An aluminum slip-on flange slides over the outside of a pipe, then is welded in place. The pipe passes through the flange bore, so the flange can be aligned with the mating flange before welding. The result is a bolted, detachable connection - you can open it for inspection, maintenance, or replacement without cutting pipe.
Compared with weld neck flanges, slip-on flanges have a simpler structure and are easier to position during installation. They fit general water, air, HVAC, marine, and compressed-air piping systems where the service conditions and project specification allow slip-on connections.
GNEE supplies aluminum slip-on flanges in standard sizes up to DN350, with larger diameters and non-standard dimensions available as custom production based on drawings.
How a Aluminum Slip-On Flange Connects
Pipe → Slip-On Flange → Weld → Gasket → Mating Flange → Bolts
Installation sequence:
Slide the flange onto the pipe.
Position and align the flange with the mating flange.
Weld the pipe and flange using the procedure specified for the aluminum alloy.
Place the gasket between the two flange faces.
Insert bolts, tighten to the specified torque.
The connection is detachable - remove the bolts to open the joint.
A slip-on flange typically has:
A center bore that the pipe passes through
A sealing face (flat face or raised face)
Bolt holes on a bolt circle
A specified thickness
The exact geometry depends on the standard, size, pressure class, and facing.
Key Advantages of Aluminum Slip-On Flange
Simple installation. No tapered neck, no precise butt-weld fit-up. The flange slides on, gets aligned, and is fillet-welded. Easier to position than a weld neck flange.
Lightweight. Aluminum density is about 2.70 g/cm³ - roughly one-third of steel (7.85 g/cm³). For systems with many flanged joints, this means easier handling, lighter supports, and lower shipping costs.
Corrosion resistance. Aluminum forms a thin oxide layer (about 4 nm) that regenerates if scratched. Good resistance in atmospheric and many freshwater environments. Not universal - seawater, strong chemicals, and galvanic contact with steel or copper need case-by-case alloy review.
Galvanic corrosion warning: When an aluminum flange contacts steel flanges, steel bolts, or copper components with moisture present, aluminum corrodes faster. Use insulating gaskets, bolt sleeves, and washers if mixing metals is unavoidable.
Easy machining. Aluminum machines cleanly - bores, bolt holes, custom PCDs, special thicknesses, and non-standard dimensions are practical to produce.
Detachable. Remove the bolts to open the joint for inspection, valve removal, gasket replacement, or future modification.
Specifications of Aluminum Slip-On Flange
| Parameter | Specification |
|---|---|
| Product | Aluminum Slip-On Flange |
| Flange type | Slip-On |
| Alloys | 1060, 3003, 5083, 6061, 6063, 6082, and other specified alloys |
| Standard size | Up to DN350 |
| Larger sizes | Custom production based on drawings |
| Pressure class | Class 150, Class 300, PN10, PN16, or per project |
| Facing | FF, RF, or specified |
| Standards | ASME B16.5, EN 1092-1, JIS, DIN, or customer drawing |
| Bore | Matched to pipe OD and flange design |
| Bolt pattern | Standard or customized |
| Surface | Mill finish or specified finish |
| Production | Standard and custom |
Pressure-temperature ratings depend on the standard, alloy, size, and temperature. Do not read the nominal class as a universal PSI value - aluminum flanges have lower pressure-temperature ratings than steel flanges of the same class.
Aluminum Alloy Options
| Alloy | Series | Density (g/cm³) | Tensile Strength (MPa, typical) | Key Characteristics | Typical Use |
|---|---|---|---|---|---|
| 1060 | 1xxx | 2.70 | 95–130 | High purity, low strength, excellent corrosion resistance and formability | Chemical piping, corrosion-resistant service |
| 3003 | 3xxx | 2.73 | 130–200 | Good strength, good formability and corrosion resistance | General purpose, tanks, heat exchangers |
| 5083 | 5xxx | 2.66 | 275–350 | High strength, excellent marine corrosion resistance | Shipbuilding, offshore, marine piping |
| 6061 | 6xxx | 2.70 | 290–310 (T6) | Heat-treatable, good strength, weldability, machinability | Structural, piping, general industrial |
| 6063 | 6xxx | 2.70 | 215–250 (T6) | Good extrusion and surface finish, moderate strength | Standard piping, architectural |
| 6082 | 6xxx | 2.70 | 300–340 (T6) | Higher strength than 6061, good weldability | Structural, engineering applications |
Tensile strength varies by temper and product form. Confirm the specific temper and specification before ordering. The strongest alloy is not automatically the right choice - selection depends on the medium, temperature, pressure, corrosion environment, welding requirements, and applicable standard.
