248221054 low temperature behavior of austenitic weldments

8/18/2019 248221054 Low Temperature Behavior of Austenitic Weldments

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Welding of austenitic stainless steels forcryogenic LNG applicationsLow Temperature Behaviour of Austenitic Weldments

Norbert Friedrich, Application Technology, Böhler Welding Austria GmbH, AustriaGerhard Posch, Head of Research & Development, Böhler Welding Austria GmbH, AustriaJosef Tösch, Research & Development, Böhler Welding Austria GmbH, AustriaJohann Ziegerhofer, Research & Development, Böhler Welding Austria GmbH, AustriaWalter Berger, Managing Director, Böhler Welding Austria GmbH, Austria

Keywords: LNG, High alloyed weldments; controlled ferrite content, cryogenic application

Abstract:Austenitic stainless steels of type AISI 304/304L and AISI 316/316L are commonly usedfor the storage and distribution of liquefied natural gas (LNG). The steels have to operateat very low temperatures, which is the reason why high requirements regarding toughnessand lateral expansion at -196°C are demanded. From the metallurgical point of view, lowamounts of delta ferrite in the weld metal are necessary to achieve the requirements. Thispaper deals with typical values for delta ferrite content and mechanic

al properties whichcan be achieved with special designed filler metals for GTAW, SMAW and FCAW.Emphasis is also given to the hot cracking susceptibility, which increases dramatically withvery low delta ferrite contents.

1 IntroductionThe demand for oil and gas is increasing steadily and forecasts (Figure 1) promote forexample a gas consumption in 2020 which is about three times higher compared to1980.To secure the supply with oil and gas new production plants, transport and storagesystems have to be installed within the next decade and many plates and tubes of variousmaterials have to be fitted together to establish the necessary tankand tubing systems.Welding plays thereby an important role.

Figure 1: World oil and gas demand (forecast) [1]


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Form the materials point of view, the handling of gas is a very interesting topic. Due to thehigh volume of gas, storage and transportation should be done with liquefied gas, becausein this case the volume of the liquid is approx. 1/620 of the equivalent gas. The mainªdisadvantageº thereby is, that gas is liquid only at very deep temperatures and the

usedmaterials have to exhibit strong toughness requirements at very low temperatures.In Figure 2 typical materials which fulfil the requirements for handling liquefied natural gas(LNG) are shown.

Application Type AlloySpherical or prismatic storage tanks forship transportation of LNG.Tubing for the main cryogenic heatexchanger.

Forgings such as flanges.Aluminium alloy 5083 (Al-4.5 % Mg)Alloy 5154 (Al - 3,5% Mg)Alloy 6000 (Al - Si)AlSometimes for large storage tankconstruction.Piping in critical applications.Low expansion 36 % Ni-Fe alloy 36NiFePiping; Small vessels.Sometimes for large storage tanksStainless steel type AISI 304 L 304 LStorage tanks

9 % Ni Steel 9 NiApplication Type AlloySpherical or prismatic storage tanks forship transportation of LNG.Tubing for the main cryogenic heatexchanger.Forgings such as flanges.Aluminium alloy 5083 (Al-4.5 % Mg)Alloy 5154 (Al - 3,5% Mg)Alloy 6000 (Al - Si)AlSometimes for large storage tankconstruction.Piping in critical applications.Low expansion 36 % Ni-Fe alloy 36NiFePiping; Small vessels.Sometimes for large storage tanksStainless steel type AISI 304 L 304 LStorage tanks9 % Ni Steel 9 Ni Figure 2: Typical applications of established base materials used for LNG [2]

The austenitic grades, especially the austenitic weldments are the focu

s of this paper. Ithas to be mentioned that beside grade AISI 304L also type AISI 316L will be used more


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often in future. For joining these grades filler metal type 308L and 316L are used.The liquefaction temperature of Methane is -163°C ( -261°F) and this factdetermines theoperating temperature of the LNG plant. The test temperature for mechanical propertieshas been set to -196°C (-320°F) due to safety reaso ns but also of the easy reproduc

ibilityof this test condition.Before setting up the requirements for LNG weldments the general mechanical propertiesof the austenitic steel and the main influences on the achieved testdata have to bediscussed.

