Material Overview
C44300 is admiralty brass, a single-phase alpha copper-zinc alloy modified with tin and inhibited with arsenic. It has been a standard heat exchanger material for more than a century because it combines good strength, excellent thermal conductivity and dependable resistance to clean seawater at a moderate cost. In ASME SB111 and ASTM B111 the alloy is supplied as seamless tube for condensers, coolers and similar service, and the same material is standardised as CuZn28Sn1 in European practice, C4430 in JIS H3300, CZ111 in the older British system and HSn70-1 in GB/T 8890. EN 12451 is the corresponding European standard for seamless copper-alloy heat exchanger tube.
The tin addition is what distinguishes admiralty brass from plain 70/30-type brasses: tin strengthens the protective surface film and improves performance in flowing seawater, while the arsenic addition suppresses the loss of zinc that would otherwise cause plug-type failures.
Chemical Composition
| Element | Requirement (mass %) | Purpose |
|---|---|---|
| Copper (Cu) | 70.0 - 73.0 | Base metal |
| Zinc (Zn) | Remainder | Principal alloying element |
| Tin (Sn) | 0.9 - 1.2 | Improves corrosion resistance, especially in seawater |
| Arsenic (As) | 0.02 - 0.06 | Inhibits dezincification |
| Lead (Pb) | 0.07 max | Residual limit |
| Iron (Fe) | 0.06 max | Residual limit |
| Others, total | 0.10 max typical for the grade | Controlled to protect ductility and conductivity |
Both the tin and the arsenic windows are narrow. Tube with tin at the lower edge of the range and arsenic below the minimum will pass a chemical check but will not behave as admiralty brass in seawater, which is why the heat analysis is read together with the dezincification test result.
Corrosion Behaviour and Service Limits
Admiralty brass resists general corrosion in clean seawater and in fresh water, and it is the classic material for power station condensers cooled by river or sea water.
Resistance to dezincification is essential because the alloy contains about 30 % zinc. ASME SB111 requires an arsenic addition and supports the assessment of performance by the ISO 6509 immersion test, which reports the maximum depth of dezincification on a sample of finished tube.
The alloy resists chloride stress corrosion cracking but is attacked by ammonia and ammonium compounds. Where the cooling water is polluted or the process stream carries ammonia, admiralty brass is replaced by a copper-nickel grade.
Velocity limits in clean seawater are generally taken as about 2 to 2.5 m/s. Above that figure, impingement attack develops at the inlet end and the tube life shortens sharply.
Sulphides in polluted water break down the protective film and accelerate attack, so a water analysis is part of the material selection process.
Tube Sizes, Forms and Applications
Seamless round tube in the outside diameter and wall combinations of the specification, supplied in straight lengths or as U-bent tubes for bundle assembly.
Finned tube for air-cooled and enhanced-surface exchangers, and tube expanded into tube sheets of naval brass or copper alloy.
Power generation condensers and closed cooling water heat exchangers using river, lake or sea water.
Marine auxiliary condensers, lubricating oil coolers and jacket water coolers on ships.
Desalination preheaters where the feed water is relatively clean and of moderate temperature.
General industrial coolers handling clean, non-ammoniacal water.
Fabrication, Rolling and Inspection
Tube is expanded into tube sheets by controlled rolling; over-rolling thins the wall and creates a stress concentration at the transition to the unrolled length.
U-bend tubes are stress-relieved after bending where the specification or the service requires it, because the bend is the highest-stressed region of the tube.
Cutting and de-burring are done without leaving abrasive particles in the bore, which would seed erosion at the tube inlet.
Eddy-current examination to ASTM E243 is applied over the full length of the tube, and the acceptance level is agreed at order stage.
Mechanical testing to ASTM E8 and a flattening or expansion test demonstrate the required ductility.
The finished bundle is hydrostatically tested and then cleaned, with the tube ends capped for transport and storage.
Ferrules or impressed-current protection are fitted at the water-box inlet where the design anticipates inlet-end erosion.
FAQ
Q: Why is arsenic added to admiralty brass?
Arsenic inhibits the selective loss of zinc from the alloy. Without it, the tube would suffer plug-type dezincification in aggressive cooling water despite meeting the copper content specified for the grade.
Q: How is dezincification resistance verified?
By the ISO 6509 immersion test on a finished tube sample, which measures the maximum depth of dezincification, supported by the arsenic content reported on the mill certificate.
Q: Can admiralty brass be used with polluted harbour water?
It is not the best choice. Ammonia, sulphides and high suspended solids all reduce tube life, and in those conditions a 90/10 or 70/30 copper-nickel grade is specified instead.
Q: What is the maximum water velocity?
Design guidance for clean seawater is generally about 2 to 2.5 m/s. Higher velocity removes the protective film and causes inlet-end and impingement attack on the tube.
Q: Is C44300 the same as aluminium brass?
No. Aluminium brass is C68700, which contains aluminium rather than the tin addition used in admiralty brass. The two grades are separate entries in ASME SB111 and have different corrosion characteristics.
Q: What should the purchase order state?
The standard and edition, the UNS number, tube size and wall, temper, length or U-bend dimensions, quantity, test requirements including eddy-current acceptance level, and the cooling water conditions if a dezincification test is required.
