Copper tubing

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Copper tubing is most often used for supply of hot and cold tap water, and as refrigerant line in HVAC systems. There are two basic types of copper tubing, soft copper and rigid copper. Copper tubing is joined using flare connection, compression connection, or solder. Copper offers a high level of resistance to corrosion, but is becoming very costly.

Types[edit]

Soft copper[edit]

Soft (or ductile) copper tubing can be bent easily to travel around obstacles in the path of the tubing. While the work hardening of the drawing process used to size the tubing makes the copper hard/rigid, it is carefully annealed to make it soft again; it is therefore more expensive to produce than non-annealed, rigid copper tubing. It can be joined by any of the three methods used for rigid copper, and it is the only type of copper tubing suitable for flare connections. Soft copper is the most popular choice for refrigerant lines in split-system air conditioners and heat pumps.

Rigid copper[edit]

Rigid copper is a popular choice for water lines. It is joined using a sweat, compression or crimped/pressed connection. Rigid copper, rigid due to the work hardening of the drawing process, cannot be bent and must use elbow fittings to go around corners or around obstacles. If heated and allowed to slowly cool, called annealing, then rigid copper will become soft and can be bent/formed without cracking.

Soldered connections[edit]

Solder fittings are smooth, and easily slip onto the end of a tubing section. The joint is then heated using a torch, and solder is melted into the connection. When the solder cools, it forms a very strong bond which can last for decades. Solder-connected rigid copper is the most popular choice for water supply lines in modern buildings. In situations where many connections must be made at once (such as plumbing of a new building), solder offers much quicker and much less expensive joinery than compression or flare fittings. The term sweating is sometimes used to describe the process of soldering pipes.

Compression connections[edit]

Compression fittings use a soft metal or thermoplastic ring (the compression ring or "olive") which is squeezed onto the pipe and into the fitting by a compression nut. The soft metal conforms to the surface of the tubing and the fitting, and creates a seal. Compression connections do not typically have the long life that sweat connections offer, but are advantageous in many cases because they are easy to make using basic tools. A disadvantage in compression connections is that they take longer to make than sweat, and sometimes require retightening over time to stop leaks.

Flare connections[edit]

Flare connections require that the end of a tubing section be spread outward in a bell shape using a flare tool. A flare nut then compresses this bell-shaped end onto a male fitting. Flare connections are a labor-intensive method of making connections, but are quite reliable over the course of many years.

Crimped or pressed connections[edit]

Crimped or pressed connections use special copper fittings which are permanently attached to rigid copper tubing with a powered crimper. The special fittings, manufactured with sealant already inside, slide over the tubing to be connected. Thousands of pounds-force per square inch of pressure are used to deform the fitting and compress the sealant against the inner copper tubing, creating a water tight seal. The advantages of this method are that it should last as long as the tubing, it takes less time to complete than other methods, it is cleaner in both appearance and the materials used to make the connection, and no open flame is used during the connection process. The disadvantages are that the fittings used are harder to find and cost significantly more than sweat type fittings.

Sizes[edit]

Copper Tubing Sizes (CTS) for Plumbing[1]
Nominal
size
Outside diameter
(OD)
[in (mm)]
Inside diameter (ID)
[in (mm)]
Type K Type L Type M
38 12 (12.7) 0.402 (10.211) 0.430 (10.922) 0.450 (11.430)
12 58 (15.875) 0.528 (13.411) 0.545 (13.843) 0.569 (14.453)
58 34 (19.05) 0.652 (16.561) 0.668 (16.967) 0.690 (17.526)
34 78 (22.225) 0.745 (18.923) 0.785 (19.939) 0.811 (20.599)
1 1 18 (28.575) 0.995 (25.273) 1.025 (26.035) 1.055 (26.797)
114 1 38 (34.925) 1.245 (31.623) 1.265 (32.131) 1.291 (32.791)
112 1 58 (41.275) 1.481 (37.617) 1.505 (38.227) 1.527 (38.786)
2 2 18 (53.975) 1.959 (49.759) 1.985 (50.419) 2.009 (51.029)
212 2 58 (66.675) 2.435 (61.849) 2.465 (62.611) 2.495 (63.373)
3 3 18 (79.375) 2.907 (73.838) 2.945 (74.803) 2.981 (75.717)

