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What causes leaks in metal piping?
This article describes the many causes of leaks in metal water pipes. We list the factors that explain green corrosion on copper pipes, leaks at pinhole perforations, leaks at pipe joints, and other leak types on metal piping. The article also discusses the important role of water chemistry and even electrical grounding mistakes in the development of pipe leaks or pipe corrosion.
Some of these leak causes may also explain leaks in metal drain piping. Our page top photo shows a water line leak that's extra trouble to repair: a break in water piping between the building interior and the water main in the street. Some careful attention to the cause of the leak (once the line was excavated) helped avoid a repeat visit of the plumbers to this home.
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.
Causes of Leaks in Metal Water Piping or Water Cylinders / Water Heaters
Reader 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
[Click to enlarge any image]
Reply: common causes of corrosion on or leaks in copper piping
Copper pipes have been in wide use since the 1850's and have been produced by a variety of methods and in a variety of thickness ranging from heavy gauge to extruded thin-wall copper.
In the U.K. light guage piping came into wide use beginning in the 1920's. A thin oxide coating (CaCO3) that forms inside copper water piping helps resist corrosion by reducing further dissolution of the copper pipe from the interior as may other natural corrosion inhibitors - (Campbell (1994)).
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. A slow leak in metal piping may be just that, very slow, actually leaking through a pinhole where the piping material is quite thin.
When you scrape at or poke at such a corroded spot the risk is that you convert a small leak that would have given you time to hire a plumber into a big emergency leak that requires that you shut down the building water supply before making a call for emergency (more expensive) plumbing repairs.
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).
Other causes of green corrosion on copper pipes, besides an actual leak (see our comment to John in just above) are listed below.
Our photo (left) shows an ingenious temporary "repair" by a homeowner who observed a small drip at a badlhy-soldered copper water pipe elbow. As the joint was hard to reach he made a tiny funnel and drain to catch the drip and direct the water to a nearby laundry sink.
While we respect all clever midnight or Sunday Afternoon emergency building repairs, this is not a long term nor reliable plumbing leak fix. It was clever, though.
Chemistry of the water and water additives, conditioners, disinfectants, particularly chlorine - (Edwards et als (1994)) and sulfides (Jacobs & Edwards (2000))
Condensation on copper piping exterior surfaces due to cold pipe temperatures on copper lines running through humid or wet areas. In our photo at below left you can see condensation on horizontal runs of cold water piping in a damp crawl area.
See CONDENSATION or SWEATING PIPES, TANKS
Cold water pitting: described by the Foundation for Water Research and posed as occurring more in hot water heaters (water cylinders), cold water pitting is more likely in cold water pipes or at the bottom of water heater cylinders that remain below 40°C (104°F), usually at private well (borehole) water systems that have pH between 7-8.2. - Foundation for Water Research (2010)
Defective or damaged plastic piping: plastic water supply or drain piping may fail and leak from a variety of causes, including improper installation or use of defective plastic piping materials
See PLASTIC PIPE LEAK CAUSES
De-zincification of brass fittings used on copper piping (also related to water chemistry)
See PEX BRASS CONNECTOR LEAKS - for a discussion of de-zincification
Electrical grounding errors or stray currents in the electrical ground system can cause corrosion and leaks in metal piping, water tanks, water heaters, ground water heat pump systems etc.
See WATER PIPING GROUND BOND
Leaks from mechanical damage, improperly made pipe connections (sloppy soldering)
Leaks due to corrosive water (cuprosolvency or improper water pH - look for blue water, pinholes in pipes, and hot water heater or hot water cylinder (in the U.K) failures.
See CORROSIVITY or ACIDITY of WATER -
Leaks due to exterior water sources: Other leaks that are dripping onto the copper piping exterior surfaces
Soldering flux corrosion: the runout of soldering paste left on copper pipes or on brass or copper pipe fittings can cause corrosion. Interestingly Oliphant (2003) pointed out that lead itself, used in soldering materials particularly before 1986 (in the U.S.) can contribute to copper corrosion.
Stagnation: if copper or other rmetal pipes are left un-used but full of water for long periods chemical changes in the system such as changes in the pH of the water may damage the protective layer on the pipe surfaces and may contribute to corrosion, particularly if the water supply is high in corrosivity.
Water contaminants: aside from water chemistry that we mention in this discussion, biological contaminants in water may cause water pipe corrosion and leaks. Particularly in soft water with a high level of carbon, the growth of biological contaminants and possibly a thin bio-film on the pipe interior surface may form.
Other water contaminants may include debris that forms a deposit on the pipe surface, often on the interior of the pipe along its bottom or at elbows.
Debris deposits in turn may permit spot or point corrosion of the copper (or other metal piping material). - LeChevallier (1993)
See WATER TREATMENT EQUIPMENT CHOICES
Water flow rate: higher speed of water flowing through pipes can increase the rate of pipe corrosion
Water temperature: depending as well on water chemistry, hot water may be more corrosive to some piping systems
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
At REFERENCES for this article we include research citations on the various causes of corrosion on or leaks in building piping systems.
