The oil and gas industry and pulp and paper industries were both important in the 1980s and 1990s as they were quick to see the benefits of duplex grades.
First lean duplex gradeThen in the late 90s, I became project manager for development of a new duplex grade, Forta LDX 2101.
This was the first commercially successful lean duplex grade, named for its relatively low use of alloying elements like nickel and molybdenum. These are costly and nickel prices fluctuate widely. Therefore, the introduction of Forta LDX 2101 and other lean duplex grades provided engineers with stainless steel that is affordable and predictable in price, has high strength and good corrosion resistance.
Today, Forta LDX 2101 is well established and we sell it in significant volumes for storage tanks, domestic heating, bridges and applications in the chemical, and pulp and paper industries, so it was a big achievement for me to be named on the patent as one of its developers.
Commercial success from pulp and paper industryLater in my carrier I became the Managing Director (MD) of Outokumpu Prefab, a subsidiary that focuses on semi-finished products bought by pulp and paper machine manufacturers.
As MD, I had overall responsibility for quality, commercial success and production. However, to focus on the duplex grades, their main attraction for paper machines is high strength and corrosion resistance. Duplex grades are used widely for pulp processing and in paper machines.
High strength enables lighter construction and less material, this is important for pulp digesters as customers need less material to build digesters and other storage or processing vessels. As a result, the construction is lighter, with savings in fabrication and welding, as well as civil and structural support.
The benefit of corrosion resistance is that paper manufacturers can have very long production cycles with no need to stop for maintenance or repair.
The suction rolls for paper machines are an interesting application as there are very high demands on their performance. The rolls have the job of extracting the water from pulp and they rotate fast in constant contact with the wet pulp..
The roll shells are fabricated as large cylinders with up to one million holes drilled through their outside walls. During the paper making process, pulp enters the body of the paper machine as a slurry containing water and paper fiber. A vacuum inside the roll draws the water into the cylinder, leaving the fibers on the roller surface to form paper.
With the wrong material for a cylinder, it’s very easy for cracks to form and run between the holes, eventually causing the entire cylinder to fail due to corrosion fatigue. Duplex stainless steel is ideal for these rolls as it has good fatigue resistance. Forta LDX 2101 has become a popular material for suction roll shells and it was nice to see the grade we developed at R&D becoming an important part of Outokumpu Prefab´s business.
Key developmentsLooking back, there have been five generations in the development of duplex stainless steel. The first was the development of the first two grades at Avesta and their adoption in the 1930s.
Then we saw the first modern duplex grade for Forta DX 2205 in the late 1970s. With time, this grade was developed to include more nitrogen and we had a better understanding of how to achieve the desired mix of austenite and ferrite. The big achievement of the first modern grades was that you can maintain the ratio between these two phases even after welding.
That meant that duplex grades could be used to create large welded structures and be used in more applications. Because of that, it was adopted widely in oil and gas and other industries during the 1980s.
Then our competitor Sandvik developed the first super duplex grade and we bought a licence to supply it to offshore oil and gas operators, who used it for seawater systems and other applications with a highly corrosive environment.
Then in 2002, we introduced the first lean duplex grade, which was designed to be affordable for general use, with high strength and corrosion resistance that is similar to the standard austenitic grades.
The fifth and most recent development is the development of more formable duplex stainless steels for applications that need complex components that provide high strength and corrosion resistance.
The challenge of developing new gradesWhen you start developing a new grade, you have a good idea of what you want to achieve but you typically don’t start with the exact composition you’ll eventually choose. It’s a matter of using a test matrix to evaluate different compositions that might give you the properties you want to achieve.
The most important challenge is to understand and anticipate the market need and communicate the benefits to the market. A new grade of stainless steel will only be a success when you have a customer that wants to buy what you’ve developed.
We also face a learning curve with new grades during production. When you’re working in the lab, it’s difficult to envisage full-scale production in the melt shop or the rolling mill. There are many process parameters which may need to be customized for the new grade and for example, high strength materials may be a challenge for rolling and coiling equipment.
Sustainability and the futureI’ve seen large growth in the market for duplex grades during my career, but the market is still relatively small compared with the entire market for stainless steel. Looking to the future, sustainability is an important trend that will most likely drive adoption of duplex grades.
One key to making the most of new opportunities will be to support customers with data and advice from our experience and offer testing in new environments.