Bluish-green stains on plumbing fixtures and distribution systems is an indicator that copper pipes are corroding and may be leaking. Copper pipe corrosion can be initiated by a multitude of reasons including water quality, water velocity, use of dissimilar metals or improper electrical grounding. Failed and leaking copper pipes can cause disruption to tenants and large repair costs to building owner and therefore should not be overlooked. The focus of this article will be defects and repairs associated with “wet” copper piping found in domestic hot and cold-water distribution systems. However, the defects discussed may be also common to other systems such as drainage pipes and HVAC lines.
Where and Why is Copper Piping Used?
Copper pipes are commonly used in the construction industry across the world. In the United States, it is manufactured to be supplied at a minimum of 99.9 percent pure copper to meet specifications established by the American Society for Testing and Materials (ASTM). It can be used in domestic hot and cold-water lines, drainage and vent lines, gas lines, along with water supply and refrigerant lines in HVAC (heating, ventilation and air conditioning) systems. Cooper piping can be expensive, however there are many advantages and reasons for using it when compared to alternative piping materials.
Advantages of Copper Pipes:
- Copper won’t degrade in UV (ultraviolet) light and can be used in areas exposed to natural daylight.
- It is very durable and capable of withstanding high pressure and water velocity.
- They are relatively lightweight and rigid, making it easy to install over long sections with supports (compared to plastic piping such as PEX, PVC or CPVC)
- Copper is naturally a corrosion-resistant material compared to other piping metals such as lead or galvanized steel.
- Copper pipes are long lasting and have been known to last between 30 to 50 years without issues.
It is up to the designer to select the type of copper pipe for use in an application. Strength, formability and other mechanical factors often determine the choice. Plumbing, mechanical and other building codes govern what types may be used. The copper piping usually used for domestic water distribution is typically either Type K, L or M. Type K has thicker walls than L and M and is often used for underground water service from the water mains to the water meter. Type M is the most common within the actual building followed by type L. The main difference between type M and L is the wall thickness and pressure rating. The most common sizes for both type L and M are half-inch and three-quarter-inch in homes and at branch offs, however can be up to eight inches in size depending on application.
Pitting and Pinhole Leaks
The most common cause of copper pipe failure is “pitting” corrosion and pinhole leaks. Pitting corrosion is the non-uniform localized attack of the wall surface of copper pipe or fitting from the inside. Eventually this will lead to perforations or small holes within the system known as pinhole leaks. A pinhole leak is a final breakthrough event of the progressive attack of pitting corrosion on copper pipes. A copper pipe can be in a condition of having significant damage by pitting corrosion, but not have pinhole leaks. Pinhole leaks can go undetected for months on end as the majority or plumbing systems are contained within walls, floors and basements.
The following are indicators that a building may have pinhole leaks;
- Copper Stains. A blueish-green stain on the pipework and fittings.
- Condition of Pipes. The copper pipes look like they have small dimples.
- Water Stains. Yellow or brown discoloration on walls, ceilings and pipework insulation.
- Active. Plumbing Leaks. Dripping noises from basements, walls and or floor voids.
- Associated Damp Issues. There is mold, mildew or microbiological growth.
- Reduced Efficiency. Reduction in water pressure and increased utility bills.
There are a multitude of why pitting corrosion and pinhole leaks occurs.
If the water is acidic (pH lower than 7.0) or alkaline (pH higher than 7.0) then it may cause copper corrosion in plumbing systems. These can be classified into three types;
Type I – 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. Factors that initiate this phenomenon include stagnation of water early in pipe life; deposits within the pipe, including dirt or carbon films, high chlorine residue, water softeners, or alum coagulation.
Type II – 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. Factors that initiate this phenomenon include higher temperatures, high chlorine residuals, or alum coagulation.
Type III – 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. Factors that initiate Type III pitting include stagnation early in the pipe life, alkaline water, and alum coagulation.
In addition to the PH levels other factors affecting the water quality may induce copper corrosion including, but not limited to, the temperature of the water along with dissolved carbon and oxygen dioxide, concentration of sulfur-bearing compounds, and microorganisms in water.
Galvanic Corrosion from Dissimilar Metals
Galvanic corrosion occurs due to a self-imposed direct current which in turn have resulted from the electrical potential between two dissimilar metals. The two dissimilar metals must be in contact in the presence of an electrolyte that allows current to flow between the two metals. The greater the difference in the electrical potential number of the two metals, the greater the corrosion rate will be for the less noble metal (see figure 1.1). In the case of domestic water plumbing systems, the “fresh potable water” acts as a weak electrolyte, and therefore if copper pipes in contact with other metals then galvanic corrosion may occur.
