Water supply piping connection: copper to galvanize (C) Daniel FriedmanCopper Water Supply & Drain Piping

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Copper plumbing, copper supply & copper drain pipes:

This article lists our in-depth articles on inspecting, testing, and repairing problems with copper plumbing:

water supply and drain waste vent piping, plumbing traps, piping materials, clogged or noisy pipes, and types of pipe hazards or product defects.

The articles at this website will answer most questions about water supply & drain piping, wells, & water tanks as well as many other building plumbing system inspection or defect topics.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Copper Building Water Supply & Drain Piping

Photograph of pipe condensation (C) Daniel Friedman

Article Contents

Types of Copper Piping used in buildings

Other types of copper building piping systems are discussed at GAS PIPING, VALVES, CONTROLS and at OIL TANK PIPING & PIPING DEFECTS.

Our page top photograph shows a remarkable method used by a homeowner to handle leaks at a poor solder joint on copper water supply piping.

Our photograph of copper water supply piping (left) tells us that this is a cold water supply line located in a humid or wet crawl area - notice the condensation on the piping? More about "sweating" cold water pipes is at CONDENSATION or SWEATING PIPES, TANKS.

The following summary notes about copper and other types of building piping are from Carson Dunlop Associates' Home Reference Book, used with permission:

Copper piping has been used extensively since the early 1950s for supply lines from the city main to the house as well as for in-building water supply and drain piping.

Copper water supply piping is typically 1/2 or 3/4 inch diameter. Copper piping is typically 1/2 or 3/4 inch diameter. Copper piping has soldered connections and the walls of the pipe are thinner than galvanized steel. Copper piping has soldered connections and the walls of the pipe are thinner than galvanized steel.

From 1950 to 1970, 1/2-inch diameter piping was used commonly for residential building water supply pipes. After 1970, 3/4-inch diameter copper service piping has been more common for building water supply piping.

Guide to K, L, and M and Other Types of Copper Pipes used in Buildigns: life expectancy, izes, thickness, durability & uses

Copper plumbing types (C) Carson Dunlop Associates

The life expectancy of copper piping is dependent on water conditions.

In many areas, its life expectancy is indefinite. In harsh corrosive water or corrosive soil conditions, it may fail within 20 years or even less.

Occasionally manufacturing defects also result in early failure of copper building piping. We discuss water pH, acidity and corrosiveness at Copper Piping FAQsbelow.

Carson Dunlop Associates' sketch (left) illustrates three types of copper piping used in buildings for water supply or drains. In order of thickness, from thinnest to thickest pipe walls, read Types M, L, or K copper.

Type M Copper pipe markings © D Friedman at

Dimensions, Sizes, Thickensses, Lengths of Copper Piping

How is Copper Piping Sold: lengths, diameters

Copper piping is sold in nominal or standard sizes in straight lengths of 12 ft. 18 ft. or 20 ft. from 1/4" diameter all the way up to 12-inches in diameter, depending on the copper type, thickness, grade, and intended application. Copper piping from 1/4" up to 2-inch in diameter is also sold in coils of 45' up to 100 ft. depending on the pipe diameter.

What is the Relationship Between Nominal Copper Pipe Size and its Actual Physical Size?

Plumbing Copper:

Copper piping discussed here and used for plumbing is 1/8" larger in diameter than its nominal diameter. So a 1/2" copper pipe will actually measure 5/8" in thickness. The actual internal diameter of a copper pipe will vary depending on the thickness of the pipe wall, even though these outside dimensions remain the same. For example, because K-copper has a thicker tube wall than Type M copper, a 1/2" K-copper pipe will have a slightly smaller inside diameter than a 1/2" L or M copper pipe.

Refrigeration Tubing Copper

Unlike copper used for plumbing (above), copper tubing used for HVACR (heating, ventilating, air conditioning & refrigeration systems), is sold in sizes that correspond to the actual outside diameter of the tubing.

What are the Standards for Copper Piping Sizes & Thickness

The copper content of copper piping meeting the ASTM standards below is virtually pure copper - or 99.9% Cu. The copper is shiny when purchased, typically having had any exterior or interior surface oxidants cleaned off using phosphorous. If you hear reference to DHP copper or C122 coppeer, this is the product being described.

The four most-relevant standards for copper pipe thickness and dimensions depend on the intended application and use and are listed as follows:

Compression Fittings for Copper Tubing Connections

Compression fittings - Wikipedia

Flexible copper tubing is usually joined to additional tubing sections or to other plumbing fittings by either compression fittings or flare fittings, depending on the application.

For example, compression fittings (photo at left, from Wikipedia) are sometimes used on copper water piping where soldering is difficult or inconvenient, but these are not used on copper gas or oil lines where flare fittings may be applied instead.

Flare fittings and compression fittings are intended for use on soft-temper copper piping and tubing. In addition to flare and compression fittings there are also other mechanical connectors that now work with soft or hard copper that do not require soldering.

Watch out: compression fittings are very convenient and easy to install on copper pipes or copper tubing, but if you fail to de-burr a freshly-cut copper pipe or tube, properly ream out the interior opening, or if you over-tighten the coupling during installation you may crack the brass or copper ring, leading to leaks at the connector.

