DUPLEX STAINLESS-STEEL PIPES

Description

Key Features

1. Dual Microstructure:
   • Duplex stainless steel consists of approximately 50% austenite and 50% ferrite, giving it its unique combination of strength and corrosion resistance. This microstructure results in improved mechanical properties compared to standard austenitic stainless steel.
2. High Strength:
   • Duplex stainless steel pipes typically have higher tensile and yield strength than austenitic stainless steel, making them ideal for high-pressure applications. Their strength-to-weight ratio also offers advantages in many structural applications.
3. Corrosion Resistance:
   • Duplex stainless steel has excellent resistance to various forms of corrosion, including pitting, crevice corrosion, stress corrosion cracking, and fatigue corrosion. This makes it ideal for applications in harsh and corrosive environments such as marine, chemical, and oil and gas industries.
4. Resistance to Chloride Stress Corrosion Cracking:
   • Duplex stainless steel performs particularly well in chloride environments, where austenitic stainless steel may fail due to stress corrosion cracking. This makes it suitable for use in seawater and other chloride-rich environments.
5. Good Weldability:
   • Duplex stainless steel pipes have better weldability than ferritic stainless steels and, in many cases, comparable to austenitic stainless steels. However, careful control of heat input during welding is necessary to avoid the formation of harmful phases.
6. Impact Toughness:
   • These pipes exhibit good toughness, even at low temperatures, which allows them to maintain their integrity and performance in colder environments.
7. Improved Fatigue and Stress Corrosion Resistance:
   • Duplex stainless steels provide excellent resistance to fatigue and stress corrosion, ensuring their reliability in demanding applications where frequent cyclic loading is involved.

Specifications

1. Grades:
   • Duplex stainless steel pipes are typically available in the following grades:
     • 2205 (UNS S32205): The most commonly used duplex stainless steel grade, offering a good balance of strength and corrosion resistance. It is resistant to both general corrosion and pitting.
     • 2507 (UNS S32750): Known for its higher resistance to pitting and crevice corrosion, this grade is used in more aggressive environments, such as seawater and chemical processing.
     • 4501 (UNS S42900): A higher-strength duplex stainless steel used in applications that require higher tensile strength and resistance to localized corrosion.
     • 2101 (UNS S32101): A lean duplex stainless steel with lower alloy content, offering good corrosion resistance and mechanical strength at a reduced cost.
2. Wall Thickness and Diameter:
   • Duplex stainless steel pipes come in various sizes and thicknesses, typically from small diameter pipes (e.g., ½ inch) to large diameter pipes used in industrial applications (e.g., 24 inches or more).
3. Pressure Ratings:
   • Duplex stainless steel pipes are available in a range of pressure ratings, with some capable of handling pressures exceeding 1000 bar, depending on the grade and thickness.
4. Temperature Resistance:
   • Duplex stainless steel pipes can withstand temperatures up to 300°C to 350°C, depending on the alloy grade, which makes them suitable for many industrial applications.

Advantages

1. Enhanced Corrosion Resistance:
   • Duplex stainless steel offers superior resistance to various types of corrosion, especially in chloride-rich environments like seawater, making it ideal for marine and offshore applications.
2. High Strength and Durability:
   • The combination of ferrite and austenite provides duplex stainless steel with a unique combination of strength and toughness, making it ideal for high-pressure and high-stress applications.
3. Lower Cost than Super-Austenitic Grades:
   • While more expensive than carbon steel or standard austenitic stainless steel, duplex stainless steel is often more cost-effective than super-austenitic grades in highly corrosive environments, offering a balance of performance and price.
4. Improved Fatigue Resistance:
   • The dual-phase structure of duplex stainless steel contributes to improved fatigue strength, making it more resilient under cyclic loading and extreme conditions.
5. Good Weldability:
   • Duplex stainless steels have improved weldability compared to ferritic stainless steels and provide solid weld joints when processed with proper care, making them easier to fabricate and install.
6. Lower Thermal Expansion:
   • Duplex stainless steel has a lower coefficient of thermal expansion than austenitic stainless steels, which makes it useful in applications where temperature fluctuations occur.