2 Strength properties austenitic steels for LNGapplication

Strength design is primarily done using room temperature properties. The all weld metalproperties at room temperature are quite similar independent of the applied weldingprocess (Figure 3).

ER308LE308LT1-4E308LT1-1E308LT0-4E308LT0-1EC308LE308L-17

E308L-15ER308L SiER308LAWS40 570 390FCAW EAS 2 PW-FD35404040423839A5[%]560 380FCAW EAS 2-FDEAS 2-UP//BB 202EAS 2-MCFOX EAS 2-AFOX EAS 2EAS 2 ±IG (Si)EAS 2 -IGBöhler Brand630 420

GMAWSAWGMAW


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SMAWSMAWGTAWProcess610 430540 350550 350

560 390580 400Rm[N/mm²]Rp0,2[N/mm²]ER308LE308LT1-4E308LT1-1E308LT0-4

E308LT0-1EC308LE308L-17E308L-15ER308L SiER308LAWS40 570 390FCAW EAS 2 PW-FD35404040

423839A5[%]560 380FCAW EAS 2-FDEAS 2-UP//BB 202EAS 2-MCFOX EAS 2-AFOX EAS 2EAS 2 ±IG (Si)EAS 2 -IGBöhler Brand630 420GMAWSAWGMAWSMAWSMAWGTAWProcess610 430540 350550 350

560 390580 400R


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m[N/mm²]Rp0,2[N/mm²] Figure 3: Mechanical properties of consumables type 308L for various welding pro

cesses

The mechanical properties are also hardly influenced by variation of the delta ferritecontent and the electrode diameter as shown in Figure 4 using for example an electrodeof type E 308L-15.

6,4 ± 7,6 550 401 3,2 E308L-156,9 ± 7,8 551 400 5,0 E308L-156,3 ± 7,5 547 395 4,0 E308L-15

9,5 ± 10,3 603 421 2,5 E308L-15Rm[N/mm²]Rp0,2[N/mm²]Ø[mm]ElectrodetypeFerrite *[FN]

6,4 ± 7,6 550 401 3,2 E308L-156,9 ± 7,8 551 400 5,0 E308L-156,3 ± 7,5 547 395 4,0 E308L-159,5 ± 10,3 603 421 2,5 E308L-15Rm[N/mm²]Rp0,2[N/mm²]Ø[mm]ElectrodetypeFerrite *[FN]*FERITSCOPE MP 30 Figure 4: Mechanical properties all weld metal BÖHLER FOX EAS 2 (AWS E308L-15)

It is very well known that decreasing temperatures increase the strength of the austeniticsteel.

Figure 5 shows some strain/stress curves for the base material at var

ious temperaturesand points out the strong effect of the temperature on the strength.


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Figure 5: Tensile test specimen stress vs. strain curves of SS grade AISI 304

3 Toughness properties of austenitic steels forLNG application

As it clearly can bee seen in Figure 5 at lower temperature the elongation, but also thetoughness of the austenitic steel decreases. To establish safe LNG constructions it isnecessary to set strong toughness requirements at operating temperatures. Therefore thelateral expansion and the impact energy are very useful material property data fordescribing low temperature toughness behaviour of the metal.

3.1 Lateral expansion and impact energy

By comparing lateral expansion and impact energy a correlation also at very lowtemperatures can be seen (Figure 6). This correlation is influenced by the weldingprocess, type of welding consumable and slag system.