Compression fittings are used with K-copper. K copper pipes and tubing can also be joined or connected using flare fittings and sweat fittings discussed below.

Flare Fittings Used for Flexible Copper Tubing Connections

Photograph of a leaky brass flare fitting

Flare fittings used on flexible copper piping and their leaks and defects are discussed at GAS LEAK DETECTION, LP / NG and GAS PIPING DEFECTS. Using a special flaring tool the soft copper tubing or piping is actually spread open or flared at its end in order to mate with the female end of the flare fitting connector shown in our photograph.

Watch out: defects in flare fittings used on flexible copper tubing can result in gas leaks out of gas piping, and in the case of oil piping such as for oil-fired heaters, flare fitting defects result in both oil leaks out of the system and air leaks into the system. Air leaks into oil piping in turn lead to improper oil burner operation and even potentially dangerous conditions. Flare fitting defects include:

Seat and flare fittings are permitted on K and L copper. LP gas tubing. These fittings are not used on refrigeration equipment.

Swaged Copper Tubing Joints

Refrigerant dryer with swaged tubing fittings © D Friedman at

Soft copper tubing can also be joined by using a swaging tool that expands the open end of one of the tubes to be joined so that its mate can be inseted into the enlarged opening, and the result sealed by soldering or brazing.

This is a common procedure when using air conditioning refrigerant tubing because of the high pressures that may be involved and the need for extra strong resistance to leaks in piping that may be subject to wide temperature variations as well as mechanical vibration.

Our photo (red arrow in photo at left) illustrates swaged fittings on copper tubing - you can see the swaged tubing joints at the left and right ends of the gray filter-dryer on this air conditioning high pressure refrigeration line exiting at the bottom of a compressor-condenser unit.

A swaging tool is inserted into the end of the copper tube and hammered inwards. As the properly-calibrated diameter of the swaging tool is forced into the copper tube, the copper expands to just the right size to accept the outer diameter of the mating section to be inserted. For example, if we are swage fitting two sections a 3/8" nominal diameter copper tube together, the swaging tool will enlarge the receiving copper tube section so that its inside diameter will accept the 3/8" outer diameter of the un-treaterd tube to be joined.

Usually we work the swaging process on tubing at ambient temperatures but some procedures call for pre-heating the copper to make it easier to expand.

Watch out: Soft copper tubing is drawn copper while hard tubing is annealed. It's easy to swage fit soft copper, usually. But if copper tubing has been repeatedly bent, that process may have annealed the copper somewhat, making it difficult to form either a flare fitting or a swaged fitting without cracking the tubing. Copper tubing may also become crack prone when exposed to mercaptan or other odorants in LP gas or natural gas. Moisture exposure and even some types of solder also can affect its susceptability to cracking later. For these reasons copper tubing is not allowed for natural gas distribution.

Sweat Fittings for Copper Pipes & Tubing

"Sweat" fittings or "soldered fittings" for copper piping refer to the traditional and perhaps most widely-used method for residential copper suppy and drain pipe connections, bends, elbows, valves, and similar fittings in buildings.

Depending on the connection required, a coupling (straight connection), 90 degree ell, 45 degree ell, tee, and even fittings that marry copper pipes of different diameters are soldered to the copper tubing or pipe to make the connection.

Sweat fittings may themselves be made of copper tubing that has been formed by machine, or from cast or milled bronze.

Table of Types of Copper Pipe or Tubing Connections, Connectors, Fittings

  Sweat Fittings Swage Fittings Flare Fittings Compression
K copperok okok
L copperok  okok
M copperok if annealed
ok if drawn-tempered
  okok if annealed
Flexible copper tubing - waterok if annealed
ok if drawn-tempered
?okok if annealed
Flexible copper tubing - LPG  ? ok  
Flexible copper tubing - HVAC refrigerantsokok    

Notes to the table: [this table is incomplete, other citations needed - ed.]

Standard: Copper Tubes, ASTM B-88M

How to Tell Brass Water Pipes from Copper Piping

Brass water piping (C) Daniel FriedmanWatch out: on older buildings brass water supply piping may have been used, and may be at or near the end of its useful life. It can be tricky to tell the difference between brass water supply piping and copper water supply piping if you are not experienced with these materials, as their colors are similar, especially when both types of piping have become an oxidized brownish color with age.

Both brass and copper are non-magnetic, so they won't respond to a "magnet" test to look for iron or steel.

Brass water supply piping, unlike copper, is a thicker material that is usually joined by threaded fittings of the same size and pipe thread specifications (NPT) as iron and galvanized iron piping.

Usually, brass piping is also so rigid that it is not bendable. Or not very bendable anyway. So in our photograph (left) of water supply piping at a bath tub in an older home, the larger-diameter left-hand pipe is surely brass, connected to a galvanized iron fitting at its bottom end. The right-hand vertical pipe may be copper tubing as is the darker copper pipe at left behind our brass one.

