Although it is a rare problem, internal pitting corrosion can occur in copper pipes, resulting in pinhole leaks. This can be very expensive to fix and lacks definitive proof of its exact cause. However, water chemistry is known to be an important factor. To help you understand this complex problem, examine the following frequently-asked questions.
What is a pinhole leak?
A pinhole leak is the final stage of pitting corrosion in copper water plumbing. It is a small hole in the pipe that develops due to excessive wear in that particular spot. Pitting corrosion can cause significant damage without causing leaks, corroding the interior pipe surface severely but not concentrated enough to cause an actual hole.
Why should homeowners be concerned about pinhole leaks?
Pinhole leaks are a major concern for the following reasons:
costly to find and repair each leak
highly variable amounts of water damage per instance
lead to loss of water resources from undetected leaks in service laterals
lead to growth of mildew and mold
lead to higher premiums for homeowner insurance or potential cancellations of it
one leak might soon be followed by another
Where are pinhole leaks most often located?
Any pipe or tube in a house could develop pinhole leaks, but most are found in cold-water, horizontal copper piping, according to the Washington Suburban Sanitary Commission (WSSC). The leaks are usually found in older homes, with 80% of those reported found in homes built before 1970.
How many homes experience pinhole leaks?
No comprehensive data has been collected on the number of homes affected by pinhole leaks. Utilities and water authorities have collected thousands of voluntarily-submitted reports from residents in the U.S. who have experienced this problem. One of the biggest reasons why accurate data is hard to gather is that many homeowners will consider the pinhole leaks a plumbing problem, so they won’t report the occurrence to their water utility.
What is copper piping?
The copper tubing that is used for domestic water supply and distribution meets specifications stating that it must be a minimum of 99.9% pure copper and silver combined. Usually, it is deoxidized with phosphorus and refereed to as C12200 (Copper No. 122) or DHP copper, but other coppers could also be used. There can be a maximum of 0.04% phosphorus in the tubing.
Why is copper piping used?
For over 50 years, copper piping has been used for domestic water supply. In the U.S., over 5.3 million miles of copper plumbing tube has been installed. Over 80% of U.S. buildings use it. The material is the most widely used because it is easy to use, resists corrosion, and resists permeation by liquids and gases that could corrode or contaminate a pipe system.
What is copper pitting corrosion?
Corrosion comes in many forms, but it is pitting corrosion that will most likely result in pinhole leaks in copper pipes. Pitting corrosion is a non-uniform attack of the wall of a copper tube, pipe, or fitting. Only a small area of the interior or waterside surface of the pipe is attacked, and the rest of the pipe is largely unaffected. While there is no definitive proof of what causes pitting corrosion, it is thought that some combinations of water chemistry factors will allow the pitting to occur, while others will not. There are three types of pitting corrosion.
Type I pitting: Associated with hard or moderately hard waters with a pH level between 7 and 7.8. This type usually occurs in cold water and creates deep and narrow pits that result in pipe failure.
Type II pitting: Occurs in certain soft waters with a pH below 7.2. It occurs rarely in temperatures less than 140 degrees F and creates narrower pitting than Type I that still results in pipe failure.
Type III pitting: Occurs in cold, soft waters with a pH above 8.0. It creates a wide, shallow form of pitting that results in blue water, byproduct releases, or pipe blockage.
What causes the pinholes to occur?
Just as there is no definitive cause of copper pitting corrosion, there is also no definitive cause of the pinholes the corrosion creates. The following are some of the possible causes and research that backs them up:
Combination of high pH, low organic matter, aluminum solids, and free chlorine (Virginia Tech, study commissioned by WSSC, December 2004)
Aggressive water, addition of water softeners, and poor workmanship (University of Florida School of Building Construction, 1997)
Aluminum-bearing compounds from concrete pipes, cement mortar lining of cast iron pipes, and aluminum coagulant carryover from treatment plants (Final report on Maryland Task Force on Pinhole Leaks in Copper Pipes)
Chloramines, which are chemicals caused by combining chlorine and ammonia (Virginia Tech, study commissioned by WSSC, December 2004)
Excessive water velocity in undersized copper tubes (A White Paper Review: History ff Use and Performance of Copper Tube for Potable Water Service, Richard O. Lewis, P.E. Lewis Engineering and Consulting, Inc.)
The variety of potential causes on this list shows just how difficult it is to pinpoint the true causes of pinhole leaks. However, some studies have also shown that things that were once thought to be contributing causes to pinhole leaks are not actually causes, or at least have little scientific basis. These factors include the following:
Manufacture of the copper plumbing materials
Grounding of electrical systems/phone systems to the piping system
Harmonic divergence (planet alignment)
Cellular phone/radio signals
Cheap/inferior or imported copper
What are some available repair options?
Various options are available for homeowners, but none of these options will address the root cause of the problem. Instead, they can only correct the symptoms and are costly to conduct. The following are some of these repair options:
application of external solder to fix the leak
replacement of a small section of tube
re-plumb of the entire house (but this does not guarantee the problem will not recur after a period of time)
re-plumb and replacement of copper with PVC or CPVC piping
purchase of potential cures – of questionable value – like magnets
What are some ways to prevent pinhole leaks?
While it is difficult to completely eliminate or prevent copper pitting from occurring in the first place, there are a few things you can do to reduce the occurrence and the resulting damage, including the following:
Inspect before you buy. Before you purchase a home, make sure to inspect the plumbing yourself, or get a licensed plumber to inspect it for you. Ask about the plumbing history and, if applicable, find out how long the house has been vacant.
Get the pH value tested. You might consider getting your water tested for its pH value. To catch variations, the water might need to be tested a number of times at several day intervals. The pH of your water should be higher than 7, so if it isn’t, make sure to talk to your water department.
Examine accessible/exposed copper piping. Look for small, bluish-green stains away from the joints, which can be an indication of a pinhole leak. At the first sign of any leak, call a licensed plumber. Keep in mind that these stains don’t necessarily indicate a leak, because they can also appear on the pipes in damp environment, such as the basement.
Purchase pipe clamps. If you do find pinhole leaks, purchase pipe clamps, which can be found at any hardware store. Install them over pinholes in order to stop leaks until the necessary repairs can be completed.
If your home plumbing system is developing pinhole leaks, make sure you get the problem fixed as soon as possible to minimize the long-term effects, and report the problem to your water department. With the ongoing research in this area, a definitive answer and a solution will hopefully arise to help homeowners suffering from this costly and frustrating problem.