What Copper Coil Is
Copper coil, also called copper coiled tube, is seamless copper tube produced by drawing the tube through dies and coiling the finished product in continuous lengths instead of cutting it into straight pieces. Coils are supplied in round, square and rectangular section, with round tube accounting for most refrigeration and air conditioning demand. The main advantage is continuity: a single coil often covers a whole installation run, so the number of brazed joints, and with them the number of potential leak paths, is reduced.
Coiled tube is normally supplied soft annealed and capped or plugged at both ends, with the inside dry and clean so that it can be charged directly into a refrigeration circuit.
Grades and Standards
| Grade | Description | Typical standard | Typical use |
|---|---|---|---|
| C12200 | Phosphorized copper DHP, P 0.015-0.040% | ASTM B280, ASTM B68 | Air conditioning and refrigeration field service |
| C12000 | Phosphorized copper DLP, P 0.004-0.012% | ASTM B68, ASTM B75 | General tube, low phosphorus requirement |
| C11000 | Electrolytic tough pitch copper, 99.90% Cu min | ASTM B75, EN 1057 | Water and general engineering tube |
In addition to the ASTM specifications, coil tube is frequently ordered to EN 1057 for water service, EN 12735-1 for air conditioning and refrigeration, and GB/T 17791 or GB/T 1527 in the domestic market. Medical gas installations use tube made to ASTM B819 with a specified cleanliness level.
Sizes and Dimensional Tolerances
Round copper coil covers a wide size range. Outside diameters run from about 0.5 mm for small capillary and instrument sizes up to about 30 mm, and wall thicknesses from about 0.3 mm to 3 mm. Refrigeration coils concentrate on outside diameters of roughly 4 mm to 22 mm, while water and general service coils are larger and are often supplied soft or half hard.
Outside diameter tolerance and wall tolerance follow the referenced standard and tighten as the wall becomes thinner.
Wall thickness is measured at several points on a section, and the minimum wall is the governing value for pressure service.
Coil diameter, coil weight and the number of lengths per coil are agreed with the customer so that the coil matches the handling equipment on site.
Tempers and Mechanical Properties
Coil tube for refrigeration and air conditioning is generally supplied in the annealed O60 temper so that it can be bent by hand or by a tube bender without cracking. The specification for annealed C12200 tube requires a minimum tensile strength of 205 MPa, verified by a tension test taken from the finished coil. The drawn tempers, supplied as half hard or hard tube, reach higher tensile strength with lower elongation, and their limits are tabulated in the referenced standard. Where a temper is critical to the forming operation, the order should state the temper designation rather than a hardness range so that the correct test can be applied.
Cleanliness, Pressure Testing and Packaging
The bore must be free from drawing lubricant, scale, metal chips and moisture. Residual contamination is checked by the cleanliness test required by the referenced standard, and the tube is dried and purged before the ends are capped.
Every coil is subjected to the pressure or leak test specified in the purchase order and must show no deformation and no leakage at the test pressure.
Surface condition is inspected visually: no cracks, pinholes, peeling, laminations, blisters, inclusions or green corrosion product, and no deep handling marks.
Coils are wound on wooden or steel carriers, wrapped in moisture barrier material and marked with grade, temper, size, coil number and weight.
Typical Applications
Split and packaged air conditioners, chillers and heat pumps.
Domestic and commercial refrigeration, including condensers and evaporators.
Connection and distribution tube in HVAC installations, where long flexible runs are needed.
Medical gas and laboratory gas systems made to ASTM B819.
Water supply, heating and solar thermal circuits using EN 1057 tube.
Instrumentation and control lines, where small diameter coils are preferred.
FAQ
Q: Why is coil tube supplied soft annealed?
Annealed tube is ductile enough to be bent and flared on site, which is essential for refrigeration and air conditioning installation work where tube is formed around building structures.
Q: What copper content does a refrigeration coil have?
Refrigeration coil is normally C12200 phosphorized copper with 99.9% minimum copper and a phosphorus content of 0.015% to 0.040%, which gives the deoxidised structure needed for brazing.
Q: How is internal cleanliness controlled?
The bore is cleaned and dried during manufacture, checked by the residue test required by the standard, then capped or plugged so that the inside stays clean until the coil is opened on site.
Q: Can coil tube be used for water service?
Yes. Coil supplied to EN 1057 is widely used for potable water, heating and solar circuits, and the temper and wall thickness are selected for the working pressure of the system.
Q: What test pressure is applied to a coil?
The purchase order states the test pressure and the test method, and the coil must show no leakage or permanent deformation at that pressure.
Q: How should coils be stored on site?
Keep coils in the original wrapping, indoors and dry, away from acids and chloride containing materials, and uncoil them without sharp bends so the tube wall is not deformed.
