To offer some insight to the theory of corrosion:
When we mine metals out of the earth, we unearth them in their naturally occuring form: What we know as looking like rust.
We take that "rust" and melt it down, compress it and form it into a mold of what it is being used for. ie piping, sheets/panels, body panels, etc.
Energy is used during the refinement process, taking it from its naturally occuring state and making it into something. That energy is basically stored in the objects current form. When you then take that object and place it back into mother nature, she sees the manipulated object with its high energy level and she sees its surroundings (which for these purposes are unmolested) as naturally occuring and thus having a "nuetral" energy level. This creates an imbalance, which is not a well accept thing in mother nature as we know.
What then happens is mother nature (through chemical reactions) allows energy (ions, or something....smoked/drank too much in college to remember details) to flow from the high energy object into the lower energy object in an attempt to balance everything. This transfer of energy reverts the high energy object back to its original state by releasing the energy we introduced into it by refining it...aka "rusting".
The best way (in terms of what we seem to be speaking of mostly here) to combat that is to introduce a non-conductive layer between the object that has a high level of stored enegry and that object that has the lower (nuetral) energy level...if they don't "see" eachother, then they cannot tell there is an imbalance and therefore no reaction will occur.