Refinishing an old metal dock frame

I am a homeowner with some fading work experience grinding down oil rigs for repainting back in the summers of my college years. My brother hauled home a frame of lake dock which is metal (iron I suspect) and has flaking paint and spots of rust to it. I have thoughts of grinding it down and refinishing it before setting it out in the lake next spring. It is too large and unwielding to work on anywhere but outside, and it is not worth the effort to bring it in to a "shop" for a professional re-finishing. What type of durable surface application would be suggested, knowing that even with a good grinding there will be pits and rust and other dirt and blemishes to contend with? Should some cleaning solution be applied, knowing that there is little that can be done to protect from the runoff from this large frame?