I make steel sculptures that are mostly hollow forms and wonder if they should have venting to allow the interiors to "breath" when situated in the outdoors. At a former job where we fabricated much larger hollow forms, the structures usually had a vent(s) to allow free exchange of air and water vapor from the inside to the outside but I always wondered if this was necessary. Would the water and oxygen inside a welded closed structure eventually get used up in creating iron oxide at which point the process would stop? I have made a few that had a bad or porous weld that did fill with water and those had to be modified to drain or the bad weld repaired if I can find it. What is the general consensus about venting fabrications like this?