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.

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 gauge 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)).

John

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.

Sal:

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 badly-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))
  
  Note that in addition to the corrosivity index of water, other factors such as reverse-osmosis treatment can make water much more aggressive, resulting in corrosion and leaks in metal piping.
  
  If an RO system treated water is causing leaks the leaks would be expected in any water supply piping that is downstream from a central or building-RO treatment system.
  
  See REVERSE OSMOSIS WATER TREATMENT
  
  Plastic piping is more resistant to the effects of water chemistry, but there too, some water contents such as high levels of chlorine can lead to failures in some plastics.
  
  See PLASTIC PIPE LEAK CAUSES
• 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
  
  and see these product defect piping leak topics:
  
  JM Eagle® DEFECTIVE PVC PolyVinyl Chloride PIPING LAWSUIT
  
  Kitek® PLASTIC PIPE LEAKS, CLASS ACTION SETTLEMENT
  
  PlumbPex® PEX PIPE LEAKS, CLASS ACTION SETTLEMENT
• 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 corrosion due to dissimilar metals. In More Reading for this article
  
  see GALVANIC SCALE & METAL CORROSION
  and
  
  see DIAELECTRIC PIPE FITTINGS
• 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.

Image above provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

See GALVANIZED STEEL WATER PIPING for a discussion of the additional factors involved in leaky galvanized steel pipes.

• Stagnation: if copper or other metal 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

AtReferences or Citations 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 the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CORROSIVITY or ACIDITY of WATER - how water chemistry corrodes pipes or water heaters / water cylinders
• LEAK TYPES, WATER SUPPLY or DRAIN PIPES - where do leaks occur and how to find them
• PEX BRASS CONNECTOR LEAKS
• PLASTIC PIPE LEAK CAUSES
• PLUMBING LEAK DETECTION METHODS
• PLUMBING LEAK DETECTION & SHUTOFF DEVICES
• RADIANT SLAB TUBING LEAKS
• SINK LEAK DIAGNOSIS & REPAIR
• WELL PIPING LEAK DIAGNOSIS

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LEAK CAUSES in WATER PIPING at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to PLUMBING SYSTEMS

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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