe before welding. Provides good flow characteristics and is used in small-bore, high-pressure lines.
Features internal threads to connect with externally threaded pipes without welding. Common in low-pressure and non-critical applications.
Used with a stub end fitting. The flange itself does not touch the process fluid and can rotate around the pipe, making alignment and assembly easier.
The entire face is flat and flush with the gasket surface. Used where space or flexibility is limited, typically in low-pressure applications.
Includes a raised sealing surface around the bore to improve gasket compression and leak resistance under moderate pressure.
A stainless steel flange is a forged or plate component used to connect piping systems. Made from stainless steel alloys containing chromium and nickel, these flanges offer excellent durability, weldability, and resistance to corrosion, pressure, and high temperatures. Common grades include 304, 304L, 304/304L grade, and 316, 316L, 316/316L dual grade, which are valued for strength and versatility. Specialty grades such as 317L, 310S, or 321H are often used in demanding environments like heat exchangers, marine systems, and aerospace applications. Learn more in our blog post: Guide to Stainless Steel Flanges.
Stainless steel is available in 304, 304L, and 316, 316L. The L designates stainless steel with a lower carbon content than the standard 304 or 316 grades. 304L and 316L are softer alloys allowing for improved weldability, and with a lower carbon content offer higher corrosion-resistance. Though the low carbon options offers greater corrosion resistance, the yield strengths are slightly lower than their standard grade counterparts. Stainless steel with high carbon content is designated with an H, as in 304H or 316H, and is preferred for improved tensile/yield strength at higher temperatures.
Dual grade 304/304L or 316/316L stainless steel material meets more than one standard. For example, 304/304L stainless steel’s chemical composition meets the certification requirements for 304 stainless steel and the requirements for 304L stainless steel. Dual grade material offers the advantages of both: standard grades (higher yield strengths), and L grades (improved weldability and higher corrosion resistance). Dual-grade stainless steel fulfills AWWA C228 material specifications.
While both 304 and 316 stainless steel are corrosion-resistant, 316 stainless steel includes nickel and molybdenum for better performance at higher temperatures and improved corrosion resistance. Because it offers better resistance to pitting corrosion from saltwater, 316 stainless steel is preferred for marine environments over 304 stainless steel.
The primary ASTM specification for stainless steel flanges is ASTM A182, which covers forged stainless steel and alloy steel flanges, fittings, and valves designed for high-temperature service. In addition, ASTM A240 applies to stainless steel plates used in manufacturing flange components.
To order SS flanges from API International, determine your required pipe size, pressure class, material, and any special standards (such as ASNI/ASME B16.5). Contact API International’s experienced team and we 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.
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