metrode welding consumables for cryogenic applications

7/27/2019 Metrode Welding Consumables for Cryogenic Applications

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Paper presented at Seminario Sobre Soldabilidad de Materials para usos criognicas

Bilbao, 25th September 2003

Welding Consumables for Cryogenic Applications

Graham Holloway

Metrode Products Ltd, Chertsey, UK

Abstract

Typical cryogenic applications for 304L and 316L stainless steels are covered, and the question whatis good cryogenic toughness for 308L and 316L weld metal? will be addressed. The various controlsthat need to be imposed on the weld metal to achieve good toughness are also reviewed. Someexamples of the projects the consumables have been used on are also highlighted.


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Welding Consumables for Cryogenic Applications

1 Introduction

The storage and distribution of various gases including liquefied natural gas (LNG) requiresmaterials that have good mechanical properties, particularly toughness, at low temperatures.

Gases are generally stored as liquids and this requires that the materials used for storage tanksand pipework are capable of withstanding the low temperatures encountered with liquefiedgases. Some examples of the liquefaction temperatures of various gases are shown in Table 1.

Table 1 Liquefaction temperatures for various gases.

Gas Liquefaction Temperature, C

Ammonia -33Propane -45 LPGCO2 -78Acetylene -84Ethane -88Ethylene -104 LEGMethane -163 LNGOxygen -183Argon -186Nitrogen -196Hydrogen -253Helium -269

The most important criterion for service at cryogenic temperatures is normally toughness, and itis important that the weld metals used are capable of achieving good toughness. Large landbased storage tanks are normally fabricated from 9% nickel steel but pipework for distributionetc is often made from austenitic stainless steel. The 9% nickel steels and 304/316 austeniticstainless steel consumables are tested down to -196C. For applications down to -269C,304/316 austenitic stainless steel (welded with fully austenitic stainless steel consumables) oraluminium are used. The materials and welding consumables suitable for use at various nominaltemperatures are shown in Table 2.

Table 2 Low temperature alloys and associated welding consumables.

Temp Alloy GTAW/GMAW SMAW FCW

-50C 1%Ni1Ni

(ER80S-Ni)Tufmet 1 Ni.B(E8018-C3)

Metcore DWA 55E(E71T-9)

-60C 2%Ni2Ni

(ER80S-Ni2)Tufmet 2Ni.B(E8018-C1)

-

-75C 3%Ni2Ni

(ER80S-Ni2)Tufmet 3Ni.B(E8018-C2)

-

-101C 3/5%Ni20.70.Nb

(ERNiCr-3)Nimrod 182KS/AKS

(ENiCrFe-3/2)-

-196C 9%Ni62-50

(ERNiCrMo-3)Nimrod NCM6(ENiCrMo-6)

-

-196C 304L/316L308L/316L

(ER308L/ER316L)

Ultramet308LCF/316LCF

(E308L-16/E316L-16)

Supercore 308LCF/316LCF(E308LT1-4/E316LT1-4)

-269C 304L/316LER316MnNF

(EN:E 20 16 3 Mn L)Ultramet 316NF

(EN: E 18 15 3 LR)Supercore 316NF

(nearest EN: T 18 16 5 NLR)


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2 Materials

As explained already, many different alloys are selected for LNG applications. This paper coversaustenitic stainless steels, 304/304L and 316/316L, and the relevant weld metals 308L and 316L.The use of fully austenitic weld metals (eg 18 15 3 L types) is not covered, these fully austeniticweld metals have excellent toughness at -196C and useful properties down to -269C. Thepaper is divided into four main areas:

typical toughness requirements, the effect of different welding processes, how weld metals achieve the required toughness and, finally, the effect of weld procedure.

3 Toughness Requirements

Design temperatures encountered for austenitic stainless steels vary considerably but forsimplicity and ease of testing, Charpy tests are normally carried out at -196C because this is aneasily achieved and convenient test temperature obtained by cooling in liquid nitrogen.

