Composition and Designation of the Two Tube Families
Copper tube is made from phosphorus-deoxidised copper, designated C12200 in the UNS system and Cu-DHP in European practice, with a copper content of at least 99.90 % and a controlled residual phosphorus level of 0.015 % to 0.040 %. The phosphorus is deliberately retained to deoxidise the melt and prevent hydrogen embrittlement during brazing, and it is also the reason the grade is not used for conductors. Brass tube is made from a copper-zinc alloy; the widely used cartridge brass corresponds to C26000 with 68.5 % to 71.5 % copper and the balance zinc, and C27000 with 63.0 % to 68.5 % copper is used where higher strength and lower cost are acceptable. In the Chinese system the same materials appear as T2 for the copper tube grade and H68 or H62 for the brass grades in GB/T 5231. Copper tube is covered by ASTM B88, ASTM B75 and EN 1057, and brass tube by ASTM B135 and the corresponding clauses of the European tube standards.
Colour, Physical and Mechanical Differences
| Property | Copper tube, Cu-DHP / C12200 | Brass tube, C26000 / H68 |
|---|---|---|
| Colour | Reddish brown to purple red | Yellow to golden yellow |
| Density | About 8.94 g/cm3 | About 8.5 g/cm3 |
| Thermal conductivity | About 340 to 390 W/(m.K) | About 115 to 125 W/(m.K) |
| Electrical conductivity | About 85 % IACS | About 27 to 30 % IACS |
| Tensile strength, annealed | About 220 MPa minimum | About 320 MPa minimum |
| Tensile strength, hard | About 290 MPa minimum | About 470 MPa minimum |
| Formability | Excellent, bends and flares readily | Lower ductility, needs larger bend radii |
Brass is the stronger and harder of the two in the same temper, and its higher zinc content raises strength at the price of ductility and conductivity. Copper retains useful strength at high temperature and keeps its conductivity, which is why it is chosen whenever heat has to be moved rather than a load carried.
Corrosion Behaviour and Dezincification
Copper resists attack in potable, neutral and many industrial waters by forming a protective oxide and carbonate film, but it is vulnerable to ammonia and ammonium compounds, to amine-based flux residues left inside a joint, and to erosion-corrosion where flow velocity is excessive. Brass offers useful resistance in mildly aggressive water, yet the zinc in the alloy can be selectively dissolved, leaving a porous copper-rich residue; this is dezincification. It is promoted by stagnant high-chloride water at elevated temperature and is most dangerous in thin-wall tube because failure is sudden. Resistance is improved by alloying control in the dezincification-resistant brasses, which carry small additions of arsenic, antimony or phosphorus, and the correct seawater materials are admiralty and naval brass or, for tube, a cupronickel such as C70600. Seawater service should therefore never be specified on the basis of a plain cartridge brass alone.
Where Each Tube Is Used
Copper tube dominates water supply, heating, chilled water, gas, refrigerant and medical gas distribution because it combines corrosion resistance with high thermal conductivity, and it is produced in straight lengths and in coils for buried and concealed routes. Brass tube is selected where strength, hardness or appearance is the primary driver: instrument and gauge lines, small-diameter hydraulic and pneumatic circuits, architectural and decorative elements, and general mechanical tube for fittings and connectors where the component has to be machined rather than bent. Where tube is required both to carry heat and to resist seawater, a cupronickel grade is used instead of either of the two materials discussed here.
Joining, Machining and Fabrication
Copper tube is joined by capillary soldering or brazing, by press fittings, and by flaring for mechanical connections, and it can be bent cold to tight radii without cracking in the annealed temper. Brass tube machines readily and is often chosen for parts produced on automatic lathes, but it calls for liberal coolant because of its low thermal conductivity, and its lower ductility means that bending is done hot or on generous radii. Both families require the correct filler and flux combination: aggressive flux must be flushed out of the pipework after installation, because residual flux is a common cause of premature failure in copper systems, and brazing of copper requires the phosphorus-deoxidised grade to avoid hydrogen embrittlement.
Specification, Inspection and Delivery
An order should state the material designation, the governing standard, the temper, the dimensional series, the length form and any test required by the project specification. Dimensional verification covers outside diameter, wall thickness and ovality, mechanical verification covers tensile strength, elongation and hardness, and integrity is confirmed by an eddy-current test or a hydrostatic test in accordance with ASTM B88 or the equivalent clause of the European standard. Tubes are supplied with capped or plugged ends to keep the bore clean, are marked with the standard, grade, temper and heat identification, and are delivered with a mill test certificate at EN 10204 3.1 that ties the analysis and mechanical results to the heat number.
Frequently Asked Questions
Q: Is brass tube stronger than copper tube?
A: Yes. In comparable tempers, brass tube is stronger and harder than copper tube, which is why it is chosen for machined fittings and hydraulic lines where load rather than thermal performance governs.
Q: Why is copper tube preferred for water and refrigerant circuits?
A: It combines a protective corrosion film with thermal conductivity roughly three times that of brass, so a heat exchanger or evaporator built from copper tube is more compact for the same duty. Copper is also easier to bend and flare on site.
Q: What is dezincification and when does it matter?
A: It is the selective removal of zinc from brass in aggressive water, leaving a weak copper-rich structure. It matters for thin-wall tube and fittings in stagnant high-chloride or high-temperature water, and it is the reason such service specifies a dezincification-resistant brass or a cupronickel.
Q: Can copper and brass tube be used in the same system?
A: Yes, but joints should use fittings appropriate to both materials and flux residues must be flushed out after installation, since trapped flux is a frequent cause of localised attack at the joint.
Q: How are the two tubes identified on delivery?
A: By the marking on the tube, which states the standard, the material designation, the temper and the dimensional type, supported by a mill test certificate at EN 10204 3.1 quoting the heat number, chemical analysis and mechanical results.
Q: What test confirms that a tube is free from through-wall defects?
A: An eddy-current test for general service or a hydrostatic test where the purchaser specifies it, both of which are recognised acceptance tests in the copper tube specifications and are reported on the inspection documents.
