Duplex Stainless Steel design consideration

lecture

1. Welding of Duplex and Super
Duplex Stainless, Steels

2. ant Alloy Development

x Stainless Steels - Microtructure, Chemical
properties

Welding of DSS & SDSS

ite, Intermetalic Phases and Do &

3. Definition: A Stainless Steel must tain a minimum of 12%chromium

1 with sufficient chromium, steel ab n from the air to form and maintain a thin, transparent

, the laye

Additional alloying elements:
Nickel (Ni), Molybdenum (Mo), Manganese (Mn) and Copper (Cu).

4. - aqueous chloride containing
media (NaCl, K

presence of impurities must be considered for material selection as

5. rrosion resistant alloys

Which types of corrosion are encountered?

Uniform corrosion

Pitting corrosion CORROSIVE
Crevice corrosion .
Stress corrosion

Intercristalline corrosion

Galvanic corrosion

Dynamical load corrosion

=>
=
=
=
=
=
=>
=

Erosion corrosion

Corrosion: destruction of metallic materials through chemical
or electrochemical reaction with their environs

6. on resistant allo

To counter the effects of corrosion, you need:

|

Elements to build a passivation layer in oxidizing media

| Cr ) (Ni) (Ti Mo

Elts enhancing the resistance against attacks of other media

LA M (Al)
(Cu Mo) =
- Se Higher Resistance
Resistance Resistance against against
against sea- chlorides in oxidation at high
water reducing media temperature

7. rostructures

thermal conductivity t thermal conductivity ||
thermal expansion | thermal expansion {|

Lattice Structure

Ferrite
Austenite

Martensite Austenite

strength

toughness

sensibility to
heat input

AAA AAA A

8. ‘stainless Steels

[C-Alloys - Nickel Alloys

IBAltoys

12. x Stainle

13. LEAN DUPLEX

STANDARD —
DUPLEX

SUPER-DUPLEX

HYPER-DUPLEX

14. LEAN DUPLEX

STANDARD —
DUPLEX

SUPER-DUPLEX

HYPER-DUPLEX

15. ical properties

Da
. How ea: sfer in the material
DL me e vim

Thermal expansion

How the heat expand the ma

16. x Steels

Chemical composition

Grade

ASTM

EN

Chemical composition (typical values wt-%)

C (max)

N

Cr

Ni Mo

LDX 2101°

Filler LDX

S32101

1.4162

[(237NL)

0.02

0.03

0.22

0.16

1e [708

7 | 25

2304

Filler 2304

S32304

1.4362

[237NL)

0.02
0.02

0.10

0.12

| <03

2205

Filler 2205

532205
E2209

1.4462

[2293NL

0.02
0.02

0.17

2507

832750

1.4410

0.02

Filler 2507

E2594

2594NL

0.03

17. Chromium Ferrite former

Austenite former

Nitrogen (N) Austenite former

denum (Mo) Less than 5 Ferrite former

Increasing Cr will increase corrosion resistan
The ferrite content increases with incre Cr; h y, too
much Cr will decrease optimal phase bala

Ni promotes a change in crystal structure
austenite.

Ni delays the formation of intermetallic phases.
N causes hustenite to form from ferrite at elevated temperatures,
allowing for restoration of an acceptable balance of austenite to
ferrite after a rapid thermal cycle in the HAZ after welding.
Additions of N increase pitting and cr
and strength
Delays the formation of int
Offsets the formation of sigma phase in high Cr, high Mo steels
Enhances pitti istance.

intermetalli

18. igma phase

Super duplex grades have a high risk of
ertain temperature

Precipitation of 1 phase at 750
1000°C
sition at 350-525°C

w heat” welding operations

19. eneral properties of duplex grades

LOX 2101

Austentic |

LOX 2404®

254 SMO

30 50 60 70

Corrosion resistance, ASTM G150 CPT

20. LOK 240 MPa

*Not yt included in API SD Appendix
The design ses shal be ¿Ren

Potential weight
saving as a substitute for 4404

~40%

mm)

21. 2Cr - DSS Interactive Requirements

Method A: 6 mass-% FeCl;
CPT: 25°C/24 h WM + BM

s . PRE, Cr%+3,3(MO+0,5WI+ 16N%
UNS 531803, UNS $ 32205 % Ferrite 30 < PRE, < 40: ferrite 35-65%
Ferrite 35 - 65% WM HAE

Rp0,2 > 450, Rm > 620MPa, Rp, RM, e
A> 25% HV40 Max. working temp 232°C
CVN -46°C > 45J PRE, Cast and wrought products
CPT G 48 A: 25°C/24h WM d

<4g/m2 WM

Ferrite 30 to 70% WM corr, test temp.* BM + WM:22°C/24 h
CVN -46°C: 27 J WM+FL CVN-40°C BM, HAZ: 54J, WM 34 J
Hardness max 36 HRC *) detection of intermetallic's e.g.

