What Is Duplex S31803?

Learn about UNS S31803

UNS S31803 is a duplex grade with a ferritic-austenitic microstructure. The alloy consists of around 40-50% ferrite in the annealed condition. The duplex microstructure has the high strength of the ferritic grades whilst retaining the corrosion resistance of the austenitic grades. It is not uncommon to see the metal used as a practical solution to chloride-induced stress cracking, which is the achilles heel of stainless steel.

Duplex stainless steels are extremely corrosion resistant, work hardenable alloys. Their microstructures consist of a mixture of austenite and ferrite phases. As a result, duplex stainless steels display properties characteristic of both austenitic and ferritic stainless steels. This combination of properties can mean some compromise when compared with pure austenitic and pure ferritic grades.

The high quality and therefore performance of  UNS S31803 is widely attributed to the high levels of chromium present as well as nitrogen and molybdenum. It has superior resistance to chloride pitting and crevice corrosion as compared to 317L stainless steel. The alloy has outstanding corrosion resistance to seawater and most concentrations of sulphuric acid. In addition, it is also resistant to sulphide stress corrosion cracking (sour-gas environments).

Duplex stainless steels S31803 were developed in the 1930’s, for demanding applications in paper mills where lesser-alloyed grades were not sufficiently corrosion resistance. Based upon a 22% chromium content, they possess the combined austenite: ferrite microstructure that provides increased strength, corrosion resistance and cost effectiveness. Duplex stainless steels S31803 are in most cases, tougher than ferritic stainless steels. Strengths of duplex stainless steels can in some cases be double that for austenitic stainless steels. Duplex S31803 are also magnetic, a property that can be used to easily differentiate them from common austenitic grades of stainless.

Chemical composition of UNS S31803

The UNS S31803 (ASTM F51) specification has largely been replaced by UNS S32205 (1.4462, ASTM F60). This reflected their desire to maximise the corrosion performance of the alloy, aided by the development of the AOD steelmaking process that allowed tighter control of composition. In addition, it also allowed the level of nitrogen additions to be influenced, rather than just present as a background element. Therefore, the highest performing duplex grade sought to maximise the levels of chromium (Cr), molybdenum (Mo) and nitrogen (N).

UNS S31803 performance

Corrosion Resistance :

Duplex stainles steels S31803 are extremely corosion resistant They have high resistance to intergranular corrosion. Even in chloride and sulphide envronments, duplex S31803 exhibivery high resistance to stress corrosion cracking. The super duplex S31803 is even more resistant to corrosion.

Heat Resistance :

The high chromium content of duplex stainless steels S31803 that protects against corrosion, causes embrittlement at temperatures over about 300'c At ow temperatures dupex stainless steels S31803 have better ductility than the ferritic and martensitic grades dupex S31803 can readily be used down to atleast 50℃.

Fabrication :

Fabnication of all stainess steels should be done only with tools dedicated to stainess steel matenials. Tooing and work surfaces must be thoroughly cleaned before use.These precautions are necessaly to avoid cross contamination of stainless steel by easily corroded metals that may discolour the surface of the fabricated product.

Machinability :

Although machinable, the high strengths of duplex stainles steels makes machining difficult. As an example,machining of 2205 is around 20% slower than for 304.

Heat Treatment :

Duplex stainless steels S31803 cannot be hardened by heat treatment. They can however be work hardened. Solution treatment or annealing can be done by rapid cooling after heating to around 1100°C.

Weldability :

Dupley stainless S31803 have good weldabit All standard welding prcesses can be used They are not quite as easily welded as the austenitic grades but low thermal expansion in duplex grades reduces distortion and residual stresses after welding.

Understanding the Applications of Duplex Steel S31803

Oil and Gas Industry:

Duplex Steel S31803 are widely used in oil and gas due to their superior corrosion resistance properties. These fittings are ideal for pipelines that carry abrasive and corrosive materials, making them a perfect choice for offshore drilling platforms, refineries, and pipelines.

Chemical Industry:

The chemical industry also heavily relies on UNS S31803 products to safely transport chemicals that require high pressure and temperature. The fittings are resistant to various chemicals, including acids and alkalis, and can withstand harsh environments, making them an ideal choice for this industry.

Marine Industry:

The marine industry is another sector that heavily relies on UNS S31803. The fittings have excellent corrosion resistance, making them ideal for seawater transportation and offshore applications. They also resist stress corrosion cracking, a common issue in marine environments.

Food Processing Industry:

The food processing industry requires pipe fittings that are resistant to corrosion and can withstand high-pressure and high-temperature applications. Duplex S31803 is ideal for this industry because they are non-toxic and hygienic. They do not leach harmful substances into the food products, making them an ideal choice for food processing applications.

Power Generation Industry:

The power generation industry relies on Duplex Steel S31803 because they can withstand high-pressure and high-temperature applications. The fittings are ideal for power plant systems, including cooling water, fuel, and steam. They have excellent corrosion resistance and are also resistant to fatigue and stress corrosion cracking, which helps ensure a long life for the fittings and reduces maintenance costs.