how to restore and protect ornamental iron railings

have sandblasted and paint regurally, knowing it will rust again and again

A ton of time may be onerous, but you don't have much of a choice. Remove all loose rust as best you can with a wire brush. It doesn't have to be perfect and you don't have to get down to bare metal. Use a rust converter paint or something like Hammerite by Masterchem.

I was going to suggest hammerite also. This stuff is tough.

Bob

I picked some up at a paint store a couple towns over couple weeks ago. While at the counter an old timer painter with a bit of an accent, pointed to me and said, "He's a good painter." I looked around, not sure if he was referring to someone else (I'm not a painter), then wondered if he knew my brother who moved years ago (he was a painter). Neither. "He's a good painter. No one knows of that paint and it is a very good paint." I was highly amused.