Duplex Pipe was originally developed in Sweden back in the 1940's. DuplexPipes were originally created to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids.
Duplex steel offers excellent resistant to corrosion and very high mechanical strength. The high corrosion resistance of duplex steel ensures significantly more uptime than carbon steels and conventional stainless steels, while the mechanical strength allows for lighter constructions, more compact system design and less welding.
Called Duplex Pipe because of its mixed microstructure with about equal proportions of ferrite and austenite, duplex steels are a family of grades, which range in corrosion performance depending on their alloy content. The chemical composition based on high contents of Cr and Mo, improves intergranular and pitting corrosion resistance, respectively. Additions of nitrogen can 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 steels.
These grades are designed to offer a super combination of heat resistance, high temperature corrosion resistance, toughness and strength, and are used in the world's most technically demanding industries.
A nickel-chromium alloy with good oxidation resistance at higher temperatures. With good resistance in carburizing and chloride containing environments. Our inconel is non-magnetic, has excellent mechanical properties and a combination of high strength and good workability and is readily weldable.
It offers improved resistance to stress corrosion cracking, pitting and crevice corrosion. With a similar ductility to an austenitic steel though duplex steel has a higher tensile strength and twice the yield strength.A duplex steel has a ductile/brittle transition at approximately -50 C. Duplex steel has a mixed microstructure of austenite and ferrite and therefore combines the best properties of austenitic and ferritic steel. It is characterised by high chromium (19-28%), molybdenum (up to 5%) and lower nickel contents than austenitic steels. Duplex stainless alloys have high corrosion resistance properties similar to austenitic type grades with good resistance to chloride stress corrosion cracking. It is more impact resistant than ferritic stainless types, embrittlement can occur with prolonged use at temperatures above 300 C.
The important elements in steels can be classified into ferritisers and austenitisers. Each element favours one structure or the other:
Ferritisers - Cr (chromium), Si (silicon), Mo (molybdenum), W (tungsten), Ti (titanium), Nb (niobium)
Austenitisers - C (carbon), Ni (nickel), Mn (manganese), N (nitrogen), Cu (copper)
Grade 430 has a predominance of ferritisers and so is ferritic in structure. Grade 304 becomes austenitic mainly through the use of about 8% nickel. To arrive at a duplex structure with about 50% of each phase, there has to be a balance between the austenitisers and the ferritisers. This explains why the nickel content of duplex steels is generally lower than for austenitics.