0,40,60,811,220 30 40 50 60 70 80

lat. expansion[mm]Ø 3,2/350 mmImpact energy [Joule] Figure 6: Relation between lateral expansion and impact energy at -196°C; consumable:BÖHLER FOX EAS 2 (E 308 L-15)

3.2 Toughness and delta ferrite content

A very important correlation can also be found between impact energy


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and delta ferritecontent of the weld metal. At higher ferrite levels the impact toughness is significant lowercompared to lower ferrite levels. As an example Figure 7 shows this influence dependingon the diameter of a stick electrode of type E308L-15 under quite extreme welding

conditions.203040506070802 3 4 5 6 7 8 9 10 11 12Ferrite content [FN]Im

pact valuesAv

[J], ISO-VØ 4,0Ø 3,2Ø 2,5Pos. PF (3G)Heat input > 2,75 kJ/mm2,545°13304 L1.43064,03,2203040

506070


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802 3 4 5 6 7 8 9 10 11 12Ferrite content [FN]Impa

ct valuesAv[

J], ISO-VØ 4,0Ø 3,2Ø 2,5Pos. PF (3G)

Heat input > 2,75 kJ/mmPos. PF (3G)Heat input > 2,75 kJ/mm2,545°13304 L1.43064,03,2 Figure 7: BÖHLER FOX EAS 2 (E308L-15); Ferrite content versus impact propertiesat ±196°C; joint welded with very high heat input i n 3G (PF)

The beneficial effect of a lower ferrite content on the deep temperature toughnessdescribed in Figure 7 also remains at higher temperatures (Figure 8).

In this diagram the temperature dependence of the impact toughness can be seen.Takingthe relation between impact energy and lateral expansion as describedearlier intoaccount, same considerations are also valid for the lateral expansion.

I

mpa


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ct ener

gy , ISO-V [

Joule]Impact

energy , ISO-V [Joule]Testing Temperature [°C]La

ter


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al Expa

nsion [mm] 2,4

1201001,6 801,2 600,8 400,4 20+20 +20 -120 -120 -196 -1962,32140All weld metal1,101,321,06

1,060,68665450877974Heat input ~ 1,1 - 1,25 kJ/mm0,702,0Ferrite acc.FERITSCOPE MP 309,1 - 11,7 FN7,1 - 9,2 FN4,3 - 6,3 FNFerrite acc.FERITSCOPE MP 309,1 - 11,7 FN7,1 - 9,2 FN4,3 - 6,3 FNSpecimen acc.AWS A5.4(Testing acc. ASTM E23)140

Figure 8: BÖHLER FOX EAS 2 (E308L-15): Influence of the ferrite content on the impactproperties down to -196°C


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As it is clearly shown, the delta ferrite content has a major influence on the deeptemperature toughness of the austenitic weld metal and the relation is quite strong: Thelower the delta ferrite content the higher toughness properties like impact energy and

lateral expansion [3]. From this point of view, the ferrite level should be kept as low aspossible to guarantee high toughness values at -196°C.On the other hand, a minimum delta ferrite is required to prevent hot cracking at all. As aminimum level therefore 3FN has been committed for SMAW, GMAW, SAW and GTAW toguarantee crack-free joints also in case of welding procedures with high heat inputs. Atferrite levels below 3FN the hot cracking susceptibility is increaseddrastically, asnumerous results of PVR-tests have shown (Figure 9).

Elongation ra

te [mm/min]d dd d+g gg g - -- - Primary d dd d - -- -Vol. % (Förster 1.053)FNmax. elon

ation rate9080706050403020100

011,8


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23,034,145,45

6,667,8crystallization Fi

ure 9: Ferrite content vs. hot crackin

susceptibility (PVR test) [4]

Goin

to the lower metallur

ical limits of the

elta ferrite content it is necessary to consi

erall a

itional effects which can lea

to a wel

metal which is below the lower limit,

in

epen

ent of the chemical composition of the consumable. The most important pointsthereby are the

etermination of the ferrite content an

the arc, especially the arc len

thon the chemical composition of the wel

metal.

