Two Dimension Systems Behind Copper Tube Specifications
Copper tube for water, gas and refrigeration service is specified in two ways. The American system fixes the outside diameter and then offers three wall thickness series, type K for the heaviest wall, type L for the intermediate wall and type M for the lightest wall. The metric system used in Europe and Asia fixes a nominal outside diameter in millimetres and quotes the wall thickness directly, with the temper class named separately.
Seamless copper tube is a non-ferrous product that is pressed and drawn, so it has no seam and can be supplied in coils as well as straight lengths. Compared with an equivalent ferrous pipe it is lighter, has much higher thermal conductivity and keeps useful strength at low temperature, which is why it dominates heat exchange equipment such as condensers and evaporators, oxygen plant piping, hydraulic and lubrication lines and instrumentation pressure tubing.
Common Sizes and Wall Thickness Series
| Nominal size | Outside diameter (mm) | Type K wall (mm) | Type L wall (mm) | Type M wall (mm) |
|---|---|---|---|---|
| 1/4 in | 9.52 | 0.889 | 0.762 | 0.635 |
| 3/8 in | 12.70 | 1.245 | 0.813 | 0.711 |
| 1/2 in | 15.88 | 1.245 | 0.889 | 0.813 |
| 5/8 in | 19.05 | 1.245 | 1.016 | 0.889 |
| 3/4 in | 22.22 | 1.245 | 1.143 | 1.067 |
| 1 in | 28.58 | 1.651 | 1.270 | 1.245 |
ASTM B88 covers this series and also lists larger sizes up to several inches. As the diameter increases, the difference between the type L and type M walls narrows, so the exact value should be read from the standard table for the size being ordered rather than interpolated. The metric alternative, EN 1057, supplies copper tube for water and gas in the same outside diameters but with soft, half-hard and hard tempers designated R220, R250 and R290, which allows the designer to match the tube to the bending and pressure requirements of the installation.
Mild copper tube produced to GB/T 1527 is available with outside diameter from 3 mm to 219 mm and wall thickness from 0.5 mm to 40 mm, supplied straight or coiled, in the M soft, Y2 half-hard, Y hard and T extra hard tempers. Typical delivery tolerances are about ±0.05 mm on the outside diameter, with wall thickness held to roughly ±0.005 mm to ±0.02 mm depending on the nominal wall and on the precision class ordered.
Weight Calculation for Copper Tube
The mass of copper tube is calculated from the cross-sectional area of the metal, the density of copper and the length. For practical ordering work the following formula gives the mass in kilograms per metre when the outside diameter D and the wall thickness t are both expressed in millimetres:
G = 0.02796 × t × (D − t)
The coefficient 0.02796 corresponds to a nominal copper density of about 8.9 g/cm³. Where the density used for a specific contract is 8.96 g/cm³, the equivalent constant is 0.02815 and the calculated mass is about 0.7 % higher, which is normally inside the mass tolerance of the standard. Two worked examples show the order of magnitude:
| Tube | Outside diameter (mm) | Wall (mm) | Mass per metre (kg) |
|---|---|---|---|
| 1/2 in type L | 15.88 | 0.889 | 0.373 |
| 3/4 in type L | 22.22 | 1.143 | 0.674 |
| 1 in type K | 28.58 | 1.651 | 1.241 |
A 15 m coil of the 1/2 in type L tube therefore weighs about 5.6 kg, and a 50 m coil about 18.6 kg. These figures are used for freight calculation, coil handling and price per unit length, and they should be recalculated whenever the wall thickness changes, because mass varies almost linearly with wall thickness for a given diameter.
Specifying a Copper Tube Order
State the product standard and the grade, for example GB/T 1527 T2, ASTM B88 type L C12200 or EN 1057 Cu-DHP R250.
Give outside diameter and wall thickness in millimetres, or the nominal size plus the wall type if the American system is used.
Give the temper, since the same size is produced soft, half-hard and hard.
Give the form and length: straight lengths of 3 m, 5.8 m or 6 m, or coils of 15 m, 25 m or 50 m.
State the tests required, such as eddy-current testing, hydrostatic testing or a grain size check, and the certificate type.
State whether the tube is for water and gas service, refrigeration service or general engineering, because the internal cleanliness requirements differ.
Why Copper Tube Is Preferred in Building Services
Copper is economical in the installed condition because it is easy to process and join, so less material and less labour are consumed per connection. It is light for the same bore, needs no protective coating in most indoor positions, and can be bent into elbows and offsets so that a run is completed with fewer fittings. It is also safe in service: a properly brazed copper installation does not leak, does not promote combustion, releases no toxic smoke and resists both internal corrosion by treated water and external atmospheric attack.
Selection between the wall series follows the duty. Type K is used for buried mains, high pressure and heavy industrial lines, type L for general domestic and commercial distribution, and type M for low pressure drainage and low duty interior runs where local codes permit it.
FAQ
Q: What do the type K, L and M designations mean?
They are three wall thickness series for the same outside diameter under ASTM B88. Type K has the heaviest wall for buried and high pressure duty, type L the standard wall for general distribution and type M the lightest wall for low pressure interior work.
Q: How is the weight of copper tube per metre calculated?
Use the relation G equals 0.02796 multiplied by the wall thickness multiplied by the difference between the outside diameter and the wall thickness, with both dimensions in millimetres, to obtain kilograms per metre.
Q: Why is copper tube lighter than steel pipe of the same bore?
Copper does not require the same wall thickness as ferrous pipe to carry the same pressure, and its density is lower, so less metal mass is needed for an equivalent duty.
Q: What tolerance applies to outside diameter and wall thickness?
A drawn copper tube is normally supplied within about plus or minus 0.05 mm on outside diameter, with wall thickness tolerance between about plus or minus 0.005 mm and plus or minus 0.02 mm depending on the wall and the precision class ordered.
Q: Which standard applies to drawn copper tube produced in China?
GB/T 1527 covers drawn copper and copper alloy tube, while GB/T 18033 covers seamless copper tube for water and gas. Both quote outside diameter and wall thickness tables and precision classes.
Q: Is the metric and imperial copper tube interchangeable?
The outside diameters of the American series are the metric rounded values of the inch sizes, so fittings are generally not interchangeable between the two systems even when the diameters appear identical.
