Aluminum Alloy 6061-T6 Flanges
We are a professional 6061-T6 aluminum alloy flange manufacturer in China, supplying slip-on flanges, weld neck flanges, blind flanges, socket weld flanges and customized aluminum piping connections for industrial gas, air separation, heat exchanger, low-temperature equipment and chemical-processing applications.
Our aluminum flanges can be manufactured from ASTM B247 / ASME SB-247 aluminum alloy forgings or rolled ring forgings, ASTM B209 plate or other approved aluminum product forms.
Flange dimensions can be produced according to ASME B16.5 dimensional patterns, EN 1092-4, approved project drawings or customer-specific dimensional requirements.
Because pressure-temperature ratings depend on the material, temper, manufacturing route, flange geometry, gasket, bolting and applicable piping code, a 6061-T6 aluminum flange should not automatically be assigned the same rating as a steel flange with similar dimensions.
6061-T6 Aluminum Flange Product Summary
| Item | Available Supply |
|---|---|
| Material | Aluminum Alloy 6061 |
| UNS designation | UNS A96061 |
| Common temper | 6061-T6 |
| Alternative condition | T651, T652 or project-specified condition |
| Primary forging standard | ASTM B247 / ASME SB-247 |
| Plate material standard | ASTM B209 / ASME SB-209 |
| Extruded raw material | ASTM B221 / ASME SB-221, when approved |
| ASME dimensional pattern | ASME B16.5 |
| European aluminum flange standard | EN 1092-4 |
| Flange types | Slip-on, weld neck, blind, socket weld, lap joint and customized flange |
| Common ratings | Class 150, 300 and 600 when supported by the applicable design code |
| PN dimensions | PN10, PN16 and other EN 1092-4 ratings |
| Common sizes | DN40, DN50, DN65, DN80, DN100, DN125, DN150, DN200 and DN300 |
| Facing | Flat face, raised face or customized facing |
| Manufacturing | Forged, rolled ring, plate-cut or machined |
| Inspection | Visual, dimensional, PMI, penetrant and pressure testing when applicable |
| Documentation | Material certificate, dimensional report and inspection records |
| Country of origin | China |
Types of 6061 Aluminum Flanges
We manufacture different aluminum flange configurations according to the piping connection, service conditions and approved design.
| Flange type | Connection method | Typical use | Important consideration |
|---|---|---|---|
| Slip-on flange | Pipe inserted into flange bore and fillet welded | General fabricated aluminum piping | Requires internal and external weld control |
| Weld neck flange | Butt welded to the pipe through a tapered hub | Higher-load or cyclic piping connections | Bore and weld end must match the connecting pipe |
| Blind flange | Bolted closure without a central bore | Closing pipe ends, nozzles and inspection openings | Thickness must be verified against pressure and temperature |
| Socket weld flange | Pipe inserted into a machined socket and fillet welded | Compact small-bore piping | Socket depth, expansion gap and weld procedure must be controlled |
| Lap joint flange | Loose backing flange used with a stub end or collar | Systems requiring easier alignment or dismantling | Stub-end and backing-flange materials must be compatible |
| Plate flange | Cut and machined from aluminum plate | Low-pressure or drawing-specific connections | Pressure rating must be established by design |
6061-T6 Slip-On Flange
A 6061-T6 aluminum slip-on flange has a bore slightly larger than the outside diameter of the connecting pipe.
The pipe is inserted into the flange and normally secured by fillet welds. Slip-on flanges are often selected for fabricated equipment and piping systems where alignment, lower component weight and straightforward installation are important.
Available configurations include:
- Flat-face slip-on flange
- Raised-face slip-on flange
- Hubbed slip-on flange
- Plate-type slip-on flange
- ASME B16.5 dimensional pattern
- EN 1092-4 PN dimensional pattern
- Customized bolt circle and facing
The pipe outside diameter, wall thickness and welding procedure should be confirmed before the flange bore is machined.
6061-T6 Weld Neck Flange
A 6061-T6 aluminum weld neck flange incorporates a tapered hub that transfers loads from the flange ring to the connecting pipe.
The flange is butt welded to the pipe, providing a smoother internal flow transition than a socket weld or slip-on connection.
Important quotation parameters include:
- Nominal pipe size
- Actual pipe outside diameter
- Pipe wall thickness
- Flange class or design pressure
- Bore diameter
- Weld-end geometry
- Flange facing
- Material temper
- Applicable piping code
The flange bore should match the connecting pipe wall thickness to minimize internal mismatch at the butt-weld joint.
