Primary vs Secondary Steel: What’s the Difference?

Steel is the most commonly used metal in the world, with a huge range of applications across construction, manufacturing and engineering. An alloy of iron and carbon in its simplest form, steel has a high strength to weight ratio, and is an incredibly versatile, durable, corrosion-resistant, low-maintenance material. It’s also infinitely recyclable, making it a more environmentally friendly option. 

Steel’s chemical and physical properties make it suitable for a range of uses in commercial and domestic architectural design, from warehouses and sporting arenas to homes and high-rise buildings, as well as in transport, tools and machinery, and home appliances, to name a few. 

While there are over 3,500 different types of steel in existence, they typically fall into two main categories – primary and secondary. They both have different properties, uses and benefits, so it’s important to understand the difference so you can make the right call for your next project. In this blog, we explore the need-to-know basics so you can make informed decisions about what type of steel you need, and when. 

What is primary structural steel? 

Primary structural steel forms the main frame of a building or structure to which the rest of the components attach. It must withstand the vertical weight of the structure itself and the changing ‘live’ loads when it’s in use, such as people and objects. 

Example of steel beams on the ceiling of a building

Uses 

Primary steel is used for structural elements like building frames, beams, columns, rafters and girders that form the main frame of the structure when bolted or welded together, 

It’s often used for some of the bolts and clips themselves, as well as certain architectural features like mezzanine floors and steel staircases. Our custom-made stainless steel staircase for a contemporary newly built home in Swansea is just one recent example in our portfolio.  

Elsewhere, primary steel is widely used for storage and handling solutions like steel stillages and steel cages. 

Process 

Primary and secondary steelmaking processes differ somewhat. Primary structural steel is usually made with high-strength, low-alloy (HSLA) steel.  

The process is called the Basic Oxygen Furnace (BOF) method, or basic oxygen steelmaking, and uses a blower or furnace to force oxygen into the molten iron, reducing its carbon content. Swiss engineer, Robert Durrer, invented this method in 1948 and around 70% of steel is still made this way today.  

Pros:  

  • Fewer impurities mean it has high tensile strength and can withstand heavy loads 
  • Durable and long-lasting – resistant to harsh environments, decay and pests 
  • Easy to install, reducing time and labour costs (pre-fabrication can reduce assembly times further) 
  • Recyclable and environmentally friendly 
  • It’s versatile and easy to fabricate to meet specific design requirements


    Cons:
     

  • More costly than secondary steel   
  • The steelmaking process uses metallurgical coal and is therefore more carbon-intensive 

 

What is secondary steel? 

Secondary steel supports primary structural steel and is normally used for smaller more functional components of a structure or machine.  

Uses 

Secondary steel is typically used where structural steel isn’t required and provides support to the main frame. Typical uses include brackets, joists, stabilisers, struts, bracing, headers and jams. Builders and manufacturers also use it to create studs, tracks and connectors that can attach roofing, walls and other interior elements to the main frame. 

Secondary steel is also used to create functional interior components like steel stairs and steel gutters, as well as larger building features such as a steel canopy, steel platform or steel walkway. 

custom staircase built by CSM

Restaurant with CSM custom staircase

Process 

Secondary steelmaking typically uses an electric arc furnace to reduce the scrap iron. It’s then blended with carbon and transformed into steel. This steelmaking process creates large yields of steel and is capable of producing around 100 tons every 40 to 50 minutes. 

Pros  

  • Cheaper to produce than primary steel and therefore more cost-effective for smaller components  
  • Recyclable and environmentally friendly 
  • Uses steel scrap, reducing the need for new materials to be mined and the associated environmental impact 
  • Steelmaking process less carbon-intensive than primary structural steel 
  • Easy to install, reducing time and labour costs  
  • It’s versatile and easy to fabricate to meet specific design requirements 

Cons 

  • Impurities make it more susceptible to weakening, cracks and fractures over time  
  • Not compliant with certain building codes – some areas stipulate that construction projects should only use primary steel 

 

How to choose the right steel for your project 

From a building frame to a steel cage, a supporting bracket to a steel gutter, primary and secondary steel play very different but equally important roles.  

While their unique properties suit them to different applications, your project will likely require a combination of both primary and secondary steel structures—the strong, durable, heavy-duty bare bones, and the smaller, supportive, and more functional components.  

Whether you’re looking to discuss your primary and secondary structure requirements or need help selecting the right type of steel, the team at CSM are on-hand to help with over 30 years of expertise and a huge range of custom steel fabrication projects under their belt.  

Click here to learn more about secondary steel or get in touch to discuss your next project.  

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