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
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 piping is used for general plumbing, above ground. Type M copper tubing walls are the thinnest used in construction, at 0.026" in wall thickness and thus more vulnerable to leaks if water being handled is aggressive or corrosive. Type M copper is color coded with red markings. We illustrate both red and embossed-in-copper markings on copper piping in our photo below.
Type L copper piping is also used for general plumbing as well as for heating system piping. Type L copper tubing walls are thicker, at 0.040". Type L copper piping is color coded with blue markings. Type L copper is intended for use in domestic water supply piping, fire protection systems, solar installations, fuel and fuel oil piping, HVAC systems, and snow melting systems. Unlike M-copper, Type L copper may be used for natural gas or LP gas piping in some jurisdictions and locations.
Type K copper piping is used for plumbing, heating, gas lines, and underground, and has a wall thickness of 0.049". Type K copper piping is color coded with green markings. K-copper is intended for use with domestic water supply piping, fire protection piping, solar applications, fuel or fuel oil piping, HVAC applications, and snow-melting systems.
Flexible copper tubing used as water piping: Flexible copper tubing can be bent around corners using special tools. This is not common since it is more expensive and can be awkward to work with in close quarters.
Copper tubing used in heating baseboards varies in thickness and durability depending on the manufacturer and product line.
Drain-waste-vent DWV copper piping is color coded yellow.
Refrigeration system copper piping used for air conditioning and some gas piping applications is color coded blue.
Medical gas distribution copper piping (in types K or L) is marked OXY/MED, OXY, MED, OXY/ACR or ACR/MED and is intended for medical gas use.
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?
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:
ASTM Standard Classifications B-698 encompasses six plumbing pipe (or "tube") standards including ASTM-B88.
Type K copper and Type L and M copper pipes are governed by Standard: ASTM B-88
Type DWV copper piping is governed by Standard: ASTM B-306. This standard also applies to copper pipes used in solar energy and other HVAC applicaitons.
Type ACR copper piping intended for use in air conditioning and refrigeration sytsems and also for natural gas or LP gas (LPG gas) is governed by Standard: ASTM-B-280. [K, L, or M Copper tubing is not allowed for natural gas distribution.]
Type OXY/MED copper piping intened for use in medical gas applications is governed by Standard: ASTM B-819
Compression Fittings for Copper Tubing Connections
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
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:
Improperly made tubing flares that are too small
Improperly made copper tubing flares that are cracked
Scratches or gouges on the copper tubing flare or on the brass flare fitting (shown in our photo, above left)
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
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
ok if annealed
ok if drawn-tempered
ok if annealed
Flexible copper tubing - water
ok if annealed ok if drawn-tempered
ok if annealed
Flexible copper tubing - LPG
Flexible copper tubing - HVAC refrigerants
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
Watch 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
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:
Defective copper piping: the pipe could have been defective from day one, e.g. with thin spots or damage that corrode through and leak
Improper type of copper piping may have been installed - see the copper piping types and applications described in the article above.
Damaged copper water piping: the pipe could have been damaged in transport or installation or even during the slab pour
Improper electrical ground or neutral wiring: on occasion a bad or improperly-connected electrical ground or another electrical problem can contribute to plumbing or other pipe corrosion at a building. In diagnosing recurrent failures in a ground water sourced air conditioning system that kept blowing out a very expensive cooling coil for we found that the problem was finally traced to unanticipated electrical currents in the ground system due to a neutral wiring error in the AC unit's controls.
Ask a licensed electrician check the home's grounding and neutral systems: that they are properly wired, that the grounding electrodes are properly sized and installed, and that there are no stray currents on the neutral system nor shorts or leaks in the wiring system (an AFCI or GFCI can help detect thee too).
Aggressive water: the water chemistry itself can be a source of metal water pipe (and even drain pipe) corrosion.
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.
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] 
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
water chemistry - see our notes just below
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].
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 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.
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.
