powder coating's technical name is "Fusion Bonded Epoxy" it bonds to metal not to itself, so as long as they sandblast and etch the metal(which is standard), it shouldn't be a problem, you can hit it with a hammer and it won't chip or anything. Since the powercoating is bonded to the metal, it should never flake or chip etc.
I sometimes specify fusion bonded epoxy on some of the jobs i do (I am a water authority engineer). A place we typicaly spec is:
Custom Powder Coatings Inc
(215) 333-9433 8451 Hegerman St
Philadelphia, PA Map