[ Duplex ]
[ Duplex ]
According to online sources, the first duplex grades were developed by Avesta Ironworks( now Outokumpu) around 1930 i These products were sold to clients requiring a material that was less susceptible to intergranular corrosion. From these modest beginnings a whole family of duplexes were to emerge. For example, technological advancements led to grades with improved ductility and weldability, followed by duplexes that could resist intergranular corrosion. Later research resulted in the so-called super duplexes, characterised by high PRE values, as well as lean duplexes which, thanks to a careful balancing of alloying elements, offer good material properties in conjunction with price stability. More recent developments include duplex steels with superior forming properties. In addition to corrosion resistance, duplex is known for its beneficial strength-to-weight ratio. This feature could become increasingly important, as outlined by Stalatube’ s Tommi Purtilo in a recent article ii:“ This weight reduction is not just a matter of convenience; it has profound implications for various industries. Lighter components can lead to easier handling and installation, reduced transportation costs, and significantly improved carbon footprint. In applications where weight is a critical factor, such as in the aerospace, automotive, and mobile applications, the use of duplex stainless steel can result in substantial cost savings and improved efficiency.”
Supplier initiatives Steel producers continue to invest, innovate, and seek new uses for duplex.
Many shipping lines have recently placed orders for duplex chemical tankers. Illustrative image.
Last December for example, Alleima announced the local production of high-performance grades at its Mehsana plant in India, stating that:“ SAF™ 2906 is tailored for use in urea production plants, while SAF™ 3006, a versatile super duplex stainless steel, serves the chemical, petrochemical, refinery, and marine industries.” In the same month, Centravis officially launched NIKOPOLIUM ® NP 2205 and NP 2507, its next generation of duplex and super duplex stainless steel tubes engineered for extreme environments. Centravis indicated that the product combines high mechanical strength, exceptional resistance to pitting, crevice and intergranular corrosion, and a widened operating temperature window from – 60 ° C up to + 350 ° C“ outperforming standard duplex and super duplex steels while approaching the corrosion resistance of nickel alloys at a significantly lower cost”. Incidentally, the name NIKOPOLIUM pays tribute to the city of Nikopol, home of Centravis’ production facility.
In June 2025, Alleima expanded its advanced materials portfolio for urea with SAF™ 2906, a super duplex stainless steel designed to withstand the most corrosive environments.
Other news in the second half of 2025 came from Nippon Steel, announcing that its NSCarbolex TM Neutral duplex stainless steel pipes will be supplied to HH Stainless Pte Ltd, a major distributor in Singapore. Meanwhile, India’ s Shyam Metalics reported having added 904L super austenitic stainless steel grade and other duplex and super duplex steels to its portfolio. In June, Sverdrup Steel stressed the benefits of lean duplexes stainless
Expert Impressions:
Raymond Cordewener, R. Cordewener Management & Consultancy BV“ More dedicated duplex grades are entering the market. My personal question is whether these grades are really required as the normal duplexes are good enough.”“ The advantage of duplex grades for bridges near to or in the sea is the fact that you can build the majority in lean duplexes and use duplex or super duplex in the more severe environmental conditions. Maintenance costs of these bridges will be reduced drastically.”“ I am regularly consulted to advise on pressure vessel fabrication, with questions about anisotropy and welding. Heat treatment and quenching are sometimes specified but special attention is subsequently required in respect of rectification / recalibration of the shape. Note that in the majority of cases heat treatment is unnecessary; however, changing fixed mindsets is an uphill struggle.”
16 Stainless Steel World April 2026 www. stainless-steel-world. net