Welding Galvanized Steel
Welding galvanized steel has gotten a bad reputation over the years (rightfully so) as the fumes produced during welding can be incredibly dangerous to the welder’s health. While it is typically a good idea to complete any welding or fabrication before galvanizing the steel (which will result in a more corrosion resistant finished product), under some circumstances steel must be welded after it is galvanized. As always, it is also important to perform your own research prior to welding to ensure the health of the welding personnel is protected, and a satisfactory weld is made. To help, here are some tips for welding galvanized steel safely and effectively.
First and foremost, proper welding personal protective equipment should be used when welding galvanized steel. This may include welding helmets, gloves, leather jackets, and steel toe boots, depending on what welding process is being used. However, unlike other welding applications, welding galvanized steel will typically require one extra piece of personal protective equipment; a respirator.
When welding galvanized steel, a respirator is required so that the zinc oxide fumes from the galvanizing are not inhaled. Inhalation of zinc oxide fumes can cause metal fume fever. This acute overexposure to zinc oxide through the respiratory system causes flu like symptoms that can be severe. Chronic overexposure to zinc oxide can result in death. It is also wise to weld in a well ventilated area, even when using a respirator.
Welding galvanized steel can pose problems other than just health risks. The zinc coating found on galvanized steels can compromise the weld. The coating makes penetration more difficult and can cause a weld to have inclusions and porosity. Lack of fusion at the toes of the weld is also common. Proper welding technique and processes must be used to mitigate these risks. If at all possible, remove the zinc coating around the weld area prior to welding. Otherwise, select a filler material that is made to be used on zinc coated materials.
Another factor that will help to make quality welds is the type of galvanizing process that was used to coat the steel. Different types of galvanizing methods will leave different thicknesses of zinc on the steel surface. Hot dipped galvanized steel and zinc thermal sprayed steel will typically have a thicker coating than zinc electroplated steel. Selecting a zinc electroplated steel can result in a better weld than thicker-coated hot dipped or zinc thermal sprayed steel. Zinc electroplated steel will also have a far more uniform coating which is important when welding automation is being considered.
Another hurdle when welding galvanized steel is maintaining corrosion resistance after welding. When galvanized steel is welded, the zinc coating at and around the weld burns away, leaving the area uncoated and unprotected. As a result, the unprotected bare weld could suffer from expedient weld failure. If corrosion resistance is still required after welding, a post-weld process must be used, such as painting the material or re-galvanizing.
Welding galvanized steel can be done safely and effectively, though there are important measures that must be taken. To weld galvanized steel in a safe manner, safety codes must be read and analyzed and proper personal protective equipment must be used to protect welders from hazards such as toxic fumes. It is also important to know all of the application specifics such as the type of galvanizing method used, the environment the weldment will be put into, the welding process being used, and the criteria to which the weld will be evaluated. When all of this is taken into consideration, welding galvanized steel can be very possible and hazard-free.