Welding Galvanised and Coated Steel
Galvanized steels are frequently welded and some other coated steels are also required to be welded occasionally. Welding galvanized is carried out regularly and most processes can be used. The main processes used today are MMA, MIG, FCAW, MCAW, and gas welding. Porosity is the major problem when welding galvanized by any process, particularly in fillet welds where gas cannot escape. For MMA cellulosic or some rutile electrodes are used, with MIG mild steel wires and argon rich mixtures with a high CO2 content are most commonly used. Some metal cored wires have been developed to cope with zinc coatings and of the flux cored wires the basic types are best. Welding over chromium plating with any arc welding process destroys the protective layer and it is not easy to effect a repair. Due to the size of components normally presented for welding, TIG is often the process chosen. Whether welding over paint is viable depends on the paint. Weld-through primers are fairly tolerant to welding although porosity is a common problem. Some other paints may allow welding to be carried out without too much difficulty but many, like the two-pack epoxy paints and marine anti-fouling paints are not really recommended for welding. Welding of tin plate is uncommon. Welding of cadmium plated steel is not advisable as the fume from cadmium welding is particularly toxic. Welding enameled or glass covered steel is not a good idea. In terms of safety it depends on the coating and the process. Apart from the potential hazards of electricity, compressed gases, heat and hot metal, the biggest problem is welding fume. Fume from some of the coatings is quite toxic and some fume can cause serious injury.
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