What Seamless Admiralty Brass Tube Is
Admiralty brass tube to ASTM B111 is a seamless copper zinc alloy tube that contains about one percent tin and a controlled arsenic addition. The tin improves resistance to dezincification, the selective loss of zinc that shortens the life of ordinary brass in cooling water, and the arsenic acts as an additional inhibitor in the same way. The result is a tube that keeps the high thermal conductivity and easy fabrication of brass while surviving cooling water, lubricating oil and fuel service for many years.
The grade is designated UNS C44300 and appears in the trade as admiralty brass or admiralty metal tube. In the aerospace and oil related industries it is found in fuel, lubricating oil, pneumatic and hydraulic support systems, in instrument and sensing lines, and in heat exchangers and coolers where a compact, corrosion resistant tube with good heat transfer is needed. Within the same ASTM B111 family, aluminium brass C68700 is preferred for clean fast flowing seawater, while the copper nickel grades are used where water quality is poorer.
Composition and Standard Requirements
| Element | Requirement for C44300 | Function |
|---|---|---|
| Copper | 70.0 to 73.0 percent | Base metal, provides conductivity and ductility |
| Zinc | Remainder | Strengthening addition |
| Tin | 0.9 to 1.2 percent | Inhibits dezincification |
| Arsenic | 0.02 to 0.06 percent | Additional dezincification inhibitor |
| Lead | 0.07 percent max | Residual only |
| Iron | 0.06 percent max | Residual only |
Tube is supplied to ASTM B111 in the annealed temper, with mechanical requirements on tensile strength, yield strength and elongation stated for the grade and temper ordered, and with grain size controlled so that the tube can be expanded into a tube sheet and bent without cracking. Tube may also be ordered stress relieved where the finished component will be exposed to an environment containing ammonia or ammonium compounds, because residual stress in a copper zinc alloy can lead to stress corrosion cracking. GB/T 8890, JIS H3300 and EN 12451 cover the same product family in other specification systems.
Dimensions are quoted as outside diameter and wall thickness with the tolerances of the ordering standard, and tube ends are supplied plain, ready for rolling, or prepared for brazed fittings. Eddy current testing is normally specified in addition to the standard mechanical tests, because it detects longitudinal and transverse defects that a hydrostatic test alone will not find.
Performance in Service
The alloy relies on a thin protective film that forms on the wetted surface in aerated water. Its thermal conductivity is high, which is the reason brass and copper nickel tube are used in condensers and oil coolers rather than stainless steel where heat transfer performance matters. Mechanical strength is adequate for pressures and temperatures encountered in fuel and oil systems, and the alloy remains ductile and easy to flare and bend.
Two limitations govern selection. First, dezincification resistance depends on the tin and arsenic additions being within the standard range, so the certified chemistry of each lot is important rather than just the nominal designation. Second, ammonia and its compounds attack stressed copper zinc alloys, so a tube that will see a contaminated atmosphere, a cleaning agent containing ammonia, or an ammonia bearing process stream should be supplied in a stress relieved condition or replaced by a copper nickel grade.
Applications in Aerospace and Oil Related Industry
Fuel, lubricating oil and pneumatic lines in engine and airframe support systems.
Oil coolers, fuel heaters and heat exchangers in aerospace and industrial plants.
Instrument, sensing and control tubing where accurate dimensions and clean bores are required.
Heat exchanger and condenser tube in refinery, petrochemical and power plant service.
Refrigeration and air conditioning coils in equipment exposed to mildly corrosive conditions.
General engineering tube where brass is specified for its combination of conductivity and strength.
Fabrication and Cleaning for Critical Service
Admiralty brass tube is bent, flared, beaded, rolled and brazed using conventional brass working practice. Annealed tube bends readily with a mandrel, and the tube should be bent in the annealed condition, avoiding cold work at the point where a joint will later be made. Brazing and silver soldering are common, and joint areas must be clean, dry and free from oil. Where a joint will be made close to an already hardened section, local stress relief reduces the risk of cracking in service.
For aerospace and oil related duty, cleanliness is part of the specification. Tube must be free from drawing lubricant, swarf and moisture, bores are often capped during transport, and suppliers can provide tube cleaned and dried to a stated non volatile residue limit where the customer's specification requires it. Tube that will carry oxygen or oxidiser rich fluids must be handled under a strict clean regime, since any hydrocarbon residue creates a safety hazard, and only methods approved for that service should be used. Tubing should be stored under cover on timber supports, away from ammonia and chloride sources, until installation.
Inspection Points and Common Pitfalls
Confirm the certified tin and arsenic content, since they determine dezincification resistance.
Confirm that stress relieved tube has been supplied where ammonia exposure is possible.
Check that eddy current testing is specified for tube that will be rolled into a tube sheet.
Keep the bore clean and dry; drawing lubricant residues and moisture cause later problems in critical systems.
Avoid over expanding the tube during installation, because the wall thins at the expansion and that becomes the failure point.
Do not use ammonia bearing cleaners or marking fluids on copper zinc tube.
FAQ
Q: What is admiralty brass tube made of?
Admiralty brass is a copper zinc alloy containing about 70 to 73 percent copper, roughly one percent tin and a controlled arsenic addition of 0.02 to 0.06 percent, with lead and iron held to low residual limits. The tin and arsenic provide resistance to dezincification.
Q: Why is arsenic added to C44300?
Arsenic is an inhibitor that suppresses dezincification, the selective removal of zinc that causes premature failure of ordinary brass in cooling water. It is a required part of the composition and is certified on the mill test report.
Q: Is admiralty brass suitable for seawater?
It is used in clean cooling water and brackish water service, but where seawater velocities are high and the water is clean, aluminium brass C68700 is generally preferred, and copper nickel grades are used where water quality or suspended solids are a problem.
Q: What causes stress corrosion cracking in brass tube?
Ammonia and ammonium compounds combined with residual tensile stress from cold work or forming. Stress relieved tube, or a copper nickel grade, is selected where that environment is possible.
Q: What tests are carried out on the tube?
Tensile strength, yield strength and elongation for the ordered temper, grain size checks, dimensional inspection, hydrostatic testing and normally eddy current testing to detect longitudinal and transverse defects.
Q: Is C44300 tube available in metric sizes?
Yes. Tube is produced to the diameter and wall thickness combinations of the ordering standard, and metric and inch series are both available, with tolerances stated in the applicable standard.
Q: How should the tube be handled before installation?
Store it under cover on timber supports with the ends capped, keep it away from ammonia and chloride sources, and leave the protective caps in place until the tube is fitted.
