Dynamic duplex materials: strong and sustainable

The pool reactor from the KIMA fertilizer plant in Aswan, Egypt. The plant was designed based on Stamicarbon’s technology. Photo provided by Stamicarbon

Even the most cautious projections for the market growth of duplex stainless steel suggest that its use will substantially increase in coming years. Its high strength, low maintenance, and resistance to pressure, corrosion and erosion make it the ideal choice for a number of applications in the process industries, while its low weight-to-strength ratio make it suitable for a number of applications in architecture, street furniture and water management. Another reason for its appeal is that 3D-printing is being extended to duplex grades.

By James Chater

Growth rates

How fast is the duplex stainless-steel sector growing, and what is its market share compared with other stainless-steel types? The answers to both questions depend on whom you ask, but, in terms of absolute growth, the answer is clear: the demand for duplex is stronger than it ever has been and will increase even more in future years. Data Bridge Market Research cautiously projects a CAGR of 3.2% between 2022 and 2030, whereas Research Nester more optimistically forecasts a CAGR of over around 7.7% from 2023 to 2035, with revenue more than doubling over the period (1).
Forecasting demand rests on certain assumptions about the growth rate of the various markets. The main driver of demand is generally agreed to be oil & gas, especially offshore, so the projected increase in demand depends on how much growth is expected from this sector, a crucial question given the need to curb CO2 emissions and transition to green energy. That said, duplex finds many uses in solar and wind energy, and in biogas pants, which often require highly corrosion resistant tanks. Moreover, the demand from architecture & construction, especially in the Asia Pacific region, and from a wide range of other industries including petrochemical, paper & pulp, and desalination, inclines one to be optimistic about future demand for duplex.

What is the maximum operating temperature for duplex?

SSW October 2022 page 21
SSW October 2022 page 21

Most users know that at above 250 °C, duplex grades can be affected by embrittlement caused by spinodal decomposition. But is 250 °C an absolute limit? What is the effect of exposure time, and do lean and super duplex behave differently? A technical paper by Outokumpu with the above title was published by Stainless Steel World October 22. Please click here to go directly to this article.

As for the growth of duplex compared with other stainless-steel types, the more optimistic projection of 7.7% for duplex is slightly above the average for all stainless-steel types combined (CAGR growth projections for stainless steel market size vary from 6.8% between 2023 and 2029 and 5.5% from 2023 to 2033.) (2). This would suggest that duplex has a slight edge over other stainless types, including austenitics (which one market report projects to grow 6.2% between 2023 and 2029) (3). To this we may add anecdotal evidence suggesting duplex is gaining over austenitics: one often reads that, at the beginning of a project, end users expect to apply an austenitic grade but are later persuaded by a supplier to use a duplex grade instead. For instance, when the City of Barcelona planned to build stainless steel tram shelters, they specified type 316 in the tender but ended up applying Stalatube’s LDX 1.4162.

The City of Barcelona built 22 tram shelters, for which Stalatube’s highstrength LDX 1.4162 lean duplex was used, instead of the 316 austenitic grade mentioned in the invitation for tenders.
The City of Barcelona built 22 tram shelters, for which Stalatube’s highstrength LDX 1.4162 lean duplex was used, instead of the 316 austenitic grade mentioned in the invitation for tenders.
A biogas plant in Japan, equipped with a 450-kW cogeneration power pant, with tanks constructed in duplex grades 1.4062, 1.4162 in the lower rings, and 1.4462 for the top rings which are in contact with the biogas. Photo by Weltec Biopower.
A biogas plant in Japan, equipped with a 450-kW cogeneration power pant, with tanks constructed in duplex grades 1.4062, 1.4162 in the lower rings, and 1.4462 for the top rings which are in contact with the biogas. Photo by Weltec Biopower.

Advantages

The per-weight price of a duplex grade may exceed that of austenitics, but its strength allows reductions in weight and bulk that more than compensate. The lighter structure and thinner walls make transportation and installation easier. Weight savings are an important consideration on oil platforms, for instance on walkways where salt corrosion occurs. Outokumpu has claimed that applying duplex to replace Hot-Dipped Galvanized (HDG) steel for walkway gratings in marine environments could enable weight reductions of up to 40% (4). Duplex combines super corrosion resistance with erosion resistance, making it very suitable for applications where solids or slurry are being handled (wastewater treatment, pulp & paper, desalination). Superior corrosion resistance makes the application of duplex highly advantage in locations that are difficult to inspect. Longer service life and reduced maintenance means less offline time and, in the case of bridges, less interruption to traffic.

Working with duplex

Choosing a duplex grade instead of an austenitic one can be risky if you do not know how to work with these materials, as they are harder and stronger. Fortunately, there is no lack of advice on-line to learn the distinctive but not very difficult art of working and welding duplex. One of the more recent guides is downloadable at: https://stalatube.com/2021/09/03/lean-duplex-blog-series-2-working-with-duplex-stainless-steel. Downloadable brochures are provided by the Nickel Institute, “Practical guide to using duplex stainless steels”, 2nd edn, 2020), ArcelorMittal (“Duplex stainless steels welding guidelines”, 2019), and the International Molybdenum Association (“Practical guidelines for the fabrication of duplex stainless steels”, 3rd edn, 2014).

