Can you weld rusty metal?

If you need to weld metal and notice a bit of rust on it, you’re probably wondering whether you can actually weld it and if the integrity of the weld will hold. The short answer is yes, you can weld rusty metal. But it isn’t quite that straightforward. There are plenty of things to consider if you need to weld rusty metal, which we’ll learn more about in this guide. 

How does metal rust? 

Metal rust or corrosion occurs when materials like steel and iron come into contact and react with water and oxygen. This forms a chemical reaction and causes oxidation of the metal, ultimately leading to visible rust on the surface. Metals placed in areas with excess moisture will rust quicker and more easily than those in drier environments. 

Environments around the coast or with high humidity such as in tropical areas will also accelerate the process of oxidation and rusting metal. Left untreated, rust can corrode and damage the metal significantly until it can no longer be used.

Why do you need to weld rusty metal? 

There are many reasons why people and businesses may need to weld rusty metal. 

Repair damaged metal structures 

Due to the rust and oxidation process, metal quality and existing welds may deteriorate and break down. Welding can help to repair the damage and restore the strength of the metal structure. This can protect the structure and ensure the safety of people who may come into contact with it. 

Salvaging old metal 

Metal recycling has many advantages. Using old metal is a good way to recycle and do your part in saving the environment, as well as saving costs along the way. Old metal, however, may have traces of rust on it which you can clean and prep before welding. 

Repair vs replacement being more cost-effective 

In instances where there has been damage to a metal structure, welding may be used to repair the issue, which could be significantly more cost-effective than having to replace it entirely. But it’s important to choose the right welding repair service to get the job done right. 

What are the challenges of welding rusty metal? 

While welding rusted metal is possible, there are some significant challenges

Reduced strength and integrity 

One of the biggest challenges of rust and oxidation is the fact that it affects the structural integrity and strength of the metal structure. When this happens, the structure may become unsafe to use, so welding may be necessary to restore it to full strength (if possible). 

Poor weld results 

Unfortunately, not all rusted metal can be salvaged. Sometimes the damage or rust may be too far gone, which means the weld will not yield a good result. In this instance, you may be better off replacing the entire structure instead of trying to fix the damage. 

What are some of the welding techniques used on rusty metal? 

There are different types of welding processes for different applications. The most common welding techniques used even on rusted metal include stick, TIG and MIG welding depending on the specific application. 

Stick welding uses a flux-coated electrode to generate a shielding gas and protect the weld from contamination. It has the ability to penetrate rust and produce a good weld when done correctly. 

MIG  welding can also be used effectively on rusted metal by using a wire electrode and a shielding gas to protect the weld from oxidation. With good control and speed, it can work well for moderately rusted metals. 

TIG welding produces a precise weld. It uses a non-consumable tungsten electrode to create an arc along with a separate filler rod to form the weld. For TIG welding to be effective, rust must be thoroughly cleaned before welding. 

Whatever technique is used, we cannot emphasise the importance of first-time accuracy enough to get good weld results because it cannot be undone or adjusted once the task is complete. That’s why it is important to use experienced welding professionals who know how to get the job right the first time. 

How should you prepare rusty metal for welding? 

Remember that rust is an additional layer over the metal, which can affect the weld quality. For this reason, it’s advisable to clean and prep the surface as much as possible to remove the rust. Prep may include thoroughly cleaning the metal to remove rust, using sandpaper and grinding. 

Once the rust is removed, it’s important to clean the metal thoroughly once again to remove any remnants or contaminants that can compromise the quality of the weld.

​​Good preparation will help create a clean and solid weld, reducing the risk of premature defects down the track. Always prioritise safety and make sure appropriate safety precautions are taken so that the integrity of the weld remains intact for any structure or surface you need.

When can’t you weld metal that’s rusted? 

While there are many cases where rusted metal can be welded, there are some instances when you simply cannot weld. 

If the metal is severely corroded, welding may compromise its structural integrity, leading to weak welds and further damage. In these instances, you may be better off replacing the metal rather than welding to repair it.

Rust can also cause the metal to become thin and brittle, especially if it is old and has been in use for several years. If you try to weld on thin metal already damaged significantly by rust, it may cause severe distortion and burn through, which will cause the project to fail.

It can also be risky to weld on surfaces where you don’t know the composition of the metal – resulting in incompatible welds and compromised weld quality.

If the metal structure is for load-bearing or structural purposes, you will need to think of whether the rust has caused irreparable damage and whether replacement is the safer alternative overall. And sometimes it’s more economical to just replace the component. 

Final thoughts 

Keep in mind that welding rusty metal can be more challenging than welding clean metal, and the resulting weld may still be weaker than a weld on clean, rust-free metal. Whenever possible, it is advisable to remove the rust or use clean metal for welding to ensure the best results and long-term durability of the weld.

If you have a rusted metal structure and want to know whether you can weld it or not, contact the welding specialists at Sydney Welders today.