Extruded Finned Tubes for Heat Exchangers – ASTM B111 C68700
Product Overview
Extruded finned tubes manufactured using ASTM B111 C68700 aluminum brass are designed for heat-transfer equipment requiring a copper-alloy tube with good thermal conductivity, mechanical strength, and resistance to corrosion in appropriately selected water-service environments.
C68700, also known as aluminum brass, is a copper-zinc alloy containing aluminum and a controlled arsenic addition. It is commonly used in condenser and heat-exchanger tubing. ASTM B111/B111M covers seamless copper and copper-alloy tubes for condensers, evaporators, and heat exchangers, including UNS C68700.
In an extruded finned-tube assembly, a finned outer sleeve is mechanically expanded over the base tube to create close contact between the two components. The fins increase the external heat-transfer area, improving heat exchange with the surrounding air or another fluid, depending on the equipment design.
Specification clarification: ASTM B111 applies to the C68700 base tube. The fin material, extrusion or expansion process, fin geometry, and finished assembly tolerances should be specified separately. If the intended product uses a C68700 base tube with an aluminum extruded fin sleeve, the aluminum alloy grade must also be identified.
Key product advantages
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Enhanced heat-transfer surface: Extruded fins increase the external surface area available for heat exchange.
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Copper-alloy base tube: C68700 offers a useful combination of strength and corrosion resistance for suitable condenser and heat-exchanger services.
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Mechanical fin-to-tube contact: A properly manufactured interference fit helps support thermal contact between the base tube and fin sleeve.
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Application-specific configurations: Tube dimensions, fin height, pitch, and length can be customized to approved drawings.
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Material traceability: Base-tube certificates and inspection documentation can be supplied according to project requirements.
Technical Specifications and Common Size Ranges
The following are representative commercial dimensions for extruded finned tubes. Final sizes depend on the heat-exchanger design, required heat-transfer duty, fin material, and customer drawings.
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Parameter
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Typical specification
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Base tube material
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ASTM B111 / ASME SB111 C68700
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Alloy designation
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UNS C68700, aluminum brass
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Base tube manufacturing
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Seamless copper-alloy tube
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Base tube outside diameter
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12.7–76.2 mm
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Base tube wall thickness
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0.7–3.0 mm
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Overall tube length
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1,000–12,000 mm
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Fin material
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Aluminum alloy or other specified material
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Fin type
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Extruded integral fin sleeve or specified extruded-fin construction
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Fin height
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5–20 mm
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Fin thickness
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0.3–1.0 mm, depending on design
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Fin pitch
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2.0–5.0 mm
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Fin attachment
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Mechanical expansion or interference fit, as designed
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Tube ends
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Plain, un-finned ends or customized end preparation
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Surface finish
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As manufactured or treated as specified
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Important: These are indicative manufacturing ranges, not dimensional requirements imposed by ASTM B111. The standard covers seamless copper and copper-alloy tubing up to 80 mm in diameter, while actual dimensional limits and tolerances must be verified against the selected product form and applicable standard edition.
Information required for a quotation
To select the appropriate configuration, specify:
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Base tube outside diameter and wall thickness.
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Total tube length and finned length.
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Fin alloy, fin height, thickness, and pitch.
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Required fin-to-tube contact or bonding criteria.
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Operating temperature, pressure, fluid composition, and cooling medium.
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Required inspection tests, material certificates, and quantity.
Chemical Composition of ASTM B111 C68700
C68700 is an aluminum brass alloy. Copper forms the principal constituent, zinc makes up the balance, and aluminum and arsenic are important alloying additions. The composition supports the alloy's strength and corrosion resistance in suitable heat-exchanger environments.
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Element
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Composition by weight (%)
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Copper (Cu), including silver
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76.0–79.0
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Aluminum (Al)
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1.8–2.5
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Arsenic (As)
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0.02–0.06
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Iron (Fe)
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0.06 max.
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Lead (Pb)
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0.07 max.
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Zinc (Zn)
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Remainder
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These limits describe the C68700 base alloy. The extruded fin sleeve may use a different alloy and must have its own material specification and certification. The material certificate and the applicable edition of ASTM B111/B111M should govern acceptance.
