There are three issues to take into consideration when welding galvanized steel. These are outlined below, along with the preventative measures Daam Galvanizing takes to mitigate these risks.
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 15mm of either side of the weld. This can be done by:
- Grinding off the zinc.
- Chipping heavier zinc coatings off with a chipping hammer/chisel.
- Burning off the zinc with an oxy-acetylene torch.
For non-critical welds that utilize hotter burning welding rods, 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:
- Prepare the bevels to eliminate the formation of a reservoir of molten zinc between the fraying surfaces at the root of the weld metal.
- Slightly increase the size of the gap at the root of the weld.
- Use a whipping motion to burn the zinc off ahead of the weld.
- Use a slightly slower travel speed.
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.
|#1 North 77BP||Low profile type, fits under a welding helmet|
|#2 North 7700||Half mask type, for use with cutting goggles|
|#3 North 7190||Disposable, low profile type, fits under a welding helmet|
Cartridges: Use with #1 and #2 above
|#1 North 7500-8||Dusts, fumes, mists, and radionuclides (zinc fumes)|
|#2 North 7500-81||Organic vapors, dusts, fumes, mists, radionuclides, radon daughters; paint, laquer and enamel mists; and pesticides (Dual protection when zinc and paint fumes are present)|
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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 procedures 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.