6061-T6 Blind Flange
A 6061-T6 aluminum blind flange is used to close the end of a pipe, valve, vessel nozzle or equipment connection.
Blind flanges can be manufactured as:
- Flat-face blind flange
- Raised-face blind flange
- Male-and-female facing
- Tongue-and-groove facing
- O-ring groove flange
- Inspection-port flange
- Drawing-specific closure flange
Blind-flange thickness must be based on the selected standard or an approved pressure-design calculation. A steel flange drawing should not be copied without confirming that the resulting aluminum flange has adequate strength for the intended service.
6061-T6 Socket Weld Flange
A 6061-T6 aluminum socket weld flange contains a machined internal socket into which the pipe is inserted.
The pipe is normally positioned with a specified expansion gap before the external fillet weld is completed.
Socket weld flanges may be considered for compact, small-bore aluminum piping systems, but the final design must account for:
- Pipe outside diameter
- Socket diameter
- Socket depth
- Minimum flange wall
- Fillet-weld dimensions
- Thermal expansion gap
- Weld-access requirements
- Internal crevice conditions
- Applicable piping code
Socket weld availability is subject to technical review because not every nominal size, wall thickness or pressure class is suitable for this construction.
ASTM B247 6061-T6 Aluminum Forgings
ASTM B247 / ASME SB-247 is the principal material specification for aluminum and aluminum-alloy die forgings, hand forgings and rolled ring forgings.
For pressure-containing or mechanically loaded aluminum flanges, a forged or rolled-ring blank is generally preferable to an unspecified cast or plate-cut blank where the project requires a recognized forging material specification.
The material purchase description should identify:
- Alloy: 6061
- Temper: T6 or other specified temper
- Product form: hand forging or rolled ring forging
- Material standard and edition
- Required mechanical properties
- Heat or lot traceability
- Inspection certificate
- Supplementary testing requirements
The current ASTM catalogue identifies ASTM B247-25 as the specification for aluminum and aluminum-alloy die forgings, hand forgings and rolled ring forgings. (Source: ASTM International.)
ASME B16.5 Aluminum Flange Dimensions
ASME B16.5 covers flange dimensions, tolerances, materials, marking, testing and pressure-temperature rating requirements for pipe flanges from NPS 1/2 through NPS 24.
The standard includes Class 150, 300, 400, 600, 900 and 1500 flanges through NPS 24, together with Class 2500 flanges through NPS 12. (Source: ASME.)
For a 6061-T6 aluminum flange, it is important to separate two requirements:
- Dimensional compatibility with an ASME B16.5 flange pattern.
- Allowable pressure-temperature rating for the selected aluminum alloy and temper.
A flange may be machined with an ASME B16.5 bolt circle, outside diameter and facing while still requiring a separate material-specific rating assessment.
A recommended technical description is:
6061-T6 aluminum alloy flange manufactured from ASTM B247 forging, with dimensional pattern to ASME B16.5 and pressure-temperature rating established under the applicable piping code.
ASME B31.3 Appendix L
ASME B31.3 Appendix L provides pressure-temperature rating provisions for certain aluminum alloy flanges, including flanges manufactured from ASTM B247 6061-T6 material.
Published ASME technical literature identifies Class 150, 300 and 600 rating provisions for 3003-H112 and 6061-T6 aluminum alloy flanges under this appendix. (Source: ASME technical publications.)
The applicable rating should be verified against:
- The project’s adopted B31.3 edition
- Flange size
- Flange class
- Design temperature
- Manufacturing material
- Temper condition
- Flange construction
- Gasket type
- Bolting material
- Joint design
An aluminum flange should therefore not be advertised simply as “ASME B16.5 Class 300” without confirming the code basis for its allowable pressure.
EN 1092-4 Aluminum Alloy Flanges
For European PN-designated aluminum alloy flanges, the relevant standard is EN 1092-4, rather than EN 1092-1.
EN 1092-4 covers circular aluminum alloy flanges in the range of:
- DN15 to DN600
- PN10 to PN63
It includes flange types, facings, dimensions, tolerances, bolting, joint-face surface finish, marking, materials and related pressure-temperature ratings. (Source: BSI.)
By comparison, EN 1092-1 is the corresponding standard for steel flanges. (Source: BSI.)
A technically correct product description is:
EN AW-6061-T6 aluminum alloy flange manufactured to EN 1092-4, PN16, DN100, flat face.
