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Corrosion is expensive!
In 1972 the National Association of Corrosion Engineers estimated
the annual cost of corrosion at $10 billion. A more extensive
study conducted in 1976 by the Battelle Memorial Research Institute
placed the annual loss at closer to $70 billion annually!
Shocked by these findings, the U.S. Congress ordered the Department
of commerce to verify these figures. Their analysis, published
in 1982, estimated the cost to be $126.3 billion a year!
When combining the corrosion cost of the nation's highways, water,
wastewater and gas systems, underground storage tanks, corrosion-related
pollution, etc., The annual loss has grown to a staggering $300
billion. This is greater than 5% of the Gross National Product
and a cost of nearly $1,500 a year per citizen!
Understanding Corrosion
Corrosion is the result of electrochemical activity. . .galvanic
action. Scientific studies have proven that metals having a higher
electrical potential will corrode and degrade in a typical corrosion
cell, while protecting other metals having a slower electrical
potential. Of all metals, Zinc has the highest electrical potential
as shown in Table-1.
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Table 1 - Practical Galvanic Series
| Metal |
**Volts |
| Zinc (Mil Specs
Anodes) |
-1.1 |
| Commercially
Pure Aluminum |
-0.8 |
| Mild Steel
(clean) |
-0.5 to -0.8 |
| Mild Steel
(rusted) |
-0.2 to -0.5 |
| Cast Iron (not
grashitized) |
-0.5 |
| Lead |
-0.5 |
| Mild Steel
in concrete |
-0.2 |
| Copper, Brass,
Bronze |
-0.2 |
| High silicon
cast iron |
-0.2 |
| **Voltages are
typical in neutral soil conditions and water measured against
a copper sulphate reference electrode. |
The most common type of corrosion cell is a simple Battery. The
outer case is made of a zinc alloy having a negative charge. .
.the anode. The center post is a carbon rod having a
positive charge. . .the cathode. Separating the two is
a filler. . .the electrolyte. In operation, the positive
current charge rushes from the zinc anode to the cathode, causing
eventual pitting of the zinc case. As the electrochemical activity
stabilizes, the battery loses strength, the aggressive nature
of the electrolyte determines the current output and the life
of the battery.
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