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
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 readingCORROSIVITY or ACIDITY of WATER or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Acidic water & copper pipe corrosion/leak risks
I get a lot of blue stains on bathtubs and sinks, which I assume is copper leached from the inside of the copper water-supply piping. I built the house about 16 years ago and replaced the water heater a few years ago.
Am I at risk of developing pin holes or other damage to the copper plumbing and other equipment, including an electric water heater, boiler, and baseboard radiation?
If that’s the case, what’s the preferred (and cheapest) solution: calcite neutralizer tank, soda ash feeder, or other?
FYI, copper level was last measured at 0.11 mg/L, well below the MCL of 1.3, so I don’t think there’s a health issue. But I figure if copper gets leached from the pipes for enough years, at some point there won’t be much pipe left.
(Oct 16, 2012) Dan said:
What would make the cold copper pipes in the house appeared burned or charred. The hot is fine. Just the cold looks this way. Any ideas?
What you describe is normal, provided there are not actual burn marks from overheating such as by a soldering torch, and in fact dark or even blackened copper piping often helps us identify cold vs hot water copper piping.
Cold water piping is seasonally wet by condensation that in turn boosts both soiling or dust collection and mild oxidation.
The result is that generally the cold water copper piping will be darker in color than the hot lines.
Question: turning the water back on after long shut-down
(Feb 19, 2013) Rich said:
The water has been shut off in a house with copper plumbing for 2+ years. Are there any special problems that could be associated with no water in piping for an extended period?
Question: Water line insurance for leakage or failure - what is pipe life-span
(Jan 29, 2014) Curtis said:
My Clifton NJ house was built in 1952 and I recently received a Exterior Water Line insurance policy in the mail covering replacement of the water line should it fail. What is the lifespan for the water line? Is this something I should be worried about?
We don't know the material of your water main, the soil corrosivity, nor how the line was installed, nor its length to the street water main, nor its depth: all of these are significant factors in water line replacement cost and life expectancy.
I'm also not sure who's selling you this sort of pig-in-a-poke insurance policy: that is, what sort of insurance are we buying when the insurer knows nothing about the property or item being insured? If I were an underwriter (I'm not qualified to be one, this is just OPINION) I'd be nervous, especially knowing that a bevy of home warranty companies marketing to home buyers and home inspectors went belly-up due to the adverse selection problem.
And I'd want to know about the policy price and who's selling it. A quick web search turned up Excelsior Insurance as a company selling water damage coverage and possibly a part of Liberty Mutual group (reputable).
It also turned up something to look into: Insurance Firm On Thin Ice In Denying Claim, Judge Rules
January 09, 1988|By Robert Bruss. - admittedly an old snafu. But a quick search shows quite a few legal disputes over collecting on insurance policies issued by the Excelsior Insurance Co. for water damage. - Is this the company offering a policy?
- re-posting your comment without the link - our software prohibits links in comments in order to protect against malware.
Thanks for the response. I have not heard of anyone needing to replace a water main into the house but suspect it must need to be done at some point...The company is HomeServe.
Certainly the lateral or in some parlance "water main" between house and street is ultimately replaced on buildings. But depending on variables I cited along with piping material and quality, wall thickness, care of installation, and soil conditions, these lines can last a long time. 20-40 years would not be unusual. In the Northeastern U.S. where lead entry mains went into homes around 1900 we saw replacements beginning to be more common 50-70 years later.
Question: leaks showing up in copper pipes, pipes feel soft
(Feb 13, 2014) Anonymous said:
I recently bought a duplex. All copper plumbing lines. Recently have had 2 leaks show up, and the pipe around leaks very soft feeling. Do I need to replace it all? firstname.lastname@example.org
The answer is ... it depends. On why the pipes are leaking; If the original installation used defective copper OR if the water supply is very corrosive then you could be facing an extensive repair.