Where the requested PN or dimension is not included in EN 1092-4, the flange should be described as manufactured according to an approved drawing rather than presented as fully compliant with the standard.
Applicable Material and Dimensional Standards
| Standard | Scope | Application to 6061 flange |
|---|---|---|
| ASTM B247 / ASME SB-247 | Aluminum forgings and rolled ring forgings | Primary material specification for forged flange blanks |
| ASTM B209 / ASME SB-209 | Aluminum sheet and plate | Plate-cut blind or low-pressure flange blanks |
| ASTM B221 / ASME SB-221 | Extruded bars, rods, profiles and tubes | Machined flange raw material when approved |
| ASTM B211 / ASME SB-211 | Rolled or cold-finished bar, rod and wire | Smaller machined components where applicable |
| ASME B16.5 | NPS flange dimensions and pressure classes | Dimensional pattern and joint configuration |
| ASME B31.3 Appendix L | Aluminum flange pressure-temperature provisions | Rating basis for applicable 6061-T6 flanges |
| EN 1092-4 | PN-designated aluminum alloy flanges | European aluminum flange dimensions and ratings |
| ASME B16.25 | Butt-welding end preparation | Weld neck flange end preparation when specified |
| EN 10204 | Inspection documents | Material certificate documentation |
| Approved drawing | Project-specific design | Nonstandard size, facing, bolt circle or pressure design |
Aluminum Alloy 6061 Chemical Composition
6061 aluminum is a heat-treatable aluminum-magnesium-silicon alloy. Magnesium and silicon are its principal alloying elements.
Typical Chemical Composition
| Element | Content, wt.% |
|---|---|
| Silicon, Si | 0.40–0.80 |
| Iron, Fe | Maximum 0.70 |
| Copper, Cu | 0.15–0.40 |
| Manganese, Mn | Maximum 0.15 |
| Magnesium, Mg | 0.80–1.20 |
| Chromium, Cr | 0.04–0.35 |
| Zinc, Zn | Maximum 0.25 |
| Titanium, Ti | Maximum 0.15 |
| Other elements, each | Maximum 0.05 |
| Other elements, total | Maximum 0.15 |
| Aluminum, Al | Remainder |
The quoted composition must ultimately comply with the material specification stated in the purchase order and material certificate. Hydro publishes the same principal composition limits for alloy 6061, including 0.80–1.20% magnesium and 0.40–0.80% silicon. (Source: Hydro alloy data.)
What Does 6061-T6 Mean?
T6 indicates that the aluminum alloy has been:
- Solution heat treated
- Quenched
- Artificially aged
This condition provides higher strength than the annealed 6061-O condition.
Related tempers may include:
| Temper | General condition | Typical consideration |
|---|---|---|
| 6061-O | Annealed | Higher formability and lower strength |
| 6061-T4 | Solution heat treated and naturally aged | Intermediate strength and formability |
| 6061-T6 | Solution heat treated and artificially aged | Common forged and machined flange condition |
| 6061-T651 | T6 condition with stress relief by stretching | Common for plate products |
| 6061-T652 | T6 condition with stress relief by compression | May be associated with forged products |
The material certificate should identify the exact temper. T6, T651 and T652 should not be treated as identical descriptions without checking the product form and applicable material specification.
Welding of 6061-T6 Flanges
Alloy 6061 can be welded using established aluminum welding processes. However, the heat from welding changes the precipitation-hardened condition around the fusion zone and heat-affected zone.
As a result, the installed weld connection should not be assumed to retain the full mechanical properties of the original 6061-T6 flange throughout the joint.
Hydro notes that 6061 is readily welded, while welds made in the T6 condition can lose strength unless appropriate post-weld heat treatment and artificial aging are applied. (Source: Hydro.)
The piping design should therefore consider:
- Reduced allowable stress in welded areas
- Qualified welding procedure
- Filler-metal selection
- Heat-input control
- Interpass temperature
- Joint preparation
- Weld inspection
- Post-weld heat treatment feasibility
- Service temperature
- Fatigue or cyclic loading
The filler metal should be selected by the project welding engineer according to the base materials, service environment, required joint strength and corrosion conditions.
Flange Facing Options
Available sealing-face configurations may include:
- Flat face
- Raised face
- Tongue and groove
- Male and female
- O-ring groove
- Serrated gasket face
- Smooth gasket face
- Customer-specific machined facing
The gasket-facing finish should be defined numerically where sealing performance is important.
