Found this on one blog if it helps:
Q: I am wondering how powder coat holds up to the elements of the sea?how does it do with the salt?I was looking into possibly having a buddy build me a t top and powder coating it.instead of building it out of sainless i have seen some hand rails on charter boats that where powder coated and seemed fine ?whats your thoughts and expierence with this?thanks guys
A: It all boils down to how well it's done. If any parts of the metal are exposed to the elements, then that's a way in for the elements and corrosion. It can be something as small as a pin-prick hole in the coating and the corrosion can spread from there.
If it's done right, and taken care of, it can last a very long time. But once it starts to go, you can almost never catch up with it. You're in a constant tail chase to keep it from spreading... We use powder coating on a lot of our gear here in the Navy. With two identical sets of railing, one of them had a damaged coating from misuse and within months the corrosion had taken over and there was noting to do but to strip it and resurface. The other looks just like the day the ship was delivered 6 years ago...