The most commonly encountered requirement is based on Charpy lateral expansion. Therequirement for 0.38mm (15mls) lateral expansion at -196C, which can be found in the ASMEcode (eg ASME B31-3), is frequently quoted even for projects which are not being fabricated toASME requirements. Although 0.38mm lateral expansion is probably the most widely specifiedrequirement, some European projects do have a Charpy energy requirement. For exampleprojects being carried out under the scope of TV sometimes specify 32J at -196C (40J/cm2).The data presented in this paper assume that 0.38mm lateral expansion at -196C is the designrequirement.

4 Welding Process

4.1 Gas-shielded processes

The gas-shielded welding processes (GTAW/TIG and GMAW/MIG) have inherently goodtoughness even at cryogenic temperatures. The gas shielding provides a metallurgically cleanweld metal with low oxygen, hence low inclusion, content.

The GTAW process in conjunction with ER308L (W 19 9 L) or ER316L (W 19 12 3 L) wireproduces exceptional toughness even at -196C. With both ER308L and ER316L it is possible toachieve typically 80J (100J/cm2) at -196C with a lateral expansion of 1.0mm, when using theargon shielded GTAW process. The GMAW process (with Ar-2%O2 shielding gas) using ER308LSi(G 19 9 L Si) or ER316LSi (G 19 12 3 L Si) wire is capable of producing typically 40J (50J/cm2) at-196C with a lateral expansion of typically 0.5mm.

These excellent impact properties can be consistently achieved using the GTAW and GMAWprocesses using standard commercially available ER308L/ER308LSi and ER316L/ER316LSi wires,Table 3.

Table 3 Representative mechanical properties from all-weld metal joints using thegas shielded processes and 316L wire

GTAW GMAW

Consumable ER316L (W 19 12 3 L) ER316LSi (G 19 12 3 L Si)Shielding gas Ar Ar-2%CO2Tensile strength, MPa 605 5590.2% Proof stress, MPa 466 413Elongation, % 4d 41 50

5d 37 47Reduction of area, % 62 73Impact properties -196C:

Impact energy, J 105 43Lateral expansion, mm 1.17 0.58


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4.2 Flux-shielded processes

The flux shielded processes SMAW/MMA, FCAW and Sub-arc (SAW) do not achieve such lowoxygen content, low inclusion content, weld metal, and hence have lower impact properties thanthe gas-shielded processes. If consistently good toughness is required at -196C, then it isnecessary to provide careful control of the welding consumable because standard commercialSMAW electrodes and FCAW wires will not achieve 0.38mm lateral expansion at -196C. The

controls required to ensure good toughness are discussed further in the next section.5 Controls required for flux shielded processes

As already discussed in Section 4, the gas shielded processes do not require any special controlsto achieve 0.38mm lateral expansion at -196C. With the flux shielded processes, controls arerequired to produce 308L/316L consumables capable of achieving good cryogenic toughness.Three areas in particular will be covered:

ferrite content alloy content type of flux.

The discussion and data presented in Sections 5.1 and 5.2 concentrate on the SMAW process butthe information presented is equally applicable to FCAW as will be seen in Section 7.

5.1 Ferrite

Various standards specify ferrite limits for austenitic stainless steels. For example, ASME IIIrequires 5FN minimum (3-10FN for service above 425C), and API 582 has 3FN minimum(although it is noted that for cryogenic service lower FN may be required). In order to achievethe 0.38mm lateral expansion requirement, Metrode controls the ferrite content of the fluxshielded processes in the range 2-5FN. The effect of ferrite on toughness is well illustrated inFigure 1, which shows data from Metrode and other sources. As can be seen, the general trendis for the lateral expansion to decrease as ferrite increases, but once the ferrite goes aboveabout 8FN the lateral expansion increases again; this is well illustrated by the E308L-16/17 series

in Figure 1. The benefit of controlling ferrite in the range 2-5FN is shown by the 308LCF seriesin Figure 1, where all the points are in the 1-4FN range with about 0.4 0.7mm lateralexpansion.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 2 4 6 8 10 12 14 16

Ferrite (FN)

LateralExpansion,mm

(at-196C)

Ultramet 308LCF

E308L-16

E308L-17

E308L-15

Figure 1 Ferrite versus lateral expansion for 308L SMAW electrodes at 196C.


