How to Weld Duplex Stainless Steel Mechanical16April09

7/31/2019 How to Weld Duplex Stainless Steel Mechanical16April09

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Av e st a We l d i n g

Ho w t o w e l dDu p l e x St a i n l e s s St e e l

LD X 2 1 0 1 2 3 0 4

2 2 0 5

2 5 0 7

B i l l A i t k e n

Na t ion a l Sa l e s Manage r

B o h l er W e l d i n g A u st r a l ia


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Av est a W el d i n g ap a r t o f t h e B h le r w e l d i n g g r o u p


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D u p l e x St a i n l ess St e el - Ch a r a ct e r i s t i cs

Austenitic-ferritic stainless steels usually referred to as Duplex steels.

Duplex means two 50% ferrite and 50% austenite.

Characteristics include:

High yield strength, double that of Austenitic or Ferritic grades of S/S.

Good ductility, easy to form with approximately 20-30% elongation.

Good impact strength >-40C.

Maximum working temperature of +250C. The high Cr in combination with Ni gives superior resistance to both pitting and crevice

corrosion.

Excellent weldability.


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D u p l e x St a i n l ess St e el - Use s

Th a n k s t o t h i s e x ce p t i o n a l co m b i n a t i o n o f st r e n g t h a n dco r r o si o n r e si st a n ce , d u p l e x s t e e l s a r e w i d e l y u s ed f o r :

Heat exchanges

Water heaters

Pressure vessels

Storage tanks

Rotors, impellers and shafts

Digesters and other equipment in pulp and paper production

Cargo tanks in chemical tankers

Desalination plants

Waste gas purifiers

Sea water systems


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D u p l ex St a in l e ss St e el - M icr o s t r u c t u r e

After welding, cooling is often very rapid and little time for austenite toform.

To help balance the structure filler metals are over-alloyed with nickel.

Nitrogen is also used as a austenite stabilizing element.

Welds between 20 to 70% ferrite are in a normal range and have goodcorrosion and mechanical properties.

Microstructure of Duplex2205 Mag. X250


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D u p l e x St a i n l ess St e el M ech a n i ca l p r o p e r t i e s

UN S N am e Yi e l d Ten si l e Elo n g a t i o n

S3 0 4 0 3 3 0 4 L 3 0 k si 7 5 k si 4 0 %

S3 1 6 0 3 3 1 6 L 3 0 7 5 4 0

S3 2 1 0 1 2 1 0 1 6 5 9 4 3 0

S3 2 3 0 4 2 3 0 4 5 8 9 1 2 5S3 2 2 0 5 2 2 0 5 6 7 9 6 2 5

S3 2 7 5 0 2 5 0 7 7 7 1 0 6 2 0


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F a b r i c a t i o n

Duplex steels are suitable for most forming operations.

However due to higher mechanical strength and low toughness,

operations such as deep drawing, stretch forming and spinning

are more demanding to perform than with Austenitic steel.

The high strength of Duplex grades, may cause a relatively high

spring back.

Segmented head 12500 x

50 mm in Duplex 2205


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Co l d Fo r m i n g

Due to the high proof strength of Duplex material, greater

working forces are required when compared to Austenitic steel.

H o t Fo r m i n g

The strength of Duplex material is low at high temperatures.Hot working should be followed by quench annealing.


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Duplex steels are characterized by high strength.

High strength also means that fatigue properties are very good.However, fatigue strength is dependent on:

The components design shape.

The welded joint itself.

The welding method and joint type are also of great significance.

Example:

A TIG welded joint has better properties than one made withcovered electrodes.


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D u p l e x St a i n l ess St e el Co r r o si o n r e si st a n c e

For the most part, the corrosion resistance of a welded joint isslightly lower than the parent material.

This is mainly due to:

The temperature cycle undergone by the weld in the HAZ.

The shape of the weld surface.

Contaminates and defects that can be generated in welding.

To achieve the best possible corrosion resistance:

The surface of the weld and the plate must be clean and even.

After welding, the weld metal and the HAZ must be pickled


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D u p l e x St a i n l ess St e el Co r r o si o n r e si st a n c e

Stress corrosion crackingcaused by grinding

Pitting caused by

grinding spatter


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D u p l e x St a i n l e ss St e e l Co r r o s i o n r e s i st a n c e. Co n t .

