Aluminum Flange — ASME B16.5 & EN 1092-1 Forged Fittings
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What Is an Aluminum Flange?
An aluminum flange is a forged or machined ring used to connect pipes, valves, pumps, and pressure vessels in low- to medium-pressure piping systems. Compared with carbon-steel or stainless flanges, aluminum flanges weigh roughly one-third as much (6061-T6 density 2.70 g/cm³ vs. A105 carbon steel 7.85 g/cm³), offer excellent atmospheric corrosion resistance, and are easier to machine-making them the default choice where weight reduction, non-magnetic behavior, or corrosion resistance matters more than ultra-high pressure or elevated temperature.
GNEE supplies seven core face types-Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ), Lap Joint, Tongue & Groove, Male & Female, and Serrated-in pressure classes ASME B16.5 Class 150 and 300, EN 1092-1 PN6 to PN40, JIS B2220 5K/10K/16K, and GOST 12820-12821. Alloys include 6061-T6, 6063-T5, 5083, 5086, 5052, 3003, and 1100-each shipped with full EN 10204 3.1 mill certificate.
Important: Aluminum flanges are designed for Class 150 / PN16 and below at service temperatures of 200°C or lower. They are not suitable for high-pressure hydrocarbon refinery service, steam lines, or strong acid/alkali piping. For those applications, specify carbon steel (A105) or stainless steel (304/316L).
Aluminum Alloys - Chemical Composition & Mechanical Properties
Below are the complete chemistry and mechanical data for the seven alloys GNEE stocks, sourced from ASTM B221, EN 573-3, and the ASM Handbook, Volume 2.
Chemical Composition (per ASTM B221 / EN 573-3)
| Alloy | Si | Fe | Cu | Mn | Mg | Zn | Cr | Ti | Others | Typical Temper |
|---|---|---|---|---|---|---|---|---|---|---|
| 1100 | ≤0.95 (Si+Fe) | - | 0.05-0.20 | ≤0.05 | - | ≤0.10 | - | - | ≤0.15 | O / H14 |
| 3003 | ≤0.6 | ≤0.7 | 0.05-0.20 | 1.0-1.5 | - | ≤0.10 | - | - | ≤0.15 | O / H14 |
| 5052 | ≤0.25 (Si+Fe) | - | ≤0.10 | ≤0.10 | 2.2-2.8 | ≤0.10 | 0.15-0.35 | - | ≤0.15 | O / H32 |
| 5083 | ≤0.40 | ≤0.40 | ≤0.10 | 0.40-1.0 | 4.0-4.9 | ≤0.25 | 0.05-0.25 | ≤0.15 | ≤0.15 | O / H116 |
| 5086 | ≤0.40 | ≤0.50 | ≤0.10 | 0.20-0.7 | 3.5-4.5 | ≤0.25 | 0.05-0.25 | ≤0.15 | ≤0.15 | O / H116 |
| 6061 | 0.40-0.8 | ≤0.7 | 0.15-0.40 | ≤0.15 | 0.8-1.2 | ≤0.25 | 0.04-0.35 | ≤0.15 | ≤0.15 | T6 / T651 |
| 6063 | 0.20-0.6 | ≤0.35 | ≤0.10 | ≤0.10 | 0.45-0.9 | ≤0.10 | ≤0.10 | ≤0.10 | ≤0.15 | T5 / T6 |
Mechanical Properties & Service Temperature Envelope (per ASM Handbook Vol. 2)
| Alloy / Temper | Tensile (MPa) | Yield (MPa) | Elong. % | Brinell HB | Max Service Temp | Best Fit For |
|---|---|---|---|---|---|---|
| 1100-O | 90 | 35 | 35 | 23 | 200 °C (392 °F) | Chemical tanks, food contact |
| 3003-O | 110 | 40 | 30 | 28 | 200 °C (392 °F) | HVAC ducts, low-stress lines |
| 5052-H32 | 230 | 195 | 12 | 60 | 200 °C (392 °F) | Marine fuel lines |
| 5083-O | 290 | 145 | 22 | 75 | 150 °C (302 °F) | Shipbuilding, cryogenic |
| 5086-H116 | 260 | 110 | - | 70 | 150 °C (302 °F) | Marine saltwater |
| 6061-T6 | 310 | 275 | 12 | 95 | 200 °C (392 °F) | Structural, general purpose |
| 6063-T5 | 186 | 145 | 8 | 60 | 200 °C (392 °F) | Architectural, anodized finish |
Temperature guidance: Aluminum alloys lose approximately 50% of tensile strength above 150 °C. The practical ceiling for sustained service is 150-200 °C depending on the alloy. Above 200 °C, always specify carbon steel (A105) or stainless steel (304/316L). The 5083 and 5086 marine alloys have a lower ceiling (150 °C) because high-magnesium alloys become susceptible to stress-corrosion cracking at elevated temperatures.
