Super Duplex Stainless Steel Pipes and Tubes
Super duplex stainless steel 32750/3270 pipes and tubes have dual phase microstructure in similar amounts of austenite and ferrite combination which gives it high resistance to stress corrosion cracking when compared to other stainless steel pipe properties.
Super duplex stainless steel 32750/3270 pipes and tubes have better corrosion resistance to a wide range of media, with extra-ordinary resistance to pitting and crevice corrosion in environments with seawater and other chlorides due to its high chromium, molybdenum, and nitrogen levels, with critical pitting temperature more than 50°C.
Chemical composition
|
GRADE |
ELEMENT |
CR |
C |
CU |
MN |
MO |
N |
NI |
P |
W |
Si |
|---|---|---|---|---|---|---|---|---|---|---|---|
|
S32750/S3260 |
min |
24 |
– |
0.5 |
– |
3 |
0.24 |
6 |
– |
– |
– |
|
max |
26 |
0.03 |
1 |
2 |
5 |
0.35 |
8 |
0.35 |
0.03 |
1 |
Production Process
Super duplex tube fittings made with super duplex 32205/31803 or UNS S32205/S31803 are manufactured with processes like ERW (Electric Resistance Welded), Seamless and EFW (Electric Fusion Welding). These SS pipe materials are made with stainless steels having different forms such as round, square, rectangle, etc. having specific end such as plain end, bevel end and threaded end with normal thickness of various schedules ranging from SCH 5 to SCH XXS.
MECHANICAL PROPERTIES
|
Grade |
Tensile Strength |
Yield Strength |
Elongation |
Hardness, MAX |
|
|---|---|---|---|---|---|
|
MPA |
MPA |
(% in 50mm) min |
HB |
HRB |
|
|
2750/2760 |
795 |
550 |
15 |
310 |
32 |
Some of the processes used in manufacturing of super duplex stainless steel pipes and tubes are cold pilgering process, Extrusion process, tube mill Process and piercing process which need to be followed by heat treatment and mechanical testing.
Fabrication and Heat Treatment
The super duplex stainless steel tubes and pipes can be forged in temperature range of 1100°C to 1250°C and if necessary it should be followed by reheat process and cooled down in still air. In annealing heat treatment process is done in range of 1025°C – 1120°C and sufficient time is to be allowed for the centre to attain furnace temperature and hold for a time sufficient with the ruling section, and water quenching is to be followed.
Specifications
Stainless steel Super Duplex Seamless Pipe : ASTM/ASME SA 790/ A 790
Stainless steel Super Duplex Seamless tube : ASTM/ASME SA 790/ A 790
Stainless steel Super Duplex ERW Pipe : ASTM/ASME SA 789/ A 789
Stainless steel Super DuplexERW Tube :ASTM/ASME SA 789/ A 789
|
GRADE |
UNS |
OLD BRITISH |
EURONORM |
||
|---|---|---|---|---|---|
|
BS |
EN |
NO |
NAME |
||
|
SUperDuplex 2750/2760 |
S32750/S32760 |
318S13 |
– |
1.4501 |
X2CrNiMoN 25-7-4 |
The super duplex stainless steel 32750/32760 has to undergo a pickling process i.e. mixture of nitric and fluoric acid along with applying surface of super duplex steel. As it has highly corrosive nature, super duplex steel needs to be immersed into a fused salt bath before it goes pickling process.
Properties
The microstructure of super duplex provides it with better strength and thus UNS S32750/S32760 has a low coefficient of thermal expansion and extreme heat conductivity than different austenitic steels and the suitable temperature to work is up to 300°C.
Super duplex stainless steel grade S32760/S32760 pipes and tubes showcase better resistance to pitting and crevice corrosion. Super duplex stainless steel has PRE which is greater than 40 as compared to the duplex grades 2205 which has 35, 24 for 316L and 33 for 904L.
Physical properties
|
Grade |
Density (g/cm3) |
Melting Range °C |
Elastic Modulus (GPa) |
Thermal Expansion coefficient (μm/m/°C) |
Thermal Conductivity (W/m.K) |
Specific Heat (J/Kg.K) 20°C |
Electrical Resistivity (μΩ.cm) |
|---|---|---|---|---|---|---|---|
|
S32750/S32760 |
7.8 |
1350°C / 2460°F |
200 |
11.1 |
14.2 |
475 |
8.5 |
Super Duplex stainless steel S32750/S32760 pipes are designed to have better strength, resistance to pitting and stress corrosion cracking. Super Duplex S32760 welded tubes are also formed to sustain highly corrosive conditions and environments where high strength is required.
Application
Super duplex S32750/S32760 pipes and tubes have exceptional corrosion resistance in environments where chloride is found. Super duplex stainless steels are widely used in oil refinery heat exchangers, pressure vessels, cargo tanks, seawater applications, desalination plants, refineries and petrochemical plants.
Some of the other applications are:
- Desalination Equipment
- Chemical process pressure vessels, piping and heat exchangers
- Marine Applications
- Flue Gas Scrubbing Equipment
- Pulp & Paper Mill Equipment
- Offshore Oil production/technology
- Oil and gas industry equipment
