Corrosion

Corrosion can be viewed as the process of returning metals to their natural state, which is the ores from which they were originally obtained.  Corrosion involves oxidation of the metal.  The metals that have standard reduction potentials less positive than that of oxygen gas, when the half-reactions are reversed and combined with the reduction half-reaction for oxygen, the result is a positive E value.  This shows that the oxidation of most metals is spontaneous.
A lot of metals form a thin oxide coating which protects their internal atoms from further oxidation.  However, to actively prevent corrosion, we can apply a coating (most commonly a paint of metal plating) to protect the metal from oxygen and moisture.  A process called galvanizing is used which involves coating steel with zinc to form a mixed oxide-carbonate coating.  Alloying is also used to prevent corrosion, which involves mixing materials to help protect them.  Another method called cathodic protection connects an active metal by a wire to the pipeline or tank to be protected.