Application & Compliance
The ASTM B111 C68700 seamless aluminum brass tube is specified for shell and tube heat exchangers, surface condensers, and evaporators where the cooling medium is seawater, brackish water, or chloride-bearing process water. In coastal power plant condensers and seawater desalination heat-reject sections, the C68700 tube resists the impingement attack, erosion-corrosion, and dezincification that limit the service life of plain brass and admiralty brass tubes. In marine and offshore cooling systems, the tube maintains wall integrity under continuous exposure to aerated seawater at flow velocities up to approximately 3 m/s. When assembled into a tube bundle and rolled or welded into a heat exchanger tubesheet, the tube provides a pressure boundary between the cooling water and the process fluid.
The tube is manufactured and tested in accordance with ASTM B111 / B111M and ASME SB111 / SB111M, the standard specification for seamless copper and copper-alloy tube for surface condensers, evaporators, and heat exchangers. The specification covers tube outside diameters up to 3-1/8 in. [80 mm] within its standard scope. Certification is available per EN 10204 Type 3.1. Third-party inspection by ABS, GL, DNV, NK, PED, AD2000, and CCS is available upon request.
Problem Solved
Two degradation mechanisms dominate copper-alloy condenser tube service: dezincification and erosion-corrosion. C68700 contains 1.8–2.5% aluminum and a controlled arsenic addition of 0.02–0.10%. The aluminum forms a hard, dense, and adherent aluminum oxide film on the alloy surface, increasing resistance to erosion-corrosion and cavitation damage. The arsenic acts as a dezincification inhibitor, suppressing the selective loss of zinc from the brass matrix that leads to plug-type failures in uninhibited brasses. The combination of these two alloying additions extends tube life in aggressive cooling waters where copper-nickel or stainless steel alternatives may suffer chloride pitting or stress corrosion cracking.
Material Specification – ASTM B111 C68700
UNS C68700 is classified as Aluminum Brass, Type B under ASTM B111/B111M. The alloy is a copper-zinc-aluminum material with controlled arsenic content. It can be supplied in O61 annealed, light drawn, or hard drawn tempers depending on the mechanical strength required for the tube-to-tubesheet joint and the internal pressure duty.
Chemical Composition (per ASTM B111 C68700)
| Element | Requirement (%) |
|---|---|
| Copper (Cu) | 76.0 – 79.0 |
| Aluminum (Al) | 1.8 – 2.5 |
| Arsenic (As) | 0.02 – 0.06 |
| Iron (Fe) | 0.06 max |
| Lead (Pb) | 0.07 max |
| Zinc (Zn) | Balance |
Mechanical Properties (Annealed O61 Temper)
| Property | Requirement / Typical |
|---|---|
| Tensile Strength | ≥ 360 MPa (52 ksi) |
| Yield Strength | ≥ 80 MPa (12 ksi) |
| Elongation in 50 mm | ≥ 50% |
| Hardness | ~60 HRB (annealed) |
Mechanical properties for O61 annealed C68700 tube per ASTM B111. Hard-drawn tempers achieve tensile strength up to approximately 600 MPa with corresponding yield strength up to 540 MPa.
Thermal and Physical Properties
Thermal conductivity of C68700 is approximately 109 W/(m·K), supporting efficient heat transfer across the tube wall in condenser and heat exchanger service. Density is approximately 8.33–8.40 g/cm³. The alloy is non-magnetic and retains good ductility at low temperatures. The combination of thermal conductivity and corrosion resistance makes C68700 suitable for thin-wall tube design while maintaining the pressure boundary in seawater-cooled equipment.
Manufacturing Process
Seamless C68700 tube is produced by extrusion, drawing, annealing, and straightening as applicable. The manufacturing sequence begins with billet or hollow preparation, followed by hot extrusion or piercing, cold drawing to the specified outside diameter and wall thickness, intermediate annealing to restore ductility, final annealing or tempering to the required condition, and straightening. The finished tube surface is supplied in mill finish or clean condition with plain ends or customized end preparation. Tubes can be furnished in straight lengths for shell and tube heat exchanger tube bundles and, when specified, in U-bend form for U-tube bundle configurations.
Size Range
Outside diameter ranges up to 3-1/8 in. [80 mm] within the ASTM B111 standard scope; other sizes are available by agreement. Wall thickness is specified according to the applicable ASTM B111 requirements and project design conditions. Straight lengths are supplied as standard, with cut-to-length options available. U-bend tubes are manufactured to customer drawings with specified bend radius and leg length.
Testing and Quality Control
Each lot of C68700 tube is subjected to the following examinations and tests in accordance with ASTM B111 / ASME SB111:
Documentation
Each shipment is supplied with Mill Test Certificates (EN 10204 Type 3.1) covering chemical composition and mechanical properties, dimensional inspection reports, eddy current and hydrostatic test reports, and material traceability records. PED documentation and notified body inspection are available when specified in the purchase order.
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