What Causes Copper Pipe to Leak?
Contrary to popular belief copper water piping doesn’t last forever. In its original design criteria, copper piping was projected to last for 20-25 years, but failure can often occur in as little as two years due to water chemistry.
Changes in water chemistry, unrelated to water quality, have caused the water to become aggressive towards the copper piping.
Copper is the most widely used material for plumbing systems because of its ease of use, resistance to corrosion, and resistance to permeation by liquids and gases, which may be sources of corrosion and contamination.
Copper piping has been used for domestic water supply for over 50 years. Since 1963, over 5.3 million miles of copper plumbing tube has been installed in about 80 percent of all U.S. buildings.
Hot or warm spots in the floor, soaked carpeting, ceilings or walls and abnormally high water bills are signs of failing copper pipes.
The State of Maryland Task Force to Study Pinhole Leaks in Copper Plumbing defines a copper pinhole leak as the perforation of copper tube, pipe or fittings used for domestic water distribution as the result of pitting corrosion initiated on the interior/waterside surface with the subsequent leakage of water.
Internal pitting corrosion of copper pipes is a rare but costly problem that leads to the formation of pinhole leaks. Although the factors that cause this problem are mostly unknown, it is well recognized that the chemistry of the water traveling through the pipes can influence the formation and propagation of pits.
A pinhole leak is a final breakthrough event of the progressive attack of pitting corrosion on copper water plumbing. A copper water plumbing system can be in a condition of having significant damage by pitting corrosion, but not have pinhole leaks. The challenge is how to discover pitting corrosion before pinhole leaks develop.
Although pinhole leaks could happen in any copper pipe or tube within a house, the Washington Suburban Sanitary Commission (WSSC) reported that the majority of pinhole leaks that their customers had reported were in cold-water, horizontal copper piping. Most of the leaks were in older homes, and 80 percent of the reports involved homes built prior to 1970.
There is no comprehensive source of information on the occurrence of pinhole leaks. Many utilities and water authorities have collected thousands of reports, submitted voluntarily by residents who have experienced pinhole leaks. Often, homeowners consider pinhole leaks as a plumbing problem, and do not report them to their water utility.
Copper (Pitting) Corrosion
There are many forms of corrosion, but pitting corrosion is most likely to culminate in pinhole leaks in copper plumbing.
Pitting corrosion is the non-uniform localized attack of the wall of copper tube, pipe, or fittings initiated on the inside surface of copper water pipes. Usually only small areas of the metal surface are attacked.
Pitting corrosion can be classified into three types:
cause: Hard Water
Type I pitting is associated with hard or moderately hard waters with a pH between 7 and 7.8, and it is most likely to occur in cold water. The pitting is deep and narrow, and results in pipe failure.
cause: Soft Water
Type II pitting occurs only in certain soft waters, with a pH below 7.2 and occurs rarely in temperatures below 140 F. The pitting that occurs is narrower than in Type I, but still results in pipe failure.
cause: Cold, Soft Water High PH
Type III pitting occurs in cold soft waters having a pH above 8.0. It is a more generalized form of pitting, which tends to be wide and shallow and results in blue water, byproduct releases, or pipe blockage.
When copper tubing is installed that is too small in diameter for the pressure and flow available, the resulting high flow rates can erode the protective coating creating areas of bare, unprotected copper. This effect can result in a high rate of corrosion wherever the protective coating is eroded.
The greatest effect of velocity occurs where the water is forced to change flow direction, such as at elbows and tees, but excessive water flow rates can be damaging to the entire plumbing system.
Currently, homeowners have several options from which to choose. However, none of the options address the root cause of the problem; they simply try to correct the symptoms. Most of the options are also costly. These options include:
- Fixing the leak by application of external solder
- Replacing a small or larger section of tube
- Re-plumbing the entire house
(However, even a complete re-plumb with new copper tubing does not guarantee that the problem will not recur after a period of time.)
- Re-plumbing and replacing copper with PVC or CPVC
- Coat the inside of existing pipes with epoxy
- Purchasing potential cures (of questionable value), such as magnets
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