3.2.1. Measure

vs. calculate

FN valuesDealin

with electro

es which are

esi

ne

for lowest safe FN levels the

iscussion mayrise if measure

or base

on the chemical composition calculate

FN values areman

atory. As the

elta ferrite content in the wel

metal is a very

oo

in

ication for the

soli ification mo e of the liqui wel metal (ferritic or austentic) the actual, the measure

ferrite value is therefore characteristic. Investi

ations have shown, that there are

ifferences between the measure

an

calculate

values [5] but there are also

ifferencesbetween results of

ifferent labs [6]. This fact shoul

be consi

ere

by settin

up therequirements for LNG projects with specifie

ferrite contents.

3.2.2. Influence of arc len

th on

elta ferrite contentThe metallur

ical

esi

n

oal for LNG consumables is to secure very low ferritecontentsin the wel

metal to

et satisfyin

tou

hness values but also to

uarantee sufficient hotcrackin

resistance. By reachin

lowest, controlle

ferrite levels in the wel

metal theinfluence of the wel

er must also be taken into account. The arc len

th is stron

lyinfluence

by the wel

er.

Ferr

ite


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conten

tacc. Förste

r 1.053 [FN]short arc (~ 3 mm)

135 A / 26 Vlon

arc (~ 8 mm)135 A / 35 VFerrite contentacc. Fö

rst


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er 1.05

3 [FN]short arc (~ 3 mm)135 A / 26 Vlon

arc (~ 8 mm)135 A / 35 V Fi

ure 10: E308L 17: Influence of arc len

th on ferrite content; PVR test specim

en [4]Wel

in

with a very lon

arc increases the nitro

en pick up an

burn off rates of alloyin

elements which is responsible for a re

uction of the ferrite contentin the wel

metal. InFi

ure 10 this effect is shown usin

a laboratory stick electro

e of type E 308L 17 with anominal ferrite content in the wel

metal of 3FN. Increasin

the arclen

th from 3mm to8mm the ferrite level

ecreases from 3FN to about 1FN [4]. In case of the very low ferritewel

metal cracks at the PVR test specimen are visible. But it has

to be mentione thatbasic electro

es are much more safety re

ar

in

this phenomena.

3.3 All wel

metal vs. 304L

base metal joints

As earlier mentione

, for wel

in

of the base metal of type 304L afiller of type 308L isuse

an

the tou

hness values of the all wel

metal are not equal to values from the joint.Comparin

Fi

ure 8 an

Fi

ure 11 this influence is shown by wel

ments with a stickelectro

e of type E308L

15.

Impact ener

y


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, ISO

V

[Joule]Impa

ct ener

y , I

SO

V [Joule]Testin

temperature [°C]Lateral expa

nsi


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on [mm]

2,4 1201001,6 801,2600,8400,420+20 +20

120

120

196

1961,99

0,880,650,71473911256480,532,0Ferrite acc. Förster 1.0537,8 10,2 FN5,0 6,1 FN

Ferrite acc. Förster 1.0537,8

10,2 FN5,0 6,1 FNThickness: 13 mmWel

in

position: 1G/PABase metal: 1.4301 (AISI 304L) Fi

ure 11: BÖHLER FOX EAS 2 (E308L 15): Impact ener

y versus ferrite content inV

joint wel

s

It can be seen, that at 196°C for the low ferrite type the lateral expansion

rops from 1,06mm in the all wel

metal

own to 0,71 mm in the joint; similar the charpy impact ener

y:from 66J to 47J. This ten

ency is also vali

for the hi

her ferrite

ra

es.