(DIN EN 1S015156-3) sigma phase

22. > Requireme
ASTM G 48 A + E - 200:

E: 6 mass-% FeCl; +19%HCI

CPT: BM and WM
o a Start temp 20°C / 24h

Ferrite 35-65% WM SAC NACE MR 0175-20
RPoz >550, Rm >795MPa, A > 25% e PRE, Cr6+3,3(MO+0,5W)+16N%
CVN -46°C > 45J % Farrite 40 < PRE, s 45; ferrite 35-
CPT: ASTM G48 A: 50°C/24h a Os

S: 20 KPA
no pits, < 4,0 g/m? => WM/BM Ya Max. working temp 232
} PRE, Cast and wrought products

NORSOK M-601(2016 ASTM A 923-8
Ferrite 30 to 70% WM corr. test temp.” BM: 40°C/24 h
IN -46°C: 27 J. WM +FL CVN-40°C BM, WM: negotiable!
CPT ASTM G 48 A: 35°C/24h WM *) detection of intermetallics
no pits, < 4,09/m? WM e.g. sigma phase
(DINEN |

25. Ferrite content differences — Heat Input & Proce

= The ferrite content in the weld metal depends largely on the process, the heat input
and the chemical composition of the filler

= Example from IA in an Outokumpu project together with Institut de la Soudure in
France:

Ferrite measurements with image analysis - LOX2101° with 2209 fillers

|
|
|
|

MAG TG

26. Ferrite in c

Based on experience, the following

ferrite content ranges can

appropriate mechanical and corrosion properties of the wel

SMAW - FCAW —
SAW

GMAW - GTAW —
PAW

All processes

Weld Metal

Weld Metal

HAZ

Ferritoscope
Ferritoscope

Point grid at > x
400

recommended to obtain the

20to 35
20 to 40

20 to 50
20 to 60

<70

27. « Selection of welding process

Depends on availability of power source, consumables,
desired properties & economics considerations.

Autogenous welding processes such as GTAW without
filler, EBW and LBW are not at all suitable for welding of
these steels because the heat creates high ferrite
‘amount and phase balance is disturbed.

for welding of these steels.

When it comes to achieving better impact toughness
values, studies and experience shows that a gas shielded
welding process gives better results as compared to that of
flux-shlelded welding process

28. « Selection of welding consumable
Matching filler chemistry to the base metal would yield a

weld metal deposit with high ferrite content, off
balancing the optimal ferrite - austenite phase required

Hence, it requires N and Ni to be added through filler wire
o to ensure phase balance

Nickel based welding consumables such as NiCrMo-10,

NICrMo-3 8 NICrMo-14 can be very well used
So for a DSS 2205 use 2209 (22Cr-9NI) welding consumable
&

for a SDSS 2507 use 2594 (25Cr-9Ni-4Mo) welding
consumable

For dissimilar welds between DSS to CS/LAS/ASS, preferably
DSS filler should be used. However case by case review is
Necessary for process consideration & design requirement.

29. « Thermal Effects of Pre-heat, Inter-pass and Heat input

DSS generally does not require any preheat however it should
be free of moisture before welding. Max 100°C preheat may
be applied to remove moisture and cooled before welding

Heat input during welding plays a vital role in optimal phase
balance and properties achieved.

Too low heat input : Weld is predominantly ferritic

Too high heat input: Slow cooling rates, chances of inter-
metallics phases to form in weld and in HAZ

Excessive inter-pass temperatures can cause embrittlement 8:
low impact values.

For SDSS max inter-pass: 100°C & for DSS max inter-pass: 120°C

DSS: Heat input 0.
SDSS: Heat input 0.

30. TxUx 60

HEAT INPUT = ———_ Kkirem]
Vx 1000

HI: 8- 12kJ/cm
HI: 10 - 15 kJ/cm

High thermal loading on the root pass increases the risk for:

U precipitation of intermetallic phases !

Q reduced corrosion resistance

31. TxUx 60

HEAT INPUT = ————_ Kkiem]
Vx 1000

HI: 8- 12kJ/cm
HI: 10 - 15 kJ/cm

High thermal loading on the root pass increases the risk for:

U precipitation of intermetallic phases !

Q reduced corrosion resistance

32. ce of Heat Input

Slow cooling rate in the case of HI > 15 kJ/cm
IxUx60
HEAT INPUT = ———————._[KJ/em]
Vsx 1000

Increased risk of precipitation of inter-metallics
Structural instability

Decreased corrosion resistance

Decreased toughness

Avoid high heat input in hot pass to
minimize sigma in root bead =
=
7
L

Bulky Root

Interpass temp. < 120°C for DSS
< 100°C for SDSS

33. - Reduced penetration
all

Weld in a gap (2-4mm - fille
- Reduced fluidity

- Wider joint preparation +

34. High nitrogen
Can be avoi
Other

Flux

FCAW porosity in superduplex weld metal — 5G (PE) position

35. than stai

Art 30% He + 1-3% C

Art 2% O2or Art 2-3% CO2

High BM nitrogen content incre
duplex pure argo!

Spatter and embedded slag short arc

dard austenitic fillers

| em slag spray arc

36. uplex s

+ TIG Welding without filler:

Crack in feeding screw in 12 mm standard duplex 2205

Welding in horizontal position

Welder unsatisfied with visual appearance -GTAW treatment without filler metal
Ferrite content locally 80-90% -brittle weld and cracked after short time in service
On whole feeding screw.. o

GTAW treatment without
filler completely forbidden
on duplex constructions

37. Austenitic fil

200h with3

Austenitic weld metal with 1
-resulted in SCC in UNS S3

fillers

38. DNV
(Rules for Ships)
SPIE-CAPAG | >40J

NAM/NL
(NSS 60)
Shell/UK
(ES 124)

39. Impact energy value:

*) measured at all weld metal (EN 1597-1)

[D
0 [phone] +20

42. To thin or thick beads increase the risk

Wrong joint preparation increase the risk due to high degree of parent metal fusion &
of nitrogen gas in the solidifying metal

Inadequate gas protection