Description
Super-Duplex Stainless Steels and their characteristics
The first-generation Duplex stainless steels were developed more than 70 years ago in Sweden for use in the sulfite paper industry. Duplex alloys were originally created to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids. Called Duplex because of its mixed microstructure with about equal proportions of ferrite and austenite, Duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content. The term “Super-Duplex” was first used in the 1980’s to denote highly alloyed, high-performance Duplex steel with a pitting resistance equivalent of >40 (based on Cr% + 3.3Mo% + 16N%). With its high level of chromium, Super-Duplex steel provides outstanding resistance to acids, acid chlorides, caustic solutions and other environments in the chemical/petrochemical, pulp and paper industries, often replacing 300 series stainless steel, high nickel superaustenitic steels and nickel-based alloys.
The chemical composition based on high contents of chromium, nickel and molybdenum improves intergranular and pitting corrosion resistance. Additions of nitrogen promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate
strength values without impairing toughness. Moreover, the two-phase microstructure guarantees higher resistance to pitting and stress corrosion cracking in comparison with conventional stainless steels.
Applications of Super Duplex
Super duplex is particularly suited for the following applications:
- Heat exchangers, tubes and pipes for processing gas and oil
- Pipes in processes containing chlorides
- Cargo tanks – piping for chemical tankers
- Shafts, rotors and hydraulic lines
The high strength and low corrosion of super duplex means it is widely used in the following industries
- Petrochemical
- Water desalinisation
- Chemical processing
- Marine and shipping
- Oil and Gas production
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