Figure 1.1. – List of Metals
Galvanic corrosion can be a common occurrence in domestic plumbing systems. For example, suppose the water filled domestic copper pipe is connected to a galvanized steel pipe by means of an adaptor at a water heater. The steel, being negative to the copper, will begin to corrode and eventually carry through to the copper. The galvanic action will usually occur within 6-inches of the point of contact, but the rust may enter the water system as a contaminant affecting the whole system. Common locations for dissimilar metals to be in contact are at water heater and plumbing fixture connection points such as sinks, baths and showers etc. In addition, copper may be in contact with steel studs within walls and floors, or cast-iron and galvanized pipes serving sanitary waster, stormwater or HVAC systems within the building.
Improper Electrical Grounding
Historically, electric supplies have been grounded via copper pipes which enter the building below grade level. Although this practice is less commonly used in buildings today, many older buildings may be grounded still in this way. Electrical grounding directs dangerous electrical charges such as lighting strikes and static electrical charges away from a building into the ground. A buildings copper pipe plumbing system provides a safe electrical ground for the electrical system as the pipes extended underground. One theory is that pinhole leaks are caused by electrolysis i.e. stray currents along the copper lines and improper electrical grounding. Improper grounding occurs where;
- The piping system isn’t grounded to the earth correctly. The pipe should be at minimum 10 feet underground.
- The copper piping should not be separated electrically by plastic water filters, sections of plastic pipe, plastic water softener bypass valves etc.
- Unnecessary electrical panels, appliances or wiring connected to the piping that is not the “ground pipe”.
Viable remedial options for improper grounding is to install jumper cables around any separations or install a ground rod at the building. As a matter of fact, the National Electrical Code (NEC) now recommends supplementing grounding to the cold-water service line with a grounding rod under current code. Do not attach a grounding wire to water pipes other than the main pipe ground. Route wires away from water pipes and don’t use galvanized nails that touch copper piping. It is highly recommended that the installation of a grounding rod be done by licensed electrician.
Repair or Replace?
When there are pinhole leaks in a building then the owner has two options. Option 1 is to find and remove the cause of the pinhole leaks and repair the existing systems. Option 2 is to replace the plumbing system pipework within the building. Choosing which option will invariably depend on the age and condition of the overall system and number of leaks occurring.
Option 1 – Repair Pipes and Pinhole Leaks
If the pipework is relatively new, say less than 20 years old, and there have only been a couple of leaks isolated to one run of pipe then a repair option should be considered. Efforts should be made to find the cause of the pipework corrosion before repairs undertaken. The repair will usually consist of cutting out and replacing deteriorated or leaking section(s) of pipe(s). The pipes should be inspected for the type of corrosion present including pitting, dissimilar metals in contact or improper grounding. The water should be tested for PH levels and other contaminations. The building owner should consider the following practices to reduce the corrosion within the system:
- Get an accurate water analysis. The water analysis should be for pH, total hardness, alkalinity, total dissolved solids, iron, manganese, nitrate, chloride, sulfate, and copper. Measure temperature as well.
- Add a water filtration or softening system to reduce hard water deposits.
- Install a calcite neutralizer tank, or a soda ash feeder to raise the pH to 7.2 to 8.0 to correct for low pH and increase the alkalinity in the water.
- Install a chlorinator or ozone system to disinfect the water before it enters the building if water has bacteria and/or sulfur odors.
- Engage with an engineer to make system design adjustments to reduce velocity. Cold line velocity should be less than 8 feet per second and hot lines should be less than 4 feet per second.
- Verify there are no dissimilar metals in contact. Relocate or reroute pipe work if necessary. Install dielectric coupling at connection points where there are two dissimilar metals such as copper pipe connecting to steel pipes at water heaters. A dielectric coupling is easily installed between the two dissimilar metals. Unlike other plumbing fittings, it has a rubber ring gasket that stops the flow of electricity between the two metals.
- Verify if there are unnecessary electrical appliances or wiring connected to the piping and if the piping system is properly grounded to an earth ground. Verify to make sure that there is electrical continuity throughout the piping system.
Option 2 – Re-pipe the Building
If the building has an old copper pipe plumbing system which is more than 20 years old and multiple leaks in sporadic locations throughout the building, then replacement should be considered. Re-piping can be very expensive to the building owner and disruptive to the occupants. When a building is undergoing a large renovation then the age and condition of the pipes should be considered nonetheless. To replace pipework down the line means removing finishes, walls and floors to access the pipework. Use of modern materials such as PEX should be considered when a buildings’ plumbing system is being replaced.