Power coating can promote corrosion cause if the seal is broken moisture will wick up under it.
Sorry but this is not accurate for powder, or for liquid for that matter.
The reality is both powder and liquid paints adhere to the substrate (metal applied to) by a mechanical bond, i.e. the paint grabs the surface irregularities and hangs on.
If the cured film gets chipped or cracked, moisture will attack the exposed substrate and start rusting. But the surrounding paint being there does not 'promote' anything. As long as the adhesion remains, it's difficult for moisture to attack the metal below.
Perhaps the best way to explain this is to review 'salt fog' testing, a somewhat standardized means of testing paint adhesion and durability.
Adhesion is helped greatly by properly preparing the substrate for accepting paint, so part of this testing is a measure of how good the pretreatment process was.
A painted panel is intentionally scratched down to bare metal and the part is then put in a chamber where a salt water combination is misted on the part. How well a paint performs in this test is determined by the amount of 'creep' adjacent to the scratched line. In other words, how far did the salt fog succeed in causing an adhesion failure along the scratched line.
A good quality powder, properly cured and applied to a properly prepared substrate, can go 1000 hrs or better with less than 1/8" of creep. That's a pretty corrosive environment for it to be experiencing.
If after the test you were to chemically strip the remaining powder off the test panel, you will see there is no corrosion of the metal beyond the 'creep' area.
So the finish is actually trying its' best to prevent corrosion from spreading.