I would want to know more about the leaks - where they occurred in the house, whether they were on hot or cold piping, and I'd like to see sharp photos of the leak; ideally you'd cut out four inches around the leak and have someone with experience examine the pipe itself - or send me photos or a pipe fragment if you like and I can make a physical exam in our lab (while we have a forensic lab here I'm not a copper expert but I suspect we can figure out what's going on by microscopic examination)
Click on the CONTACT link at page bottom or top for mailing details if you want to pursue it.
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Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission to InspectAPedia to use illustrations from The Illustrated Home which illustrates construction details and building components. Carson Dunlop Associates' home inspection education products include
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 Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at firstname.lastname@example.org
 "Pitting Corrosion in Copper Tubes – Cause of Corrosion and Counter-Measures", Mattsson, E.; Fredriksson, A.-M., British Corrosion Journal, Volume 3, Number 5, September 1968 , pp. 246-257(12), Maney Publishing, Quoting the article abstract:
An investigation of failures of hard-drawn copper water pipes (phosphorus-deoxidised copper) in service due to pitting corrosion was conducted from November, 1962 to February, 1965. Fifteen cases were reported. All those about which information could be obtained came from hot water installations and occurred in water with a low pH (?7) and a HCO3- content of, at the most, 100 mg/l but generally below 50 mg/1. Failures not due to pitting corrosion (i.e. caused by erosion and corrosion or corrosion fatigue) occurred in waters with a higher pH and higher HCO3- content.
A laboratory investigation into the ability of the corrosion products to counteract further corrosion in different types of water was also carried out, using an electrolytic cell which, in principle, was a model of an active pit in a copper tube. This led to the following conclusions, which are in good agreement with the results obtained from the examination of service failures:
If the pH value of the water is high enough, the copper dissolved by the corrosion can be precipitated as basic copper salt. At low pH values such precipitation does not take place.
If the [HCO3?]/[SO42?] ratio in the water is high, dissolved copper can be precipitated as basic copper carbonate in the neighbourhood of the corrosion site and counteract further corrosion.
At a low [HCO3?]/[SO42?] ratio, crusts of basic copper sulphate will be precipitated at some distance from the corrosion site and may lead to a high corrosion rate.
Pitting is not likely to occur in hot water tubes of hard copper if the pH is ? 7·4 and the [HCO3?]/[SO42?] ratio ?1 (the concentrations given in mg/1). The critical values mentioned are approximate and may be adjusted in the light of future experience.
 "Health and aesthetic impacts of copper corrosion on drinking water",
Dietrich AM, Glindemann D, Pizarro F, Gidi V, Olivares M, Araya M, Camper A, Duncan S, Dwyer S, Whelton AJ, Younos T, Subramanian S, Burlingame GA, Khiari D, Edwards M., Virginia Tech, Blacksburg, VA 24061-0246, USA. email@example.com, Water Sci Technol. 2004;49(2):55-62., Abstract
Traditional research has focused on the visible effects of corrosion--failures, leaks, and financial debits--and often overlooked the more hidden health and aesthetic aspects. Clearly, corrosion of copper pipe can lead to levels of copper in the drinking water that exceed health guidelines and cause bitter or metallic tasting water. Because water will continue to be conveyed to consumers worldwide through metal pipes, the water industry has to consider both the effects of water quality on corrosion and the effects of corrosion on water quality. Integrating four key factors--chemical/biological causes, economics, health and aesthetics--is critical for managing the distribution system to produce safe water that consumers will use with confidence. As technological developments improve copper pipes to minimize scaling and corrosion, it is essential to consider the health and aesthetic effects on an equal plane with chemical/biological causes and economics to produce water that is acceptable for public consumption.
Other water supply and drain piping and water pressure articles:
PB (polybutylene with mechanical fittings) Piping leaks: especially in mobile homes and in the U.S. South, for example trailers and double-wides throughout Florida that were piped with this material - per M Cramer. See "Polybutylene Piping: Time Bomb?" Daniel Friedman, Journal of Light Construction, August 1996 [Technical Q&A].
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