3.4 Wel

in

position

Impacte

ner


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y , IS

O

V [Joule]Test temperature [°C]

Lateral expan

sion [mm] 2,4 1201001,6 801,2600,8400,420+20 +20

120

120

196

1962,141,200,850,7143

4111162


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540,592,0Ferrite acc. FERITSCOPE3,2 4,3 FN (1G)3,3 4,8 FN (3G)1,68

93Thickness: 15 mmWel

in

position: 1G/3G3G1GBase metal: 1.4301 (AISI 304L)Impact

ener

y , ISO

V [Joule]Impactener

y , I

SO


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V [Joul

e]Test temperature [°C]Lateral e

xpansion [mm]

2,4 1201001,6 801,2600,8400,420+20 +20 120 120 196 1962,141,200,850,71434111162540,592,0Ferrite acc. FERITSCOPE3,2

4,3 FN (1G)3,3

4,8 FN (3G)

Ferrite acc. FERITSCOPE3,2 4,3 FN (1G)3,3

4,8 FN (3G)


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1,6893Thickness: 15 mmWel

in

position: 1G/3GThickness: 15 mmWel

in

position: 1G/3G3G

1GBase metal: 1.4301 (AISI 304L) Fi

ure 12: BÖHLER EAS2 PW FD (LF) (E308LT1 4):Impact ener

y in various wel

in

positions: 1G/PA an

3G/PF

In Fi

ure 12 the influence of the wel

in

position on the tou

hnessproperties is shown.It´s not

etrimental by comparin

the charpy values, more si

nificant

eviations aremeasure

in case of the lateral expansion.

3.5 Influence of shrinka

e on impact ener

y

A very

etrimental influence was observe

cause

by internal stresses.If these stressesare re

uce

by plastic

eformation (visible as shrinka

e), it was notpossible to improvethe tou

hness by usin

an optimise

bea

sequence with small bea

s´. An example as itcan be seen in the GTAW samples (Fi

ure 13).

low shrinka

e 74 6 (9)

hi h shrinka e 53 6 (9)hi

h shrinka

e 54 8 (13)Remarks Impact ener

yISO V [Joule]avera

eLayers(Bea

s)Bea

sequencelow shrinka

e 74 6 (9)hi

h shrinka

e 53 6 (9)hi

h shrinka

e 54 8 (13)Remarks Impact ener

yISO

V [Joule]avera

eLayers(Bea

s)Bea

sequenceBase metal: AISI 304L; Wel

in

position: 1G/PA; Thickness: 15 mm (Gap: 3 mm) Fi

ure 13: GTAW with BÖHLER EAS 2

IG; impact ener

y of joint wel

s at

196°C

3.6 Test specimen preparation

Besi e the above mentione aspects a further point has to be taken into account when

iscussin

eep temperature tou

hness properties: the preparation of the test sp


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ecimens.Investi

ations have shown, that the achieve

impact tests results at very low temperaturesare stron

ly influence

how the notch into the test specimen was ma

e. The sharper thecutter use

for preparin

the notch the hi

her the impact values (Fi

ure 14). With

increasin wear of the cutter the plastic eformation at the roun of the notch increasesan

the measure

Charpy impact value

ecreases.

102030405060U

se

Hi

h spee

steel cutterType HSS E (SCHNADT)Carbi

e millin

cutterType CK20 (SCHNADT)NewImp

act ener

yAv[Joule], ISO

V55


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4840325248Ne

wSpecimen from V JointAISI304; th. = 12 mm; 1G4944Use

Fi

ure 14: Influence of new an

use

cutters for preparin

the notch on charpy test

specimen on tou

hness values at

196°C

4 Settin

up requirements for LNG stainlesssteels wel

ments

To achieve an optimum between

eep temperature tou

hness an

hot crackin

susceptibility, a narrow win

ow for the ran

e of

elta ferrite for the wel

metal has to be

efine

as shown in Fi

ure 15 vali

for BÖHLER FOX EAS 2 (E308L

15).

80

6040203 6 1227 J4

12 FN*Deltaferrite [FN]Inpact ener

y[Joul

e]


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ISO

VRisk for

hotcrackin

9Best ran

e inwel

e

joints3 8 FN*Acc. to IIW;All wel

metal;General applications1 2 Fi

ure 15: BÖHLER FOX EAS 2 (E308L 15); Ferrite content versus impact ener

y at

196° Besi

e this ªmetallur

icalº orientate

requirement re

ar

in

the

elta ferrite contentvarious

esi

n co

es

efine minimum values for tou

hness to secure safe constructions.