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One concern that is sometimes expressed with austenitic consumables having low ferrite levels isthe risk of solidification cracking. Most codes and specifications that specify a minimum ferritedo so because of the hot cracking risk, and at a typical ferrite of ~3FN the controlled ferrite (CF)consumables might be considered to be at risk. Numerous weld procedures and projects havebeen carried out with Ultramet 308LCF and 316LCF SMAW consumables and no solidificationcracking or microfissuring problems have ever been encountered. The reason for this is thatdespite the low ferrite, the composition is controlled to achieve a Cr:Ni ratio which produces a

desirable primary ferrite solidification mode. This tolerance to cracking can also bedemonstrated by superimposing the 308LCF range on the Suutala diagram, Figure 2.

Figure 2 Suutala diagram with the 308LCF composition range superimposed.

5.2 Alloy control

The composition of the CF type consumables is controlled to achieve the optimum ferrite level(Cr:Ni equivalent ratio) but there is also found to be a dependence on the actual chromiumequivalent. This dependence on chromium equivalent is more noticeable with the 316L alloythan 308L, and the most obvious result of this is that with the 316L types Mo is controlled in therange 2.0 2.5%. This means that the 316L controlled ferrite SMAW electrodes and flux coredwire conform to the AWS specifications (E316L-16 and E316LT1-4) which have a Mo requirementof 2.0 3.0%, but not the Euronorms (E 19 12 3 L R and T 19 12 3 L P) which require 2.5 3.0% Mo. Although not reviewed here, the good cryogenic toughness of low chromiumequivalent weld metal is also displayed by the lean 316 type 16.8.2.

5.3 Flux type

With CMn and low alloy steels, it is traditionally accepted that the best impact properties areachieved using fully basic flux systems. With austenitic stainless steels, the effect is far lesspronounced, Figure 3. The basic coated electrodes, E316L-15, produce a higher impact energyat a given lateral expansion, but the basic coating on its own is no guarantee of achieving0.38mm lateral expansion. Because it is necessary to control composition and ferrite contentwhatever flux type is used, (E3XXL-15/16/17), the Metrode consumables use rutile flux systemswhich offer the best operability and welder appeal.

308LCFrange

308LCFrange


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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50 60 70

Charpy Energy, J

LateralExpansion

,mm

E316L-16/17

E316L-16CF

E316L-15

Figure 3 -196C impact properties for 316L SMAW electrodes.

6 Weld Procedure

The mechanical properties of austenitic stainless steel welds are not generally considered to besignificantly affected by welding procedure. A series of sub-arc welds made with heat inputsbetween 1.0 and 2.7KJ/mm showed an increase in toughness with increasing heat input, Table4. The reason for this is not certain, but it is suspected that the reduction in the number of runsdeposited reduces the strain ageing effect and hence improves the impact properties.

Table 4 Effect of heat input/number of runs on impact properties of 316L sub-arcwelds produced with the same wire and flux in 22mm thick plate.

-196C PropertiesHeat input,kJ/mm *

Number ofruns in joint

Ferrite, FNCr+Mo,

% Charpy energy,J

Lateral expansion,mm

1.0 27 5 21.3 28 0.30

1.8 17 7 21.3 34 0.42

2.7 10 7 21.0 46 0.48

* Heat input altered by varying travel speed with current and voltage constant at 300A and 30V.

The effect can also be seen with SMAW electrodes. The larger diameter electrodes , on average,produce higher impact properties, Figure 4. This could again be attributed to the larger diameterelectrodes being deposited using a higher heat input hence producing larger weld beads withfewer runs per joint.


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0.35

0.4

0.45

0.5

0.55

0.6

0.65

26 28 30 32 34 36 38 40 42

Charpy Energy, J

LateralExpan

sion,mm

2.5mm

3.2mm

4.0mm

5.0mm

Figure 4 Impact energy versus lateral expansion at 196C for 316LCF electrodes.

7 Flux Cored Wires

The information that has been gained over many years of manufacturing controlled ferrite SMAWelectrodes has now been applied to flux cored wires. The compositional and ferrite aims for theflux cored wires are the same as for the SMAW electrodes. This means that the wires conformto E308LT1-4 and E316LT1-4 with a ferrite aim of 2-5FN. As with the SMAW electrodes, the316L flux cored wire conforms to the AWS specification (E316LT1-4) but not necessarily to theEN specification (T 19 12 3 L P). The wires are based on a rutile flux system and are suitable forall-positional pipe welding using standard Ar-20% CO2 shielding gas.

