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Is structural steel corrosion resistant?

Structural steel is not corrosion-resistant on its own. However, there are several methods to protect structural steel from corrosion.

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Is structural steel corrosion-resistant, and is it likely to rust over time?

Here is what you can expect when it comes to steel corrosion

As a steel fabrication company that uses a lot of structural steel, we would love to tell you that structural steel generally doesn’t corrode, but that’s not exactly true. To be fair, it usually won’t corrode if you can keep moisture and oxygen away from it, but we tend to have ample amounts of both on planet Earth.

So, the answer to both questions in the opening sentence is quite simple. Structural steel is not corrosion-resistant, and it will generally corrode and rust over time – particularly if it’s exposed to the elements.

That’s because structural steel is primarily made of iron, which is a material that is very susceptible to corrosion when exposed to moisture and oxygen. The good news is that there are many ways to protect structural steel from corrosion; we’ll look at these in this blog.

How does structural steel corrode?

As we highlighted above, structural steel is made primarily of iron, that’s been optimised for use in the building industry. As well as iron, it also contains carbon and, depending on the application, other alloying elements such as tungsten, zirconium, cobalt or nickel.

To get a little technical, when structural steel does corrode, it undergoes an electrochemical process. The iron in the steel is oxidised to produce rust, which occupies approximately six times the volume of the original material consumed in the process.

To corrode structural steel, it must be exposed to both moisture and oxygen simultaneously. As we highlighted above, if one or both of these aren’t present, corrosion will not occur.

How is structural steel protected?

There are several methods to protect structural steel from corrosion. These include:

  • Applying protective coatings, such as paint or epoxy to provide a barrier that prevents moisture and oxygen from coming into contact with the steel. These coatings are effective at preventing corrosion as long as they remain intact.
  • Galvanisation is a process where steel is coated with a layer of zinc. Zinc is a highly corrosion-resistant element, and when it does corrode, it forms a protective layer over the steel, preventing further corrosion. Galvanised steel is commonly used in outdoor and marine environments.
  • Stainless steel contains chromium, which forms a thin, self-repairing oxide layer on the surface when exposed to oxygen. This oxide layer makes stainless steel highly corrosion-resistant and suitable for a wide range of applications.
  • Another method involves using sacrificial anodes, usually made of a more reactive metal like zinc or aluminium, to protect the structural steel. These sacrificial anodes corrode in place of the steel, extending its lifespan.
  • Structural steel can also include specialised corrosion-resistant alloys, such as nickel-based alloys, which are designed to withstand harsh environmental conditions without the need for coatings or other protection methods.

Corrosion-resistant by design

It’s also important to point out the importance that design can play in reducing corrosion in structural steel. A well-thought-out design can incorporate various strategies to reduce the risk of corrosion and extend the service life of structural steel components:

  • It’s crucial that designers who work with structural steel consider the specific environment in which the structure will be located, accounting for factors like exposure to saltwater, industrial pollutants, or acidic substances.
  • Effective drainage systems are essential in design to ensure water does not accumulate on steel surfaces, which can accelerate corrosion. 
  • Proper ventilation is another critical consideration, as it aids in maintaining optimal environmental conditions and prevents moisture buildup.
  • Designers must also select appropriate materials and coatings based on the anticipated environmental conditions. 
  • Additionally, the design should facilitate ease of access for inspections and maintenance, enabling early detection of corrosion issues and timely remediation.  

How long can structural steel last?

While structural steel generally can corrode, if structures are well-designed, protected and maintained, they can last for many years and often centuries

Take the example of Australia’s most iconic steel structure, the Sydney Harbour Bridge. It undergoes a regular maintenance and repainting cycle to protect it from corrosion and maintain its iconic appearance. 

The bridge is regularly inspected, and virtually every piece of the bridge is repainted approximately every 15 years. 

The repainting process is perhaps a bit more thorough than a DIY job around the home, too. It involves removing all the old paint, sandblasting, applying a primer, an intermediate coat and then finally a topcoat. 

It’s one of the reasons why the Sydney Harbour Bridge has lasted nearly 100 years and why it’s likely to last for many hundreds of years to come.

Will structural steel produced today still be around in 100 years

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