Welding School

Welder Welding on Galvanized Roof

The successful welding of galvanized steel is so widely accepted that there is very little recently-published mechanical property data comparing uncoated versus galvanized weld properties. The welding industry recognized fifty years ago that welds on galvanized steel and welds on uncoated steel are of comparable strength if the quality of the welds is comparable. Recent publications on welding galvanized steels deal with weld toughness, porosity control, weld appearance, restoring corrosion resistance and other issues that are much more complex than the strength of the weld. When using SMAW (”stick”) welding, galvanized steel can be welded in the same manner as uncoated steel. When using MIG or flux cored welding, one may have to adjust the voltage slightly to control spatter, and one may have to clean the welding gun of spatter and zinc oxide deposits more frequently that when welding uncoated steel. Hobart makes a flux cored wire called “Galvacore” that some users have had good success with when welding galvanized steel. When difficulty is encountered welding galvanized steel that was not encountered during welding uncoated steel, it is usually because the Welding Engineer has not accounted for the volume of gas that is evolved by the vaporization of zinc during welding. The thicker the zinc coating, the more fumes are generated, and those fumes have to be able to escape easily into the atmosphere and not be forced through the liquid weld metal. For example, welding galvanized plates to form a T-joint is a commonly troublesome situation. Since the galvanized edge of one plate is butted against another galvanized surface, the zinc vapors that are formed at the abutting surfaces will not be able to escape to atmosphere easily as the zinc is vaporized. Instead, they will blow into the weld pool, creating porosity or a poor weld surface. This is aggravated when welding conventionally hot-dipped products, since the edges frequently have excessively heavy zinc coatings. One solution is to separate the parts by 1/16 inch using wire spacers or fixtures which will leave a gap for the zinc vapors to escape easily. Other approaches are to use a slight (15°) bevel on one member (Figure 1), to remove the zinc from the faying surfaces by shearing or mechanically cuting the plate where the faying surfaces will meet, and to abrasively remove most of the zinc from one or both of the faying surfaces (Figure 2). Any of these methods will significantly reduce the amount of zinc between the parts, and this will reduce the volume of gas evolved, improving weld quality.

Conclusion: This is all really great technical speak and some good overall general knowledge on welding on galvanized steel. Unfortunetly, I have a lot of hands on knowledge about this subject after the last job i just completed. No welder alive likes to weld on galvanized. The vapors are terrible and it pops irratically which can result in some nice burns if your not very carefull and sometimes even if you are. I have found that if you clean the weld area real good. My definition of “real good” would be grinding the area until a significant amount of sparks are coming from your grinder. The galvanized coating does not emit sparks. When you reach metal with you’re grinder it will start throwing sparks. I usually weld my first pass with 6010 rod to create some good base metal. Then i aplly 7018 over that to get a nice looking weld on galvanized steel.