Mechanical Properties of C68700
Mechanical properties depend on the tube temper, manufacturing condition, and applicable product requirements. The values below are indicative of annealed C68700 tubing; the purchase specification and applicable ASTM B111/B111M edition should determine the final acceptance limits.
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Mechanical property
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Indicative value
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Tensile strength
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345 MPa minimum*
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Yield strength
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125 MPa minimum*
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Elongation
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Depends on temper and wall thickness
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Hardness
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Depends on temper and test method
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*Indicative values reported for annealed C68700 tube; confirm the applicable temper-specific requirements before publishing them as guaranteed acceptance values.
The tube's temper is important because annealed, light-drawn, and hard-drawn conditions can have different strength and ductility. The completed finned assembly must also meet the specified dimensional tolerances and fin-to-tube contact requirements.
Inspection and Testing Methods
Quality assurance should verify both the C68700 base tube and the finished extruded finned-tube assembly. The inspection plan should distinguish tests required by ASTM B111/B111M from additional checks specified for the finned product.
1. Dimensional inspection
Measure base-tube outside diameter, wall thickness, overall length, fin height, fin pitch, fin thickness, finned length, and end dimensions. Verify conformity with the approved drawing and tolerances.
2. Chemical composition analysis
Verify the C68700 base alloy using heat-analysis certificates and, where required, product analysis. Check the fin material separately against its specified alloy grade.
3. Mechanical testing
Perform tensile, expansion, flattening, and other applicable tests according to the required standard, temper, and purchase order. These tests help verify mechanical properties and forming performance.
4. Eddy-current or other specified nondestructive testing
Eddy-current examination can detect certain tube-wall discontinuities. Hydrostatic or pneumatic testing may also be required, depending on the specification, equipment design, and agreed test plan.
5. Fin attachment and visual inspection
Examine fin alignment, pitch uniformity, surface condition, fin deformation, tube-end quality, and the fit between the fin sleeve and base tube. Additional contact or pull-off tests can be agreed upon where suitable for the design.
ASTM B111/B111M includes requirements for applicable mechanical and expansion testing, residual-stress testing, and specified pressure or nondestructive tests. Not every listed test necessarily applies to every order; the applicable standard edition and purchase requirements determine the test scope.
Quality documentation
Depending on project requirements, the following documents can be provided:
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Material Test Certificate for the C68700 base tube.
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Chemical composition and mechanical test reports.
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Dimensional inspection records.
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Eddy-current, hydrostatic, or other required test records.
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Fin-material certification and finished-product inspection reports.
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Heat-number traceability and packing inspection records.
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Third-party inspection reports where contractually required.
Main Applications of C68700 Extruded Finned Tubes
C68700 is principally a condenser and heat-exchanger tube alloy. Its suitability for a particular extruded finned-tube application depends on the fluid chemistry, temperature, pressure, and fin material.
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Condensers and evaporators: For compatible heat-transfer services requiring copper-alloy tubing.
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Industrial heat exchangers: For selected process heating and cooling applications.
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Water-cooled heat-transfer equipment: Where the water chemistry and operating conditions are suitable for aluminum brass.
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Specialized finned-tube assemblies: Where the thermal design benefits from increased external surface area and the tube-fin combination is engineered for the service.
For seawater or other aggressive cooling media, confirm corrosion suitability with the equipment designer. C68700 should not be assumed suitable for every water chemistry or operating environment.
Why Choose Our Extruded Finned Tubes?
Our extruded finned tubes can be manufactured to customer drawings and project-specific requirements, with attention to alloy traceability, dimensional consistency, and finished-product quality.
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Specified base alloy: C68700 aluminum brass manufactured to the agreed ASTM B111 requirements.
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Customized fin geometry: Fin height, pitch, thickness, and finned length tailored to the thermal design.
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Controlled assembly: Fin-to-tube contact and dimensional quality verified against the agreed inspection plan.
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Quality documentation: Material certificates and inspection reports available according to contractual requirements.
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Project-oriented supply: Custom lengths, end preparations, packaging, and documentation for industrial heat-exchanger projects.
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