Two copper-zinc alloys dominate seawater condenser service, and they are frequently confused in trade listings: C44300, the arsenical admiralty brass, and C68700, the aluminum brass. The distinction matters because the aluminium addition in C68700 forms a protective surface film that raises resistance to erosion and impingement, while the arsenic in C44300 suppresses dezincification. Buyers who specify by name alone can therefore receive a tube that meets the dimensional drawing but not the durability expected in service.
Grade clarification: within ASTM B111 the grade C44300 is arsenical admiralty brass, the composition designated CuZn28Sn1As in the European system. Aluminum brass is the separate C68700 grade and is normally ordered under that UNS number. Both are seamless tube products for surface condensers, evaporators and heat exchangers, and both are produced in the annealed and drawn tempers of the specification.
Material Definition and Applicable Standards
ASTM B111/B111M covers seamless copper and copper alloy tube and ferrule stock up to 3 1/8 in. (80 mm) inclusive in diameter for condensers, evaporators and heat exchangers.
ASME SB111 mirrors the specification for code-stamped equipment.
EN 12451 covers seamless copper alloy heat exchanger tubes in the European system, where the C44300 composition is written CuZn28Sn1As and the aluminum brass composition is written CuZn20Al2.
GB/T 8890 and JIS H3300 cover the same products for the Chinese and Japanese markets.
Both alloys are supplied in annealed and drawn tempers; the temper is stated on the purchase order because it controls bendability, rolling behaviour and the property table that applies.
Chemical Composition of the Two Seawater Brasses
| Element | C44300 admiralty brass | C68700 aluminum brass |
|---|---|---|
| Cu | 70.0 - 73.0 % | 76.0 - 79.0 % |
| Sn | 0.9 - 1.2 % | Not specified |
| Al | Not specified | 1.8 - 2.5 % |
| As | 0.02 - 0.06 % | 0.02 - 0.06 % |
| Fe | 0.06 % max | 0.06 % max |
| Pb | 0.07 % max | 0.07 % max |
| Zn | Remainder | Remainder |
The higher copper content of aluminum brass supports the formation of an aluminium oxide film on the water side. That film is what gives aluminum brass its reputation in high-velocity seawater, but it also makes the alloy sensitive to damage in water containing significant sulphide or ammonia, where the film does not form reliably.
Mechanical Properties, Service Range and Sizes
Annealed C44300 tube carries a minimum tensile strength of approximately 310 MPa and a minimum yield strength of approximately 105 MPa at 0.5 % extension under load, with a 20 % outside diameter expansion requirement.
Tension testing follows ASTM E8/E8M, hardness is checked to ASTM E18 where ordered, and thermal performance data are reported from the physical property tables of the specification.
Both alloys are suitable for typical cooling water service through the temperature range at which copper alloy condenser tube is applied, with the water chemistry rather than temperature governing the limit.
Tube is produced by the seamless process from small diameters up to the 80 mm diameter limit of ASTM B111, in straight lengths, U-bends or coiled form.
Wall thickness is selected from the design pressure and the corrosion allowance; heavier walls are used at inlet ends and in abrasive or high-velocity water.
Applications
Seawater and brackish water condensers for power generation, marine propulsion and district cooling.
Multi-stage flash and multi-effect desalination plant, including brine heaters and heat recovery sections.
Refinery and petrochemical coolers with saline cooling water on the tube side.
Air conditioning and refrigeration condensers, and industrial cooling circuits with treated water.
Evaporators in salt, sugar and chemical processing where the product side must be heated through a corrosion-resistant wall.
Selection, Processing and Installation Guidance
Select C68700 aluminum brass for high-velocity clean seawater with a well formed protective film, and C44300 admiralty brass for lower-velocity cooling water, polluted water, or where the film cannot be maintained.
Do not use aluminum brass in water with appreciable sulphide or ammonia content, because the protective film is attacked and pitting or stress corrosion cracking follows.
Roll tubes into the tubesheet with controlled expansion so that residual stress remains low and the joint stays tight without cracking the tube ends.
Provide inlet ferrules or protective coatings in the impingement zone, which is the most common location for failures in both alloys.
Keep steel and copper alloy components electrically separated, and apply cathodic protection where the design requires it, since brass is cathodic to steel in seawater.
Inspection Points and Common Pitfalls
Confirm the grade actually supplied against the composition certificate, because admiralty brass and aluminum brass are frequently listed under interchangeable trade names.
Check that tube is seamless and that eddy current examination to ASTM E309 covers both ends of each length.
Verify wall thickness and eccentricity, which are not visible from the outside and which determine the erosion allowance.
Review grain size and temper before bending or flaring, since a drawn temper can crack when formed cold.
Store tube dry and capped; chloride-bearing moisture and organic acid residues cause shallow bright corrosion that becomes a leak path after installation.
FAQ
Q: Is C44300 aluminum brass?
No. C44300 is arsenical admiralty brass containing tin and arsenic. Aluminum brass is the separate grade C68700, which contains aluminium instead of tin.
Q: Which alloy performs better in seawater?
Aluminum brass C68700 usually performs better in clean, fast-flowing seawater because of its protective surface film, while admiralty brass C44300 is often preferred in polluted or low-velocity water where that film is difficult to maintain.
Q: What properties does ASTM B111 require for annealed C44300?
A minimum tensile strength of approximately 310 MPa, a minimum yield strength of approximately 105 MPa at 0.5 % extension under load, and an outside diameter expansion of 20 % of the original diameter.
Q: What limits the temperature of these brass tubes?
The limit is set by the cooling water chemistry and by ammonia or oxygen in the condensate rather than by a single temperature figure. Above the recommended range, dezincification and stress corrosion cracking become the governing risks.
Q: How are aluminum brass and admiralty brass tube supplied?
Both are supplied as seamless tube to ASTM B111 in annealed and drawn tempers, in straight lengths, U-bends or coils, with the outside diameter, wall thickness, length and temper stated on the order.
Q: Why does the arsenic content matter?
Arsenic is a deliberate inhibitor that prevents preferential loss of zinc. Without it, these brasses dezincify quickly in seawater, leaving a porous copper sponge that fails under pressure.
