Aluminium brass exists because admiralty brass kept failing in one specific way. Raise cooling water velocity high enough and impingement attack strips the protective film off a condenser tube faster than the tube can rebuild it, and the wall quietly thins from the inside out until it splits. Two percent aluminium fixes that. The film it forms is alumina, tough enough to reform about as fast as fast-moving water can tear it away. USA Piping Solution supplies aluminium brass tubes to ASTM B111 in C68700, plain and integral low fin, for condenser and cooler duty at velocities admiralty brass cannot hold. For standard-velocity service, our Admiralty Brass Fin Tube page covers the conventional choice.
The Chemistry That Does the Work
| Element | C68700 Content | What It Does |
|---|---|---|
| Copper (Cu) | 76.0 – 79.0% | Carries thermal conductivity and the alloy's base corrosion behaviour |
| Aluminium (Al) | 1.8 – 2.5% | Forms the tenacious alumina film that resists impingement at high water velocity; below 1.8% the film is too thin to protect, above 2.5% the alloy embrittles |
| Arsenic (As) | 0.02 – 0.06% | Inhibits dezincification, exactly as in admiralty brass |
| Zinc (Zn) | Balance | Strength and cost; kept in the alpha-phase range for cold workability and stress-corrosion resistance |
Note the narrow aluminium window. That 1.8 to 2.5% band is not a manufacturing tolerance, it is the working range of the alloy: too little and the protective film never becomes tough enough to matter, too much and the tube loses the ductility it needs to be expanded into a tube sheet. Equivalents are CZ110 in British practice and CuZn20Al2 under ISO.
Where Aluminium Brass Sits Against the Alternatives
| Condition | Alloy | Reasoning |
|---|---|---|
| Fresh or lightly brackish water, normal velocity | Admiralty brass C44300 | Lowest cost of the inhibited brasses |
| Seawater or brackish water at high velocity, or where admiralty has already failed by impingement | Aluminium brass C68700 | The alumina film is what admiralty's tin addition cannot match at velocity |
| Polluted, sulphide-bearing, or warm seawater | Cupro-nickel 90/10 or 70/30 | Copper-nickel handles chemistry that defeats both brasses |
| Any ammonia contact | Not a copper alloy | All copper alloys crack in ammonia; specify stainless or steel |
The step beyond this alloy is on our Copper Nickel 90/10 Pipes & Tubes page; the step below is admiralty brass.
Specifications
| Alloy | C68700 aluminium brass (arsenical), UNS C68700 |
| Equivalents | BS CZ110 · ISO CuZn20Al2 · EN CW702R |
| Standard | ASTM B111 / ASME SB111 (seamless condenser tubes and ferrule stock) |
| Forms | Plain (bare) condenser tube · integral low fin tube |
| Typical OD | 15.9 – 31.8 mm (5/8" – 1-1/4") condenser sizes |
| Temper | Annealed (O61) standard for condenser and tube-sheet expansion service |
| Fin Geometry | Low fin, typically 19 – 26 fins per inch where finned |
Applications
- Power Station Condensers: particularly plants drawing high-velocity or turbulent cooling water where admiralty tubes have a service history of impingement failure.
- Desalination Plants: MSF and MED heat-reject and recovery sections.
- Marine & Offshore Coolers: shipboard and platform seawater coolers.
- Oil Coolers: raw-water-cooled lube and hydraulic oil coolers.
- Condenser Retubes: the common upgrade path when an admiralty bundle keeps failing at the inlet ends. See Condenser Tubes for the full range.
Admiralty Tubes Failing at the Inlet? Send the History →
Testing, Certification & Availability
Tube ships to ASTM B111 with mill certification, eddy-current and hydrostatic testing per the standard, and full heat traceability; our Quality Policy page covers the program. Retube enquiries move fastest with the original tube-sheet specification: send OD, wall gauge, length, quantity, and whether plain or low fin.
Related Products
- Admiralty Brass Fin Tube
- Copper Nickel 90/10 Pipes & Tubes
- Condenser Tubes
- Heat Exchanger Tubes & Pipes
- U-Bend Heat Exchanger Tubes
Frequently Asked Questions
What is the difference between aluminium brass and admiralty brass?
The inhibiting film. Admiralty brass uses roughly 1% tin for erosion resistance; aluminium brass uses 1.8 to 2.5% aluminium, which forms a tougher, faster-healing oxide. Both carry arsenic against dezincification. In practice aluminium brass is specified where cooling water velocity is high enough that admiralty tubes suffer impingement attack.
Is aluminium brass the same as aluminium bronze?
No, though the names get confused and some suppliers list C68700 loosely as aluminium bronze. Aluminium brass is a copper-zinc alloy with a small aluminium addition. Aluminium bronzes are copper-aluminium alloys with far higher aluminium content and different applications entirely.
Do you supply aluminium brass in finned form?
Yes, integral low fin rolled from the tube wall, the same construction used on admiralty and cupro-nickel condenser tube. State plain or finned with your enquiry, along with fin count if finned.
Can aluminium brass be used with ammonia?
No. Like all copper alloys it is subject to stress corrosion cracking in ammonia and ammonium compounds. Specify stainless or steel where ammonia contacts the tube.