The inquiry should identify:
- Facing type
- Surface roughness
- Gasket material
- Gasket dimensions
- Bolt material
- Bolt tightening method
- Design pressure
- Design temperature
Direct contact between aluminum and dissimilar metals should also be evaluated for galvanic-corrosion risk.
Standard Manufacturing Sizes
Our commonly manufactured aluminum flange sizes include:
| DN size | Approximate NPS | Available flange types |
|---|---|---|
| DN40 | 1½ in | Slip-on, blind, weld neck |
| DN50 | 2 in | Slip-on, blind, weld neck, socket weld subject to review |
| DN65 | 2½ in | Slip-on, blind, weld neck |
| DN80 | 3 in | Slip-on, blind, weld neck |
| DN100 | 4 in | Slip-on, blind, weld neck |
| DN125 | 5 in | Slip-on, blind, weld neck |
| DN150 | 6 in | Slip-on, blind, weld neck |
| DN200 | 8 in | Slip-on, blind, weld neck |
| DN300 | 12 in | Slip-on, blind, weld neck |
Other dimensions can be manufactured according to raw-material availability, forging capacity, machining capacity and approved drawings.
The size list represents manufacturing capability rather than guaranteed stock availability.
Manufacturing Process
1. Technical Review
Before production, we review:
- Flange type
- Material standard
- Alloy and temper
- Size
- Pressure class or PN rating
- Facing
- Bore
- Pipe wall thickness
- Bolt circle
- Bolt-hole quantity
- Design pressure
- Design temperature
- Applicable code
- Inspection requirements
2. Raw-Material Control
Raw materials are checked for:
- Material specification
- Alloy designation
- Temper
- Heat or lot number
- Chemical composition
- Mechanical properties
- Dimensions
- Surface condition
- Material certificate
3. Forging or Blank Preparation
Depending on the product design, flange blanks may be produced from:
- Hand forgings
- Rolled ring forgings
- Aluminum plate
- Approved extruded stock
- Customer-specified semifinished material
4. CNC Machining
Machining operations may include:
- Outside-diameter turning
- Bore machining
- Hub machining
- Socket machining
- Bolt-hole drilling
- Spot facing
- Gasket-face machining
- Bevel preparation
- Marking
5. Final Inspection
Completed flanges are checked against the drawing and purchase order before packing.
Inspection and Testing
| Inspection or test | Purpose |
|---|---|
| Material certificate review | Verify alloy, temper and product standard |
| Visual inspection | Check workmanship and surface condition |
| Dimensional inspection | Verify OD, thickness, bore, bolt circle and facing |
| Positive material identification | Verify aluminum alloy where specified |
| Hardness testing | Support temper verification when applicable |
| Tensile testing | Verify material properties under the material specification |
| Dye penetrant testing | Detect surface-breaking defects |
| Ultrasonic testing | Examine thicker forgings when specified |
| Pressure testing | Verify a completed assembly where technically applicable |
| Surface roughness measurement | Verify sealing-face finish |
| Third-party inspection | Independent verification by SGS, BV, TÜV or another nominated agency |
A loose flange is not normally hydrostatically tested in isolation unless a specific test fixture and acceptance procedure are defined. Pressure testing is more commonly performed on the completed piping assembly or equipment connection.
Material Marking and Documentation
Flanges can be marked with:
- Manufacturer identification
- Alloy
- Temper
- Material standard
- Flange type
- Nominal size
- Class or PN designation
- Facing
- Heat or lot number
- Purchase-order number
- Drawing number
Available documents may include:
- Material test certificate
- Chemical-composition report
- Mechanical-property report
- Dimensional inspection report
- Hardness-test report
- Penetrant-test report
- Ultrasonic-test report
- Surface-finish report
- Certificate of conformity
- Third-party inspection release
- Packing list
- Manufacturing drawing
Applications of 6061-T6 Aluminum Flanges
6061-T6 aluminum flanges are commonly considered for equipment and piping systems where low component weight, machinability, weldability and corrosion resistance are required.
Typical applications include:
- Oxygen-production equipment
- Air-separation equipment
- Industrial gas systems
- Deep-cooling equipment
- Low-temperature processing equipment
- Chemical equipment
- Heat exchangers
- Coolers
- Vaporizers
- Intercoolers
- Aluminum pressure vessels
- Lightweight process piping
- Marine auxiliary equipment
- Transportation systems
- Customized machinery
Material selection must be approved for the actual gas or liquid, operating temperature, pressure, cleanliness requirement and piping code.
