Aluminum Brass: Composition, Properties, and Applications

• Aluminum brass (UNS C68700) is a copper-zinc alloy with 1.8–2.5% aluminum and 0.02–0.06% arsenic, conforming to ASTM B111

• The aluminum addition forms a self-healing oxide film that resists impingement attack in high-velocity seawater

• C68700 outperforms admiralty brass (C44300) in turbulent fluid systems and polluted marine environments

• Primary uses: condenser tubes, heat exchanger tubes in power stations, desalination plants, and offshore systems

• Available through specialized suppliers as seamless tubes with third-party inspection coordination per project ITP requirements

Aluminum brass is a copper-zinc-aluminum alloy specified as UNS C68700, engineered specifically for heat transfer applications where seawater or aggressive industrial fluids are in continuous contact with tube walls. It’s the go-to alloy when admiralty brass runs out of performance headroom.

Aluminum brass is a copper-zinc alloy enhanced with aluminum (1.8–2.5%) and arsenic (0.02–0.06%). The aluminum forms a thin, self-renewing aluminum oxide film on the tube surface, which resists both uniform corrosion and the localized erosion that occurs under turbulent, high-velocity flow. Arsenic suppresses dezincification, the selective leaching of zinc that degrades standard brasses in chloride-rich environments.

The result is an alloy that holds up where admiralty brass and standard brasses fail: high flow rates (above 2.5 m/s), seawater with suspended solids, and systems prone to impingement attack at tube inlets.

C68700 follows a tightly controlled elemental balance under ASTM B111 and equivalent international standards.

The copper-to-zinc ratio keeps the alloy in the alpha-phase microstructure, which is essential for cold workability and resistance to stress-corrosion cracking. Aluminum content below 1.8% provides insufficient oxide protection; above 2.5% it embrittles the alloy and reduces formability.

The European equivalent is CuZn20Al2 (EN 12449 / EN 12451), and the British designation is CZ110. These designations refer to the same alloy family and carry comparable mechanical guarantees.

C68700’s key performance data across the properties that matter most for heat exchanger and condenser tube selection:

Aluminum brass is used where durability, heat transfer, and resistance to harsh fluids are essential:

C68700 aluminum brass tubes are specified in applications that combine heat transfer duty with corrosive fluid exposure.

Condenser tubes in power generation

Steam surface condensers in thermal and nuclear power stations are the largest single application. The alloy’s combination of thermal conductivity and corrosion resistance makes it effective for both once-through seawater cooling systems and closed-loop systems using brackish water.

Heat exchanger tubes in desalination and refining

Shell-and-tube heat exchangers in multi-stage flash desalination plants and petroleum refinery cooling trains specify C68700 where water quality varies and velocity control isn’t always possible. The self-healing oxide film compensates for intermittent high-flow conditions.

Marine cooling systems

Shipboard central cooling, bilge, and ballast systems use aluminum brass where continuous seawater circulation creates erosion risk. C68700 is specified across naval, commercial shipping, and offshore platform applications.

Industrial process cooling

Petrochemical and chemical processing facilities use C68700 in process coolers and aftercoolers where cooling water quality may be variable and flow rates exceed what admiralty brass can tolerate.

• More corrosion-resistant than admiralty brass

• Stronger than standard brass alloys

• Performs under high fluid velocity (>2.5 m/s)

• Longer lifespan in aggressive or polluted waters

• Good biofouling resistance without coatings

The two alloys share the same copper-zinc base but differ in their secondary alloying element and their resulting performance envelope.

Admiralty brass (C44300) remains the right choice for lower-velocity, less aggressive environments. Specifying C68700 when C44300 would perform adequately adds unnecessary cost. The selection decision typically comes down to water quality, flow velocity, and the consequences of early tube failure. A proper material selection review, combined with an ITP that requires mill certification and third-party inspection, reduces specification risk on either alloy.

You can read more about admiralty brass tube specifications in our C44300 admiralty brass guide.

For applications that exceed what C68700 can handle, highly polluted seawater, ammonia environments, or systems requiring greater mechanical strength, copper-nickel alloys (C70600 and C71500) are the typical upgrade path.

Copper-nickel tubes provide superior resistance to sulfide attack and biofouling under more extreme conditions, at a higher material cost. The choice between aluminum brass and copper-nickel usually comes down to the severity of the water chemistry and the project’s lifecycle cost tolerance.

Aluminum brass tubes for heat exchanger and condenser service are produced as seamless drawn tube to ASTM B111 (or equivalent EN, BS standards). The manufacturing sequence runs from continuous casting of the alloy billets through hot extrusion, multi-pass cold drawing, and final annealing to achieve the required temper and dimensional tolerances.

Third-party inspection under a project-specific Inspection and Test Plan (ITP) covers:

• Chemical composition verification (mill certification + independent heat analysis)

• Dimensional inspection (OD, wall thickness, straightness)

• Hydrostatic testing per ASTM B111 requirements

• Visual and eddy current testing for surface defects

• NCR documentation for any non-conformances

For project orders, Admiralty Industries coordinates Bureau Veritas inspection at the mill to confirm compliance against the project ITP before shipment. This keeps the procurement chain documented from melt through delivery, relevant for power, refinery, and nuclear projects where material traceability is a contract requirement.

Admiralty Industries supplies aluminum brass tubes to ASTM B111 and international equivalents, with available forms including:

• Seamless tubes in standard heat exchanger and condenser dimensions

• Custom cut lengths and diameters for specific tubesheet layouts

• Mill certification packages with chemical and mechanical test reports

• Bureau Veritas third-party inspection coordination for project orders