For unprotected steel under conditions of complete immersion, rusting will result in an average reduction in thickness of 0.075 mm per year of face exposed to sea water, and 0.050 mm in per year in fresh water.
When the size of the exposed iron admits of it, its freedom from rust may be very much promoted by first heating it thoroughly and then dipping it into, or brushing it well with, hot linseed oil.
All structured steelwork should be primed and preferably given a coat of red oxide paint before erection except the surfaces to be riveted in contact and the surfaces which will be in contact with concrete.
Iron and steel work can be protected from rust as a temporary measure by means of a coat of white-wash or by covering it with slaked lime. Iron exposed to the weather can also be protected (temporary measure) by a coat of paint made with pulverized oxides of iron, linseed oil, and a drier. A coat of cement wash is also applied with advantage. Painting with simple coal tar does not prevent rusting iron.
Where the sea atmosphere is likely to have a corrosive effect on the steel work, the steel work after being thoroughly scrapped and cleaned should be given a coat of raw linseed oil before the first coat of red lead paint is applied, and immediately after the steel work has been cleaned.
