Hi VICK1,

You indicated that you had the galvanized coating removed for the full penetration moment welds, but not for the 3/8" fillet welds. If you allow welding over the galvanized coating, the welds will be subjected to cracking as a result of intergranular penetration of zinc into the weld metal. Cracks could occur anywhere in the weld, but they most commonly occur at the throat of a fillet weld. Steel is embrittled by molten zinc. Zinc has considerable solid solubility in iron, and the two metals form an intermetallic compound at the melting temperature of zinc. Molten zinc may attack carbon steel weld metal along the grain boundaries and form a brittle compound that fractures when a residual tensile stress of sufficient magnitude is present. Cracking is most prevalent when the galvanized coating is present at the root of the weld, particularly with fillet welds. Whether cracking occurs in these fillet welds depends on factors such as the thickness of the coating, the method of galvanizing, joint restraint, electrode classification, and welding process. I don't know what thicknesses are being welded, but welds made by the SMAW process on base metals less than 1/2" thick are usually not susceptible to zinc penetration cracking because the higher heat input and slower welding speed with the process volatilizes away a greater amount of zinc ahead of the molten pool. Both the silicon content and penetration characteristics of the electrode are important considerations when welding over galvanizing. Weld metal containing about 0.2 % silicon or less is usually free from zinc penetration cracking. An electrode low in silicon is recommended, however, electrode selection should not be based on silicon content alone. Electrodes such as 7015 or 7016 are highly susceptible to cracking. If your engineer is willing to allow a reduced tensile strength in the weld metal, 6012 or 6013 electrodes have low crack sensibility. If you're allowing welding over galvanizing, it may be a good idea to run procedure qualification tests with whatever electrode is chosen, but keep in mind that batches of galvanizing can be produced under varying conditions and may react differently with respect to welding. Seems to me that the easiest and more reliable thing to do would be to just have the welders remove the coating, regardless of the joint being welded.