The microstructure of duplex seamless pipe is approximately 50% ferrite (body-centered cubic structure) and 50% austenite (face-centered cubic structure) crystal structure. The two phases coexist as a stable mixture, but this is different from two-phase alloys, where one of the two phases appears as a precipitate. The alloying elements in duplex stainless steel tubes are ferritic (eg chromium, silicon, molybdenum) or austenitic (eg carbon, nickel, nitrogen), which means that they favor the formation of the ferritic and austenitic phases, respectively. As a professional duplex stainless steel pipe manufacturer in China, Yuhong Group provides quality super duplex tubing solutions.
DIFFERENT TYPES OF DUPLEX STEEL PIPE
Duplex stainless pipe are part of the stainless steel family. Duplex( austenitic-ferritic) means their metallurgical structure consists of two phases. Compare with the normal 304 316 stainless steel, they can provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion, and higher strength. And it has higher Chromium 20%-28%, and lower nickel, up to 9% and 0.05-0.50% than austenitic stainless steel, which gives good cost benefits.
DUPLEX STAINLESS STEEL PIPE GRADES
The most widely used is ASTM ASTM (American Society for Testing and Materials International), and ASME(American Society of Mechanical Engineers). And the general standard for the duplex stainless steel seamless or welded tube or pipe can be ASTM A789/ASME SA789, ASTM A790/ASME SA790, ASTM A928/ASME SA928. They give very detailed requirements on the material, test, and others.
DUPLEX SS SEAMLESS PIPE APPLICATIONS
Pipe duplex is known for its excellent combination of good mechanical properties and high corrosion resistance. The wide range of advantages means that it can be used in many different applications: for example, chemical processing, transport, and storage in the industrial sector, such as seawater heat exchange for high chloride environments and production of chemical containers. The SS duplex pipe can also be applied to pipelines for oil and gas production and transportation, such as oil and gas exploration and offshore drilling platforms.
Nickel alloys are the most outstanding and useful materials in the manufacture of pipes and tubes for industrial applications. Their inherent properties make them versatile. Nickel alloys are particularly resistant to corrosion and can be used in high-temperature environments. Because nickel alloys are highly ductile, they can be processed very efficiently into pipes and tubes while maintaining the corresponding strength. This makes them ideal for heat exchangers in chemical processing. Nickel-based tubing is also used in steam generators, aircraft systems, and oil and gas extraction.
DUPLEX STEEL PROPERTIES
At elevated temperatures, mechanical properties such as strength and toughness, as well as corrosion resistance, of dual-phase steels are reduced. This phenomenon is called embrittlement. The worst temperature at which embrittlement occurs is 475 °C; however, the formation of α' phases can begin to occur at temperatures as low as 300 °C, which limits the maximum service temperature for dual-phase steels.
Typical duplex pipe material has higher yield strengths than typical martensitic, austenitic, and ferritic stainless steels. However, since intermetallics begin to precipitate above 300 °C and become brittle near cryogenic temperatures, their operating temperature range is narrow.
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