The requirements to weld galvanized steel raises three questions.

1. What procedures must be modified or employed to maintain the integrity and quality of the weld?
2. What precautions should be taken to protect the welder from zinc fumes?
3. How should the weld be repaired to maintain the integrity of the galvanized coating?
   

1. Weld Procedures


If molten zinc gets into the molten weld metal, it can cause inferior welds and weld cracking. For structural quality welds the zinc should be removed in the immediate area of the weld and within 15 mm of either side of the weld. This can be done by:

i) grinding the zinc off.

ii) chipping heavier zinc coatings off with a chipping hammer or a chisel.

iii) burning the zinc off with an oxy‑acetylene torch; such as would occur during bevelling to prepare the material. (Adequate ventilation should be provided ‑ see Zinc Fume.)

For non-critical welds when hotter burning welding rods are used, the heat of the welding process can vaporize the zinc before it can run into the weld metal. The following procedures are recommended to reduce the availability of molten zinc near the weld.

i)   Prepare the bevels to eliminate the formation of a reservoir of molten zinc between the fraying surfaces at the root of the weld metal.

ii)   Slightly increase the size of the gap at the root of the weld.

iii)   Use a whipping motion to burn the zinc off ahead of the weld.

iv)   Use a slightly slower travel speed.

The publication "Welding Zinc‑Coated Steel" published by the American Welding Society, Inc. provides excellent detailed information on the recommended procedures to weld galvanized steel. The American Hot Dip Galvanizers Association reprints from the Welding Journals provide additional information.

2. Zinc Fume

While zinc fume is non‑toxic, excessive dosages can result in zinc fume fever ‑ an extremely unpleasant reaction with symptoms that resemble a serious fever. However, recovery is generally rapid and there appears to be no long‑term affects from zinc fumes. Mechanical or natural ventilation or an approved respirator and eye protection should be utilized when welding galvanized steel. Of course, removing the zinc before welding will significantly reduce this concern. Drinking milk can both reduce the risk of getting zinc fume fever, and also reduce the fever if you have it.

The following respiratory equipment will provide the necessary protection when welding and/or cutting galvanized steel.

3. Repair

Repair procedures are well specified in ASTM A780. In addition, our "Specification for Hot Dip Galvanizing", "Repair Procedures #27" in our in‑house training program, and "Field Repair Procedure" in this brochure, specifically detail how to repair damaged galvanized steel. It should be noted that in addition to the repair, the zinc adjacent to the damaged area will provide cathodic protection which unlike paint films, will prevent underfilm corrosion of the adjacent material and will significantly retard corrosion of the bare areas.