What Admiralty Brass Tube Is
UNS C44300 under ASTM B111/B111M is arsenical admiralty brass, a copper zinc alloy containing about 71 % copper with deliberate additions of tin and arsenic. The tin improves resistance to impingement attack and strengthens the alloy, while the arsenic addition of 0.02 to 0.06 % is an inhibitor that suppresses dezincification, the selective removal of zinc that destroys ordinary brass in cooling water. Admiralty brass tube has been the workhorse of steam condensers and oil coolers in clean fresh and brackish water service for many decades because it combines good heat transfer, useful strength and moderate cost.
The grade is normally supplied as seamless tube in the annealed temper for roller expansion, and in drawn tempers where higher strength is required. It is produced to a controlled grain size so that the tube expands into a tubesheet without cracking, and it is available with eddy current examination for wall integrity.
Chemical Composition of UNS C44300
| Element | Requirement |
|---|---|
| Copper (Cu) | 70.0 to 73.0 % |
| Tin (Sn) | 0.9 to 1.2 % |
| Arsenic (As) | 0.02 to 0.06 % |
| Lead (Pb) | 0.07 % maximum |
| Iron (Fe) | 0.06 % maximum |
| Zinc (Zn) | Remainder |
The arsenic range is not optional for cooling water service. Arsenical grades resist dezincification; the non-arsenical versions of the same base alloy do not, and the difference is visible in the tube wall after only a few years. The copper range is also important because zinc rich material with copper below 70 % is far more sensitive to selective attack.
Mechanical, Thermal and Working Properties
| Property | Value |
|---|---|
| Tensile strength, annealed, minimum | 310 MPa (45 ksi) |
| Yield strength at 0.5 % extension, minimum | 105 MPa (15 ksi) |
| Elongation, annealed | 40 % minimum |
| Tensile strength, cold worked | Up to about 600 MPa |
| Thermal conductivity | About 109 W/(m·K) |
| Electrical conductivity | About 28 % IACS |
| Hot working range | About 700 to 800 C |
The annealed material balances useful strength with high elongation, which is what makes roller expansion and U-bending possible. Cold worked tube reaches much higher strength but becomes sensitive to stress corrosion cracking, so a stress relief treatment is standard practice after cold forming where the environment contains ammonia or amines. The alloy supports cold bending, flaring and brazing, and it machines more freely than the copper nickel grades.
Equivalent Grades in Other Standards
| Standard system | Designation | Remarks |
|---|---|---|
| ASTM B111/B111M | C44300 | UNS number, arsenical admiralty brass |
| BS 2871 Part 3 | CZ111 | British tube designation |
| DIN 1785 | CuZn28Sn1 | German designation |
| EN 12451 | CuZn28Sn1As | European heat exchanger tube standard |
| JIS H3300 | C4430 | Japanese tube designation |
| IS 1545 | Admiralty brass tube | Indian standard for condenser tube |
| Chinese practice | HSn70-1 | Tin bearing brass grade to GB/T 5231 |
When substituting between these designations, verify the tin and arsenic ranges rather than relying on the alloy name alone, because some older national versions specify slightly different limits. All the designations above describe the same 70/30 type brass family with tin and arsenic additions.
Applications and Service Limits
Steam surface condensers and air ejector coolers in power stations using clean cooling water.
Oil coolers, compressor intercoolers and lube oil exchangers in refineries.
Heat exchangers and evaporators in fresh water desalination and process plants.
Feedwater heaters and drain coolers in steam cycles.
Condensers in HVAC and marine plant where the cooling water is not saline.
Admiralty brass is not a seawater alloy in the full sense. It is suitable for clean fresh and brackish water at moderate velocity, typically up to about 2 m/s, but polluted water with high chloride content, ammonia, amines or hydrogen sulphide will attack it. In those conditions cupro nickel grades such as 90/10 copper nickel are the correct choice. Dezincification resistance is evaluated by the standardised test in ISO 6509, while susceptibility to stress corrosion cracking from ammoniacal environments is assessed by the ammonia vapour test method ASTM B858.
Fabrication and Inspection Notes
Tube is expanded into tubesheets after the holes have been properly prepared and cleaned, and the expansion should be uniform along the joint to avoid over-rolling at the ends. Cold bending and flaring are carried out on annealed material, and any heavily cold worked region should be stress relieved before the exchanger enters service. Brazing is straightforward, but residual flux must be removed because flux residues are corrosive in a wet environment.
Inspection to ASTM B111/B111M includes tension, flattening, flaring and expansion tests, with grain size checked on annealed tube. Eddy current examination to ASTM E243 is the usual non-destructive check for wall continuity, and hydrostatic or pneumatic proof testing is applied when specified. Mill certificates record the heat number, chemical analysis including arsenic and tin, mechanical results and the temper supplied.
FAQ
Q: What is the difference between admiralty brass and plain brass tube?
Admiralty brass contains about 1 % tin and 0.02 to 0.06 % arsenic. The tin improves resistance to impingement attack and the arsenic inhibits dezincification, so the tube lasts far longer than plain brass in cooling water.
Q: Which grades are equivalent to C44300?
CZ111 in BS 2871 Part 3, CuZn28Sn1 in DIN 1785, CuZn28Sn1As in EN 12451, C4430 in JIS H3300 and the tin bearing brass HSn70-1 in Chinese designation practice all describe the same alloy family.
Q: Can admiralty brass be used with seawater?
Only in clean, low velocity brackish duty. For genuinely saline or polluted water, cupro nickel 90/10 or 70/30 is the correct material because brass alloys lose zinc and suffer impingement attack in those conditions.
Q: Why is stress relief needed after cold working?
Cold worked brass is susceptible to stress corrosion cracking in ammoniacal or amine bearing environments. A stress relief treatment after forming removes the residual stress and prevents cracking in service.
Q: What minimum strength does the tube have?
Annealed tube to ASTM B111/B111M has a minimum tensile strength of 310 MPa and a minimum yield strength of 105 MPa at 0.5 % extension, with elongation of at least 40 %. Cold worked tube can reach about 600 MPa.
Q: How is dezincification resistance verified?
Dezincification resistance is checked by the standardised test in ISO 6509, and separate susceptibility to stress corrosion cracking is assessed by the ammonia vapour test method ASTM B858. Both are relevant when the cooling water may contain ammonia or amines.
