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Duplex Stainless Steel – An Overview

Duplex Stainless Steel

Duplex stainless steel is a type of alloy composed of two different grades of stainless steel. This alloy has a higher strength than traditional austenitic stainless steel, making it a popular material for many applications. In this blog post, we’ll take a closer look at the microstructure, welding, types, ultrasonic velocity, density, chloride resistance, applications, and codes of duplex stainless steel.

Duplex stainless steel Microstructure

The microstructure of duplex stainless steel is largely composed of austenite and ferrite phases. The ratio between these two phases depends on the specific grade of duplex stainless steel being used. Generally speaking, higher ferrite levels will improve toughness, while higher austenite levels will lead to improved strength and corrosion resistance.

Duplex stainless steel Welding

Duplex stainless steel can be welded using several different methods, such as shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and flux cored arc welding (FCAW). Each method has its advantages and disadvantages, so it’s important to choose the right one for the job.

Duplex stainless steel welding is an advanced fabrication technique which is becoming increasingly popular in certain industries. It produces strong, durable welds which allow for an enhanced product that is resistant to corrosion and other environmental stresses. The process involves a high-performance filler stainless steel rod being used to bring the metal together, while a flux covered electrode increases the strength of the weld with its controlled burn rate. The advantages of duplex welding are becoming more apparent as its use continues to increase, including improved corrosion resistance and improved resistance to tension forces, making it particularly attractive to industries such as oil and gas exploration and automobile manufacturing.

Duplex stainless steel Types

There are several different grades or types of duplex stainless steel available, including lean duplex (LDX 2101), standard duplex (2205 or S31803/S32205), and super duplex (2507 or S32750/S32760). Each grade has its own set of characteristics that make it suitable for certain applications.

Lean Duplex Stainless Steel

Lean duplex stainless steel has a low nickel content (4-6%) and contains less molybdenum than standard duplex stainless steel. This makes it more affordable but also makes it less resistant to corrosion in certain environments. Lean duplex stainless steels are mainly used in applications that don’t require high levels of corrosion resistance, such as food processing equipment, domestic appliances, chemical storage tanks, water tanks, and piping systems for non-aggressive media.

Standard Duplex Stainless Steel

Standard duplex stainless steels contain higher levels of molybdenum (2-3%) and nickel (8-10%). The increased levels of these elements make them highly resistant to pitting and crevice corrosion in a wide range of environments. Standard duplex stainless steels are used in applications that require superior corrosion resistance, such as marine components, desalination plants, heat exchangers, pulp & paper mills, oil & gas platforms, offshore structures, pressure vessels, chemical processing equipment, firewalls & HVAC systems.

Super Duplex Stainless Steel

Super duplex stainless steel is a material that has seen a dramatic increase in use over the last few years. Combining corrosion resistance, durability and strength, it is ideal for high stress environments like offshore oil rigs and deep sea platforms. Super duplex stainless steel also offers tremendous cost savings, as its unique properties help manufacturers stretch often limited budgets without compromising on quality or safety. As its popularity continues to grow, engineers and contractors are finding new ways to make this extraordinary material work for them in a range of applications.

Duplex stainless steel Ultrasonic Velocity

Ultrasonic velocity is an important property when it comes to choosing the right grade for a particular application. It measures how quickly sound waves travel through a material which can give insight into its properties, such as hardness, ductility, and elasticity. Generally speaking, higher velocities indicate greater hardness, while lower velocities indicate greater ductility and elasticity, which makes them more suitable for bending or forming operations.

Duplex stainless steel Density

The density of duplex stainless steel in kg m3 depends on the specific grade being used but typically ranges from 7500-8000 kg m3 depending on the composition and heat treatment applied to the material.

Duplex stainless steel Chloride Resistance

Chloride ions can be corrosive to many materials, including some types of stainless steels, so it’s important to know if your chosen grade is resistant or not before exposing it to high concentrations of chlorides in seawater or saltwater environments. Generally speaking, most grades are highly resistant, but it’s still best practice to test in real-world conditions before committing to any particular material choice.

Duplex stainless steel Uses

Duplex stainless steels are commonly used in industries such as oil & gas production facilities, chemical processing plants, and food processing facilities due to their high strength and corrosion resistance properties.

Food Processing

Duplex stainless steel is often used in food processing due to its high resistance to corrosion. The steel is commonly used in equipment such as food processors, blenders, and mixers.

Chemical Processing

Duplex stainless steel is also resistant to corrosion from chemicals, making it ideal for use in chemical processing. The steel is often used in storage tanks, piping, and other equipment that comes into contact with corrosive chemicals.

Oil and Gas

Duplex stainless steel is used in a variety of oil and gas applications due to its high resistance to both corrosion and stress. The steel is often used in offshore drilling rigs, pipelines, and storage tanks.

Power Generation

Duplex stainless steel is also used in power generation due to its high resistance to corrosion from both water and heat. The steel is often used in boilers, turbines, and other power generation equipment.


Duplex stainless steel is resistant to corrosion from salt water, making it ideal for use in desalination plants. The steel is often used in pipes, pumps, and other equipment that comes into contact with salt water.

Architecture and Construction

Duplex stainless steel is also used in architecture and construction due to its aesthetic appeal and durability. The steel is often used in cladding, roofing, and structural applications

Duplex Stainless Steel Code

The American Society for Testing Materials (ASTM) has designated several code numbers for each type which can help identify them for specific applications. These codes include ASTM A240/A240M-18a for lean duplex LDX2101; ASTM A249/A249M-17a for standard duplex 2205; ASTM A276/A276M-17a for super duplex 2507; ASTM A789/A789M-17a for super duplex 2507; ASTM A473/A473M-17a for super duplex 2507; ASTM A479/A479M-17afor super duplex 2507; and others based on specific application requirements such as ASTM B862-19bfor welded tubes made from super duplex 2507 material etc.


Duplex Stainless Steel provides superior strength and corrosion resistance compared with traditional austenitic grades making it ideal for many industrial applications requiring high-performance materials, such as oil & gas production equipment, chemical processing plants, etc. Understanding its microstructure along with welding requirements, types available, ultrasonic velocity, density, chloride resistance, codes & applications will help you make an informed decision about what type & grade is best suited for your needs. So if you need a strong yet corrosion-resistant material, then consider using DSS!

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