Duplex is a Fe-Ni-Cr alloy that has a two-phase ferritic-austenitic stainless-steel microstructure when it is at room temperature.
Combining austenitic grades and ferritic comes with an advantage. It means that the resultant metal comes with an enhanced metallurgical structure. It consists of two phases that benefit from the properties of both microstructures. These properties also make duplex steel highly popular in heavy industries like chemical processing, gas, nuclear, and oilfield service.
Creating duplex flanges
The characterization of Duplex steels is characterized by molybdenum (up to 5%), high chromium (19-28%), and lower contents of nickel than austenitic stainless steel. The most used duplex stainless steels are 2205 (5% Nickel, 22% Chromium) and 2507 (7% Nickel, 25% Chromium). 2507 is also known as a “super duplex” due to its higher corrosion resistance.
You can trace the origin of duplex steels to the 1920s, with the first cast made in Sweden in 1930. However, the popularity of using the only duplex started to rise around 30 years ago when steelmaking technology became more advanced.
The two types of metallic structures used to make duplex are ferritic and austenitic. They are fit for many scenarios, but they both have a weakness that inhibits their use for 100% of applications.
Austenitic comes with lower resistance/strength to reduce stress corrosion cracking. Ferritic comes with poorer low-temperature toughness, poorer weldability, and lower strength.
Producing a chemical composition can help combine ferritic and austenitic. This results in metal with resistance to stress corrosion cracking, good toughness, good weldability, and higher strength.
The high strength of the duplex stainless steel flange means that the range of 0.2% PS for current duplex grades is from 400-500 MPa. It can lead to reduced section thickness and reduction in flange weight. The advantage of this is particularly significant for structural applications, such as bridges, storage tanks, and pressure vessels.
One negative aspect is that duplexes can be brittle at extreme temperatures. It means that its use is restricted from a maximum temperature of 300 degrees to a minimum temperature of -50 degrees.
Advantages of Duplex
Duplex stainless steel comes in with an array of benefits. These include:
As with all stainless steel, corrosion resistance depends on the composition of the stainless steel with nitrogen, molybdenum, and chromium being essential. Duplex stainless steel is corrosion-resistant, and even in sulfide and chloride environments, duplex stainless steel exhibits very high resistance to stress corrosion cracking (SCC). It is a type of corrosion that may occur when a particular set of factors are present: A corrosive environment, tensile stress, and a sufficiently high temperature.
Duplex stainless steels have approximately double the strength of regular ferritic or austenitic stainless steels.
Ductility and toughness
Duplex stainless steel can exceed the ductility and toughness of ferritic grades, although they are not as touch as austenitic grades.
The duplex stainless steel variants tend to have good weldability. You can use the standard welding processes, even though they are not easy to weld compared to the austenitic grades.
Duplex stainless steel comes with lower thermal expansion and higher heat conductivity than austenitic steel. Duplex grades can easily be used down to temperatures of at least -50C. At low temperatures, they have better ductility than ferritic grades of steel.
Duplex stainless steels have lower contents of molybdenum and nickel than their austenitic counterparts. The lower alloying content means that duplex stainless steel can cost lower. Further to this, it is also possible that you can reduce the thickness of duplex stainless steel as it comes with increased yield strength. Thinner products mean the possibility of significant weight savings.
Ductility and toughness
Duplex stainless steel exceeds the ductility and toughness of ferritic grades, although they are not as tough as austenitic grades.
Benefits of stainless steel super duplex pipes
Stainless steel super duplex pipes require less cost compared with austenitic and ferritic grades. The material shows outstanding yield and tensile strength. The two properties of material offer the best choice for companies. Super duplex pipes are available with a small thickness and prevent comptonization of performance and quality.
Here, super duplex is a term that came into use in the year 1980 to represent the high alloying ability and performance. Stainless steel super duplex contains high chromium. It makes the pipes resistant and suitable to work in caustic solutions containing chlorine and acid. These conditions are present in the petrochemical and chemical industries. Super duplex stainless steel acts as the replacement for regular mild steel material when possible.
Features of stainless steel super duplex pipes
Stainless-steel super duplex pipes show corrosion-resistant and high strength. They are super helpful in chemical and marine industries. The pipes of these kinds work well in wire lines and architecture. Stainless-steel super duplex pipes are also helpful in pulley equipment and lifting. The stainless-steel super duplex pipes show improved corrosion resistance compared with regular duplex steel. The material also displays good tensile strength and yield with outstanding ductility and toughness. Stress corrosion and cracking corrosion abilities of stainless-steel super duplex pipes make them useful in versatile industrial applications.
The stainless-steel super duplex pipes are useful in offshore platforms, chemical processing plants, and heat exchangers. The mechanical properties of super duplex stainless steel pipes consist of proof stress, hardness, and elongation.
Duplex stainless steel is one of the most functional metals that you can use in commercial applications. It received its name from the fact that it consists of two kinds of grades of metal that include ferritic-austenitic stainless steel. The flanges in these duplex grades come with good benefits that can prove that it is the right choice to select them.
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