How To Safely Weld Galvanised Steel?

Galvanizing is ubiquitous in the industry, it provides a durable, corrosion-resistant coating that prolongs the life of mild steel components and structures for decades. However, when needing to make repairs or improvements, welding can be troublesome.

In this article, we’ll go over the best way to weld galvanised steel, and what precautions are needed.

What is Galvanised Steel?

Galvanizing is a surface treatment process that adds a layer of zinc to the outer surface of a part. This prevents it from corroding, and in many cases can last upwards of 50 years, even in harsh conditions.

It is used across industries, from structural steelwork to hand tools to vehicle chassis. There are a few different methods of galvanizing, depending on the size and shape of the part, but the resultant layer of zinc always poses a problem when welding.

For more information on the process, check out our guide here.

Can You Weld Galvanised Metal?

Yes, a metal that has been galvanised can be welded, however, the fumes are toxic to humans, and it should be avoided wherever possible.

It is strongly recommended that the zinc is removed from the area to be welded, and within a 1-2” radius around it, depending on the thickness. This can be done by mechanical means, i.e. grinding it off, or chemically.

Safety Precautions When Welding Galvanised Metal

When welding galvanised metal, the burning of the zinc coating causes an odorous and visible plume of thick smoke, this is incredibly bad for your health and should not be inhaled.

In an ideal world, the galvanised coating should be removed completely before welding, but at the very least it should be mechanically removed in the local area.

Sufficient local and general extraction should be used, to remove as much of the fume as possible, and any operators nearby should be wearing appropriate respiratory protection.

Best Way to Weld Galvanised Steel

If you cannot avoid welding galvanised steel, there are a few things you can do to make it as safe and effective as possible:

Strip the Galvanising First

Part of the galvanising process includes acid cleaning the parts. Many galvanising plants can strip entire components of previous zinc coatings, leaving the bare metal. This can then be welded as normal.

The downside to this process is cost, most galvanisers charge around the same amount as galvanising to strip and process parts, so it’s often only worth it with large or complex components.

Clean the Joint

Any zinc present in the joint will cause both weld composition issues as well as create a zinc fume in the air. The joint should be cleaned along its entire length, and on the reverse side too.

Heat transfer to the back of the joint can be enough to burn the zinc, again causing potential weld quality issues as well as fumes and smoke.

Use MIG Welding

It would be possible to use TIG, but the weld joint would need to be extremely clean of remaining zinc to avoid constant issues with the tungsten electrode becoming fouled up.

MIG gives a good balance between control and speed, and when used with an active shielding gas can achieve good penetration.

How to Prevent Corrosion When Welding Galvanised Steel

As the main reason for galvanising a part is to protect it from corrosion, it will always be a requirement to retain that corrosion resistance after welding galvanised steel.

Unfortunately, the only way to fully protect the steel is to strip and re-coat the parts. If this is not possible, some level of protection can be achieved using a zinc-rich paint, often called cold galvanising spray.

Prepare the surface sufficiently, as with any painting process, making sure to cover any areas where the galvanised coating has been damaged or reduced.

Welding Pre-Galvanised Sheet

Pre-galvanised sheet is a great resource, allowing sheet metal parts to be made corrosion-resistant without any post-processing. Welding a pre-galvanised sheet is possible, but requires the same health consideration discussed below.

The weld itself and the immediate area around it will require further painting or plating to resist corrosion, it may be better to manufacture it out of an un-coated sheet and have it plated afterward.

Is Welding Galvanised Steel Safe?

Unless significant precautions have been taken, welding galvanised material is extremely dangerous. The fumes that are created from burning the zinc coating are very toxic to humans.

Only if the fume can be completely isolated from any operatives in the area, by both local and general ventilation, and any persons nearby are wearing appropriate respirators, should galvanised steel be welded or heated.

What is Metal Fume Fever?

A consequence of welding or cutting galvanised steel is Metal Fume Fever. This is a short-term illness that presents with flu-like symptoms, including sickness, fever, muscle aches, and difficulty breathing.

It can be avoided by using the correct personal protective equipment whilst welding, or avoiding welding galvanised metal together.

Does Milk Prevent Metal Fume Fever?

An old trick used by metalworkers since the Second World War was to drink lots of milk during and after welding galvanised steel, the theory being it protects you from hazardous zinc fumes. In many workplaces, it was provided to the workers for this reason.

Unfortunately, there are no scientific studies that substantiate this practice, we would suggest that whilst milk may be beneficial for other reasons, it should not be used in replacement of the proper respiration and extraction equipment!

Alternatives to Welding Galvanised Steel

Even with the correct equipment on hand, it is still advisable to avoid welding or cutting galvanised steel at all. There are some alternatives that may be possible:

• Have the part stripped and re-galvanised. Other benefits are better corrosion protection and better weld quality.
• Use bolted connections instead. If you need to attach one or more galvanised components together, consider drilling holes and using bolts instead, that way no zinc fumes are produced