Figure 5 shows a plot of Charpy energy versus lateral expansion comparing the impact properties

at -196C of standard wires with controlled ferrite wires for both 308L and 316L. The benefits ofthe CF type wires is very well illustrated with all of the data for the CF types exceeding 0.38mmlateral expansion at -196C.

(a)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

10 15 20 25 30 35 40 45

Charpy Energy, J

LateralExp

ansion,

mm

308LSC308LCF


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(b)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

10 15 20 25 30 35 40 45

Charpy Energy, J

LateralExpansion,mm

316LSC316LCF

Figure 5 -196C impact properties for flux cored wires: (a) 308L (b) 316L.

8 Applications

Numerous successful procedures have been carried out with the CF SMAW electrodes, and manytonnes of electrodes have been used on projects all round the world. Most of the projects thatthe electrodes have been used on are pipelines and process pipework, some examples are givenhere.

The CF electrodes were originally designed over 10 years ago to satisfy the requirements ofMobil/Ralph M Parsons for the SAGE (Scottish Area Gas Evacuation) project terminal at StFergus. The plant, run by ExxonMobil, has now been processing gas for nearly eleven years. Anumber of weld procedures were completed covering different welding processes and pipe sizes,an example of a PQR run for this project is shown in Figure 6. This procedure is for an ASME 6G

/ EN H-L045 joint in 200mm diameter schedule 160 (23mm wall thickness) pipe completed withGTAW and SMAW.

More recently tonnage quantities of the CF consumables have been used in Kazakhstan on theKarachaganak Project where the contractors were CCC-Saipem. The CF electrodes were used on304/316 process pipework. There has also been significant quantities of pipework welded withthe CF consumables on the Mesaieed Q-Chem petrochemical complex in Qatar. The contractorswere Snamprogetti and the CF consumables were used specifically on the NGL-4 plant (naturalgas to liquids plant) which will produce ethane rich gas feedstock for the ethylene plant.


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Weld Procedure RecordMaterial ASTM A312 type 316L pipe

8 inch Schedule 160Weld Details

Filler Metal 316S92 / Ultramet 316LCF

Classification ER316L / E316L-16

Process GTAW / SMAW Gas Shield Ar

Current DC- / DC+ Position 6G

Preheat / InterpassTemperature 15/150C

PWHT None

23mm

60

1.5mm

3mm

8nb

RunNo

mm

CurrentAmp

ArcVolts

Travel Speedmm/min

HeatInput

kJ/mmProcedural Comments

1 2.4 90 10 50 1.3 Argon gas shield:

2-4 2.5 60 23 75 1.0 Torch 10 l/min

Rem 3.2 80 24 80 0.9 Purge 15 l/min

Analysis C Mn Si S P Cr Ni Mo Nb Cu FN

SMAW 2.5mm 0.021 0.7 0.6 0.014 0.026 17.1 12.2 2.2 0.01 0.11 2

SMAW 3.2mm 0.023 0.7 0.6 0.013 0.026 17.2 12.0 2.1 0.01 0.11 3

Charpy Cap RootTensile(transverse)

Ferrite

Ferritescope -196C J mm J mm

58 0.48 38 0.48

526MPa Cap 2.3 Weld 55 0.46 35 0.48

554MPa Mid 3.8 56 0.62 37 0.56

Failed in Root 2.7 70 1.18 65 1.17

pipe. FL 60 0.76 70 1.04

74 0.90 92 0.99186 1.64 138 1.52

FL + 2mm 180 1.72 160 1.67

1.99 180 1.85Hardness

HV (10)PM HAZ

WeldMetal

HAZ PM

2.81 2.47 2.47

Cap 176 204 205-225 190 171 FL + 5mm 298 2.73 2.83 2.83

Root 197 225 215-235 233 193 298 2.83 2.66 2.66

Figure 6 Weld procedure, using 316LCF electrodes, from the SAGE project.

metrode welding consumables for cryogenic applications

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