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| According to some estimates, corrosion costs the United
States more than $1 billion a year. Copper corrosion in home plumbing
systems is an extremely common phenomenon, which can have many causes.
Besides actual piping failure, the telltale blue stains the oxidized
copper leaves on sinks, tubs, and fixtures can identify copper corrosion.
Often laundry and even blonde hair can be tinted blue. Copper can
be toxic, and water-containing levels over 1.0 mg/L should not be
used for drinking. If there are iron pipes present, the water can
be colored rust or reddish, and contains metallic or sulfur odors,
and sediment. |
 |
 |
Iron pipe nipples
corroded, filled
with rust and sludge |
Copper piping corrosion
with pin hole leaks |
| Eventually corrosion can cause the piping
to fail, in some cases in less than 10 years. |
| The main causes are: |
| • |
Low pH (acid water) or high pH (alkaline water)
on private well systems. |
| • |
 |
|
Other water chemistry causes, such
as high levels of dissolved oxygen, high levels of salts dissolved
in the water, and/ or corrosion-causing bacteria such as sulfate or
iron bacteria. |
| • |
|
|
Electrochemical causes, such as improper grounding
of electrical appliances to the copper piping. |
| • |
High velocity of water, relative to size of piping,
causing hydraulic wear on the piping. |
| • |
Sand, sediment or other grit causing hydraulic
wear on the piping. |
| Once corrosion starts in a piping, electrons can begin
to flow between the corrosion sites, causing the copper to dissolve
into the water. Since water contains oxygen, the copper ions “rust”
or oxidize, to blue color. This same process happens in galvanized
iron piping, causing rust stains and red water. |
| 1. |
Identify the source and severity of the problem
by inspection of the piping system and water analysis: |
| • |
|
|
Check to see if there are unnecessary electrical
appliances or wiring connected to the piping. |
| • |
Check to see if the piping system properly
grounded. |
| • |
Verify to see that there is electrical
continuity through out the piping system. |
| • |
|
|
Check for pH and see if the water is corrosive,
and/or perform a Langlier Index (see Table 2 in the next page,
or you can use our Online
Langlier Index Calculator). |
|
| 2. |
Identify the source and severity of the
problem by inspection of the piping system and water. |
| 3. |
Install a calcite neutralizer tank, or
a soda ash feeder to raise the pH to 7.0 to 8.0 to correct for low
pH and increase the alkalinity in the water. |
| 4. |
Install a phosphate feeder before the copper
piping. Phosphate will coat the piping and reduce or slow down the
corrosion effects, by coating the interior surfaces of the piping
with phosphate and causing an insulation surface to be built up. |
| Corrosion Background Information |
| Corrosion is “the deterioration of a substance
or its properties due to a reaction with its environment.” Corrosion
in plumbing systems is due to physical and chemical reactions between
the pipe material and water. Metals have a tendency to return to their
natural state, with some metals being more active than others, and
as a result are likely to enter their solutions (i.e. water in the
case of pipe fixtures) if contact is made. |
| The process of corrosion can be described as electrochemical.
As mentioned before, when a metal is placed into a solution it has
a tendency to enter the solution as an ion or it may be the case that
it combines with another element in the water already present to form
another compound. At this point, electrons (electricity) will leave
particular areas of the metal to travel to others to set up a type
of current. |
| The electrons point of departure is called the “anode”.
The absence of electrons at this site will cause corrosion cells to
appear around this area. The destination of these electrons is the
“cathode” whose function is to carry the electrons through
the solution and back to the anode. Dissolved oxygen in water solutions
will react with whatever reaction products are initially present at
both the anodic and cathodic regions, making it a major contributor
in the internal corrosion of piping systems. |
| Anodic areas are nearly unavoidable because piping is
never homogeneous in its makeup and therefore will have more active
sites than others. Other possible anode formations could occur in
pipes subject to stress cracks, differential oxygen concentrations
caused by biological growth in pipes, as well as sediment deposits
and corrosion product accumulation. |
| Homes in some areas are more likely to experience corrosion
because of local building codes. This is because homeowners are mandated
to “bond” their electrical systems with their plumbing
in order to redirect stray current to the ground. This process is
a contributing factor to “electrolysis”- the “decomposition
into ions of a chemical compound in a solution by the action of an
electric current passing through the solution”. The process
takes place when electrical current travels through the water and
in doing so, aids in the development of corrosion sites in the piping. |
| Steps to Take to Correct Corrosion
by Electrical Currents or Factors |
| Continuity of a piping system can be important. If there
are dielectric unions on the water heater and corrosion is evident,
a jumper wire should be joined between the inlet and outlet piping
to provide electrical continuity of the piping. |
| If a plastic filter housing, plastic water softener
bypass or any other type of insulating part or device that interrupts
the electrical continuity of the piping is present, jumper wires and
proper grounding clamps should be installed by a qualified electrician. |
| Other preventative measures to reduce or slow down the
corrosion include upgrading electrical grounds, raising the pH of
the water by installing a neutralizing filter, and /or by using phosphate
feeder can coat the interior of the piping and provide protection
against corrosion. |
| ***Caution: do not attempt
to work on electrical grounds yourself.*** Use a qualified
electrical contractor or electrician and follow all local building
codes and the National Electrical Code. |
| Other Corrosion Factors |
| Factors that might lead to corrosion include water characteristics,
size of home, improperly constructed piping systems, and improper
grounding. |
| Characteristics of Water that
Affect Piping Corrosion: |
| Flow Velocity:
The flow velocity of water can lead to corrosion in piping. High velocity
waters combined with other corrosive characteristics can lead to a
more rapid deterioration of materials. High velocity waters can also
affect pipe corrosion by increasing the rate at which dissolved oxygen
comes into contact with metal surfaces. The transport of corrosion
products may also be increased with higher water velocities. On the
other hand, extremely low velocities can contribute to stagnation,
which may form pitting and biological growth. |
| Temperature: The
temperature of water has complex and varied effects on corrosion.
