What Is Admiralty Brass?
Admiralty brass is a copper-zinc alloy developed for ships and coastal power plant service, where ordinary brass fails by selective loss of zinc. It sits close to the 70/30 brass composition but carries deliberate additions of tin and a dezincification inhibitor. In modern designation systems the most widely used composition is UNS C44300, with C44400 and C44500 covering the antimony and phosphorus inhibited variants.
The alloy family is also called admiralty metal. In older literature the two names are used loosely, but in purchasing documents the distinction matters: the term admiralty brass should always be tied to a UNS number or to a product specification such as ASTM B111 so that composition, temper and inhibitor type are unambiguous.
Its reputation rests on three properties that are difficult to combine in one material. It resists moving seawater and brackish water, it transfers heat efficiently because of its high copper content, and it retains enough strength and ductility to be expanded into tube sheets and rolled to close tolerances. That combination is why condenser and heat exchanger tubing remains its largest single application.
Composition of C44300 Admiralty Brass
C44300 is defined by the standard composition below. Copper forms the balance of the structure, zinc provides strength through solid solution, tin improves resistance to seawater corrosion, and the arsenic addition is present specifically to inhibit dezincification.
| Element | Content (wt.%) | Function |
|---|---|---|
| Copper | 70.0-73.0 | Base element, governs conductivity and colour |
| Tin | 0.9-1.2 | Improves corrosion resistance in seawater and flowing water |
| Arsenic | 0.02-0.06 | Dezincification inhibitor |
| Lead | 0.07 max | Impurity, limited for weldability |
| Iron | 0.06 max | Impurity |
| Zinc | Remainder | Solid solution strengthener |
C44400 substitutes antimony for arsenic and C44500 substitutes phosphorus, which is often preferred where the finished tube will be used in potable or food-contact water systems. All three are covered as copper-alloy tube by ASTM B111, while the equivalent European grades appear in EN 12451 and EN 12449 for tube and EN 12164 for rod. In the Chinese system the corresponding designation is HAl77-2 in related work, while HSn70-1 covers the tin-bearing admiralty type composition.
Mechanical Properties and Tempers
Admiralty brass tube is supplied in the annealed condition for expansion into tube sheets and in lightly drawn tempers where extra stiffness is needed for longer spans. Under ASTM B111 the temper designation is tied to the required tensile strength, 0.5 percent extension yield strength and elongation, and the annealed O61 condition is the normal starting point for condenser and heat exchanger work.
| Property | Typical annealed condition (O61) |
|---|---|
| Tensile strength, minimum | 345 MPa (50 ksi) |
| Yield strength at 0.5 percent extension, minimum | 140 MPa (20 ksi) |
| Elongation in 50 mm, minimum | 35 percent |
| Thermal conductivity | Approximately 110 W/m.K at room temperature |
| Density | Approximately 8.53 g/cm3 |
The relatively high copper content gives the alloy thermal conductivity well above that of the copper-nickel grades, which allows thinner walls and lower tube counts for the same duty. Its modulus and ductility also allow roller expansion into tube sheets without cracking.
Admiralty Brass Compared with Naval Brass
The two names are often confused because both were developed for marine service, but they occupy different roles. Naval brass is stronger and harder because it carries a higher zinc content, while admiralty brass offers distinctly better resistance to dezincification. The practical rule is to specify admiralty brass for heat exchanger and condenser tubing, and naval brass for structural items such as tube plates, fasteners and shafts where strength is the primary need.
| Feature | Admiralty brass | Naval brass |
|---|---|---|
| Typical UNS numbers | C44300, C44400, C44500 | C46400, C46500 |
| Approximate copper content | 71 percent | 60 percent |
| Tin | 0.9-1.2 percent | Approximately 0.75 percent |
| Structure | Predominantly alpha | Alpha-beta duplex |
| Strength and hardness | Moderate | Higher |
| Dezincification resistance | Excellent, inhibited | Good to moderate |
| Usual product forms | Seamless tube, plate, rod | Rod, bar, forging stock, plate |
Applications of Admiralty Brass
Because the alloy was designed around water-side corrosion, most applications involve heat transfer or seawater containment.
Steam surface condensers and auxiliary condensers in power stations and on board ships.
Shell and tube heat exchangers in refineries, chemical plants and desalination units.
Feedwater heaters, lube oil coolers and air coolers where cooling water is brackish or saline.
Marine piping, sea water service lines, valve trim and pump components.
Distiller tubing and evaporator tubing in fresh water generation plants.
Plumbing and sanitary applications when the antimony or phosphorus inhibited variants are specified for potable water contact.
Service limits follow the water chemistry. The alloy performs well in clean seawater at moderate velocity but is vulnerable to impingement attack if flow exceeds the velocity permitted for the tube size, and to ammonia attack in the presence of oxygen, which can cause stress corrosion cracking of cold-worked material. Residual stresses after forming should therefore be relieved, and flow velocities kept within engineering guidance.
Fabrication, Welding and Inspection Points
Admiralty brass tube is normally joined by roller expansion into tube sheets, by brazing, or by welding in larger assemblies. Fusion welding is possible but the presence of arsenic makes fume control necessary, and the low zinc content reduces but does not eliminate the risk of zinc evaporation in the arc. Where welding is required, a matching filler or a copper-based filler selected for the service environment should be used and the joint should be stress relieved.
Annealed tube can be bent, flared and swaged. Cold working raises strength and lowers ductility, so a final anneal is advisable before any operation that requires substantial deformation. For critical condensers the usual inspection programme includes dimensional checks against ASTM B111, hydrostatic or pneumatic pressure testing, eddy current testing of the tube wall, and verification of grain size and residual stress where stress corrosion cracking is a concern.
Dezincification resistance should be confirmed by the composition of the finished tube rather than assumed from the grade name, since the inhibitor addition is what separates a serviceable tube from one that will fail in a few years of seawater duty.
FAQ
Q: What is admiralty brass?
Admiralty brass is a copper-zinc alloy with copper in the 70 to 73 percent range, tin at roughly 1 percent and a small addition of arsenic, antimony or phosphorus that inhibits dezincification. UNS C44300 is the standard composition.
Q: What are the main uses of admiralty brass?
Its main uses are condenser and heat exchanger tubing, marine piping, pump and valve components and distiller tubing, especially where cooling water is seawater or brackish.
Q: What is the difference between admiralty brass and naval brass?
Naval brass is stronger and harder because of its higher zinc content, while admiralty brass resists dezincification better. Admiralty brass is preferred for exchanger tubing and naval brass for structural items such as tube plates and fasteners.
Q: Why is arsenic added to admiralty brass?
Arsenic, antimony or phosphorus acts as a dezincification inhibitor. It changes the corrosion mechanism at the metal surface so that zinc is not selectively dissolved, keeping the tube sound in chloride-bearing water.
Q: Can admiralty brass be welded?
It can be welded and brazed, though fume control is needed because of the arsenic addition and joints should be stress relieved. Roller expansion and brazing remain the most common joining methods for condenser tubes.
Q: Which standard covers admiralty brass tube?
ASTM B111 covers copper and copper-alloy tube including C44300, C44400 and C44500 in their specified tempers. European equivalents are found in EN 12451 and EN 12449.