Nine Aluminum Flange Types - Pick by Service
Each type below is manufactured to ASME B16.5 or EN 1092-1 dimensional tolerances. Click through for full dimension tables, or send your flange schedule for a same-day quote.
Aluminum Slip-On Flanges (SO)
ASME B16.5 Class 150 / EN 1092-1 PN10
Slides over the pipe and is fillet-welded on both sides. The most economical flange for low-pressure air, water, and oil lines. Easy to align bolt holes during assembly.
Aluminum Welding Neck Flanges (WN)
ASME B16.5 Class 150 & 300
Long tapered hub transfers stress concentration into the pipe wall. Best where pressure fluctuations or thermal cycling occur. The aluminum weld-neck flange is ideal for piping systems that need full-penetration weld integrity.
Aluminum Blind Flanges (BL)
ASME B16.5 Class 150
Seals the end of a pipe for pressure testing or future expansion. Custom drill patterns available for any gasket configuration. As an aluminum blind flange supplier, GNEE stocks standard and custom patterns.
Aluminum Socket Weld Flanges (SW)
ASME B16.5 Class 300
Pipe seats into a recessed socket and then fillet-welded. Used on small-bore (under 2″) high-pressure lines where vibration is a concern. Provides a smooth bore transition.
Aluminum Threaded Flanges (TH)
ASME B1.20.1 NPT
No welding required. Threads onto matching NPT pipe. Used on low-pressure, small-diameter lines that need fast assembly or disassembly - ideal where hot work permits are not available.
Aluminum Lap joint flanges
ASME B16.5 Class 150
Loose flange + stub end combination. The flange rotates freely for easy bolt-hole alignment. Ideal for corrosive service where the stub end can be alloy-selected separately from the backing flange.
Large-Diameter Aluminum Pipe Flanges (>48″)
Rolled plate + welded + machined
For wind tower internals, structural frames, and marine bulkheads. Rolled from ASTM B209 plate, welded with qualified GTAW/PAW procedures, then machined flat. Up to 5 m OD (197 in.).
Aluminum Reducing Flange
ASME B16.5 Class 150
Connects different NPS sizes in a single joint. Available in concentric or eccentric configurations. Eliminates the need for a separate reducer plus flange.
Square & Rectangular Flange
Custom geometric
Custom-shaped flanges for ductwork, handrail bases, and architectural connections. Fabricated from 6063-T5 plate with anodized finish available.
Dimension Tables
Slip-On & Threaded Flange - ASME B16.5 Class 150 (Aluminum)
| NPS (in) | DN | Flange OD (in) | Bolt Circle (in) | Bolt Holes | Bolt Dia (in) | Rated Pressure @ 72 °F |
|---|---|---|---|---|---|---|
| 1/2 | 15 | 3.50 | 2.38 | 4 | 0.62 | 150 psi (Class 150) |
| 3/4 | 20 | 3.88 | 2.75 | 4 | 0.62 | 150 psi |
| 1 | 25 | 4.25 | 3.12 | 4 | 0.62 | 150 psi |
| 1-1/4 | 32 | 4.62 | 3.50 | 4 | 0.62 | 150 psi |
| 1-1/2 | 40 | 5.00 | 3.88 | 4 | 0.62 | 150 psi |
| 2 | 50 | 6.00 | 4.75 | 4 | 0.75 | 150 psi |
| 2-1/2 | 65 | 7.00 | 5.50 | 4 | 0.75 | 150 psi |
| 3 | 80 | 7.50 | 6.00 | 4 | 0.75 | 150 psi |
| 4 | 100 | 9.00 | 7.50 | 8 | 0.75 | 150 psi |
| 6 | 150 | 11.00 | 9.50 | 8 | 0.88 | 150 psi |
| 8 | 200 | 13.50 | 11.75 | 8 | 0.88 | 150 psi |
| 10 | 250 | 16.00 | 14.25 | 12 | 1.00 | 150 psi |
| 12 | 300 | 19.00 | 17.00 | 12 | 1.00 | 150 psi |
