Galvanized flanges are steel flanges coated with zinc through a hot-dip galvanizing process, in which the iron or steel is immersed in a bath of molten zinc at a temperature of around 450 °C (842 °F). This type of flange coating provides a durable barrier against corrosion. This protective layer ensures long service life in demanding environments such as water systems, outdoor structures, oil and gas facilities, and industrial piping. Because zinc acts as both a physical shield and a sacrificial coating, galvanized flanges deliver reliable performance with minimal maintenance.
Hot-dip galvanizing creates a metallurgical bond between zinc and steel, forming a barrier against corrosive elements. The zinc layer also provides cathodic protection, which means that if the coating is scratched, the surrounding zinc will corrode preferentially, safeguarding the underlying steel.
The service life of galvanized coatings is directly tied to thickness: the thicker the zinc layer, the longer the time to first maintenance. For outdoor or highly corrosive environments, this makes galvanized flanges a cost-effective, low-maintenance choice compared to uncoated or painted alternatives.
Because the hot-dip process immerses the entire part, you get uniform coverage even in hard-to-reach areas, hollow sections, edges, and recesses. The coating grows perpendicularly to the steel surface, maintaining consistent thickness across intricate geometries. This ensures there are no weak “uncoated” zones vulnerable to corrosion.
The most recognized specification for hot-dip galvanizing is ASTM A123/A123M – Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products. This specification outlines requirements for coating application, thickness, finish, and adherence across several product categories, including:
Structural shapes, plates, strip and bar
Pipe and tubing
Wire and reinforcing bar
According to ASTM A123/A123M, the coating must be continuous, smooth, and uniform, free of bare spots or defects that would impact performance. Coating thickness is determined by the material category and steel thickness, with the goal of providing strong adhesion and long-term corrosion resistance.
| Grade | Thickness (µm) | Thickness (mils) | Weight (g/m²) |
|---|---|---|---|
| 35 | 35 µm | 1.4 | 245 |
| 45 | 45 µm | 1.8 | 320 |
| 60 | 60 µm | 2.4 | 425 |
| 75 | 75 µm | 3.0 | 530 |
| 100 | 100 µm | 3.9 | 705 |
Used in plant piping and utility lines, they provide durable, low-maintenance connections for general services.
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.
Galvanized flanges are steel flanges coated with zinc using a hot-dip process, which provides corrosion resistance and extended service life.
The zinc coating protects against rust and moisture, which makes them more durable and low-maintenance than uncoated or painted flanges.
Yes. They are manufactured in compliance with ASTM A123/A123M and other recognized galvanizing specifications.
• 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:
• Material: Stainless Steel
- Sand Casting:
• Material: A536, Stainless Steel, Ductile Iron
- Investment/Lost-Wax/Precision Casting
• Material: 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 | 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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