Welding guide for slip-on flange alloys:
| Alloy | Typical Filler Wire |
|---|---|
| 1060 | 1100 or 4043 |
| 3003 | 4043 or 5356 |
| 5083 | 5183 or 5356 |
| 6061 | 4043 or 5356 |
| 6063 | 4043 or 5356 |
| 6082 | 4043 or 5356 |
Confirm the welding procedure and filler metal with the manufacturer before production.
Dimensions to Confirm
DN alone does not define a complete flange. When ordering, confirm:
| Dimension | Description |
|---|---|
| OD | Flange outside diameter |
| Bore | Center opening (matched to pipe OD) |
| T | Flange thickness |
| PCD / BCD | Bolt circle diameter |
| Bolt hole diameter | Size of each hole |
| Number of holes | Total bolt-hole quantity |
| Facing | FF, RF, or other |
| Pipe OD | Actual pipe outside diameter |
For standard flanges, these dimensions are set by the applicable standard, nominal size, and pressure class. For custom flanges, provide a dimensioned drawing.
Example of a complete inquiry: "6061-T6 Aluminum Slip-On Flange, DN150, ASME B16.5, Class 150, RF, 100 pcs, chilled water." This gives the supplier everything needed to quote accurately. Compare with "Please quote DN150 aluminum slip-on flanges" - that leaves alloy, standard, class, facing, and quantity unknown.
Slip-On vs Other Flange Types
| Type | Pipe Connection | Main Feature | Typical Consideration |
|---|---|---|---|
| Slip-On | Pipe passes through flange | Simple structure | General piping |
| Weld Neck | Butt weld | Tapered neck | More demanding service |
| Socket Weld | Pipe inserted into socket | Compact connection | Small-bore piping |
| Lap Joint | Used with Stub End | Flange rotates | Frequent dismantling |
| Blind | No center bore | Closes opening | Pipe/equipment closure |
| Threaded | Threaded connection | No welding | Selected threaded systems |
| Plate | Fabricated/welded | Custom dimensions | Tanks, custom systems |
Slip-On vs Weld Neck: Slip-On - pipe passes through the flange and is fillet-welded. Weld Neck - pipe butt-welds to a tapered neck. Slip-On is simpler and easier to position; Weld Neck provides a smoother stress transition for demanding pressure, temperature, or cyclic service when the engineering design requires it. Neither "Slip-On = low pressure" nor "Weld Neck = high pressure" is a universal rule.
Slip-On vs Socket Weld: Slip-On - pipe passes completely through. Socket Weld - pipe fits into a recessed socket (does not pass through). Clear difference in cross-section. Socket Weld is common for smaller-bore piping; Slip-On covers a broader range of general piping.
Slip-On vs Lap Joint: Slip-On - flange welds directly to the pipe. Lap Joint - flange slides over a Stub End welded to the pipe, so it can rotate for easier bolt-hole alignment and removal. Use Lap Joint for frequent dismantling; use Slip-On for standard installations.
Standards and Interchangeability
| Standard | Origin | Pressure Designation | Scope |
|---|---|---|---|
| ASME B16.5 | US | Class 150, 300, etc. | Pipe flanges NPS 1/2 to NPS 24 |
| EN 1092-1 | Europe | PN10, PN16, etc. | European flange standard |
| JIS B 2220 | Japan | Various | Japanese and some Asian projects |
| DIN | Germany | PN designations | Replacement orders and legacy systems |
ASME and EN flanges are not interchangeable. Different OD, bolt circle, bolt-hole count, hole size, thickness, and facing. DN150 ASME ≠ DN150 EN - always confirm the mating flange standard. For replacements, send a drawing or the existing flange dimensions.
Applications of Aluminum Slip-On Flange
Water treatment plants: Filter lines, backwash lines, clear water piping, utility water, water tank connections. Check the alloy against water chemistry and operating conditions.
Marine and shipbuilding: Dockside water lines, fresh-water piping, compressed-air piping, utility piping on vessels. Only specific alloys (typically 5083 or 5086) are suitable for marine service - not all aluminum alloys are marine-grade. Conduct a corrosion assessment for actual seawater exposure.
HVAC and cooling: Chilled water, condenser water, cooling water, air-handling systems. Among the most common applications for aluminum slip-on flanges.
Factory compressed air: Main lines, branch lines, equipment connections, air distribution. Aluminum piping is popular for compressed-air systems because it is lightweight and does not rust inside. Confirm flange pressure rating against the actual system design.