Blind Flange - ASME B16.5 Class 150
| NPS (in) | Flange OD (in) | Bolt Circle (in) | Bolt Holes | Bolt Dia (in) | Thickness (in) |
|---|---|---|---|---|---|
| 1/2 | 3.50 | 2.38 | 4 | 0.62 | 0.44 |
| 3/4 | 3.88 | 2.75 | 4 | 0.62 | 0.50 |
| 1 | 4.25 | 3.12 | 4 | 0.62 | 0.56 |
| 1-1/4 | 4.62 | 3.50 | 4 | 0.62 | 0.62 |
| 1-1/2 | 5.00 | 3.88 | 4 | 0.62 | 0.69 |
| 2 | 6.00 | 4.75 | 4 | 0.75 | 0.75 |
| 3 | 7.50 | 6.00 | 4 | 0.75 | 0.94 |
| 4 | 9.00 | 7.50 | 8 | 0.75 | 0.94 |
| 6 | 11.00 | 9.50 | 8 | 0.88 | 1.00 |
| 8 | 13.50 | 11.75 | 8 | 0.88 | 1.13 |
| 10 | 16.00 | 14.25 | 12 | 1.00 | 1.19 |
| 12 | 19.00 | 17.00 | 12 | 1.00 | 1.25 |
Weld Neck Flange - ASME B16.5 Class 150
| NPS (in) | Flange OD (in) | Bolt Circle (in) | Bolt Holes | Bolt Dia (in) | Hub Base Dia (in) |
|---|---|---|---|---|---|
| 1/2 | 3.50 | 2.38 | 4 | 0.62 | 1.94 |
| 1 | 4.25 | 3.12 | 4 | 0.62 | 2.56 |
| 2 | 6.00 | 4.75 | 4 | 0.75 | 3.62 |
| 3 | 7.50 | 6.00 | 4 | 0.75 | 5.00 |
| 4 | 9.00 | 7.50 | 8 | 0.75 | 6.19 |
| 6 | 11.00 | 9.50 | 8 | 0.88 | 8.50 |
| 8 | 13.50 | 11.75 | 8 | 0.88 | 10.62 |
| 10 | 16.00 | 14.25 | 12 | 1.00 | 12.75 |
| 12 | 19.00 | 17.00 | 12 | 1.00 | 15.00 |
For Class 300 dimensions, refer to ASME B16.5 Table 2 (available on request). GNEE stocks both Class 150 and Class 300 in 6061-T6.
Loose Plate Flange - EN 1092-1 PN10 (Aluminum)
| DN | d1 (mm) | Type | b (mm) | Approx. Weight (kg) |
|---|---|---|---|---|
| 10 | 17.2 | C | 12 | 0.20 |
| 15 | 21.3 | C | 12 | 0.18 |
| 20 | 26.9 | C | 12 | 0.24 |
| 25 | 33.7 | C | 12 | 0.24 |
| 32 | 42.4 | C | 16 | 0.52 |
| 40 | 48.3 | C | 16 | 0.58 |
| 50 | 60.3 | C | 16 | 0.70 |
| 65 | 76.1 | C | 16 | 0.85 |
| 80 | 88.9 | C | 18 | 1.04 |
| 100 | 114.3 | C | 18 | 1.18 |
| 125 | 139.7 | C | 18 | 1.43 |
| 150 | 168.3 | C | 18 | 1.70 |
| 200 | 219.1 | C | 20 | 2.49 |
| 250 | 273.0 | C | 22 | 3.24 |
| 300 | 323.9 | C | 22 | 3.72 |
| 400 | 406.4 | C | 25 | 6.94 |
| 500 | 508.0 | C | 28 | 9.32 |
| 600 | 609.6 | C | 30 | 12.13 |
| 700+ | - | - | - | Inquire per project |
Surface Finish Options
| Finish | Roughness Ra (µm) | Typical Use | Source |
|---|---|---|---|
| Stock finish | 3.2-6.3 | General service, soft gaskets | ASME B16.5 |
| Spiral serrated | 3.2-6.3 | Spiral-wound gaskets | ASME B16.5 |
| Concentric serrated | 3.2-6.3 | Solid metal gaskets | ASME B16.5 |
| Smooth | ≤1.6 | Jacketed gaskets, sanitary | ASME B16.5 |
| Anodized | - | Architectural, decorative | Custom |
Where Aluminum Flanges Are the Right Call
Aluminum flanges earn their place where one or more of these conditions apply:
- Weight budget-every kilogram saved cuts support structure and shipping cost
- Ambient or mildly elevated temperature (≤ 200 °C, see mechanical properties table above)
- Low to medium pressure (Class 150 / PN16 and below)
- Atmospheric or mild chemical corrosion - not strong acids or alkalis
- Non-magnetic requirement (instrumentation, electronics)
- Anodized architectural finish required for exposed installations
Marine & Shipbuilding
5083 and 5086 flanges on seawater lines, ballast systems, and exhaust ducts. Both alloys meet ASTM B928 for marine service. Salt-air corrosion resistance extends service life compared to carbon steel.
