19 May 2017

The difference between galvanised and stainless steel
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Galvanised and stainless steel variations

When it comes to materials for ducting, galvanised and stainless steel look exactly the same to the untrained eye, but they are in fact completely different in terms of composition, weight, strength and application. It is important to be able to know the key differences and tell them apart when choosing ductwork and steel hoppers, as each type of steel is suitable for a particular use and work environment.

In today’s post, we’ll explore the difference between galvanised and stainless steel, which of these alloys are suitable for various applications, including fabrication, ductwork and more.

Galvanised steel

Galvanised steel is created during the process of applying a protective zinc coating to steel or iron, which prevents rusting. Some of the most common methods of creating this type of steel are by hot-dip galvanising, where parts of the steel are placed into a bath of molten zinc, and electro-galvanising, which is done by immersing steel in an electrolyte solution. Galvanised steel is covered in a rust-protective layer, which is approximately a millimetre thick.  This layering can wear off over time, and if scratched or damaged, can begin to rust.

Stainless steel

The manufacture of stainless steel involves a mixture of chromium and regular carbon steel. Unlike galvanized steel, stainless steel has chromium throughout, which means that it has a protective layer in place at all times. Stainless steel is an excellent material for ductwork, and any machinery or systems which have moving parts, as it is scratch resistant. Stainless steel is also non-reactive to corrosive chemicals, which is beneficial for the industrial and manufacturing sectors.

Stainless steel is extremely durable, which provides a lot of cost saving benefits, it resists corrosive and harsh substances, cannot rust and is extremely strong. Unlike other materials, stainless steel remains strong and will even retain its shape in extreme heat.

Corrosion resistance between galvanised and stainless steel

How galvanised and stainless steel are treated to protect against corrosion and rust are done so differently. Here’s how:

Galvanised steel

Galvanised steel has a protective coating of zinc to cover the underlying steel that not only prevents oxidation, but even if the zinc coating is damaged (which can expose small amounts of iron to the air), the remaining zinc coating is more reactive than steel. Essentially, this makes the remaining zinc more likely to attract an oxygen molecule than the iron, preventing rust from forming on the steel.

Stainless steel

Stainless steel is protected by the added layer of chromium (with additional other elements – depending on the manufacturer). In simple terms, rust can happen on stainless steel when iron in the steel reacts with oxygen around it. But with the added chromium (which reacts with oxygen to create a protective layer called chromium oxide), this can halt corrosion (so long as there’s enough chromium in the steel). The amount of chromium and other elements in different types of stainless steel determines how well they resist rust.

Galvanised vs stainless steel

Both galvanised and stainless steel are designed to be resistant to rust and corrosion. However, there are some key differences between how they’re made and protected, which makes one alloy more suitable than the other (depending on its use). 

If stainless steel becomes scratched, it can still maintain corrosion resistance around the affected area. However, if the zinc layer on galvanised steel is damaged, it can leave the underlying carbon steel exposed and vulnerable. Plus, stainless steel is generally seen as more “aesthetically pleasing” than galvanised steel – thanks to its gleaming appearance, but it can be more costly than galvanised steel.

Uses of stainless steel

  • High integrity ductwork
  • Food processing equipment
  • Pharmaceutical manufacturing equipment
  • Aerospace engine components
  • Kitchen appliances
  • Certain types of fasteners

Uses of stainless steel

  • DW114 ductwork
  • Automotive components
  • Some types of fasteners
  • Structural beams
  • Metal cabinetry
  • Railing
  • Walkways
  • Traffic signs
  • Electric poles

Galvanised vs stainless steel – Which is better?

One type of steel can sometimes be better than the other, depending on various factors such as its application, cost, and much more. Let’s compare galvanised steel with stainless steel over a number of factors.

1. Durability

Stainless steel is stronger than galvanised steel due to its tensile strength – though this can vary based on the elements combined to create stainless steel. This is why it’s often preferred to use in ductwork and in industrial applications within construction.

2. Heat conduction

Both stainless steel and galvanised steel conduct heat similarly. However, when dealing with galvanised steel, the melting point of zinc must be factored in. If it overheats, there’s a risk of causing a fire, so it isn’t a first choice in temperature-critical environments.

3. Weld

Both galvanised steel and stainless steel can be welded. While welding galvanised steel (steel coated with a zinc-rich layer) to stainless steel, it’s crucial to remove zinc during the weld, otherwise, this can become brittle and crack along the zinc penetration line – ruining your weld – no matter which type of weld you perform.

4. Commercial cost

Stainless steel is typically more expensive than galvanised steel because of a variety of different factors – including what it’s treated with. However, if you have specific requirements and require decent longevity and ease of welding, then stainless steel may be the way to go. 

Galvanised vs stainless steel – which should I choose?

Galvanised steel is great for small-budget projects, or when working with chlorinated water. It’s great for projects that require outdoor use, such as outdoor ducting and ventilation, frames, roofing and the like.

On the other hand, stainless steel is perfect for welding and has much better strength and corrosion resistance – making it perfect for fabrication projects – particularly large ones.

Ready to chat ductwork for your business? Contact Airmatic to find out more about our stainless steel and galvanised ductwork solutions.

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