Copper Pipe Materials Used for Freezer and Refrigeration Piping
Freezer and cold store piping uses a small, well-established set of copper materials. The choice is driven by three requirements: a clean and dry bore that will not contaminate the refrigerant, reliable joints under vibration and thermal cycling, and a tube that stays leak tight and does not corrode at the operating temperature of the system.
The materials normally met in freezer work are oxygen-free copper tube, C12200 deoxidised high phosphorus copper tube, C10200 oxygen-free copper tube and tin-coated (tinned) copper tube for low-temperature service.
Composition and Properties of the Common Grades
| Grade | Composition | Key properties | Typical freezer use |
|---|---|---|---|
| Oxygen-free copper tube | Copper 99.95% min, no deliberate deoxidant | Very high conductivity, good ductility and weldability, no oxygen-bearing inclusions, so no risk of embrittlement in reducing atmospheres | Refrigerant piping and critical circuits where high conductivity and vacuum tightness are required |
| C12200 DHP copper tube | Copper 99.9% min with residual phosphorus from deoxidation | High tensile strength and thermal conductivity, good corrosion resistance, excellent brazing behaviour | Connecting pipework, water and brine lines, general freezer piping |
| C10200 oxygen-free copper tube | Copper 99.95% min, oxygen-free without deoxidant | Good cold working performance, high conductivity, no hydrogen embrittlement risk | Instrument and cable conduit, semiconductor and precision equipment, high-purity tie-ins |
| Tin-coated copper tube | Copper tube with a bonded tin coating on the outside surface | Improved corrosion resistance in damp and mildly aggressive conditions and easier soldering | Condenser and evaporator tube, low-temperature coils in humid or coastal installations |
Two clarifications are worth making, because they are frequently confused in practice. Oxygen-free copper designated C10200 carries a minimum copper content of 99.95%, while the oxygen-free electronic grade C10100 carries 99.99% minimum; suppliers should be asked for the actual copper content and the residual oxygen level when the grade matters. Second, C12200 contains residual phosphorus, which is beneficial for brazing but lowers electrical and thermal conductivity relative to oxygen-free copper, and which means the tube should not be heated in a strongly reducing or hydrogen-bearing atmosphere, because phosphorus-deoxidised copper is susceptible to hydrogen embrittlement.
Standards and Supply Conditions
Refrigeration and air conditioning tube is normally ordered to ASTM B280 for seamless copper tube for air conditioning and refrigeration field service, or to EN 12735-1 for seamless round copper tube for piping systems in air conditioning and refrigeration. Water and brine lines may follow ASTM B88, GB/T 1527 or EN 1057, while tube for general service is covered by ASTM B68 and ASTM B75. Mechanical properties, wall thickness and tolerances are governed by the specification for the ordered temper.
Supply condition matters as much as grade. Refrigeration tube is supplied in soft annealed temper in coils for bending on site, and in straight lengths in hard or half hard temper for risers and headers. Tube should arrive with capped or plugged ends, clean and dry inside, and it should be stored and cut so that the bore stays free of swarf, moisture and dust. For freezer work the residual moisture and oil content of the tube is critical, because water in a refrigerant circuit forms acid, freezes at the expansion device and causes copper plating on compressor parts.
Common Piping Types and Sizes
| Pipe type | Function | Usual material | Common outside diameters |
|---|---|---|---|
| Refrigerant piping | Carries refrigerant between compressor, condenser, expansion device and evaporator | Oxygen-free or C12200 tube, tinned tube in exposed or humid locations | 6 mm, 8 mm, 10 mm and the corresponding fractional sizes |
| Inlet and outlet water piping | Water cooling and cooling water recirculation | C12200 or C10200 tube | 15 mm, 22 mm, 28 mm |
| Cable conduit | Energising and interconnecting cables between equipment | C10200 tube | 10 mm, 12 mm, 15 mm |
| Control and capillary lines | Pressure sensing, thermostatic expansion valve sensing bulbs and purge lines | Soft annealed oxygen-free tube | Small bore capillary sizes |
The pipe diameter for a refrigerant line is set by the pressure drop and the refrigerant velocity on the suction, discharge and liquid sides, not by habit; on long runs or with refrigerants that operate at higher pressure, both the diameter and the wall thickness need to be recalculated. Wall thickness must be adequate for the design pressure of the refrigerant in use, and for higher-pressure refrigerants the tube should be ordered to the appropriate schedule rather than to a nominal size alone.
