Copper Tube in Plumbing and Air Conditioning Service
ASTM B68 covers seamless copper tube supplied in the bright annealed temper for heat exchangers and similar equipment, while the plumbing and air-conditioning trades work to the related documents ASTM B88 for water tube and ASTM B280 for air-conditioning and refrigeration tube. All three specifications share the same family of high-purity copper grades and the same dimensional philosophy, so C11000 tube ordered for plumbing and cooling systems is generally quoted against ASTM B75, with the temper and dimensional tables of the specific service document.
C11000 electrolytic tough pitch copper contains at least 99.90 % copper plus silver. It has excellent thermal and electrical conductivity, good resistance to atmospheric and water-side corrosion, and the ductility needed for bending, flaring and forming on site. Where the tube must be brazed or welded, a deoxidised grade such as C12200 is normally selected instead, because phosphorus additions prevent the reaction between oxygen in the metal and hydrogen in the flame.
Chemical Composition and Physical Data
| Item | Value |
|---|---|
| Copper plus silver | 99.90 % min |
| Oxygen | 0.02 - 0.04 % typical |
| Density | 8.94 g/cm³ |
| Melting point | 1,083 °C |
| Thermal conductivity | 394 W/(m·K) |
| Electrical conductivity | 100 % IACS nominal |
Copper is the traditional material for potable water and refrigerant circuits because it is not attacked by the biofilm and bacteria that colonise plastic and steel pipe, it does not add taste or colour to water, and it can be fully recycled at end of life. Its low thermal expansion and high burst strength also make it tolerant of freeze events when compared with polymer systems.
Dimensional Table: Type K, L and M Water Tube
| Nominal size, in | Outside diameter, mm | Type K inside diameter, mm | Type L inside diameter, mm | Type M inside diameter, mm |
|---|---|---|---|---|
| 1/4 | 9.53 | 7.75 | 8.00 | 7.90 |
| 3/8 | 12.70 | 10.21 | 10.92 | 11.43 |
| 1/2 | 15.88 | 13.41 | 13.84 | 14.45 |
| 3/4 | 22.23 | 18.92 | 19.94 | 20.60 |
| 1 | 28.58 | 25.27 | 26.04 | 26.80 |
| 1 1/4 | 34.93 | 31.62 | 32.13 | 32.79 |
| 1 1/2 | 41.28 | 37.62 | 38.23 | 38.79 |
| 2 | 53.98 | 49.76 | 50.42 | 51.03 |
Type K has the heaviest wall and is used for underground and buried services, Type L is the general purpose choice for above-ground domestic and commercial work, and Type M is the lightest wall for drains, vents and low pressure duties. All three types are supplied in soft temper coils for small sizes and in hard drawn straight lengths of 3 m or 6 m.
Working Pressure Reference
| Outside diameter, mm | Wall thickness, mm | Maximum working pressure, N/mm2 |
|---|---|---|
| 15 | 1.0 | 6.7 |
| 22 | 1.2 | 5.7 |
| 28 | 1.2 | 4.2 |
| 35 | 1.5 | 4.1 |
| 42 | 1.5 | 3.4 |
| 54 | 2.0 | 3.6 |
The figures are typical maximum working pressures for half-hard copper tube in water service and are quoted for guidance only; the governing values are those of the design code applied to the project, after any temperature derating, joint derating and corrosion allowance have been considered.
Air Conditioning and Refrigeration Practice
Refrigeration and air-conditioning circuits are built from dehydrated copper tube supplied in coils or straight lengths with capped ends, so that the bore stays dry and free of scale. The tube must be cut with a rotary cutter rather than a saw, reamed so that no swarf enters the circuit, and purged with dry nitrogen during any brazing operation to prevent internal oxide formation. Joints are made with phosphorus-bearing brazing filler for copper-to-copper connections and with silver-bearing filler where a copper-to-brass or copper-to-steel joint is required. After assembly the circuit is pressure tested, evacuated and charged; residual moisture is the most common cause of capillary blockage and acid formation in a new system.
For chilled water, condenser water and condensate drain lines the same material is used in larger diameters, and supports are spaced to control vibration and thermal movement. Where a refrigeration circuit operates at low temperature, insulation is applied continuously to prevent condensation on cold surfaces.
Joining, Support and Water Quality Guidance
Capillary soldering, press fittings, flaring and brazing are all accepted joining methods; the choice depends on pressure, temperature and access.
Flux residues must be flushed out after soldering because they are aggressive to copper in the presence of moisture.
Support spacing should control sag and allow axial movement; copper expands noticeably over long hot water runs.
Water chemistry should be reviewed for very low pH, high chloride or high dissolved carbon dioxide, all of which shorten service life.
Burying tube in contact with cinders, ash or aggressive soil should be avoided, and sleeving should be used through walls and slabs.
Because copper is a noble metal in the galvanic series, direct connection to galvanised or carbon steel components should be made with dielectric unions to avoid accelerated corrosion of the steel part.
Inspection and Documentation
Tube is inspected for dimensions, wall thickness, straightness, surface defects and temper, with eddy current testing used where soundness of the wall is critical. Hydrostatic and pneumatic tests verify pressure tightness, and grain size is checked on annealed material intended for bending and expansion. A mill test certificate to EN 10204 3.1 is issued with each shipment, and ends are capped for transport so that the bore arrives clean.
FAQ
Q: Which copper grade is used for domestic water tube?
Phosphorised deoxidised copper C12200 is the base grade of the water tube specification because it can be brazed and welded safely. C11000 electrolytic tough pitch copper is used for colder, lower risk duties and for heat transfer where its slightly higher conductivity is valuable.
Q: What is the difference between Type K, L and M tube?
The three types differ only in wall thickness and therefore in inside diameter and pressure rating. Type K is the heaviest, Type L is the general purpose wall and Type M is the lightest wall used for low pressure services.
Q: Can copper tube be used with natural gas?
Yes, copper is widely used for fuel gas lines where local codes permit, provided the correct temper and wall are selected and joints are made with approved brazing or mechanical fittings.
Q: Why is nitrogen purging necessary when brazing refrigerant pipe?
Heat plus air forms copper oxide on the bore. Nitrogen displaces the air so that the internal surface stays bright; otherwise the loose oxide migrates through the circuit and blocks valves, strainers and capillary tubes.
Q: How is tube protected during storage and transport?
Coils and straight lengths are supplied wrapped or capped, and material should be stored indoors, clear of the ground and away from carbon steel offcuts or any chemical that could attack the surface.
Q: Does copper tube need insulation on cold lines?
Yes. Insulation controls condensation, limits heat gain and protects the tube from contact with aggressive building materials. Vapour sealing of the insulation is as important as its thickness.
