What C44300 Admiralty Brass Tube Is
C44300 is the UNS designation for admiralty brass, a copper-zinc-tin alloy developed for condensers, evaporators and heat exchangers that operate on seawater, brackish water and other chloride-bearing cooling media. ASTM B111 and ASME SB111 govern the seamless tube form, covering seamless copper and copper-alloy condenser tubes and ferrule stock. The same alloy family is also supplied as sheet, strip, rod, pipe and tube-sheet ferrule stock.
Uninhibited 70/30 brass fails in salt water by dezincification, the selective dissolution of zinc that leaves a porous and mechanically weak copper residue. Admiralty brass blocks that mechanism with controlled tin and arsenic additions, which is why it has been a standard marine condenser material for generations while plain brasses remain restricted to fresh-water and mildly aggressive duty.
Chemical Composition and Mechanical Properties
| Element | Requirement, % |
|---|---|
| Copper (Cu) | 70.0 - 73.0 |
| Tin (Sn) | 0.9 - 1.2 |
| Arsenic (As) | 0.02 - 0.10 |
| Lead (Pb) | 0.07 max |
| Iron (Fe) | 0.06 max |
| Zinc (Zn) | Remainder |
ASME SB111 applies the same limits as ASTM B111, so a tube qualified to one specification is normally acceptable under the other. Tin strengthens the matrix and shifts the corrosion process away from selective leaching, while the arsenic addition suppresses dezincification at the grain boundaries.
| Property | Typical value |
|---|---|
| Density | 8.53 g/cm³ |
| Melting range | 899 - 938 °C |
| Thermal conductivity at 20 °C | About 109 W/(m·K) |
| Specific heat at 20 °C | 0.09 cal/(g·°C) |
| Linear expansion, 20 - 300 °C | 20.2 × 10-6/°C |
| Tensile strength, temper O61 | 310 MPa (45 ksi) min |
| Yield strength, temper O61 | 105 MPa (15 ksi) min |
Seamless tube is normally ordered in the annealed O61 temper, which combines the highest ductility with practical immunity to stress-corrosion cracking. Cold-drawn tempers are available where higher strength is needed, but they reduce the margin available for rolling the tube into a tube sheet.
Why Admiralty Brass Survives Cooling Water
The alloy relies on two mechanisms. First, the tin content stabilises a protective copper-oxide film that forms quickly in aerated water and limits metal loss. Second, arsenic additions are effective at very low levels and passivate the zinc-rich phase that would otherwise be attacked preferentially. Susceptibility to dezincification is verified with the accelerated test defined in ISO 6509, while resistance to stress-corrosion cracking is assessed with the ammonia vapour test of ASTM B858.
Admiralty brass performs best in clean or moderately polluted seawater at moderate flow rates, with a continuous water film and without entrained sand or air bubbles. Where cooling water carries abrasive solids, high free-flow velocity or severe impingement, aluminium brass C68700 or copper-nickel C70600 and C71500 are the more suitable choices. Water-side deposits should be avoided because stagnant, oxygen-depleted pockets under sludge can initiate localised attack.
Typical Applications
Surface condensers, auxiliary condensers and feedwater heaters in thermal power stations.
Shell-and-tube heat exchangers in refineries, petrochemical plants and chemical works.
Marine cooling systems, sea-water service coolers and shipboard heat exchangers.
Multi-stage flash and other desalination plants, where the tube side handles brine.
Evaporator, distiller and refrigeration condenser tubing, plus ferrule stock for tube-sheet connections.
Selection, Fabrication and Installation Notes
Tube selection starts with the cooling-water chemistry: chlorides, dissolved oxygen, temperature, flow velocity and the solids load all influence the expected service life. Wall thickness is chosen so that the remaining section after the corrosion allowance still satisfies the design pressure, and the tube is usually specified with a minimum wall rather than a nominal wall.
Expanding and rolling into tube sheets is the standard joining method; limit expansion to avoid over-straining the tube wall.
The expansion (pin) test and the flattening test of ASTM B153 give a practical check on ductility before installation.
U-bends should be formed with a mandrel and stress-relieved after bending so that residual stress does not promote cracking in service.
Do not couple admiralty brass directly to a less noble metal without insulation or a sacrificial anode; galvanic corrosion will concentrate at the joint.
Brazing and soldering are straightforward; silver brazing is preferred for high-integrity joints, with a flux suited to copper-zinc alloys.
Inspection and Acceptance
Finished tube should be checked dimensionally for outside diameter, wall thickness, length and straightness, and verified for temper against ASTM B111. Eddy-current examination performed to ASTM E243 is the usual method for detecting longitudinal and transverse defects in copper-alloy tubes, and it is normally combined with a hydrostatic or pneumatic pressure test. The mill certificate should confirm copper, tin and arsenic ranges, the dezincification test requirement, and the physical tests required by the order.
FAQ
Q: What is admiralty brass tube?
A seamless copper-zinc-tin alloy tube, UNS C44300, used for condensers and heat exchangers handling seawater, brine and other chloride-bearing cooling water.
Q: Why are tin and arsenic added to C44300?
Tin strengthens the alloy and arsenic inhibits dezincification, the selective zinc loss that destroys plain brass in salt water.
Q: What are the C44300 composition limits?
70.0 - 73.0% copper, 0.9 - 1.2% tin, 0.02 - 0.10% arsenic, 0.07% max lead, 0.06% max iron, and zinc as the remainder, as required by ASTM B111.
Q: Which temper is supplied for heat exchanger service?
Admiralty brass tube is normally supplied in the annealed O61 temper, with minimum tensile strength of 310 MPa and minimum yield strength of 105 MPa.
Q: How is dezincification resistance verified?
By the accelerated laboratory test defined in ISO 6509, supported by the mercury-free corrosion data and service record that the alloy family has accumulated in marine condensers.
Q: What are the international equivalents of C44300?
CuZn28Sn1 under European designations, CZ111 under the British tube series, C4430 under JIS H3300, and HSn70-1 under GB/T 8890.
Q: Can C44300 tube be used in fresh water as well?
Yes. The alloy is fully suitable for fresh water, river water and steam condensate, although in soft, low-chloride water the special corrosion advantages over a lower-cost brass are reduced.
