Duplex Stainless Steel Material Standard DSS

Duplex Stainless Steel Type

Duplex stainless steel DSS is divided into two sub-families, DSS (22%Cr) and SDSS (25%Cr). SDSS has better corrosion resistance and may also be used for seawater service. SDSS may be preferred to DSS also for its higher strength, resulting in reduced wall thickness, which may be of interest and even necessary for HPHT issues (typically inlet and injection systems).

Duplex Stainless Steel DSS 22% Cr

DSS has significantly better corrosion resistance than SS316, with typically PRE value of 35. It has a relatively lean chemistry, particularly with regards to nickel, and is therefore less sensitive to fluctuations in the price of alloying elements. Since duplex materials have high strength,i.e. the yield strength is more than twice of that of SS316, significant weight and cost saving may be obtained, particularly at high pressure where considerable wall thickness reductions may be obtained.

DSS has significantly better resistance to CSCC than SS316. Due to the generally better corrosion resistance, it is also acceptable to mitigate CSCC by coating, which makes it possible to use DSS at high temperatures.

Super Duplex Stainless Steel SDSS 25%Cr

SDSS is mainly used when additional corrosion resistance is required compared to DSS. Also when the higher strength enables reduced wall thickness it may be cost and weight effective to SDSS in lieu of DSS. SDDS can be used up to maximum operating temperature 20˚C in sweater systems with crevices and max 1.5 ppm free chlorine. It is a relatively cost efficient material for seawater purposes due to the relatively low content of expensive alloying elements compared to other seawater resistant materials like SS6Mo, alloy 625, alloy C276/C22, and titanium. Its PREN value of above 40 is required for seawater service

Duplex stainless steel DSS are divided into two sub-families, 22 Cr DS and 25 Cr DS. 22 Cr DS has become the workhorse among the CRAs used in process systems. 25 Cr DS has better corrosion resistance and may also be used for seawater service. 25 Cr DS may be preferred to 22 Cr DS also for its higher strength, resulting in reduced wall thicknesses. Duplex SS (all types) have to be treated as sensitive materials wrt. possible formation of unwanted brittle inter metallic phases during manufacturing (heat treatment) and fabrication (welding).

22 Cr DS has significantly better corrosion resistance than SS 316L, with typical PRE value of 35. Since duplex materials have high strength, i.e. the yield strength is more than twice to that of 316L, significant weight saving may be obtained, particularly at high pressure where considerable wall thickness reductions may be obtained.

22 Cr DS has significantly better resistance to CSCC than SS 316L. Due to the generally better corrosion resistance, it is also acceptable to mitigate CSCC by coating, which makes it possible to use 22 Cr DS at high temperatures.

25 Cr DS is mainly used when additional corrosion resistance is required compared to 22 Cr DS. Also when the higher strength enables reduced wall thickness it may be cost and weight effective to use 25 Cr DS in lieu of 22 Cr DS.

25 Cr DS can be used up to maximum operating temperature 30 °C in seawater systems with max 1.5 ppm free chlorine. 25 Cr DS is a relatively cost efficient material for seawater purposes due to the relatively low content of expensive alloying elements compared to other seawater resistant materials like 6Mo, alloy 625, alloy C276, and titanium.