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Can You Weld Galvanised Steel?

Date: 21-12-2023

Can You Weld Galvanised Steel - Alphaweld Insights

Galvanised steel is a perfect choice for applications where steel parts are exposed to atmospheric corrosion. However, joining galvanised steel is challenging because the zinc layer on the galvanised steel's surface behaves differently than carbon steel and is hazardous to inhale.

What is Galvanised Steel

Galvanised steel is either hot-dipped or electro-galvanised with a layer of zinc over its entire surface. Zinc prevents corrosion of the steel beneath it and ensures a long service life of the galvanised structure. Usually, welding is performed before galvanising.

However this is not possible when galvanised steel elements must be assembled or repaired on-site by welding -- and this is where things become tricky, as the zinc can interfere with the welding process.

You can recognise hot galvanised steel with its rough and dull colour, while thin, zinc-plated steel may appear as a shiny, metallic patchwork with a crystal-like pattern. Galvanised steel is often applied for pipes, structural elements, bolts, nuts, and sheet metals. So, knowing how to weld it is a crucial skill for professional welders.

Why Welding Galvanised Steel is Challenging

Welding galvanised steel is challenging because of two primary concerns: fume hazards and the possibility of producing bad welds. Both problems are easy to prevent with the right approach. First, let's address the welding issues you can encounter when joining galvanised steel, and then we'll show you some of the best ways to prevent hazardous zinc-oxide fume exposure.

Steel Embrittlement by Liquid Zinc

During arc welding of galvanised steel, the zinc coating melts and can penetrate into the welded metal. This phenomenon is sometimes referred to as zinc-penetration cracking because it can lead to cracking along the throat of the weld and the heat affected zone (HAZ).

One of the most common reasons for zinc-penetration cracking is using a filler metal wire with high silicon and magnesium content. These two elements can concentrate in the microstructure of the base metal and create compositions that can be easily intruded by zinc.

Therefore, you might get better results when using a MIG wire like the ER70S-4 Lincoln Ultramag, especially at the root, where the zinc-penetration cracking is more likely to occur. The ER70S-4 contains less silicon than the commonly used ER70S-6, which you can use for fill passes after depositing the root pass.

You will also benefit from grinding out the zinc coating around the joint as much as possible. This will reduce the amount of available zinc that can penetrate the metal and cause cracking. It's especially important to remove very thick zinc coatings because the susceptibility of zinc-penetration cracking increases with the thickness of the galvanised layer. 

Porosity from Zinc Evaporation

Zinc evaporates in the form of gas as you weld, and this vapour must leave the weld puddle. If the gas becomes trapped in the weld, you will get porosity that can impair the weld's strength and quality.

Two primary factors contributing to the porosity when welding galvanised steel are the welding speed and the amount of present zinc. Welding with a reduced welding speed allows the zinc to evaporate and leave the weld puddle, while a high solidification rate prevents it. Likewise, if you grind off most of the galvanised zinc layer, zinc vapour is less likely to get trapped in the joint.

Increased Spatter

MIG welding galvanised steel produces more spatter than carbon steel, even if you try to adjust the MIG induction on your machine. It's hard to prevent this problem, but it's helpful to reduce the wire diameter from 1.2 mm to 0.8 mm. Further diameter reduction won't help much, so unless you need a 0.6 mm wire, it's best to stay at 0.8 mm for productivity gain.

One of the ways to fight additional spatter is to use anti-spatter products on the welded metal and the MIG gun nozzle. These compounds can make it significantly easier to remove the spatter by reducing the adherence of the spatter to the base metal and the nozzle. 

While you should always wear full welding PPE gear, it's particularly important to protect against molten spatter when welding galvanised steel. Since this material causes more spatter than plain carbon steel, we recommend Elliotts Big Red Welding Gloves as they can take some beating. These gloves have certificates for protection against heat and fire (EN407) and mechanical risks (EN388 and AS/NZS 2161.3:2005).

How to Prevent Zinc Fume Poisoning When Welding Galvanised Steel

Since welding galvanised steel causes zinc vapour in the form of welding fumes, it's critical to prevent inhaling these gases. Fumes from welding galvanised steel can cause metal fume fever, which will give you severe flu-like symptoms.

You'll recognise the metal fume fever if you experience any of these symptoms:

• Severe thirst
• Muscle pain
• Shivering
• Throat dryness and pain
• High fever
• Nausea and vomiting
• Congestion
• Convulsions
• Hallucinations (extreme cases)

Horrible. That's the best way to describe metal fume fever. While this condition is acute and your symptoms will withdraw in about 48 hours, inhaling zinc oxide can cause long-term health problems.

First, welding fumes can trigger another underlying health problem, leading to more severe acute health issues. Next, welding fumes can cause chronic respiratory, digestive, cardiovascular, and neurological problems. And finally, welding fumes cause cancer.

Remember, you won't only inhale zinc oxides, but manganese, iron, silica, and other hazardous substances that are present in all steels and electrodes. And many of those compounds are significantly more dangerous than zinc.

So, how do you prevent zinc and other metallic oxides from entering your lungs?

By stopping them at their source. That's the best way to prevent acute and chronic health disorders resulting from welding fumes.

The Translas 8XE 250 MINI MIG single extraction system captures up to 98% of welding fumes directly at the source by using a specialised MIG welding gun. We also supply dual extraction systems and high power units for welding with extreme amperages.

Translas extraction systems capture the welding fumes as soon as they evaporate from the weld puddle. Their MIG welding torches have specialised nozzles that capture the welding fumes using their high power vacuum units. The fume capture action doesn't affect the shielding gas coverage, so there are no downsides to using the source capture method to eliminate the welding fumes.

A purified air-powered respirator, or PAPR, is another way to prevent welding fumes from entering your lungs. PAPR welding systems are usually a part of a welding helmet, and they filter out the welding fumes from the surrounding area and deliver fresh air right under the helmet. For example, the 3M Speedglas G5-01TW comes with the HD Adflo PAPR system. Together, they provide UV/IR and respiratory hazard protection. However, PAPR systems can't protect others in the work area, unless they wear one too. Respiratory PPE systems are an important part of a welding fume prevention plan, but they may not always be sufficient to bring the exposure below the maximum permissible exposure limits.

Need Assistance Choosing Welding Equipment for Galvanised Steel?

If you are unsure about the suitable filler metal, welding process, shielding gas, or protective equipment you may need for your galvanised steel welding job, contact the experts at Alphaweld - call (08) 9456 8000 or send us an online enquiry and we'll be happy to help.