Tanks and vessels: Tank nozzles, vessel nozzles, water and air connections, equipment interfaces. For custom nozzles, provide a drawing.
Industrial utility systems: Water, air, and selected non-corrosive utility services where aluminum is compatible with the medium.
Custom Aluminum Slip-On Flanges
Not every piping system uses standard dimensions. GNEE can produce custom slip-on flanges for:
Special OD or bore
Non-standard PCD or bolt-hole patterns
Special thickness or facing
Non-standard pipe OD
Diameters larger than DN350
Custom equipment connections
Best information to provide: a dimensioned technical drawing. If no drawing is available, provide OD + bore + thickness + PCD + bolt-hole diameter + number of holes + pipe OD + facing. A photo of the existing flange helps with initial identification.
GNEE Manufacturing and Quality
GNEE produces aluminum slip-on flanges for standard and custom requirements. A typical production flow:
Raw material → Cutting → Machining → Bolt-hole processing → Face machining → Inspection → Surface treatment if required → Packaging
For custom products, production follows the approved drawing and technical specification.
Dimensional inspection before shipment covers: OD, bore, thickness, PCD, bolt-hole diameter, hole count, facing dimensions, and overall dimensions. Material documentation can be provided when required by the order. Project-specific inspection procedures can be agreed before production.
Packaging protects flange faces, bolt holes, machined bores, and finished surfaces during transport. Options include protective film, individual protection, cartons, pallets, wooden cases, and custom export packaging, adjusted to container loading and customer requirements.
Why Choose GNEE
Standard sizes up to DN350, larger sizes customized based on drawings
Alloys in stock: 1060, 3003, 5083, 6061, 6063, 6082
Custom dimensions: OD, bore, PCD, thickness, bolt-hole pattern, facing
Application-based material selection: GNEE reviews media, temperature, pressure, application, and required standard before confirming material and configuration - not just nominal strength
Certifications: GNEE holds ISO and CE certifications.
FAQ
What is the difference between Slip-On and Weld Neck flanges?
Slip-On: pipe passes through the flange and is fillet-welded. Weld Neck: pipe butt-welds to a tapered neck with a smoother stress transition. Slip-On is simpler and easier to position; Weld Neck is used for more demanding pressure, temperature, or cyclic service when required by engineering design.
What is the difference between Slip-On and Socket Weld flanges?
The pipe passes completely through a Slip-On flange. In a Socket Weld flange, the pipe fits into a recessed socket and does not pass through. Socket Weld is common for small-bore piping; Slip-On covers general piping.
What is the difference between Slip-On and Lap Joint flanges?
A Slip-On flange welds directly to the pipe. A Lap Joint flange slides over a Stub End welded to the pipe, so it rotates for easier bolt-hole alignment and removal. Use Lap Joint for frequent dismantling.
Are aluminum slip-on flanges suitable for water?
Yes, for many water services - provided the alloy, pressure, temperature, and water chemistry are appropriate for the specific application.
Can aluminum slip-on flanges be used for seawater?
Some alloys - particularly 5083 - are used in marine environments. But seawater service requires careful evaluation of alloy compatibility, corrosion, galvanic effects, and system design. Not all aluminum alloys are marine-grade.
What aluminum alloy is best for slip-on flanges?
There is no single best alloy. 6061-T6 is a common choice where strength and machinability matter; 5083 for marine service; 1060 and 3003 for less demanding, corrosion-focused applications. Selection depends on the medium, temperature, pressure, and welding requirements.
What sizes are available?
Standard aluminum slip-on flange sizes up to DN350. Larger diameters can be produced as custom orders based on drawings.
Can GNEE make custom aluminum slip-on flanges?
Yes. Custom OD, bore, PCD, thickness, bolt-hole patterns, facing, and other dimensions can be produced based on drawings and project requirements.
What information do I need for a quotation?
Flange type, alloy, DN/NPS or pipe OD, standard, pressure class, facing, quantity, and application. For custom flanges, a dimensioned drawing is strongly recommended.
GNEE Aluminum Slip-On Flange Supplier
GNEE supplies aluminum slip-on flanges for water treatment, HVAC, marine, shipbuilding, compressed air, tanks, vessels, and industrial utility systems. Standard configurations up to DN350; larger or non-standard flanges evaluated based on customer drawings.
For a quotation, send your size, alloy, standard, pressure class, facing, quantity, and application. If you are not sure which alloy or configuration is suitable, provide the medium, temperature, pressure, and pipe information - GNEE can review the requirements before production.