4.1 Requirements for austenitic LNG wel

ments

There are 2 main

esi

n co

es available an

they

escribe the tou

hness requirements in

etail: ASME Co

e [7] focuses on lateral expansion an

set the minimu

m esi n limit to³0,38mm. The comparable European Co

e, TÜV [8], favours the charpy impactener

y.The minimum allowable value has to be ³32J. Depen

in

on the use

esi

n co

e thelateral expansion or the charpy impacts values are the characteristic material property

atafor selection of the filler metal.Besi

e these major

esi

n co

es various customer

relate

requirements are existin

.They are often a mix of these two co

es an

can be exten

e

with some furtherrequirements re

ar

in

elta ferrite content an

/or minimum heat input.To fulfil these requirements special low ferrite electro

es for use in LNG plants were

evelope

. Fi

ure 16

ives a small overview an

points out the essential selectioncriterions as FN (measure

), lateral expansion an

charpy tou

hness at

196°C.

3

65

73

64 88

11FN

40 0,60FCAW E316LT1 4E316LT1

1


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EAS 4 PW FD (LF)67 0,60 SMAW E316L 15 FOX EAS 4 M (LF)45 0,75FCAW E308LT1 4E308LT1 1EAS 2 PW FD (LF)1,06

1,17Lateral expansion[mm] 196°CFOX EAS 2EAS 2 IGBöhler Bran

SMAWGTAWProcess112ER308L

66ISO V[J] 196°CE308L 15AWS3

65 73 64

88

11FN40 0,60

FCAW E316LT1 4E316LT1

1EAS 4 PW FD (LF)67 0,60 SMAW E316L 15 FOX EAS 4 M (LF)45 0,75FCAW E308LT1

4E308LT1 1EAS 2 PW FD (LF)1,061,17Lateral expansion[mm]

196°CFOX EAS 2EAS 2 IGBöhler Bran

SMAWGTAWProcess112ER308L66ISO V[J]

196°C

E308L 15AWS


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Fi

ure 16: Special

esi

ne

, mostly low ferrite filler metals for LNG applications withtypical values

5 Conclusion

As it can be shown, the elta ferrite content of the austenitic wel metal has a hu

einfluence on the tou

hness properties of especially at low temperatures. The lower theferrite content the hi

her the tou

hness of the wel

metal. But there

uction of the

eltaferrite has its limits: a minimum ferrite level is necessary to prevent hot crackin

.Dealin

with LNG applications of austenitic steels an

wel

ments it is necessary to controlthe ferrite content by the chemical composition an

the wel

in

parameters to fin

an

optimum between hi

h tou

hness properties an

hot crackin

resistance.To

evelopªsafeº filler metals also the influence of hi

her heat inputs, plastic

eformation,but also thearc len

th on the impact values has to taken into account.

6 References

[1] Information from OMV; 2005

[2] L. Smith: ªProperties of metallic materials for LNG servicesº; Stainless Stell

Worl ,Oct. 2001

[3] G. Holloway, Z. Zhan

, A. Marshall: ªStainless Steel Arc Wel

in

Consumables forCryo

enic Applicationsº; Stainless Steel Worl

2004; KCI Publishin

BV

[4] E. Folkhar

et al: ªWel

in

Metallur

y of Stainless Steelsº, Sprin

erVerla

, Wien,1988

[5] J. Tösch, G. Posch, J. Zie

erhofer: ¹Ferrite contents in stainless steel FCAW

wel

sª; IIW

oc. II

C 289

04

[6] J. C. M. Farrar: ªThe Measurement of Ferrite Number (FN) in Real Wel

mentsº;IIW

Doc. II 1531

04

[7] Internat. Pipin

co

e ASME B31.3.

[8] V

TÜV Information Sheet ªGui

elines on suitability of wel

in

filler metalsº; 1980

248221054 low temperature behavior of austenitic weldments

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