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Called Duplex Pipe because of its mixed microstructure with aboutequal proportions of ferrite and austenite, duplex stainless steels are afamily of grades, which range in corrosion performance depending on their alloycontent. The chemical composition based on high contents of Cr and Mo, improvesintergranular and pitting corrosion resistance, respectively. Additions ofnitrogen can promote structural hardening by interstitial solid solutionmechanism, which raises the yield strength and ultimate strength values withoutimpairing toughness. Moreover, the two-phase microstructure guarantees higherresistance to pitting and stress corrosion cracking in comparison withconventional stainless steels.

Duplex is a stainless steel made from a mixture of austenite andferrite phases. Like most austenitic stainless steels, duplex has a strongresistance to corrosion, similar to those of a Type 304 and 316.

Unlike similar steels, duplex also displays an improved resistanceto localized corrosion, particularly pitting, crevice corrosion and stresscorrosion cracking. And because duplex has a lower nickel and molybdenumcontent than other austenitic stainless steels, it can prove a more costeffective option due to a lower alloying content.

Due to its Ferritic qualities, duplex steel also shows very goodresistance to stress corrosion cracking when compared to standard austenitic. In some cases, the strength of duplex steelcan be up to double that of the most commonly used grades of stainless steel.

Duplex becomes brittle at extreme temperatures so its use isnormally restricted to a maximum temperature of 300 degrees. Duplex also showssigns of embrittlement at –50 degrees.

Benefits:
Stronger than 300 series stainless steel which also brings weightadvantages.
Cheaper than some stainless steels.
High resistance to pitting, crevice corrosion and stress corrosioncracking.
Higher heat conductivity and lower thermal expansion thanaustenitic steels.

Uses:
Pipes for production and transportation of oil and gas
Structural and mechanical components
Heat exchangers
Cooling pipes
Cargo vessels and containers
High strength wiring