Refrigerant Compatibility and System Cleanliness
Copper is compatible with the common refrigerants, including R410A, R32, R134a, R404A and R744, and with the mineral, polyolester and polyvinyl ether lubricants used with them. Several of the newer refrigerants are classified as mildly flammable (A2L) or flammable (A3), which affects charging, ventilation, leak detection and equipment room requirements rather than the copper tube itself, but the design of the piping and the brazing procedure must still follow the equipment manufacturer's instructions.
Cleanliness is the single most important field issue. Braze joints should be made with a nitrogen purge, using copper-phosphorus filler for copper-to-copper joints, which needs no flux, and the appropriate silver filler with flux for joints to brass or steel. Flux residues must be removed, since they are corrosive inside a sealed circuit. After fabrication, the pipework should be pressure tested, evacuated to the manufacturer's required vacuum level and held to confirm that no moisture remains, before charging. Moisture and oxidized scale are the two most common causes of early compressor failure in freezer installations.
Selection and Installation Checklist
When selecting tube, confirm the grade and copper content, the temper and wall thickness, the cleanliness of the bore, the end capping and the mill certificate. When installing, use bending rather than fittings wherever possible, protect the tube from mechanical damage and from contact with dissimilar metals that could cause galvanic corrosion, allow for thermal expansion and contraction in long runs, insulate suction lines to prevent condensation, and support coils and risers so that vibration does not fatigue the joints. For low-temperature freezer rooms, insulation and vapour sealing should be continuous, because condensation on cold pipe is a corrosion and ice-damage risk as well as an energy loss.
FAQ
Q: Which copper tube should be used for freezer refrigerant lines?
For most freezer piping, seamless C12200 or oxygen-free copper tube to ASTM B280 or EN 12735-1 is suitable. Where the highest conductivity or absolute cleanliness is required, use oxygen-free copper tube to C10200, and consider tin-coated tube in humid, coastal or otherwise mildly aggressive installations.
Q: What is the difference between C12200 and C10200 tube?
C12200 is deoxidised with phosphorus and contains a small residual of it, giving excellent brazing behaviour with a slight reduction in conductivity. C10200 is oxygen-free without a deoxidant, so it has higher conductivity and no risk of hydrogen embrittlement, but it is not deoxidised in the same way and is usually more expensive.
Q: Why must refrigeration pipework be purged with nitrogen when brazing?
A nitrogen purge excludes oxygen from the hot tube bore and prevents the formation of copper oxide scale. Scale particles released into the circuit can block capillary tubes, damage valve seats and contaminate the compressor, so purging is standard practice for refrigeration work.
Q: Why is tinned copper tube used in freezer systems?
The tin coating protects the outer surface against atmospheric corrosion in damp, salt-laden or otherwise aggressive surroundings and improves solderability. It is common on condenser and evaporator tube and on low-temperature coils where condensation and coastal air shorten the life of bare copper.
Q: What sizes of copper pipe are common in freezer piping?
Refrigerant lines are commonly 6 mm, 8 mm and 10 mm outside diameter and the equivalent fractional sizes; water and cooling water lines are commonly 15 mm, 22 mm and 28 mm; cable conduit is commonly 10 mm, 12 mm and 15 mm. Final sizes must be calculated from the pressure drop and refrigerant velocity of the actual system.
Q: Can carbon steel fittings be used with copper tube?
They can be used where a suitable transition joint and insulation against galvanic action are provided, but for refrigerant circuits copper alloy or brass fittings are preferred because they avoid dissimilar metal effects and are simpler to braze. Any steel component in a copper circuit should be electrically insulated and protected against moisture.