Applications

This is why duplex grades are finding ever more uses across a wide range of industries, including oil & gas, chemical & petrochemical, food & drink, paper & pulp, water management (including desalination), architecture & street furniture, and bridges. Let us examine some of these.
The oil & gas, petrochemical and chemical industries remain the primary drivers for duplex stainless-steel demand. After the Covid lull, all these industries are booming.
Duplex is used in subsea umbilicals in offshore installations, and several orders have recently been placed with suppliers such as Alleima and Tubacex. In a first of its kind, a gas project in Oman applied duplex type 2205 for a 24-inch pipeline that is 34km in length. The line pipe is coated and buried to ensure its external corrosion protection. Heat exchangers in chemical and petrochemical plants require duplex grades. Mayr & Wilhelm recently chose Alleima’s duplex SAF™ 2205 stainless steel for the tubing of its shell-and-tube heat exchanger.

Alleima duplex SAF™ 2205 stainless steel heat exchanger tubing, used in chemical and petrochemical plants.
Alleima duplex SAF™ 2205 stainless steel heat exchanger tubing, used in chemical and petrochemical plants.
3D-printed impeller in Osprey® 2507 superduplex, used in harsh offshore environments in the oil & gas business. Made by Sandvik Additive Manufacturing and the BEAMIT Group.
3D-printed impeller in Osprey® 2507 superduplex, used in harsh offshore environments in the oil & gas business. Made by Sandvik Additive Manufacturing and the BEAMIT Group.
Mannesmann Stainless Tubes DMV 29.7 super duplex provides solutions in seamless tubing and pipe for heat exchanger applications.
Mannesmann Stainless Tubes DMV 29.7 super duplex provides solutions in seamless tubing and pipe for heat exchanger applications.

Superduplex, such as DMV25,7N from Mannesmann Stainless Tubes continues to be the leading material selected not only for conventional oil & gas applications but also CCUS (carbon capture, utilisation, and storage) developments.
A special subtype of petrochemical is urea and ammonia production, used in fertilizers. The leading technological provider is Stamicarbon, which is building a new generation of low-energy plants, in the USA, Sub-Saharan Africa, China’s Jiangxi province, and other places. The high-pressure equipment for these plants is in superduplex stainless steel Safurex®; whilst the latest developments from Mannesman Stainless Tubes of DMV 29.7 super duplex provide solutions in seamless HX tubing and pipe.

The DESMI scrubber-grade pump. The DESMI exhaust gas cleaning systems (EGC systems), known as scrubbers, reduce sulphur content from exhaust gas. The pumps are made in superduplex to handle high temperatures and severe corrosion.
The DESMI scrubber-grade pump. The DESMI exhaust gas cleaning systems (EGC systems), known as scrubbers, reduce sulphur content from exhaust gas. The pumps are made in superduplex to handle high temperatures and severe corrosion.

Another area in which duplex grades are required is CCS (carbon capture & storage) technology. This involves separating the CO2 from other combustion gases, compressing and transporting it to the sequestration location, and inserting it into the subsurface reservoir. To withstand the acidic conditions, only the highest grades can be used, including duplex or superduplex for pump and pipe connections.
Finally, duplex stainless steel’s weight properties and low maintenance make it ideal for any load-bearing functions (architecture, cranes, bridges) or where a favourable strength-to-weight ratio is required. In water management, duplex’s combination of corrosion/erosion resistance and high strength comes into its own. An example of this is sluice gates, which regulate water flow in rivers and estuaries, where duplex is increasingly being adopted. Flood risks due to global warming require sluice gates that are taller and stronger. Industeel supplied 36 tonnes of duplex 2205 plate for eight sets of sluice gates across the river Couesnon near Mont St-Michel. The plate was used to clad the gates’ coated carbon steel frame. The Slussen lock in Stockholm, Sweden, serves to protect the local population from flooding and separate drinking water from brackish water. It is located in a heavily travelled neighbourhood in the city centre. As part of a project to widen the discharge canals, new sluice gates are being installed, made of 2205 duplex supplied by Outokumpu. They are larger than the gates they replace, allowing more water to be evacuated in the event of flooding. Also in Sweden, the rotten wooden sluice gates at Gårda Damme, Gothenburg, were replaced by five sluice gates built from Outokumpu’s 2404 duplex grade.

Conclusion

We have seen that, when strength and resistance to extreme corrosion and high pressures are required, standard duplex and superduplex grades are increasingly seen as ideal, even indispensable; and that in water management and architectural projects, standard and lean grades are becoming more popular. Duplex is also likely to become more mainstream as it is increasingly adopted for the 3D and WAAM manufacturing processes.

3D printing

Additive manufacturing or 3D printing has long been applied to nickel and titanium alloys to make aircraft parts and prosthetic devices. Now duplex is catching up, and there are clearly opportunities for components such as heat exchangers, offshore platforms, chemical processing equipment, boilers, and pressure vessels. Alleima (formerly Sandvik) collaborated with BEAMIT to produce superduplex impellers for use in offshore installations. The Japanese construction company Takenaka Corp. Worked with MX3D to produce a duplex structural connecter using the WAAM (Wire Arc Additive Manufacturing) method. In April 2022 3D Metalforge announced it had developed printing parameters for additive manufacturing in superduplex. Also, ADDere has developed laser-wire additive manufacturing systems, with a laser heating and closed-loop control system, which allows for precise heat control across the entire 3D printing process.

About this Featured Story

This Featured Story appeared in Stainless Steel World November 2023 magazine. To read many more articles like these on an (almost) monthly basis, subscribe to our magazine (available in print and digital format) – SUBSCRIPTIONS TO OUR DIGITAL VERSION ARE NOW FREE.

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