Reaction rates increase in warm temperatures so that if you take nothing
else into consideration, how water is generally more corrosive than
cold water. |
| Water Chemistry:
The relationship between the pH, alkalinity, and carbon dioxide in
water is important to understand because imbalances in the three can
lead to metal corrosion. pH is a measure of the concentration of hydrogen
ions in water. These ions are responsible for accepting the electrons
transported when a metal corrodes, therefore the measurement of pH
is very useful in determining corrosion levels. Alkalinity is a measure
of the water’s ability to neutralize acids. Low alkalinity,
with low pH combined, can equal a corrosive water condition. |
| Field and Laboratory Analysis |
| To determine corrosion, the first step is a physical
inspection of the piping. Signs of pipe corrosion include: |
| • |
Blue stains from copper on pipes and fixtures,
or rust stains if on iron piping. |
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A toilet flush tank with blue, rust or green
stains indicating corrosion. |
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A metallic taste indicating the presence of iron
or zinc corrosion from iron pipes. |
| • |
Holes in pipes, as well as leaks
and clogs. These problems can lead to a reduction of water pressure,
the structural failure of pipes, and corrosion products becoming lodged
into the water. |
| • |
Odors from bacterial activity. |
| There are many causes and signs of
corrosion in the field that can be observed, see Table 1 for the more
common symptoms and causes. |
| Table 1. Typical Problems Related
to Corrosion: |
| Problem |
Potential Cause |
| Red water or reddish-brown staining of fixtures and
laundry |
Corrosion of iron pipes or presence of iron in raw water |
| Bluish stains on fixtures |
Corrosion of copper lines |
| Black water |
Sulfide corrosion of copper or iron lines |
| Foul taste and/or odors |
By-products from microbial activity |
| Loss of water pressure |
Excessive scaling, tubercle build-up from pitting corrosion, leak
in system from pitting or other type of corrosion |
| Loss of water pressure |
Build-up of sand or grit from the water source, or corroded distribution
piping outside the home or plumbing system |
| Lack of hot water |
Build-up of mineral deposits in hot water system |
| Short service life of household plumbing |
Rapid deterioration of pipes from pitting or other types of corrosion |
| Water Testing for Corrosion
(You can use our Online
Langlier Index Calculator) |
| To determine the corrosion potential
for the water, the “Langlier Saturation Index” can be
used. To calculate the saturation it is necessary to determine the
alkalinity, pH, calcium hardness (or total hardness), conductivity
and total dissolved solids content of the water. The saturation index
is then determined based on a particular water temperature, typically
25 C. |
| In addition, it is recommend having
the water checked for evidence of testing the water for lead and copper.
This is conducted by determining the lead and copper content of the
water after the water has been left in the piping overnight. |
| If your piping is newer than 10 –
20 years old, it is unlikely you have leaded pipes. Copper testing
can be done inexpensively, by using a home test kit. If your piping
is copper, and it tests positive for copper residual during a “first-draw”
test, then you likely have corrosion occurring. |
| For water testing, use a first draw
sample. The first draw sample is the first one-liter of water collected
from a cold water tap which has been shut off for at least six hours.
This is the sampling procedure EPA is requiring community water systems
to use to determine compliance with the new action levels. Samples
are then analyzed for copper, and in some cases lead. |
| It is strongly recommended that a
homeowner or new homeowner have of the water tested at least once
every few years. |
| Corrosion Index (Langlier Saturation
Index) |
| The Langlier Saturation Index is
a means of evaluating water quality data to determine if the water
has a tendency to be corrosive or scale forming. In order to use this
index, the following laboratory analysis is needed: pH, conductivity,
total dissolved solids, alkalinity, and total hardness. This can give
you an idea of the corrosion potential of the water. However, in certain
cases corrosion can still be occurring even if the water is has a
neutral Langlier Index. |
| If you have copper piping, and a
first-draw sample (after the water has sat in the pipes for 12 hours
or more) tests positive for high levels of copper (over .2 ppm for
instance), then you have corrosion occurring no matter what the Langlier
Saturation Index indicates. |
| In manipulating the data, the actual
pH of the water is compared to the theoretical pH (pHs) based on the
chemical analysis. The Saturation Index = pH - pHs |
| The Saturation Index is typically
either negative or positive and rarely 0. A Saturation Index of zero
indicates that the water is “balanced” and is neither
scale forming or corrosive. A negative SI indicates that the water
is corrosive. Corrosive water can react with the household plumbing
and metal fixtures resulting in the deterioration of the pipes and
increased metal content of the water. This reaction could result in
aesthetic problems, such as bitter water and stains around basins
or sinks, and in many cases elevated levels of toxic metals. |
| A positive Saturation Index indicates
that water may be scale forming. The scale, typically a carbonate
residue, could clog or reduce the flow in pipes, cause buildup on
hot water heaters, impart an alkali taste to the water, reduce the
efficiency of the water heaters, and cause other aesthetic problems.
Table 1 presents a typical range of SI that may be encountered in
a drinking water and a description of the nature of the water and
general recommendations regarding treatment. |
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