Duplex Stainless Steel Welding

8/11/2019 Duplex Stainless Steel Welding

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WHAT ARE DUPLEX STEELS

Duplex Steels are also called FERRITIC-

AUSTINITIC steels.

Duplex Steels have approx. 50% ferritic and 50%austinitic structure.

Ferrite provides Strength and Resistance to

localized Corrosion and also refines austinitic

structure.

Austinite provides Toughness and Weldability


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DUPLEX STEELS


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UNS

N

u

m

be

r

D

up

le

x

Gr

ades

Typeb C Mn P S Si Cr Ni Mo N Cu Other

S31200 ... 0.030 2.00 0.045 0.030 1.00 24.0-26.0 5.5-6.5 1.20-2.00 0.14-0.20 ... ...

S31260 ... 0.03 1.00 0.030 0.030 0.75 24.0-26.0 5.5-7.5 2.5-3.5 0.10-0.20 0.20-0.80 W0.10-0.20

S31803 ... 0.030 2.00 0.030 0.020 1.00 21.0-23.0 4.5-6.5 2.5-3.5 0.08-0.20 ...

S32001 ... 0.030 4.0-6.0 0.040 0.030 1.00 22.0-23.0 1.00-3.00 0.60 0.05-0.17 1.00

S32205 2205 0.030 2.00 0.030 0.020 1.00 19.5-21.5 4.5-6.5 3.0-3.5 0.14-0.20 ...

S32304 2304 0.030 2.50 0.040 0.030 1.00 21.5-24.5 3.0-5.5 0.05-0.60 0.05-0.20 0.05-0.60

S32520 ... 0.030 1.50 0.035 0.020 0.80 24.0-26.0 5.5-8.0 3.0-4.0 0.20-0.35 0.50-2.00

S32550 255 0.04 1.50 0.040 0.030 1.00 24.0-27.0 4.5-6.5 2.9-3.9 0.10-0.25 1.5-2.5

S32750 2507 0.030 1.20 0.035 0.020 0.80 24.0-26.0 6.0-8.0 3.0-5.0 0.24-0.32 0.50

S32760 ... 0.030 1.00 0.030 0.010 1.00 24.0-26.0 6.0-8.0 3.0-4.0 0.20-0.30 0.50-1.00 c

S32900 329d 0.06 1.00 0.040 0.030 0.75 23.0-28.0 2.5-5.0 1.0-2.0 ... ...

S32950 ... 0.03 2.00 0.035


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HEAT TREATMENT

Thermo-Mechanical treatment is carried out

by rolling at 900-950C which results in

fine dispersion of ferrite and austinite which

are called Micro-Duplex steels having grain

size upto 3-10 micro metre.These steels

exhibit super plasticity means ductilities ofabout 500% at temperatures near 950C.


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PHYSICAL PROPERTIES

Thermal conductivity is higher than

austinitic stainless steels.

Temp(F) 68 200 400 600 800

SAF 2205 9.0 9.5 11.0 11.5 12.5

AISI 316 L 8.5 9.0 10.0 11.0 11.5


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CORROSION RESISTANCE


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Pitting Corrosion

Pitting resistance is determinedby Cr,Mo and N contents.We define Pitting

Resistance Equivalent(PRE).PRE=%Cr+3.3*%Mo+16*%N

PRE number for some steels

Alloy %Cr %Mo %N PRE

SAF 2205 22.2 3.2 0.18 35.06

AISI 316 L 17 2.1 _ 24

AISI 317 L 18 3.5 _ 30


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Resistance to SCC

Austinitic steels are prone to

SCC above 60C but Duplex Steels according

to laboratory tests have good resistance to

SCC.


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MECHANICAL PROPERTIES

Hardness Tensile strength %Elongation

SAF 2304 230 BHN 600-820N/mm 25

SAF 2205 260 BHN 680-900N/mm 25

YIELD STRENGTH

0.2% offset 1.0% offset

SAF 2304 400N/mm 450N/mm

SAF2205 450N/mm 500N/mm


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MECHANICAL PROPERTIES

Impact Strength:

Good impact

strength both at higher

and lower temperatures.


