Duplex steel pipes are a popular choice for various industrial applications due to their unique combination of high strength, excellent corrosion resistance, and good weldability. They are used in industries such as oil and gas, chemical processing, and marine engineering, among others. In this blog, we will discuss duplex steel pipes and the grades of duplex steel pipes in the UNS standard.
What is Duplex Steel?
Duplex steel is a type of stainless steel that contains a two-phase microstructure consisting of both austenitic and ferritic grains. This unique microstructure provides duplex steel with excellent corrosion resistance, high strength, and good weldability. Duplex steel is commonly used in environments where conventional austenitic stainless steels would be prone to stress corrosion cracking and pitting corrosion.
What are Duplex Steel Pipes?
Duplex steel pipes are pipes made from duplex steel. They are available in a variety of sizes and dimensions and are commonly used for transporting fluids and gases in corrosive environments. Duplex steel pipes can withstand high temperatures and pressures and are known for their excellent resistance to corrosion and erosion.
What are Duplex Steel Seamless Pipe ?
Duplex steel seamless pipes are a type of duplex stainless steel pipe that are manufactured without any welding or joints. These pipes are created by piercing a solid billet of duplex stainless steel and then rolling it into a seamless pipe.
What are Duplex Steel ERW Pipe?
Duplex steel ERW (Electric Resistance Welded) pipes are made from duplex stainless steel material through the process of forming and welding. These pipes are produced using a high-frequency electrical current to create a weld between the edges of the steel strip or coil. The welding process used to manufacture ERW pipes makes them more cost-effective than seamless pipes.
Duplex steel welded pipes are made by joining two pieces of duplex steel using different welding techniques such as TIG, MIG, or submerged arc welding. These pipes have a welded seam running along their length and are available in various sizes and thicknesses.
Grades of Duplex Steel Pipes in UNS Standard
The UNS standard, also known as the Unified Numbering System, is a system for identifying metals and alloys. The UNS standard provides a unique identifier for each material, making it easier to find and compare materials across different countries and industries. The following are some of the grades of duplex steel pipes in the UNS standard:
UNS S31803: This grade is also known as duplex 2205 and is the most commonly used duplex steel pipe. It contains 22% chromium, 5% nickel, and 3% molybdenum.
UNS S32750: This grade is also known as super duplex 2507 and is a high-performance duplex steel pipe. It contains 25% chromium, 7% nickel, and 4% molybdenum, along with nitrogen, which provides it with superior corrosion resistance.
UNS S32760: This grade is also known as super duplex 32760 and is a highly corrosion-resistant duplex steel pipe. It contains 25% chromium, 7% nickel, and 3.5% molybdenum, along with nitrogen and tungsten.
UNS S32205: This grade is also known as duplex 2205 and is similar to UNS S31803. It contains 22% chromium, 5% nickel, and 3% molybdenum, along with nitrogen.
UNS S32550: This grade is also known as duplex 255 and is a high-strength duplex steel pipe. It contains 25% chromium, 5% nickel, and 3% molybdenum, along with nitrogen and copper.
Chemical Composition
Duplex steel is a type of stainless steel that contains a two-phase microstructure consisting of both austenitic and ferritic grains. The chemical composition of duplex steel pipes varies depending on the grade. The following table shows the chemical composition of some of the common grades of duplex steel pipes:
| Grade | Chemical Composition |
|---|---|
| UNS S31803 | 22% Chromium, 5% Nickel, 3% Molybdenum |
| UNS S32750 | 25% Chromium, 7% Nickel, 4% Molybdenum |
| UNS S32760 | 25% Chromium, 7% Nickel, 3.5% Molybdenum |
| UNS S32205 | 22% Chromium, 5% Nickel, 3% Molybdenum |
| UNS S32550 | 25% Chromium, 5% Nickel, 3% Molybdenum, 2% Copper |
Physical & Mechanical Properties
Duplex steel pipes have excellent physical and mechanical properties, making them suitable for various industrial applications. The following table shows the physical and mechanical properties of some of the common grades of duplex steel pipes:
| Grade | Density (kg/m3) | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) |
|---|---|---|---|---|
| UNS S31803 | 7700 | 620-880 | 450-550 | 25-30 |
| UNS S32750 | 7800 | 800-1000 | 550-800 | 15-20 |
| UNS S32760 | 7800 | 750-930 | 550-750 | 25-30 |
| UNS S32205 | 7700 | 620-880 | 450-550 | 25-30 |
| UNS S32550 | 7800 | 800-1000 | 550-800 | 15-20 |
Applications
Duplex steel pipes are widely used in various industries due to their excellent physical and mechanical properties. Some of the common applications of duplex steel pipes include:
Oil and gas industry: Duplex steel pipes are used for transporting oil and gas in corrosive environments.
Chemical processing industry: Duplex steel pipes are used for processing corrosive chemicals.
Marine engineering: Duplex steel pipes are used for transporting fluids in offshore platforms and ships.
Construction industry: Duplex steel pipes are used for building bridges and tunnels.
Conclusion
Duplex steel pipes are a popular choice for various industrial applications due to their unique combination of high strength, excellent corrosion resistance, and good weldability. The UNS standard provides a unique identifier for each material, making it easier to find and compare materials across different countries and industries. The grades of duplex steel pipes in the UNS standard include UNS S31803, UNS S32750, UNS S32760, UNS S32205, and UNS S32550. Each grade has its unique properties and is suitable for specific applications.
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