Typical critical pitt ing t emperat ures (CPT) as per ASTM G48 parent m etal and

weld, br ushed and pickled TIG joint .


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D u p l e x St a i n l e ss St e e l Co r r o s i o n r e s i st a n c e. Co n t .


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LD X 2 1 0 1

- N i ck e l p r i ce in f l u e n ce o n A ll o y Su r ch a r g e

Nickel LME

AAF

$/ton

0

200

400

600

800

1000

8000 $/ton 10000 $/ton 15000 $/ton

1.4301LDX 2101


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14

12

10

8

6

4

2

16 12 8 4 0[mm]

Minimal thicknessaccording to standard = 6 mm

Required thickness LDX 2101

[m]

Required thickness 304

LD X 2 1 0 1

- Co st a d v an t a g e - Tan k

1.4301

64.9 ton

LDX 2101

36.6 ton


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Du p l ex St a i n l ess St e e l W e ld i n g m e t h o d s

All conventional welding methods can be used i.e.

MMAW, GMAW, GTAW, SAW, FCAW, PAW & LAW.

Property requirements, positional weldability and

productivity usually determine the choice of weldingmethod


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MMAW

Excellent for positional welding or single sided welding where accessis limited.

DC+ gives best results.

A short arc should be used. This gives the best stability and reduces

the risk of nitrogen pick-up. The later can lead to pore formation andincrease surface oxidation.


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GMAW

Good for welding sheet/plate up to 6mm.

Welding is usually from two sides but material


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SA W

High productivity with excellent weld finish.

Work environment considerably better than other methods.

Disadvantage is that it is restricted to horizontal position.

Large heat input, consequently small job present a problem.

A basic agglomerated flux must be used.


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FCAW

Suitable for material over 5mm.

Single-sided welding possible using a ceramic backing. Fast and efficient process.

Excellent surface appearance.


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La se r , l a se r h y b r i d a n d p l a sm a w e l d i n g

Are all high productivity methods.

If filler metal is not used the workpiece must but heat treated.

Penetration can be controlled.

Low heat input. Zero tolerance for weld preparation.


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D u p l e x St a i n l ess St e el Sh i e l d i n g g a s se le ct i o n

Sh i e l d i n g ga se s


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D u p l ex St a in l e ss St e el W e ld j o i n t p r e p ar a t i o n


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D u p l ex St a in l e ss St e el W e ld j o i n t p r e p ar a t i o n


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D u p l ex St a in l e ss St e el Ta ck w e ld i n g

To prevent shrinkage during welding precise tacking is important.

For material up to 6mm tack length should be 10-15mm.

Above 6mm tack length should be 20-25mm.

Distance between tacks is 150-200mm.

In single sided welding, the entire tack must be ground away

before welding. In double sided welding it is sufficient to grind away the beginning

and the end of the tack.


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D u p l ex St a in l e ss St e el St a r t s an d st o p s

St r i k i n g a n d ex t i n g u i sh i n g t h e ar c

Important to use the correct technique when striking and

extinguishing the arc. In regards to the metallurgical, mechanical and corrosion properties,

each start and stop is critical.

Avoid arc scars always strike arc in joint.

If scars occur they must be carefully repaired by grinding andpolishing or in worst case, repair welding.

All crater cracks and slag inclusions must be removed.

Grinding scars


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D u p l ex St a in l e ss St e el Pl an n i n g t h e w e ld s eq u e n c e

Ro o t b e a d s

To ensure correct metallurgy and structure of the final weld, the rootgap must be sufficient to allow the correct quantity of filler metal.

Must have the correct geometry i.e. no concavity, undercutting orlack of fusion.

Best possible productive welding method.

Single sided TIG root bead


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Fi l l e r b eads

Must be deposited with the highest possible productivity.

Generally speaking, welding is carried out with the highestpossible heat input that is consistent in maintaining propertiesand weldability.

Visual inspection between passes. Slag residues and welding oxides removed before depositing

next layer.

So m e w e l d i n g p r o c e ss co m b i n a t i o n s : TI G root pass + MMA, MI G, or SAW fill passes MMA root pass + SAW or FCAW fill passes


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Th e cap bead

Primarily intended to give the weld good corrosion resistance andsome structural integrity.

