What Purple Copper Tubing Means in Industry Terms
Purple copper tubing is the descriptive name used in Chinese copper production for seamless tube drawn from essentially unalloyed, high-purity copper. The name comes from the reddish-violet colour of a freshly pickled copper surface, and it distinguishes pure copper tube from brass tube, bronze tube and copper-nickel tube. In export documentation the same material appears as copper tube, copper pipe, red copper tube, ETP copper tube, DHP copper tube or oxygen-free copper tube, depending on the grade and the standard the order is placed against.
All purple copper tubing shares the same base properties: very high electrical and thermal conductivity, excellent cold formability in the annealed condition, good resistance to atmospheric and fresh-water corrosion, and a characteristic tendency to form a protective oxide film rather than to corrode uniformly. What changes between grades is the residual deoxidiser content, and that single variable controls conductivity, weldability and suitability for reducing-atmosphere service.
Grades, Composition and Governing Standards
Four grades cover the great majority of industrial demand. C11000 (electrolytic tough pitch, ETP) is the general-purpose grade; C12200 (phosphorus-deoxidised, DHP) is the welding and refrigeration grade; C10200 (oxygen-free, OF) and C10100 (oxygen-free electronic, OFE) serve high-conductivity and vacuum applications.
| Grade / UNS | Description | Copper content | Deoxidation | Typical tube standard |
|---|---|---|---|---|
| C10100 | Oxygen-free electronic | 99.99 % min | None; oxygen 0.0005 % max | ASTM B170, ASTM B188 |
| C10200 | Oxygen-free | 99.95 % min | None; oxygen 0.001 % max | ASTM B152, ASTM B280 |
| C11000 | Electrolytic tough pitch | 99.90 % min | Residual oxygen 0.02–0.04 % | ASTM B88, ASTM B75 |
| C12200 | Phosphorus-deoxidised | 99.90 % min | Phosphorus 0.015–0.040 % | ASTM B88, ASTM B280 |
Metric and European orders are usually placed against EN 1057 for sanitary and heating tube, EN 12735-1 and EN 12735-2 for air-conditioning and refrigeration tube, GB/T 1527 and GB/T 18033 for Chinese seamless copper tube, or JIS H3300 for copper and copper-alloy seamless tube. Dimensional tolerances, temper designations, testing frequency and marking requirements all follow the standard that is named on the purchase order, so the standard number should always be specified rather than left to the mill's discretion.
Conductivity, Thermal Performance and Physical Data
Conductivity is the property that separates the grades most clearly. Residual oxygen in solution in ETP copper is not harmful to conductivity but does make the material unsuitable for hydrogen-bearing brazing atmospheres; phosphorus in DHP copper protects against hydrogen embrittlement but reduces conductivity.
| Property (typical, annealed) | C10100 | C10200 | C11000 | C12200 |
|---|---|---|---|---|
| Electrical conductivity, % IACS | 101–102 | 100–101 | 100–101 | 80–85 |
| Thermal conductivity, W/(m·K) | about 390 | about 390 | 390–400 | about 340 |
| Density, g/cm³ | 8.94 | 8.93 | 8.89 | 8.94 |
| Melting range, °C | about 1083 | about 1083 | 1065–1085 | about 1083 |
| Modulus of elasticity, GPa | 117 | 117 | 117 | 117 |
The coefficient of thermal expansion is approximately 17 × 10⁻⁶ per °C over the normal service range. Yield and tensile strength depend on temper rather than on grade: soft annealed tube is supplied in the 200–260 MPa tensile range, half-hard tube reaches roughly 250–320 MPa, and hard-drawn tube is typically above 310 MPa. The applicable product standard sets the minimum values for the temper ordered, and the mill certificate should be read against that standard.
Where Purple Copper Tubing Is Used
HVAC and refrigeration: C12200 and C10200 tube to ASTM B280 for refrigerant lines, condensers and evaporators, where cleanliness, pressure tightness and freedom from hydrogen embrittlement are essential.