Common wall-thicknesses of copper tubing in the USA are "Type K", "Type L", "Type M", and "Type DWV":[2]

  • Type K has the thickest wall section of the three types of pressure rated tubing and is commonly used for deep underground burial such as under sidewalks and streets, with a suitable corrosion protection coating or continuous polyethylene sleeve as required by code. In the United States it usually has green colored printing.
  • Type L has a thinner pipe wall section, and is used in residential and commercial water supply and pressure applications. In the United States it usually has blue colored printing.
  • Type M has an even thinner pipe wall section, and is used in residential and commercial water supply and pressure applications. In the United States it usually has red colored printing.
  • Type DWV has the thinnest wall section, and is generally only suitable for unpressurized applications, such as drains, waste and vent (DWV) lines. In the United States it usually has yellow or light orange colored printing, common sizes being 1-¼" , 1-½", and 2" copper tube size.

Types K and L are generally available in both hard drawn "sticks" and in rolls of soft annealed tubing, whereas type M and DWV is usually only available in hard drawn "sticks".

In the American plumbing industry, the size of copper tubing is designated by its nominal diameter, which is 18th inch less than the outside diameter. (This nominal diameter does not match any other physical dimension on the pipe; it may be larger or smaller than the inside diameter depending on the size of pipe). The American refrigeration industry uses different copper pipe called ACR (air conditioning and refrigeration field services) pipe, which is sized directly by its outside diameter (OD) and a type letter indicating wall thickness. Therefore, 1 inch nominal type L copper tube and 1 18th inch type D ACR tube are exactly the size with different size designations. ACR pipe is manufactured without processing oils that would be incompatible with the oils used to lubricate the compressors in the AC system.

Except for this difference between ACR (types A and D) and plumbing (types K, L, M and DWV) pipes, the type only indicates wall thickness and does not affect the outside diameter of the tube. Type K 12 inch, type L 12 inch, and type D 58 inch ACR all have the same outside diameter of 58 inch.

Common wall-thicknesses in Europe are "Type X", "Type Y" and "Type Z", defined by the EN 1057 standard.

  • Type X is the most common, and is used in above groundservices including drinking water supply, hot and cold water systems, sanitation, central heating and other general purpose applications.
  • Type Y is a thicker walled pipe, used for underground works and heavy duty requirements including hot and cold water supply, gas reticulation, sanitary plumbing, heating and general engineering.
  • Type Z is a thinner walled pipe, also used for above groundservices including drinking water supply, hot and cold water systems, sanitation, central heating and other general purpose applications.

In the plumbing trade the size of copper tubing is measured by its outside diameter in millimetres. Common sizes are 15 mm and 22 mm.[3] Tubing in 8mm and 10mm outside diameters is called "micro bore" and is easier to install although there is a slightly increased risk of blockage from scale or debris. It is sometimes used for central heating systems and 15mm adaptors are used to connect it to radiator valves.

Thin-walled types used to be relatively inexpensive, but since 2002 copper prices have risen considerably due to rising global demand and a stagnant supply.

Lead leaching[edit]

Generally, copper tubes are soldered directly into copper or brass fittings, although compression, crimp, or flare fittings are also used. Formerly, concerns with copper supply tubes included the lead used in the solder at joints (50% tin and 50% lead). Some studies have shown significant "leaching" of the lead into the potable water stream, particularly after long periods of low usage, followed by peak demand periods. In hard water applications, shortly after installation, the interior of the pipes will be coated with the deposited minerals that had been dissolved in the water, and therefore the vast majority of exposed lead is prevented from entering the potable water. Building codes now require lead-free solder. Building Codes throughout the U.S. require the use of virtually "lead-free" (<0.2% lead) solder or filler metals in plumbing fittings and appliances as well.

