Poul-Erik Arnvig, Vice President for Product Management in Europe, sees the market being driven by sustainability: “Today, duplex grades are a small part of the total stainless steel market, with total global demand of less than one million tonnes per year. That compares with demand of 45 million tonnes for all types of stainless steel and one billion-tonnes for carbon steel.
He continues: “There’s a lot of opportunity for growth. In almost every application where you’re using a standard austenitic grade like 304 or 316, it could be replaced by a duplex stainless steel based on the total lifecycle cost advantage.”
An ideal material for bridges
Elisabet Alfonsson, a Product Manager who has led the development of duplex grades over three decades said: “We’re seeing a change of mindset with sustainability. New markets and new applications are going to emerge based on environmental sustainability, long life and the need to reduce the carbon footprint. Bridges and structures have a lot of potential right now as local authorities want bridges that don’t need regular maintenance, where the materials don’t degrade and will provide a long lifetime.”
Peder Claesson, Head of Project Sales agreed: “Many bridges in Europe built after the second world war are now suffering corrosion and need a lot of maintenance. Duplex stainless steel is often cheapest in the long run for bridges and also as rebar in reinforced concrete, where a duplex grade can extend the life of a bridge from 80 to 300 years.
Strength and safety
Peder continued: “Duplex stainless steel is ideal wherever you need high strength and long life. For example, in storage tanks, the walls of train carriages or in sedimentation tanks in the mining industry. There’s also a lot of opportunity for wind turbines. Coated carbon steel is fine for windmills if they only need a life of 15 years but when you want renewables to be more sustainable, you need a longer life so there’s opportunity for duplex grades to build wind turbines.
“We might see more use of super and hyper duplex grades in the chemical industry and gas pipelines in hot coastal climates, where high salt concentrations and high temperatures can create extremely corrosive environments.
“There could also be potential for duplex stainless steel to replace glass reinforced plastic (GRP) gratings to provide fire resistance or to provide a long life.”
Making the most of fabrication and welding
Erik Schedin, a researcher into design and fabrication, agrees that strength is important for new applications: “Another example where strength is important is in pressure vessels. With a duplex material, the total cost of a pressure vessel is often cheaper than building it from an austenitic grade. However, customers need to learn how to work with it.
“One area where they need support is how to weld duplex grades, for example the energy input, filler material, shielding gas and the welder needs the right certification for working with duplex grades. Customers also need to remember that they’re handling the final surface quality from the start. Unlike carbon steel, you can’t paint over scratches or surface defects so you need to take care and use the right tooling.”
Replacement for carbon steel
Marie-Louise Falkland, a senior technical manager who has led production and research teams, sees potential for duplex grades to replace carbon steel: “Duplex grades are the most sustainable long-term alternative to painted and protected carbon steel in general engineering. They last a long time and don’t need repainting or shot blasting.”
Like Erik, she believes that education is key: “We need to educate the market as many people are still not aware of the benefits of duplex stainless steel. It’s our job to provide advice on how to select the right grade and how to work with duplex grades in fabrication and welding.
“We’re also working hard on R&D to produce the right data that proves the benefits of duplex grade so that standards authorities can help engineers benefit from the properties of duplex grades.”
A material for the future
Poul Erik Arnvig sums it up: “After 90 years of duplex stainless steel, the fact that the number of duplex stainless steel producers is growing shows that these grades are here to stay. Where we differ from other producers is our long legacy and expertise with duplex grades, going all the way back to the first grades in Avesta in 1930.
“We’re still working hard to pass that expertise on to our customers to help our them get maximum benefit. I’d always advise customers to try out a duplex grade.”
We are celebrating the 90 years of duplex stainless steel. Duplex stainless steel was originally developed by Outokumpu in Avesta, Sweden in 1930. As the original inventor of duplex we have both experience and expertise to take the material further.