A duplex pipe features, at the same time, the qualities of a ferritic SS pipe (high resistance to corrosion cracking and high tensile strength) and of an austenitic SS pipe (easy manufacturing and good resistance to corrosion and erosion). Duplex pipes 2205 (UNS S31803/UNS S32205) are used for applications below 600 degrees (F). We recommend purchasing the ASTM A790 specification from the ASTM website or the IHS store to get a complete understanding of this topic.
WHAT IS DUPLEX STEEL?
Duplex stainless steel (UNS S31803/UNS S32205) is a nitrogen-enhanced stainless steel developed to overcome the issues of the 300 series stainless steels as 316L and 317L (chloride stress corrosion cracking, under tensile stress in cases where the metal is exposed to fluids containing chlorides or by steel exposure to high temperatures).
The term “duplex” refers to a family of stainless steels that have double structure – i.e. they are neither a fully austenitic SS structure, like 304 stainless, nor a standard ferritic, such as the 430 series. The microstructure of duplex steels consists of austenite pools surrounded by a continuous ferrite phase (approx 40-50% ferrite). Therefore, duplex pipes combine the qualities of ferritic and austenitic stainless steel materials.
UNS 2205 duplex steel finds application in marine projects, oil & gas exploration, closed loops water systems, desalinization plants, hydrocarbons storage and transportation, downstream refining, pulp, and paper.
DUPLEX CORROSION RESISTANCE
Duplex stainless steel shows a superior corrosion resistance to grade 316 for most applications (excellent resistance to localized corrosion including intergranular, pitting and crevice corrosion; the CPT of 2205 is generally at least 35ºC). Duplex is also resistant to chloride corrosion cracking (SCC) at temperatures up to about 150ºC. Grade 2205 duplex will often perform well in environments which cause premature failure of the standard austenitic grades of series 300 stainless steel. It has also stronger resistance to seawater corrosion, compared to stainless steel 316.
It should be noted that despite Duplex stainless steel shows good high-temperature oxidation resistance, 2205 suffers from embrittlement if kept at temperatures above 300ºC for some period of time. (a situation that can be rectified only by a full solution annealing treatment). For this reason, Duplex stainless steels are never used for temperatures in excess of 300ºC
Duplex pipes match the following fittings materials: ASTM A815 (butt weld fittings) and ASTM A182 F51 / F53 / F55 (flanges / forged socket weld – threaded fittings).
DUPLEX PIPE CHEMICAL COMPOSITION AND MECHANICAL PROPERTIES
|Commercial Name||UNS Designation||ASTM Specifications for Duplex Grades||Chemical Composition||Min.Tensile (KSI)||Min.Yield
|UNS S31803||ASME SA-182 (F51), SA-240, SA-798, SA-790, SA-815
ASTM A182 (F51),A240, A276, A479, A789, A790, A815, A928, A988, SAE J405
|C 0.30 max
Mn 2.00 max
P 0.030 max
S 0.020 max
Si 1.00 max
|UNS S32205||ASME SA-182 (F60), SA-240, SA-798, SA-790, SA-815
ASTM A182 (F60), A240, A276, A479, A480, A798, A790,
A815, A928, A988, SAE J405
|C 0.30 max
Mn 2.00 max
P 0.030 max
S 0.020 max
Duplex pipes are manufactured according to the ASME B36.19 standard.
SUPER DUPLEX PIPE
WHAT IS SUPER DUPLEX?
Super duplex stainless steel is a variation of the duplex steel alloy which is used in the oil & gas, chemical, power generation, mechanical and desalination industries:
- oil & gas production equipment
- Offshore platforms
- heat exchangers
- process and service water systems
- fire-fighting systems
- injection and ballast water systems
- high-pressure RO plants and seawater piping
- high strength and corrosion-resistant parts in mechanical applications
- FGD systems (power generation)
- Utility and industrial scrubber systems
- Absorber towers
The high chromium and molybdenum content of Super Duplex makes it extremely resistant to uniform corrosion by organic acids like formic and acetic acid. Super Duplex also provides excellent resistance to inorganic acids, especially those containing chlorides. The pitting Resistance equivalent of Super Duplex, calculated by PREN = Cr + 3.3Mo + 16N, will exceed 40 in most material forms.
SUPER DUPLEX PIPES CHEMICAL COMPOSITION AND MECHANICAL PROPERTIES
|Trade Name||UNS||Super Duplex Industry Specifications||Chemical Composition||Min.Tensile
|SAF 2507®||UNS S32750||ASTM A182 F53, A240, A276, A479, A789, A790, A815, A928, A988
|C 0.030 max
Cu 0.5 max
Mn 1.20 max
P 0.035 max
S 0.020 max
Si 0.8 max
|UNS S32760||ASTM A182 F55, A240, A276, A314, A473, A479, A789, A790, A815, A928, A988
|C 0.03 max
Mn 1.0 max
P 0.03 max
S 0.01 max
Si 1.0 max
DUPLEX PIPE PRICES
Looking for the price of duplex pipes ASTM A790? Click on the image and check our online duplex pipe price estimation tool!
The tool estimates the price for duplex pipes manufactured in Europe and Asia, for example:
What is a schedule 40 duplex pipe price (6 inches, ASTM A790 2205)?
Even if our price estimates are reliable, prices shall always be double checked with duplex pipe manufacturers and distributors.
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