Corrosion[edit]

Copper water tubes are susceptible to: cold water pitting caused by contamination of the pipe interior, typically with soldering flux; erosion corrosion caused by high speed or turbulent flow; and stray current corrosion, caused by poor electrical wiring technique, such as improper grounding and bonding.

Pin holes[edit]

Pin-hole leaks with pitting initiating on the exterior surface of the pipe, can occur if copper piping is improperly grounded or bonded. The phenomenon is known technically as stray current corrosion or electrolytic pitting. Pin-holing due to poor grounding or poor bonding occurs typically in homes where the original plumbing has been modified; homeowners may find that a new plastic water filtration device or plastic repair union has interrupted the water pipe's electrical continuity to ground, when they start seeing pinhole water leaks after a recent install. Damage occurs rapidly, usually becoming obvious about six months after the ground interruption. Correctly installed plumbing appliances will have a copper bonding jumper cable connecting the interrupted pipe sections. Pinhole leaks from stray current corrosion can result in thousands of dollars in plumbing bills, and sometimes require the replacement of the entire affected water line. The cause is fundamentally an electrical defect, not a plumbing defect; once the plumbing damage is repaired, an electrician should promptly be consulted to evaluate the grounding and bonding of the entire plumbing and electrical systems.

The difference between a ground and a bond is subtle. See Ground, for a complete description.

Stray current corrosion occurs because: 1) the piping system has been connected accidentally or intentionally to a DC voltage source; 2) the piping does not have metal-to-metal electrical continuity throughout its length; or 3) if the voltage source is AC, one or more naturally occurring minerals coating the pipe interior may act as a rectifier, converting AC current to DC . The DC voltage forces the water within the piping to act as an electrical conductor (an electrolyte). Electric current leaves the copper pipe, moves though the water across the nonconductive section (a plastic filter housing, for example), and reenters the pipe on the opposite side. Pitting occurs at the electrically negative side (the cathode), which may happen to be either upstream or downstream with respect to the water flow direction. Pitting occurs because the electrical voltage ionizes the pipe's interior copper metal, which reacts chemically with dissolved minerals in the water creating copper salts; these copper salts are soluble in water and wash away. Microscopic pits eventually grow and consolidate to form pin holes. When one is discovered, there are almost certainly more that have not yet leaked. A complete discussion of stray current corrosion can be found in chapter 11, section 11.4.3, of Handbook of Corrosion Engineering, by Pierre Roberge.[4]

Detecting and eliminating poor bonding is relatively straightforward. Detection is accomplished using a simple DC voltmeter, with test probe leads placed in various locations in the plumbing. Typically, a probe on a hot pipe and a probe on a cold pipe will tell you if there is improper grounding. Anything beyond a few millivolts is significant, and potentials of 200 mV are common. A missing bond will show up best in the area of the gap, as the measured electrical potential dissipates over distance. The missing bond is usually located near the cold water inlet to the building, as filtration and treatment equipment are usually added there, but pinhole leaks can occur anywhere downstream or upstream from the interruption of electrical continuity.

Correcting the problem is a simple matter of either purchasing a copper bonding jumper kit, composed of copper cable at least #6 AWG in diameter and two bronze ground clamps for affixing it the plumbing. See NFPA 70, the U.S. National Electrical Code Handbook (NEC), section on bonding and ground for details on selecting the correct bonding conductor wire size.

A similar bonding jumper wire can also be seen crossing gas meters, but for a different reason.[further explanation needed]

However, if homeowners are experiencing shocks or large sparks from plumbing fixtures or pipes, it is more serious than a missing bond. Larger voltages may be caused by a live electrical wire bridging to the plumbing, and improper or missing plumbing system grounding. Such a situation poses an electrical shock hazard and potential fire danger; an electrician should be consulted immediately.

See also[edit]

References[edit]

  1. ^ Copper tube sizes
  2. ^ Copper Tube Handbook, the Copper Development Association, New York, USA, 2006
  3. ^ Pipe sizes
  4. ^ Roberge, P. R. (1999). Handbook of Corrosion Engineering (1st ed.). McGraw-Hill Professional. ISBN 0-07-076516-2.