Heat exchange: seamless tube to ASTM B75 and copper-alloy tube to ASTM B111 for shell-and-tube exchangers, condensers, evaporators and steam condensers.
Plumbing and sanitary services: C12200 or C11000 tube to EN 1057, ASTM B88 and GB/T 18033 for potable water, heating and gas distribution.
Electrical and power: bus pipe, bus tube and conductor tube to ASTM B188, plus transformer, switchgear and earthing connections that depend on high conductivity.
Renewable energy and electronics: photovoltaic array wiring, substation connections, plasma deposition and sputtering targets, particle accelerator components.
Transport: battery-cooling plate and motor-winding tube for electric vehicles, and marine and offshore piping in the DHP and copper-nickel families.
Temper Selection, Bending and Joining
The temper determines how the tube behaves on site. Annealed tube (O60) bends readily to a centre-line radius of about 1.5 to 2 times the outside diameter for ACR work and is the normal choice where the tube must be manipulated in a trench or on a coil. Light-drawn and hard-drawn tempers hold a straight form and carry higher pressure ratings but must be bent with a bender and a mandrel, or formed in a larger radius.
Joining follows the grade: soft soldering and silver brazing suit all four grades; press-fit and mechanical fittings are used widely on sanitary tube; and fusion welding is practical on C12200 because the phosphorus content suppresses porosity, whereas C11000 welded in a hydrogen-bearing flame atmosphere can suffer internal steam voids. Where severe bending is performed, a re-anneal at approximately 400–600 °C restores ductility; the tube is then purged, cleaned and capped before installation. Cutting should be by rotary cutter or fine-tooth saw, with all burrs removed and the cut end deburred and reamed so that flow is not disturbed.
Inspection Points and Common Pitfalls
Typical quality controls are eddy-current testing to ASTM E243, hydrostatic or pneumatic pressure testing, dimensional and wall-thickness verification, grain-size and temper verification on a cut sample, and a residue check for refrigeration tube where the internal cleanliness limit of the product standard applies. For C11000 destined for reducing atmospheres, an embrittlement test in hydrogen is available.
The most frequent ordering errors are misuse of the term "purple copper" for brass or copper-nickel tube, omission of the temper from the enquiry, and selection of ETP copper for refrigeration work when DHP is required. A fourth recurring issue is confusion between the annealed and hard-drawn pressure ratings: the safe working pressure for a given diameter and wall is defined by the product standard for the temper supplied, not by the alloy alone.
FAQ
Q: What is the difference between purple copper tubing and brass tubing?
Purple copper tubing is unalloyed copper with a copper content of 99.90 % or higher, while brass tubing is a copper-zinc alloy. Purple copper delivers higher conductivity and better cold formability; brass delivers higher strength and better machinability.
Q: Which grade should be used for refrigeration and air-conditioning lines?
Use DHP copper C12200 to ASTM B280, or oxygen-free C10200 where maximum conductivity and zero hydrogen-embrittlement risk are required. Both are supplied cleaned, purged and capped for ACR service.
Q: Why does C12200 have lower conductivity than C11000?
Residual phosphorus, added to deoxidise the melt, remains in solid solution and scatters electrons. This reduces conductivity to roughly 80–85 % IACS while greatly improving weldability and resistance to hydrogen embrittlement.
Q: Can purple copper tubing be welded rather than brazed?
Yes. Phosphorus-deoxidised grades such as C12200 are readily welded and brazed without porosity; tough-pitch C11000 should be brazed or welded only where the atmosphere is free of hydrogen, otherwise internal defects can form.
Q: What is the normal supply condition of copper tube?
Seamless copper tube is normally supplied as soft annealed coils or straight lengths in temper O60, or as light-drawn and hard-drawn straight lengths. Soft tube is preferred for field bending and hard-drawn tube for exposed, self-supporting runs.
Q: How should the tube be stored before installation?
Keep ends capped, store indoors on dry dunnage, and avoid contact with steel or with chloride-bearing materials. Copper surfaces should not be allowed to collect standing water or construction dust that can later promote pitting.