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APPLICATIONS

Heat exchangers where chloride bearing water or

brackish water is used as cooling medium

For use in dilute sulphuric acid solutions. For handling of organic acids e.g acetic acids.

In refineries and as flow lines for extraction of oil

and gas from sour wells.


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CERTIFICATION

Approved by the American Society ofMechanical Engineers (ASME) for use in

boilers and presssure vessels. NACE MR 01759 (sulphide stress

cracking resistent material for oil fieldequipment)

ASME B31.3 Chemical plant andpetroleum refinery piping.


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WELDING OF DUPLEX STEELS

The procedure that is carried out in welding ofDuplex steels is as followed

1-Cleaning Before Welding:-

Duplex stainless steels aremore sensitive to contamination and moisture thanother steels. As impurities effect corrosion resistanceand mechanical properties of weldment.

2-Joint Preparation:-For duplex steels,a weld joint mustfacilitate full penetration.the root gap must be widerthan that of austinitic steels.


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Filler Metals:-Filler metals must always be used in weldingof duplex steels because PWHT is not made so

ductility and corrosion resistance can decrease due

to loss of austinite content in weld metal.WeldingWelding without filler metal must be avoided for

all duplex steels in high quality demanding

applications where quench annealing cannot be

performed after welding.


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Sandvik C

max

Si Mn Pmax

Smax

Cr Ni Mo N

22.9.3

Covered

0.03 1.0 0.8 0.025 0.020 22.5 9.5 3 0.14

22.8.3

Wire

0.020 0.5 1.6 0.020 0.020 22.5 8 3 0.14

23.12.2

Covered

0.04 0.8 1.0 0.03 0.03 23 13 2.7

_

22.15.3

Wire

0.025 0.4 1.5 0.025 0.020 21.5 15 2.7 _


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GMAW Welding

1-Wire Electrode:-

Sandvik 22.8.3.L should be chosen as filler metal forSAF 2205 and SAF 2304.

2-Shielding Gases:-Spray arc: Argon,oxygen(1-3%)

Short arc: Argon,Carbon dioxide(1-3%)

3-Backing Gases:-

Backing gases are required regardless of jointdesign.Argon,argon-nitrogen mixtures,nitrogen or Formler gasare used.


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Typical Parameter Settings

Wire dia Current Voltage

Spray arc transfer

0.8 170-200 26

1.2 180-260 29

1.6 230-350 30

Short arc transfer0.8 90-120 19-21

1.2 110-140 20-22


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TIG Welding

1-TIG Rods:-

Sandvik 22.8.3L is used for SAF 2205 SAF 2304 andSandvik 25.10.4.L is used for SAF 2205 and SAF 2507.

2-Shielding Gases:-

Argon,argon+2%nitrogen or argon helium mixtures.

3-Baking Gases:-

Backing gases are required regardless of joint design.Argon,argon-nitrogen mixtures,nitrogen or Formler gas are used.


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4-Typical Parameter Settings:-

Parameter settings in TIG welding are largelydependent upon the material thickness,type of joint etc.For

example a typical root pass may use 100amps/11 volts at atravel speed of 60mm/min giving a heat input of 1.1kj/mm .

SAW WELDING

1- Wire electrodes and flux:-

Sandvik 22.8.3L is used for SAF 2205 SAF 2304and Sandvik 25.10.4.L is used for SAF 2205 and SAF2507.The flux sandvik 15W is recommendedfor all threegrades.


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2-Typical Parameter Settings:-


2.4 250-450 28-32

3.2 300-500 29-34

4.0 400-600 30-355.0 500-700 30-35


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SMAW WELDING

1- Covered electrodes:-

Sandvik 22.9.3L is used for SAF 2205 SAF 2304

and Sandvik 25.10.4.LR is used for SAF 2205 and SAF 2507.2-Typical Parameter Settings:-


2.0 35-55 22-28

2.5 50-75 22-283.25 70-120 22-28

4.0 90-160 22-28

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Duplex Stainless Steel Welding