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Galvanized steel is made by coating steel with a layer of zinc. This material treatment process helps protect the steel from rusting and corrosion. Its low cost and long durability make galvanized steel a popular option for many industrial applications. However, when it comes to welding, galvanized steel poses some serious challenges. The foremost challenge is the risk to the welder’s health.
When galvanized steel is welded, the zinc coating on the steel vaporizes and forms zinc oxide and lead oxide. When inhaled, zinc oxide can lead to what is called metal fume fever, causing the welder to experience flu-like symptoms for a couple of days. However, the cause for serious concern comes from the lead oxide, which results from the traces of lead found in galvanized steel. Unlike zinc oxide, the effects of lead oxide are long-term and can cause serious health issues. Hence, when welding galvanized steel, you must put safety before everything.
Another major complication when welding galvanized steel is that the vaporized zinc can mix with the weld pool and add porosity to the weld, reducing the overall weld strength.
Following are some valuable tips that can come in handy when you need to weld galvanized steel, to help you overcome these two major challenges.
Tip #1: Safety first
You might be tempted to forego your safety gear for small welds. However, you definitely don’t want zinc oxide fumes to enter your system. Taking proper safety measures protects you from toxic fumes and other airborne toxins when welding galvanized steel.
Consider using a respirator when handling these types of welding jobs. This device will help you breathe properly by filtering out all the contaminants in the air. Another critical safety measure is to ensure proper ventilation. Ensure that the place where you weld has adequate ventilation or introduce some form of forced ventilation if you’re working in a closed environment.
Another safety practice that many experienced welders follow is drinking milk before and after welding. Milk introduces calcium into the body, which is effective in removing zinc traces from your system.
Tip #2: Remove zinc from the weld area if possible
When welding, any form of surface coating on the base metal introduces some complexity to the entire process. This is especially true of the zinc coating on galvanized steel, as we have seen.
The zinc coating makes it difficult to weld using an arc welder, as the coating prevents the arc from catching the metal. Also, the zinc coating will produce more splatter compared to a non-coated metal.
For better weld quality, always consider removing the zinc coating from the weld area. Apart from eliminating the risk of zinc poisoning, this process will also give you a stronger weld.
Tip #3: Use the correct weld method
If you plan to remove the zinc coating from the metal before welding, you can use your existing welding method for the steel. However, if you want to weld over the zinc coating, you will need to use a high-quality MIG welder paired with a deep penetrating wire, like ER70S-2. Stick welding or shielded metal arc welding are also excellent choices for welding galvanized steel. The prime advantage of these welding methods is that they create flux with welding, which helps the impurities in the weld to rise up, making it easier for you to remove them.
If you compare both welding methods for galvanized steel, MIG welding is more advantageous than stick welding. This is primarily because MIG welding can achieve higher quality welds on galvanized steel, thanks to the higher penetration. You can go for the spray transfer mode first with ER70S-2 or ER70S-3 and then use a welding gun rated at 400 amps or more and a power source rated at 400 amps. Additionally, maintaining a whipping motion will give you better results in terms of control, as this process will start to volatize the zinc in front of the weld pool.
Tip #4: Do not forget to re-galvanize
When you weld over a galvanized steel surface, the extreme heat will cause the zinc coating at the weld point and nearby surface to burn away. This exposes the base metal to the atmosphere and can cause it to rust. Therefore, you must cover the metal once you complete the weld. To solve this problem, you can either apply a coat of paint or re-galvanize the metal piece completely.
Tip #5: The thickness of the zinc coating will affect the quality of the weld
Not all galvanized steel is created equal. Based on the type of galvanization process, the thickness of the zinc coating will vary. For example, hot-dip galvanizing produces a thinner coating compared to zinc-rich paint. When working with thicker zinc coats, the resulting fumes from welding will be higher, and there will be higher chances of zinc mixing with the weld pool, creating weaker weld joints.
Tip #6: Leave out large gaps for butt welds
With galvanized steel, the weld will have a tough time penetrating through the zinc coating to the metal beneath. Hence, it is recommended that you leave a large enough gap for butt-welding to achieve the correct amount of weld penetration. A slow, side-to-side movement of the arc will make the process much easier.
Tip #7: Use anti-spatter spray
When welding galvanized steel, one thing is sure: no matter the technique you use, the zinc impurities will produce a ton of splatter. The amount of splatter will be proportional to the thickness of the zinc coating. In order to effectively deal with this issue, coat the surface with an anti-splatter spray. The use of this spray makes it easier to remove the splatter once you finish welding.
Welding galvanized steel is a bit more time-consuming than other standard welding jobs. In addition, expertise also plays a significant role in the final weld quality and finish. The best approach you can take is to remove the zinc coating from the weld area if possible for a good quality weld. If you plan to go ahead with welding on the galvanized coating, take all the necessary safety precautions and make sure you follow our tips for a high-quality weld!