For oxygen service, the flange material alone does not establish suitability. Cleaning, lubricant control, gasket selection, ignition risk, particle contamination and oxygen-service procedures must also be specified.
Advantages of 6061-T6 Aluminum Flanges
Low Component Weight
Aluminum has a substantially lower density than carbon steel and stainless steel, helping reduce equipment and piping-system weight.
Good Machinability
6061-T6 can be accurately machined into bolt holes, sealing faces, hubs, sockets and customized connection geometries.
Heat-Treatable Strength
The T6 temper provides higher strength than annealed 6061 conditions.
Weldable Construction
6061 can be incorporated into welded aluminum piping systems when the weld-joint design and reduced heat-affected-zone properties are properly considered.
Custom Manufacturing
Flanges can be manufactured to ASME dimensional patterns, European PN standards or customer drawings.
Information Required for Quotation
Please provide the following information when requesting a quotation:
- Flange type
- Nominal size
- Pipe outside diameter
- Pipe wall thickness
- Material grade
- Required temper
- Raw-material standard
- Dimensional standard
- Class or PN rating
- Design pressure
- Design temperature
- Flange facing
- Bore diameter
- Bolt-hole quantity
- Bolt-hole diameter
- Bolt-circle diameter
- Surface-finish requirement
- Quantity
- Inspection requirements
- Material-certificate requirements
- Third-party inspection requirements
- Packing requirements
- Delivery destination
For customized flanges, a detailed dimensional drawing should be provided.
Frequently Asked Questions
What is a 6061-T6 aluminum flange?
A 6061-T6 aluminum flange is a bolted piping or equipment connection manufactured from heat-treated aluminum alloy 6061. Common types include slip-on, weld neck, blind and socket weld flanges.
Which ASTM standard covers forged 6061 aluminum flanges?
ASTM B247 / ASME SB-247 is commonly specified for 6061 aluminum forgings and rolled ring forgings used as flange blanks. (Source: ASTM International.)
Can a 6061 flange comply with ASME B16.5?
A 6061-T6 flange can be manufactured to the dimensional pattern of ASME B16.5. Its pressure-temperature rating must also be verified under the applicable piping code and material-specific rating rules.
What is the difference between ASME B16.5 and ASME B31.3 Appendix L?
ASME B16.5 establishes standard flange dimensions and general flange requirements. ASME B31.3 Appendix L provides pressure-temperature provisions for applicable aluminum alloy flanges, including certain ASTM B247 6061-T6 flanges.
Is EN 1092-1 the correct standard for aluminum flanges?
No. EN 1092-1 is intended for steel flanges. EN 1092-4 is the corresponding PN-designated standard for aluminum alloy flanges.
Can 6061-T6 be used for socket weld flanges?
Yes, subject to engineering review. The socket dimensions, pipe wall, weld size, expansion gap, design pressure and reduced weld-zone properties must be considered.
Does welding affect the T6 condition?
Yes. Welding changes the heat-treated condition in and around the weld and can reduce local strength. The welded-joint allowable stress must follow the applicable design and welding requirements.
Can a blind flange be machined from 6061-T651 plate?
It may be possible for approved low-pressure or drawing-specific designs. However, T651 plate and T6 forging are different product forms, and substitution requires approval from the purchaser or piping designer.
Are Class 150 and PN16 the same?
No. Class 150 and PN16 belong to different flange-standard systems. They may have different dimensions, bolt patterns, materials and pressure-temperature ratings and should not be treated as interchangeable.
What documents can be supplied?
Available documents include material certificates, chemical and mechanical reports, dimensional inspection reports, NDT reports, surface-finish records, certificates of conformity and third-party inspection releases.
6061-T6 Aluminum Flange Manufacturer in China
As an experienced 6061-T6 aluminum flange manufacturer in China, we supply slip-on, weld neck, blind, socket weld and customized aluminum flanges for international industrial equipment and piping projects.
Our manufacturing scope includes:
- Raw-material procurement
- Forged and rolled-ring blank sourcing
- CNC machining
- Bore and socket machining
- Gasket-face finishing
- Dimensional inspection
- Material traceability
- NDT coordination
- Documentation
- Export packing
Each inquiry is technically reviewed to confirm the correct material specification, temper, dimensional standard, pressure-rating basis, connecting pipe dimensions and inspection scope before production.
