Dynamic duplex materials: strong and sustainable

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.

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.

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.

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. 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 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. 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 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.