A weld within sight of the sea is rusting within a fortnight if it is left bare, and on this island everything is within sight of the sea.
So nothing outdoors is left bare. The weld is ground back, the mill scale taken off, primed with a zinc rich primer and painted, and that is inside the two hours rather than a second visit somebody has to pay for.
It is also why we would rather do a gate in the yard than on site where the job allows it. Two hours in the yard with proper preparation outlasts four hours on a footpath, and it costs you less.