Continue reading at PLASTIC PIPE LEAK CAUSES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Baylis, John R. "PREVENTION OF CORROSION AND" RED WATER"." Journal (American Water Works Association) 15, no. 6 (1926): 598-633.
Beale, David J., Michael S. Dunn, Paul D. Morrison, Nichola A. Porter, and David R. Marlow. "Characterisation of bulk water samples from copper pipes undergoing microbially influenced corrosion by diagnostic metabolomic profiling." Corrosion Science 55 (2012): 272-279.
Campbell, Hector S. "A natural inhibitor of pitting corrosion of copper in tap‐waters." Journal of Applied Chemistry 4, no. 12 (1954): 633-647.
"Cause of Copper Corrosion in Plumbing Systems, A Review of Current Knowlege", Foundation for Water Research, Allen House, the Listons, Liston Road, Marlow, Bucks SL7 1FD U.K., TEL: +44 (0) 1628 891589, Website: www.fwr.org, retrieved 30 Jan 2015, original source: http://www.fwr.org/copper.pdf
Boulay, Nicolle, and Marc Edwards. "Role of temperature, chlorine, and organic matter in copper corrosion by-product release in soft water." Water research 35, no. 3 (2001): 683-690.
Campbell, H. S. "Pitting corrosion in copper water pipes caused by films of carbonaceous material", Journal of Applied Chemistry, Vol. 77 1950
Edwards, Marc, and Abhijeet Dudi. "Role of chlorine and chloramine in corrosion of lead-bearing plumbing materials." Journal (American Water Works Association) (2004): 69-81.
Dietrich, A. M., D. Glindemann, F. Pizarro, V. Gidi, M. Olivares, M. Araya, A. Camper et al. "Health and aesthetic impacts of copper corrosion on drinking water." Water Science & Technology 49, no. 2 (2004): 55-62.
Edwards, M., Schock, M. R. and Meyer, T. E., "Alkalinity, pH and copper corrosion by-product releases", Journal of the American Water Works Association, March 1996
Fuji T., Kodama T. and Haruo B. "The effect of water quality on pitting corrosion of copper tube in hot soft water", Corrosion Science, Vol 24, No. 10 pp 901-912. 1984
Jacobs, S., and M. Edwards. "Sulfide scale catalysis of copper corrosion." Water Research 34, no. 10 (2000): 2798-2808.
Karalekas Jr, Peter C., Christopher R. Ryan, and Floyd B. Taylor. "Control of lead, copper, and iron pipe corrosion in Boston." Journal (American Water Works Association) (1983): 92-95.
LeChevallier, Mark W., Cheryl D. Lowry, Ramon G. Lee, and Donald L. Gibbon. "Examining the relationship between iron corrosion and the disinfection of biofilm bacteria." Journal (American Water Works Association) (1993): 111-123.
Lytle, Darren A., and Mallikarjuna N. Nadagouda. "A comprehensive investigation of copper pitting corrosion in a drinking water distribution system." Corrosion Science 52, no. 6 (2010): 1927-1938.
Mattsson, Einar. "Corrosion of copper and brass: practical experience in relation to basic data." British Corrosion Journal 15, no. 1 (1980): 6-13.
MCNEIILL, LAURIE S., and Marc Edwards. "Iron pipe corrosion in distribution systems." Journal (American Water Works Association) (2001): 88-100.
Oliphant, R. J. Causes of copper corrosion in plumbing systems. Foundation for Water Research, 2003.
Oliphant, R. J., "Contamination of potable water by lead from leaded copper alloys", . 2nd International conference on Water Pipeline Systems 1994. BHR Group Conference Series Publication No. 10. Mechanical Engineering Publications Limited (MEP), London. ISBN 0 85298 921 0
Reyes, A., M. V. Letelier, R. De la Iglesia, B. González, and G. Lagos. "Microbiologically induced corrosion of copper pipes in low-pH water." International Biodeterioration & Biodegradation 61, no. 2 (2008): 135-141.
Rushing, Jason C., and Marc Edwards. "The role of temperature gradients in residential copper pipe corrosion." Corrosion science 46, no. 8 (2004): 1883-1894.
Schock, Michael R. "Causes of temporal variability of lead in domestic plumbing systems." Environmental monitoring and assessment 15, no. 1 (1990): 59-82.
Sosa, M., S. Patel, and M. Edwards. "Concentration cells and pitting corrosion of copper." Corrosion 55, no. 11 (1999): 1069-1076.
Wagner, D., W. Fischer, and H. H. Paradies. "Copper deterioration in a water distribution system of a county hospital in Germany caused by microbially influenced corrosion–II. Simulation of the corrosion process in two test rigs installed in this hospital." Materials and Corrosion 43, no. 10 (1992): 496-502.
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