Duplex stainless steel tubes have a microstructure that is 50% ferritic and 50% austenitic. This composition gives them better strength than ferritic or austenitic steels.

Duplex stainless steel tube is a very useful metal that is widely used around the world. It gets its name from the fact that it is composed of two different grades of metal.

Essentially, duplex steel is a Fe-Ni-Cr alloy with a two-phase ferritic-austenitic stainless steel microstructure at room temperature.

Duplex steels are characterized by high chromium content (19-28%) and molybdenum content of up to 5%, while the nickel content is lower than that of austenitic stainless steels. The most commonly used Duplex stainless steel tubes are 2205 (22% Cr, 5% Ni) and 2507 (25% Cr, 7% Ni); 2507 is called "super duplex" because of its higher corrosion resistance.

The advantage of combining ferritic and austenitic steel grades is that the resulting metal has a metallurgical structure consisting of two phases and therefore benefits from the properties of both microstructures.

These properties make duplex steels highly sought after in heavy industries such as the oil and gas nuclear industry and chemical processing.

Benefits of Duplex stainless steel tube

Duplex stainless steel tubes offer a range of advantages, such as

1. Strength: Duplex stainless steel tubes are approximately twice as strong as ordinary austenitic or ferritic stainless steels.
2. Toughness and ductility: Duplex stainless steel tubes are tougher and more ductile than ferritic stainless steels, although they are not as tactile as austenitic stainless steels.
3. Corrosion resistance: As with all stainless steels, corrosion resistance is largely dependent on the composition of the stainless steel, with the amount of chromium, molybdenum and nitrogen being the most important. Duplex stainless steel tubes are extremely corrosion resistant and exhibit very high resistance to stress corrosion cracking (SCC) even in chloride and sulfide environments, SCC is a type of corrosion that occurs in the presence of a specific set of factors: tensile stress, a corrosive environment and sufficiently high temperatures.
4. Heat Resistance: Duplex stainless steel tubes have higher thermal conductivity and lower thermal expansion than austenitic steels. Duplex grades can easily be used at temperatures down to at least -50°C because they have better ductility than ferritic grades at low temperatures.
5. Cost: Duplex stainless steel tubes have lower nickel and molybdenum content than austenitic stainless steels. This lower alloy content means that Duplex stainless steel tubes are less costly. In addition, the thickness of Duplex stainless steel tube can be reduced because of its higher yield strength. Thinner products mean that weight can be significantly reduced.
6. Weldability: Duplex stainless steel tubes tend to have good weldability and can be welded using all standard welding processes, although they are not as easy to weld as austenitic stainless steels.

The wide range of advantages of Duplex stainless steel tubes means that they can be used in many different applications, such as: chemical processing, transportation and storage; pipelines for oil and gas production and transportation; oil and gas exploration and offshore drilling rigs; oil and gas refining marine environment; pollution control equipment; pulp and paper industry; chemical plants; structural and mechanical components; heat exchangers; and cooling tubes.