• Superior Yield Strength: Duplex stainless steel exhibits more than double the yield strength of conventional austenitic grades while maintaining adequate ductility for forming operations. This allows for 30-50% reduction in wall thickness when manufacturing storage tanks or pressure vessels.
• Excellent Stress Corrosion Resistance: Even the lowest-alloyed duplex grades offer superior resistance to stress corrosion cracking compared to austenitic stainless steels, particularly in chloride-containing environments.
• Enhanced Corrosion Performance: The widely-used 2205 grade provides better corrosion resistance than 316L in many media. Super duplex grades can replace high-alloy austenitic stainless steels and even nickel-based alloys in aggressive environments such as acetic acid and formic acid.
• Improved Localized Corrosion Resistance: At equivalent alloy content, duplex grades demonstrate superior wear corrosion and fatigue corrosion performance.
• Lower Thermal Expansion: The coefficient of thermal expansion is closer to carbon steel, making duplex stainless steel ideal for composite plates, linings, and connections with carbon steel components.
• Higher Energy Absorption: Under both dynamic and static loading conditions, duplex stainless steel absorbs more energy than austenitic grades, providing better performance in collision or explosion scenarios.

• Better Mechanical Properties: Comprehensive mechanical properties, especially ductility and toughness, surpass ferritic grades without the sensitivity to brittleness.
• Superior Localized Corrosion Resistance: Except for stress corrosion resistance, all other localized corrosion performance exceeds that of ferritic stainless steels.
• Excellent Workability: Cold working and cold forming capabilities are significantly better than ferritic grades.
• Improved Weldability: Generally requires no preheating before welding and no post-weld heat treatment.
• Broader Application Range: Suitable for a wider variety of industrial applications and environments.

• Temperature Limitations: Heat resistance is lower, with operating temperatures limited to below 300°C (572°F).
• Reduced Ductility: Lower ductility and toughness, with greater work hardening effect during cold processing. Higher initial force is required for tube and plate deformation. Grades containing 25% Cr are more difficult to hot work.
• Intermediate Temperature Embrittlement: A medium-temperature brittleness zone exists, requiring strict control of heat treatment and welding processes to prevent detrimental phase formation.

• Higher Cost: Due to higher alloy element content, duplex stainless steel is relatively more expensive. Standard ferritic grades typically contain no nickel, making them more economical for certain applications.

Pulp and Paper Industry

As one of the earliest adopters of duplex stainless steel, this industry uses these alloys to replace 304 and 316 austenitic grades in sulfuric acid and sulfurous acid digesters. The result is improved corrosion resistance, higher strength, reduced wall thickness, and lower overall equipment weight.

Chemical Processing Industry

The chemical industry encompasses a broad range of complex operating conditions. Storage tanks for industrial wet phosphoric acid, traditionally made from 316L or 317L with thick walls, can now utilize 2205 duplex grade. With nearly double the strength, wall thickness and weight are significantly reduced. Additionally, 2205 provides superior localized corrosion resistance in industrial sulfuric acid environments, especially in the presence of chloride ions.

Food and Beverage Industry

Processing in this industry often involves hot solutions containing chloride ions. Duplex stainless steel offers unique advantages in stress corrosion cracking resistance. Different grades can be selected based on specific environmental requirements, typically providing cost advantages over austenitic alternatives.

Transportation Industry

The high strength and excellent corrosion resistance of duplex stainless steel make it ideal for chemical tanker construction. The 22% Cr duplex grades are most commonly used, reducing vessel weight and fuel consumption while meeting the corrosion resistance requirements for various cargo types.

Construction Industry

Coastal regions experience marine atmospheres with significantly higher chloride ion concentrations than inland areas. Duplex stainless steel’s seawater corrosion resistance and high strength make it ideal for such environments. Many offshore oil platforms now use duplex stainless steel for blast walls and structural components.

Petrochemical Industry

Petrochemical environments are characterized by high reaction temperatures and media often containing high or medium concentrations of chlorides, which can induce stress corrosion cracking in stainless steels. This sector requires not only standard duplex grades but frequently demands super duplex stainless steel for the most challenging applications.

Oil Refining Industry

One of the largest users of duplex stainless steel, with applications in atmospheric and vacuum distillation units, catalytic cracking, and hydrodesulfurization systems. Additionally, duplex stainless steel use is increasing in sour gas and oil production for production tubing liners, onshore and offshore pipeline systems, and heat exchangers.

What is duplex stainless steel?

Duplex stainless steel is a type of stainless steel with a microstructure consisting of approximately equal proportions of ferrite and austenite phases (typically 50/50, with neither phase less than 30%). This dual-phase structure combines the advantages of both austenitic and ferritic stainless steels, offering superior strength, excellent corrosion resistance, and good weldability while reducing nickel content for cost efficiency.

What is the maximum operating temperature for duplex stainless steel?

Duplex stainless steel should be used at temperatures below 300°C (572°F). Above this temperature, the material may experience intermediate temperature embrittlement due to the formation of sigma phase and other intermetallic compounds, which can significantly degrade mechanical properties and corrosion resistance.

What is PRE value and why is it important?

PRE (Pitting Resistance Equivalent) is a formula used to predict the pitting corrosion resistance of stainless steels: PRE = %Cr + 3.3(%Mo) + 16(%N). Higher PRE values indicate better resistance to pitting and crevice corrosion. Standard duplex grades have PRE values of 32-33, high-alloy grades reach 38-39, and super duplex grades exceed 40, making them suitable for the most demanding corrosive environments.

What are the main applications of duplex stainless steel?

Duplex stainless steel is widely used in the pulp and paper industry, chemical processing, oil and gas extraction, petrochemical plants, marine applications (including chemical tankers and offshore platforms), food and beverage processing, construction in coastal areas, wastewater treatment facilities, and heat exchanger systems. Its high strength and corrosion resistance make it ideal for pressure vessels, storage tanks, and piping systems.

How does duplex stainless steel compare to 316L?

Duplex stainless steel offers several advantages over 316L: nearly double the yield strength (allowing 30-50% reduction in wall thickness), superior stress corrosion cracking resistance (especially in chloride environments), better pitting and crevice corrosion resistance, and a lower thermal expansion coefficient closer to carbon steel. The widely-used 2205 grade provides better overall corrosion resistance than 316L in many industrial environments, often resulting in lower total lifecycle costs despite higher initial material prices.

Published by

FUSHUN METAL Technical Team

Category

Technical Blog