Corrosion of a steel tank or copper pipe is an electrical and chemical
of the metal. It is sometimes called "electrolysis". It causes pits
holes in one place an not in another. The electrical component of
the movement of electrons across a metal surface like electricity
copper wire. Because of this, the corrosion rate can be measured in
affected by resistance and voltage differences.
Electricity flows from a high voltage potential to a lower voltage
like water flows from a high
elevation to a lower elevation. Electricity, like water, is affected by
and pressure. All metals have energy stored within them relative to the
energy it took to create them from ore. Magnesium has the most energy
it. Zinc and aluminum have slightly less energy followed by steel then
Lead, brass and copper have lower energy which causes them to be only
affected by the corrosion process. Carbon, a metal, and gold have the
levels of all the above metals. They all have a unique voltage that can
measured. If two different metals are placed in a substance such as
that conducts electricity and connected together, you can measure an
current that will flow from the metal with the most stored energy to the
the least stored energy. This is how batteries work.
The chemical component of corrosion involves the combination of water
and other negatively charged ions with positively charged iron to form
which we call rust. Dissolved salt and other minerals in water
When a tank corrodes, the iron atoms break away from the steel surface.
this leaves pits in the steel which eventually become holes. Corrosion
anode. Therefore, pits occur at anodic spots on the surface. Protection
cathode. Therefore, the unpitted areas are cathodic spots.