HVAC & Ventilation
6063-T5 slip-on flanges on rectangular and spiral ductwork, TDC/TDF systems. Lightweight for easy field assembly; anodized finish available for exposed runs in commercial buildings.
Cryogenic & Low-Temp Service
5083 retains toughness down to -196 °C (-320 °F) per ASTM B928. Used on LNG cold boxes, refrigeration skids, and cryogenic transfer lines. Confirm with engineering for your specific temperature cycle.
Architectural & Structural
Handrail base flanges, curtain wall supports, decorative column collars. Anodized 6063-T5 is the default choice for visible installations - available in clear, bronze, black, and custom colors.
Food, Beverage & Pharmaceutical
3003 and 1100 alloys in non-corrosive process lines. Both are listed under NSF/ANSI 61 for potable water contact. Smooth-finish flanges for sanitary connections available on request.
Instrumentation & Electronics
Non-magnetic 6061-T6 on instrument air lines, sample lines, and equipment housings where magnetic interference must be avoided. Ideal for MRI facilities, laboratory piping, and semiconductor cleanrooms.
How GNEE Manufactures Aluminum Flanges
Three production routes - each chosen by size, volume, and tolerance requirement:
Forging (1/2″ - 24″)
Billets meeting ASTM B221 → hot forging at 400-480 °C → T6 / T651 heat treatment per ASTM B918 → CNC finishing. Forged aluminum flange production delivers the highest strength and grain structure integrity.
Best for: Class 300, high-strength structural, pressure-critical applications.
Plate Cutting + Machining (1/2″ - 48″)
ASTM B209 aluminum plate → waterjet or plasma cut to blank → multi-axis CNC turning and drilling → surface finish to specification. The custom aluminum pipe flange route for mid-volume orders.
Best for: Custom sizes, short lead times, prototype quantities.
Rolling + Welding (>48″)
Plate rolled to ring → qualified GTAW/PAW weld procedure → stress relief → machining flat. Large diameter aluminum flange construction for wind towers and marine bulkheads.
Best for: Oversized structural flanges, marine bulkhead connections.
Quality Documentation - Every Shipment Includes:
- EN 10204 3.1 mill certificate - chemical composition + mechanical test results
- 100% dimensional inspection report - OD, bolt circle, hole diameter, thickness, face finish
- Material test report - alloy verification by OES spectrometry
- Third-party inspection available - SGS, BV, TUV, and all major shipyard surveyors (book 7 days ahead)
Packaging & Shipping
Aluminum flanges are securely packed for safe international transportation. Sealing faces and machined surfaces are protected with plastic caps, film, or suitable separators to prevent scratches, impact, dust, and moisture. Depending on flange size, quantity, and shipping method, products can be packed in wooden cases, plywood cases, cartons, or reinforced pallets. Customized packing, shipping marks, package labels, and export documentation are available according to customer requirements.
Standards & Certifications
| Standard | Scope | Applies To |
|---|---|---|
| ASME B16.5 | Pipe flanges & flanged fittings, NPS 1/2″-24″ | All aluminum forged flanges |
| ASME B16.47 | Large-diameter flanges NPS 26″-60″ | Custom large-diameter |
| EN 1092-1 | Steel & alloy flanges PN2.5-PN400 | All PN-class flanges |
| DIN 2633 | Weld-neck flange PN16 | Reference standard |
| JIS B2220 | Japanese flanges 5K/10K/16K/20K | APAC market |
| GOST 12820/12821 | Russian flanges | CIS market |
| KS 1503 | Korean flanges | Korean market |
| EN 10204 3.1 | Material test certificate | All shipments (default) |
| ASTM B221 | Extruded aluminum pipe & tube | Raw material specification |
| ASTM B209 | Aluminum plate | Raw material specification |
| ASTM B918 | Heat treatment of aluminum alloys | T6 / T651 tempering |
| ASTM B928 | High-Mg alloys for marine service | 5083 / 5086 marine flanges |
| NSF/ANSI 61 | Drinking water system components | 1100 / 3003 potable water lines |
ISO 9001, PED 2014/68/EU, ASME U-stamp, and DNV/ABS/LR marine class society certifications are available-confirm scope and validity with our sales team for your specific project requirement.
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Aluminum Flange - Frequently Asked Questions
Send Us Your Drawing or Flange Schedule
Tell us the standard (ASME / EN / JIS / GOST), pressure class, alloy, size, face type, finish, quantity, and destination port. Our export team returns a full landed-cost estimate - FOB Tianjin / Shanghai, CIF, or DDP - within 24 business hours.
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