Duplex Pipes & Tubes

Duplex Pipes & Tubes

Duplex stainless steel pipe fittings with grade 2205/31803 stainless steel consist of almost the same proportions of austenite and ferrite when they are properly heat treated. This microstructure of duplex stainless steel pipe grades equips it with more stress corrosion resistance cracking when compared to stainless steel 304 and 316L. Duplex stainless steel 2205 has a microstructure and has a more amount of chromium, Molybdenum, and Nickel content which is why it has significantly improved pitting and crevice corrosion resistance when exposed to chloride.

Chemical composition

GRADE

 

NI

CR

MO

C

MN

SI

P

S

N

S31803

MIN

4.5

21

2.5

0.08

MAX

6.5

23

3.5

0.03

2

1

0.03

0.02

0.2

S32205

MIN

4.5

22

3

0.14

MAX

6.5

23

3.5

0.03

2

1

0.03

0.02

0.2

Production Process

Processes such ERW (Electric Resistance Welded), Seamless and EFW (Electric Fusion Welding) are utilized to manufacture pipes and tubes with different forms such as round, square, rectangle, etc. with very specific ends as a plain end, bevel end, and threaded end which come with a nominal thickness of different schedules ranging from SCH 5 to SCH XXS.

Specifications

GRADE

UNS

OLD BRITISH

EURONORM

SWEDISH SS

JAPANESE JJ

BS

EN

NO

NAME

Duplex 2205/31803

S32205/S31803

318S13

1.4462

X2CrNiMoN 22.5.3

2377

SUS 329J3L

Stainless steel Duplex Seamless Pipe : ASTM/ASME SA 790/ A 790

Stainless steel Duplex Seamless tube : ASTM/ASME SA 790/ A 790

Stainless steel Duplex ERW Pipe          : ASTM/ASME SA 789/ A 789

Stainless steel DuplexERW Tube          : ASTM/ASME  SA 789/ A 789

Some of the popular processes used to manufacture duplex stainless steel pipe fittings are cold pilgering process, extrusion process, tube mill process, and piercing process where heat treatment and mechanical testing are recommended after the process.

Fabrication and Heat Treatment

Duplex Stainless steel has extra-ordinary hot formability with comparatively low forming loads i.e. the minimum of 1230°C. If hot forming happens at low temperatures, deformation may take place in weaker yet less ductile ferrite. Thus the ideal hot forming temperature is between 1100°C to 1150°C.

Solution annealing is recommended after hot forming followed by rapid quench which fully restores the mechanical properties and corrosion resistance of the duplex stainless steel pipe grades. Holding time is recommended for duplex stainless steel pipe fittings at temperatures of 650°C – 980°C before the previous full annealing.

Properties

Duplex Stainless steel tube suppliers will have a full chart of its properties which suggests that it has higher yield strength than SS304 & SS316L, and has corrosion cracking prevention properties very well due to the chromium oxide layers. Hence the corrosion rate is low in environments where humidity and chloride are found.

Physical properties

Grade

Density
(kg/m3)

Elastic Modulus
(GPa)

Mean Co-eff of
Thermal Expansion
(μm/m/°C)

Thermal Conductivity
(W/m.K)

Specific Heat 0-100°C

Electrical Resistivity
(nΩ.m)

0-100°C

0-315°C

0-538°C

at 100°C

at 500°C

(J/kg.K)

2205

7.82

190

13.7

14.2

20

418

850

The corrosion resistance of the duplex stainless steel tube and pipes is due to the formation of non-reactive chromium oxide (Cr2O3) film that is found adhered tightly to the surface of the metal. This coat of the chromium oxide acts as a barrier and protects the metal against corrosion which is perfectly suitable for marine applications such as pipelines and grills for oil, sewage, and water, risers for oil. 

Mechanical properties

Grade

Tensile Strength

Yield Strength

Elongation

Hardness, MAX

2205/1803

MPA

MPA

(% in 50mm) min

HB

HRB

655

485

25

290 max

30 max

Applications

Duplex stainless steel pipe fittings & tubes have various applications due to their stress corrosion resistance capability & high tensile, yield strength.

Some of the popular applications where duplex stainless steel pipe fittings and tubes used are:

  1. Pressure vessel, tanks, piping, and heat exchanger in the chemical processing industry 
  2. Handling of gas and oil where piping, tubing, and heat exchangers are needed.
  3. Effluent scrubbing system 
  4. Pulp and paper industry digesters, bleaching equipment, and stock-handling system 
  5. Rotors, fans, shafts, and press rolls where the combined requirement of strength and corrosion resistance is needed.
  6. Cargo tanks for ship and trucks 
  7. Food processing equipment
  8. Biofuels plants.