What T2 Purple Copper Tube Is
T2 purple copper tube is a seamless, non-ferrous metal tube produced by pressing and drawing. The colour that gives the material its name comes from the natural purple-red shade of high-purity copper, and the T2 designation is the Chinese GB/T 5231 grade for a copper with a copper plus silver content of at least 99.90%. The corresponding American designation is UNS C11000 electrolytic tough pitch copper, and the Japanese equivalent is C1100. The alloy offers high electrical and thermal conductivity together with good ductility and formability, so it can be bent, flared, expanded and joined by soldering or brazing. It is widely used in air conditioning and refrigeration circuits, hot and cold water supply lines, chemical process pipework, mechanical equipment and general fabricated products.
Chemical Composition and Oxygen Control
The table below gives the GB/T 5231 limits for T2 copper. Silver is counted together with copper because it behaves like copper in service. The residual elements are held low to protect conductivity, and the oxygen limit is the key difference between the tough pitch and deoxidised grades.
| Element | Limit (wt.%) |
|---|---|
| Copper plus silver | 99.90 minimum |
| Oxygen | 0.06 max |
| Tin | 0.002 max |
| Zinc | 0.005 max |
| Lead | 0.005 max |
| Nickel | 0.005 max |
| Iron | 0.005 max |
| Antimony, arsenic, sulfur, bismuth | Trace limits, each controlled individually |
Tough pitch copper such as T2 contains dissolved oxygen, which has no significant effect on conductivity or processing performance at room temperature but becomes a problem in a reducing atmosphere. At elevated temperature the dissolved oxygen reacts with hydrogen to form steam at the grain boundaries, a mechanism known as hydrogen embrittlement. For that reason T2 is not recommended for service or processing above about 370 C in a reducing atmosphere, including annealing and some welding operations.
Comparison of T2 and TP2 Copper Tube
TP2 is the phosphorus-deoxidised companion grade to T2, and the two are often offered side by side for tube applications. The phosphorus addition removes the dissolved oxygen, which eliminates hydrogen embrittlement and makes TP2 the better choice for welded assemblies and for heat exchanger tube that must be brazed or annealed repeatedly.
| Element | T2 | TP2 |
|---|---|---|
| Copper plus silver | 99.90 minimum | 99.85 minimum |
| Phosphorus | Not a deliberate addition | 0.013 - 0.050 |
| Oxygen | 0.06 max | 0.01 max |
| Tin | 0.002 max | 0.01 max |
| Iron | 0.005 max | 0.05 max |
| Nickel | 0.005 max | 0.01 max |
The small conductivity penalty of the residual phosphorus in TP2 is accepted in exchange for weldability and freedom from hydrogen embrittlement. Both grades are supplied in annealed, light-drawn and hard tempers according to the required strength and bend radius.
Physical and Mechanical Properties
Density: 8.96 g/cm³, the reference value used for all mass calculations.
Melting point: 1083 C.
Colour: purple-red in the clean, unoxidised condition.
Conductivity: high electrical and thermal conductivity, the primary reason the grade is selected.
Formability: excellent ductility, suitable for bending, flaring, expanding and deep drawing.
Joining: readily soldered and brazed; TP2 is preferred when welding is required.
Corrosion: good resistance to atmospheric attack and to many industrial waters.
Calculating the Mass of a Copper Tube
Tube mass is calculated from the density of copper and the annular cross-section of the tube. For T2 and TP2 tube the industry formula is:
G = 8.96 x pi x wall thickness x (outside diameter - wall thickness) / 1000
where G is the mass per metre in kilograms, wall thickness and outside diameter are both in millimetres, and 8.96 is the density of copper in grams per cubic centimetre. The expression in brackets represents the mean circumference of the wall, so the formula is simply density multiplied by the cross-sectional area multiplied by one metre of length. As a worked example, a tube of 10 mm outside diameter with a 1 mm wall gives 8.96 x 3.1416 x 1 x 9 / 1000, or about 0.253 kg per metre. The same calculation is used to prepare quotations and to check delivery mass against calculated mass.
Applications of T2 Purple Copper Tube
Air conditioning and refrigeration: refrigerant lines, condenser and evaporator coil tube.
Water supply and heating: domestic hot and cold water tube, gas lines and solar thermal circuits.
Chemical and process industry: cooling coils, condensers and general pipework handling non-aggressive media.
Mechanical equipment: bushings, seals, gaskets and machined components produced from tube stock.
Electrical industry: conductor tube, busbar assemblies and conductive components, including electrode holders and EDM electrodes.
Ordering and Handling Points
An order for T2 or TP2 tube should state the grade, temper, outside diameter, wall thickness, length, temper tolerance, test requirement and the standard that governs the delivery, for example GB/T 18033 for seamless water tube, ASTM B88 for water tube or ASTM B280 for air conditioning and refrigeration tube. Tube is normally supplied in straight lengths or in soft coils, cleaned and capped, and the bore should be dry and free of drawing lubricant before it is installed in a refrigeration circuit. Store coils and lengths away from ammonia and sulfur-bearing atmospheres, keep the ends sealed to prevent contamination, and anneal only in a controlled atmosphere when the grade is tough pitch copper such as T2.
FAQ
Q: What does T2 mean in copper tube?
T2 is the GB/T 5231 designation for high-conductivity pure copper containing at least 99.90% copper plus silver, equivalent to UNS C11000 and Japanese C1100.
Q: Why is it called purple copper tube?
High-purity copper has a distinctive purple-red colour in its clean condition, which is why it is described as purple or red copper in Chinese, and the name distinguishes it from brass and bronze products.
Q: What is the difference between T2 and TP2?
TP2 contains 0.013 - 0.050% phosphorus, which removes dissolved oxygen and prevents hydrogen embrittlement, making it the better choice for welded and repeatedly annealed assemblies. T2 is the tough pitch grade.
Q: Can T2 copper tube be welded?
It can be soldered and brazed readily, but welding or annealing in a reducing atmosphere is risky above about 370 C because dissolved oxygen causes steam formation and cracking. TP2 is the safer grade for those operations.
Q: How is the weight of a copper tube calculated?
Mass per metre in kilograms equals 8.96 times pi times wall thickness times outside diameter minus wall thickness, divided by 1000, with dimensions in millimetres.
Q: Which temper should be ordered?
Soft annealed tube is used where bending to tight radii is needed, while light-drawn and hard tempers are selected where higher strength or a straight, self-supporting run is required.