Undercut, unevenness, excessive reinforcement, gaps, etc all havea negative impact on corrosion resistance.

Aesthetic considerations are often also important.


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D u p l ex St a in l e ss St e el W e ld i n g t e ch n i q u e s

In the flat position there should be no weaving.

Vertical up position weaving of up to 20mm is advantageous.

For Sub-Arc a 10-15 forehand welding direction increasespenetration. This allows the root face edge to be welded up to 8mm.

Avesta 3D Electrodes

Competitor


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D u p l ex St a in l e ss St e el D ist o r t i o n a n d p r e h e a t i n g

D i s t o r t i o n

Coefficient of expansion is lower than austenitic steels.

It is slightly higher than carbon steels.

However, this does not mean that tack welding can besimplified.

P r e h e a t i n g

On a whole, S/S do not require preheat.

Welding takes place at room temperature At low temperatures a maximum of 50C preheat is

advisable to drive off any moisture.


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Du p l ex St a i n le ss St ee l I n t e r p ass t e m p er a t u r e

LDX 2101 is 150C

2304 and 2205 welded below 200C

SAF 2507 is far more sensitive and should not be welded above100C.

Thermal conductivity is same as austenitic and lower thancarbon steel. This means it takes longer to reach the correctinterpass temperature.

Interpass temperature must be measured.

Avoid thermal cryons.


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D u p l ex St a in l e ss St e el H ea t i n p u t

Ge n er a l r e co m m e n d a t i o n s

2304 max. 2.0kJ/mm

2205 max. 2.5kJ/mm

LDX 2101, SAF 2507 max. 1.5kJ/mm

Duplex should not be welded with too low a heat input.

Could cause high cooling rates resulting in ferrite above 70%

Minimum heat input is 0.5kJ/mm

Heat input = U X I

V X 1,000

U = voltageI = currentV = speed mm/s


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D u p l ex St a in l e ss St e el Po st w e ld t r e at m e n t

Clean prior to pickling to

remove contaminates withAvesta cleaner 401.

Pickle for 1 hour with RedOnepickling paste.

Rinse methodically.


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BEFORE W ELDI NG A slightly wider root gap and joint angle than for standard stainless steel. Thoroughly clean joint. Only stainless brushes should be used. Preheating is normally not recommended. Joint preparation by Plasma cutting should be followed by grinding to

remove oxide layer. Electrodes and Sub Arc Flux should be re-baked before welding.

Conc l us i ons


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Conc l us i ons

DURI NG W ELDI NG Use the right heat input. Avoid striking the arc outside the joint. Use the correct root gas. Keep welding Gun 90 to joint Do not draw a long arc when welding

Avoid excessive weaving. Heat input from 0.5-2.5kJ/mm Interpass temperature 100-200C Avoid rapid cooling and low heat inputs.

Tig is strongly recommended for root passes in one-sided welds. Welding against copper-backing should be avoided because of the risk

of too rapid cooling.


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Conc l us i ons

AFTER W ELDI NG

Thorough cleaning of all slag and oxide on and around the weld mustbe removed.Brushing should be done manually because of the risk of micro-crevices.Post weld heat treatment is not normally needed.Pickling recommended.


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Full range of consumables for welding stainless steel and nickel base alloys

Covered electrodes MIG wire TIG wire Sub arc wire and flux Flux cored wire

Martensitic, austenitic,austenitic-ferritic (duplex),fully austenitic and heat

resistant steels anddissimilar weldingbetween stainless andmild steel or nickel basealloys.

Av est a W e ld i n g co n s u m a b l e r a n g e


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Pa st e / Ge l S o l u t i o n B a t h Cleaning N e u t r a l i s i n g P a s s i v a t i n g Accessor ies

All pickling products conform tointernational standards:ASTM A-38 0, BSI CP-301 2, KW U RE-AVS 8 ,RCCM F-50 00 -60 00

Av e st a Fi n i s h i n g Ch e m i ca l r a n g e


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w w w. a v e s t a w e l d i n g . c o m

Our web - site contains a lot of interesting and useful

information about welding andpickling of stainless steel.

Be st i n St a i n l e ssYou are welcome to visit us on

www.avestwelding.com

www.avestafinishing.com

Documents

How to Weld Duplex Stainless Steel Mechanical16April09