Copper tubes are composed of 99.9% pure copper and small quantities of alloying elements in accordance with standards published by ASTM. They are available in both hard and soft tempers, the latter meaning that the tube has been annealed to soften it. Hard tubing is joined by capillary fittings. Soft tubing can be joined in a variety of additional ways, including compression fittings and flaring. Both are produced as seamless constructions. Copper tubes are used in plumbing, HVAC, refrigeration, medical-gas delivery, compressed-air systems, and cryogenic systems. In addition to plain copper tubes, tubes are available in specialty alloys.

There is some inconsistency in the terminology for copper tubes. When the product is formed into coils, it is sometimes referred to as copper tubing owing to the increase in flexibility and the ability to bend the material more readily. But that distinction is not by any means a universally practiced or accepted one. In addition, some of the rigid wall straight lengths of copper tube are sometimes referred to as copper pipe. The use of these terms may vary from supplier to supplier.

These tubes are alike except for differences in wall thickness, with Type K having the thickest walls and as a result the highest pressure-rating. Specified by a nominal size that is 1/8 inch smaller than the OD, these tubes are available in sizes from 1/4 to 12 inches in straight lengths, both drawn (hard) and annealed (soft). The two heavier-walled tubes are also available coiled up to 2 inches nominal diameter. Manufacturers color-code the three types with green for K, blue for L, and red for M.

Type K and L are suitable for pressure service such as with air compressors and natural- and LP-gas delivery (K for underground, L for interiors). All three types are suitable for domestic water service (Type M is preferred), handling fuel and fuel oils (Type L, preferred), HVAC applications (Type L, preferred), vacuum installations, etc.

Tube for drainage, waste, and vent applications is thin-walled, with lower pressure ratings. It is available in nominal sizes from 1-1/4 to 8 inches and color-coded yellow. It available in drawn, straight lengths of 20 ft., although shorter lengths are commonly stocked.

Tubes for transmitting medical gases are Type K or L with special cleanliness requirements. Oils used in the manufacture of the tubes must be removed to prevent their combustion in the presence of oxygen and to ensure the health of patients. The tubes are normally plugged and capped after cleaning and brazed during installation under a nitrogen purge.

Tubes for air conditioning and refrigeration are specified by the actual OD, the one exception in this group. Sizes range from 3/8 to 4-1/8 inches for straight lengths and from 1/8 to 1-5/8 inches For coils. As a group, these tubes have higher pressure ratings for like diameters.

Copper tubes are available in several alloys for special applications. Beryllium copper tubing can approach the strength of steel alloy tubing, and its fatigue-resistance makes it especially useful in specialty applications, such as for bourdon tubes. Copper-nickel alloys offer high resistance to seawater corrosion, and the tubing is often used in marine applications where resistance to barnacle growth is an added benefit. Cupro Nickel 90/10, 80/20, and 70/30 are common designations for this material. OFHC or Oxygen-Free High-Conductivity copper tubes are often used for waveguides and the like. Titanium-clad copper tubes are available for use in corrosive heat-exchanger applications.

As mentioned, copper tubes are easily joined using heating methods such as soldering and brazing. While these methods are sufficient and expedient for domestic water applications, etc., heating does anneal drawn tubing and this lowers its pressure rating.  Several mechanical methods are available that do not alter tube characteristics. These include flared joints, roll-groove joints, press-connect joints, and push-connect joints. These mechanical joining methods are handy in cases where using flame or heat is unsafe. Another plus is that some of these mechanical joints are readily disassembled.

Another method, used where many branches must emerge from a single main, makes use of an extruding tool to form the outlets directly in the tubing. This method requires brazing of the final connections but eliminates the use of many, many fittings.

This article presented a summary of the types of copper tube. For more information on additional products, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products.

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