Zinc-plated flanges, often referred to as electro-galvanized flanges, are typically steel flanges that are coated with zinc through electrodeposition, a process in which zinc is deposited onto the metal surface using an electric current. This process creates a uniform protective layer that shields the metal from moisture and corrosive environments.
Zinc coatings extend service life in a wide range of environments, including transportation, marine, aerospace, and industrial utilities. Zinc-plated flanges are a reliable choice for protecting carbon and low alloy steels used in flanged connections, as the zinc acts as a sacrificial anode, corroding before the underlying steel.
Electroplated zinc forms a strong barrier against moisture and oxidation. In addition, supplementary finishes (e.g., chromates, passivates, or phosphates) can further improve resistance, appearance, and durability.
ASTM B633 defines thickness classes ranging from 5 µm to 25 µm, with thicker coatings extending time to first maintenance. Zinc plating can provide years of dependable protection at a lower cost than other coating methods.
Because electrodeposition is electrically driven, the zinc layer develops evenly across the flange surface. This results in smooth coverage even on edges and recesses, which provides consistent performance without weak spots.
Specification for zinc plated (electrodeposited) coatings is ASTM B633-23 – Standard Specification for Electrodeposited Coatings of Zinc on Iron and Steel. This specification outlines requirements for zinc coating application, thickness, supplementary finishes, and hydrogen embrittlement considerations. It applies to a wide range of iron and steel products that need corrosion protection, including:
Flanges, nuts, bolts, and fasteners
Automotive, aerospace, and marine hardware
Industrial components exposed to corrosive atmospheres
According to ASTM B633-23, coatings must be electrodeposited non-alloyed zinc and may be applied in one of four standard thickness classes (5–25 µm). This standard also specifies restrictions for high-strength steels (>1700 MPa), as these materials are susceptible to hydrogen embrittlement during electroplating.
| Class (Fe/Zn) | Thickness (µm) | Typical Service Notes |
|---|---|---|
| Fe/Zn 5 | 5 µm | Light indoor, mild conditions |
| Fe/Zn 8 | 8 µm | Moderate indoor, occasional moisture |
| Fe/Zn 12 | 12 µm | Suburban/urban outdoor, light industrial |
| Fe/Zn 25 | 25 µm | Severe or very severe service, marine/coastal |
Zinc plated flanges are used in vehicle assemblies because of their resistance to condensation, road salt, and moisture.
Zinc plated flanges help prevent corrosion in aerospace systems, especially for components exposed to varying atmospheric conditions.
Zinc plating delivers barrier protection against degradation and is ideal for hardware exposed to saltwater and high humidity.
Equipment Zinc plated flanges are widely used in machinery, piping systems, and production lines.
Zinc plated flanges are commonly used in applications exposed to moderate weathering or indoor condensation, including hardware from HVAC networks and construction fittings.
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.
Steel or iron flanges coated with zinc using electrodeposition for corrosion protection.
Zinc plated flanges provide a thinner, smoother, more uniform finish ideal for indoor to moderate outdoor conditions. Hot-dip galvanized flanges offer a thicker, rougher layer for long-term heavy-duty outdoor service.
Yes — they follow ASTM B633-23, which defines classes of thickness, finishing options, and performance criteria.
To order zinc plated flanges from API International, determine your required pipe size, pressure class, material, and any special standards (such as ASME B16.5). Contact API International’s experienced team and we will help you select the right flange for your application.
• 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) | Stainless Steel, Carbon 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 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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