Don't worry about that odd little machine in bottom center of the photo - we were collecting an air sample in this wall cavity.

Copper Supply or Drain Pipe Pinhole Leaks: cause, cure, prevention

Water chemistry, Electrical Grounding, Netural Wiring, & Copper Pipe Pinholing & Leaks

In a building where leaks are found recurrent in copper piping there are several possible explanations including these possible causes for the pinhole leak in copper water piping under a building concrete floor slab as well as at other locations:

If the pH is low <6.0, the hardness low generally<50ppm, the alkalinity low generally <40ppm, the water could be considered extremely “soft” and aggressive to the home’s metallic plumbing system. If the chlorides are elevated >100ppm this would only compound the problem. The water should be treated to make the water less aggressive by raising the pH, alkalinity or hardness. - CT DOH.[1]

See CORROSIVITY or ACIDITY of WATER for details about aggressive, acidic or corrosive water and its effect on building plumbing systems.

See GREEN STAINS from WATER SUPPLY for details about green stains on plumbing fixtures or on laundered fabrics or in the water itself: causes & cures.

Summary of the issue around grounding building water piping

Many sources, including the Connecticut DOH have pointed out a long-standing disagreement & confusion about the reasons for grouinding building water supply piping. For example

AWWA opposes the grounding of electric systems to pipe systems conveying drinking water to a customer’s premises. ... AWWA asserts that a water utility has no direct or indirect responsibility in connection with the installation of water pipe grounding systems or for the maintenance of the integrity of any grounding attachment or connection made to a water pipe system. [AWWA 5/15/2003] [1]

This statement is a bit of a red herring. Water and some plumbing associations are concerned about building owner complaints about metal water supply pipe corrosion and leakage that might be traced to or blamed on the electrical grounding of those systems. Wishing to avoid those complaints the industry, under the aegis of warning that water suppliers can't be responsible for the failure of such an electrical ground [a valid caveat] a warning is issued that also gives relief for metal piping leaks caused by a variety of other problems such as

More to the point, metal water piping is grounded not to provide an electrical ground for the building (we agree completely that water piping as a ground is unreliable for many reasons, (such as inclusion of non-conductive plastic piping, diaelectric fittings, water meters, etc). Metal water piping is bonded to a building ground system as an important safety precaution to protect building occupants from electrocution hazards should live electrical wires or components come in contact with building piping, faucets, fixtures, etc.

In a properly-wired building, the grounding conductor and bonding system do not normally carry current, and would not be blamed for copper pipe pinholing etc. The grounding system is intended to conduct electrical current only in the event of a fault or emergency [such as a lightning strike or a hair dryer dropped into the bath tub or sink].

Details about the code requirements and reasons for grounding metal water piping are at WATER PIPING GROUND BOND

How to Check for Electrical System Problems that Corrode Copper Water Pipes

[For buildings served by private well water] Should the problem persist and the well water is still blue and it is discovered that the private well’s metal discharge line has an electrical “grounding” clamp, have them contact a licensed electrician to investigate the situation.

The electrician would check the main circuit panel for a faulty, missing or improperly secured “neutral” wire. He could also test the plumbing to see if there is any stray AC or DC current.

There should not be any current, even in milliamps! If there is current, the improperly functioning or shorted device/ appliance should be found and repaired. He should also check that the house plumbing has a greater resistance (>25 ohms) than the grounding rod(s). The ground wire to the plumbing system should not be removed as it is mandated in the CT Building Code but it should not be the primary carrier of stray electrical current or voltage surges to “ground” - CT DOH.[1]

List of Common Causes of Leaks in Copper Water Piping

Question: green stains, corrosion, gritty material around copper pipes & pipe fittings or connections

(Jan 14, 2015) JohnGotts said:
What is the green gritty mineral buildup around some sweat joints in my boiler installation?
Can it be removed or should it be left alone?

30 January 2015 Sal said:
If your house water main is green near the electric ground connection does that mean the ground wire is going bad or is bad

Reply: common causes of corrosion on or leaks in copper piping

Green corrosion on copper water piping indicates a problem in this photo (C) Daniel FriedmanSee LEAK CAUSES in WATER PIPING for a catalog of the various causes of leaks in copper or other metal water piping.


Most likely it's an oxide of copper caused by corrosion. Look at it closely to be sure there are no leaks.

Watch out: never "pick" at or probe corrosion.The risk is that you convert a small leak into a big emergency leak that requires that you shut down the building water supply.


Watch out: Green corrosion on a water pipe that is found only around the electrical ground is worth some further checking: stray electrical currents or improper grounding could be causing the corrosion that you see.

Some green corrosion on copper piping is common and may not necessarily mean a leak is present. For example we may see corrosion where solder flux ran out around a solder joint during pipe connections by sweating (copper soldering).

At LEAK TYPES, WATER SUPPLY or DRAIN PIPES - we describe the types of leaks that occur in water supply and drain piping with an eye (or an ear) towards leak detection and towards hidden leaks in buildings


Continue reading CORROSIVITY or ACIDITY of WATER or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


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COPPER PIPING in BUILDINGS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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