The dual character found in the alloy’s microstructure gives duplex steel pipe its name. Duplex Steel Seamless Pipes can be utilized in a welded condition and have good mechanical properties. The Seamless Duplex Pipe is considered superior to austenitic alloys ASTM A312 TP304 or TP316 because it offers much greater corrosion resistance. Comparing the Duplex Steel Welded Tubes to the typical austenitic stainless steel grades, the tensile strength is significantly higher. The offshore oil and gas industry nearly exclusively uses duplex steel pipes. Duplex Pipe’s lower nickel content is what makes the metal affordable.
Properties of Duplex Steel Pipes
Compared to austenitic stainless steels, duplex steel pipes have higher chromium levels (19–28%), higher molybdenum contents (up to 5%), and lower nickel contents. The two most popular duplex stainless steels are 2507 (25% chromium, 7% nickel) and 2205 (22% chromium, 5% nickel); 2507 is also referred to as “super duplex” due to its superior corrosion resistance. A metal with a two-phase metallurgical structure that benefits from both microstructures’ qualities is produced by combining ferritic and austenitic grades.
Advantages of Duplex Steel Pipes
- Tenacious & Ductile: Although they are not as soft as austenitic grades, duplex stainless steel pipes are more ductile and robust than ferritic grades.
- Strength: The strength of duplex steel pipes is nearly double that of conventional austenitic or ferritic stainless steel products.
- Corrosion Resistance: As with all stainless steel grades, the main factors affecting corrosion resistance are the composition of the stainless steel pipe, with the amounts of chromium, molybdenum, and nitrogen being the most significant. Duplex Steel Seamless Pipes have a very high resistance to stress corrosion cracking and are incredibly corrosion resistant, even in conditions with chloride and sulfide (SCC). Tensile strain, a corrosive environment, and a high enough temperature are necessary conditions for SCC, a particular type of corrosion.
- Weldability: Although they are not quite as easily welded as the austenitic grades, duplex steel pipes typically have high weldability and can be utilized with all conventional welding techniques.
- Heat Resistance: Compared to austenitic steels, duplex steel pipe has a higher heat conductivity and a lower thermal expansion. Due to its superior ductility at low temperatures compared to ferritic grades of steel, duplex grades of steel can be used down to at least -50°C with ease.
- Low cost: The nickel and molybdenum content of duplex steel pipes is lower than that of austenitic steel pipes. Duplex stainless steels can be more reasonably priced due to their reduced alloy content. Furthermore, duplex stainless steel’s thickness may be lowered due to its improved yield strength.