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Dúplex Welding
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This Presentation is provided to you by: WPSAmerica.comIndustry Standard Welding Procedures Software for AWS and ASME Codes
Welding Practicefor the Sandvik Duplex Stainless SteelsSAF 2304, SAF 2205 and SAF 2507
Presented by
Frank Babish
Key PointsMetallurgical ConsiderationsWelding ProcessesComposition differences Base Metal and Filler MetalGood Mechanical and Corrosion Properties of WeldsImportance of Heat Input and Interpass TemperatureRole of NitrogenPost Weld CleaningDissimiliar JoiningJoint Design
Characteristics of Duplex stainless steelsExcellent resistance to stress corrosion cracking Very high mechanical strength Excellent resistance to pitting and crevice corrosion High resistance to general corrosion in a variety of environmentsLow thermal expansion High resistance to erosion corrosion and corrosion fatigue Good weldabilityLower life cycle cost
Duplex microstructureThe austenite islands (light) are embedded in a continuous ferrite (dark) matrix.The duplex microstructure typically contains 45-65% austenite and 35-55% ferrite.AusteniteFerrite
Yield Strength 0,2%Austenitic vs Duplex Stainless Steel
Coefficient of expansion(x10-6)C-1Austenitic stainless steelsapprox. 17Duplex stainless steelsapprox. 13Carbon steelapprox. 11,5
Thermal expansion, per C (20-100C)
Solidification mechanism of Duplex stainless steelAs duplex stainless steels solidify the grain structure transform from a fully ferritic material to a balanced austenite and ferrite microstructure
Solidification mechanism of a Duplex Stainless Steel
HAZ of weld in SAF 2507
Stress strain curvesAustenite, ferrite and duplex0,00,20,40,60,802004006008001000 austenite duplex (2205) ferriteStress [MPa]Strain
Reasons for the high strength of duplex stainless steelsl Content of ferrite
l Fine grained structure
l Nitrogen
Embrittling of Duplex Stainless Steels
Welding Processes
Conventional Processes
GTAWGMAWSAWSMAWFCAW
Avoid
AutogenousLow Energy ProcessesOr Perform PWHT
Filler Metals for the Welding of Duplex Stainless Steels
Mechanical properties of the Duplex Stainless SteelsSandvikUNSYield strengthTensile strengthElong.Hardness0,2% offset1,0% offsetA5VickersMPaksi.MPaksi.MPaksi.%min.min.min.min.min.min.min.approx.
SAF 2304S323044005845065600-82087-11925230SAF 2205S318034506550073680-88099-12825260SAF 2507S327505508064093800-1000116-14525290
Mechanical Properties of All Weld MetalFiller metalWeldingRpo,2Rp1,0RmA5ZImpact strength, JSandvikprocessMPaMPaMPa%%RT-40C
23.7.LTIG525595708345817115623.7.LSAW1)503671341017223.8.LRMMA62768177326466246
22.8.3.LTIG6107602820716022.8.3.LSAW1)57866477533531398422.9.3.LRMMA51273433524422.9.3.LTFCAW620-81630445643
25.10.4.LTIG672851286415011625.10.4.LSAW1)6877578782747916425.10.4.LRMMA6458502846331)Using Sandvik 15W flux
Mechanical properties of welded joints.Cross-weld tensile testParent metalFiller metalWeldingRp0.2MPaRmMPaA5, %SandvikSandvikprocessmin.typicalmin.typicaltypical
SAF 230423.7.LTIG4004466006503023.7.LSAW1)4004526006893023.8.LRMMA40046260064730
SAF 220522.8.3.LTIG4505536807842922.8.3.LSAW1)4505886807572622.9.3.LRMMA4505886807572822.9.3.LTFCAW45058568076028
SAF 250725.10.4.LTIG5506458008483225.10.4.LSAW1)5506288008423425.10.4.LRMMA550628800846331)Using Sandvik 15W flux
Charpy-V impact strength of welded jointsParent metalFiller metalWeldingImpact energy, JSandvikSandvikprocessRT-40C
SAF 230423.7.LTIG2137423.7.LSAW1)1051723.8.LRMMA4638
SAF 220522.8.3.LTIG28213322.8.3.LSAW1)544222.9.3.LRMMA524322.9.3.LTFCAW5544
SAF 250725.10.4.LTIG1107825.10.4.LSAW1)1005825.10.4.LRMMA58391)Using Sandvik 15W flux
Quench annealing of Duplex Steel weldsSandvikHolding temperatureQuenching C mediaSAF 2304930 - 1050WaterSAF 22051020 - 1100WaterSAF 25071080 - 1120Water
Intermetallic phase
Recommended heat inputSteelHeat inputInterpass temperature
SAF 23040,5 - 2,5 kJ/mm
The roll of NitrogenNitrogen is a very important alloying element in DSSImproves corrosion resistance Improves austenite reformation
At TIG welding, the loss of nitrogen is compensated for by using Ar + 1 - 2%N2 as a shielding gas
Ferritic area in SAF 2507 weld owing to the loss of nitrogen in fusion lineShielding gas Ar 99,99%
Nitrogen addition to the shielding gasAr 99,99%Ar + 5% N2
Ferrite content in TIG-welds, SAF 2507Filler Shielding Root Ferrite content, vol-%metal gas gas + error with 95%Sandvik confidence interval25.10.4.L Ar Ar 55 + 4,525.10.4.L Ar 90% N2 + 10% H2 59 + 4,025.10.4.L Ar + 5% N2 90% N2 + 10% H2 33 + 4,0
Nitrogen Content in TIG welds of SAF 2507.N=0,25% in the filler metalFiller metal ShieldingRootWeight-% NSandvik gasgasin deposit
25.10.4.L Ar90% N2 + 10% H2 0,23
25.10.4.L Ar + 3% N290% N2 + 10% H2 0,27
25.10.4.L Ar + 6% N290% N2 + 10% H2 0,33
GMAW SHIELDING GASES
General recommendations:Short arc welding gives very convex beads.Ar+30 He+1 O2
Spray arc weldingAr+30 He+1 O2 (22Cr duplex)Ar+2 CO2(Super duplex)
Pulsed arc weldingAr+30 He+1 O2 (22Cr duplex)Ar(99,996%) for super duplex
Nitrogen Analysis from the Top of a TIG weld% Nitrogen in position (oclock)Analysis at35671112
Welder No. 10,170,180,150,160,190,19Top side
Welder No. 20,18-0,190,19-Top side0,20-0,210,20-Root side
Welder No. 30,22-0,210,20-Top side0,21-0,210,20-Root side
In all cases the filler metal had a nitrogen content of 0,25%
Stress relieving temperatures325 + 25C for 10 hours
Post Weld Cleaning
Dissimilar JointsSAF Carbon steelAISI 200AISI 904L,and 300-Sanicro 28,series254 SMO, etc.
2304 22.8.3.L22.8.3.L22.8.3.L 22.9.3.LR22.9.3.LR22.9.3.LR 22.9.3.LT22.9.3.LT22.9.3.LT
2205 22.8.3.L22.8.3.L22.8.3.L 22.9.3.LR22.9.3.LR22.9.3.LR 22.9.3.LT22.9.3.LT22.9.3.LT
2507 25.10.4.L25.10.4.LSanicro 60 25.10.4.LR25.10.4.LRSanicro 60
Joint preparationOne sided butt welding
Joint preparationButt welding from both sides
Tube to tube sheet welding.Joint preparation>WT>1.5 x WT45>3 mm (0.12) or >1.5 x WTr >1.5 x WTabcd
Hydrogen pick-up from covered electrodes Sandvik 25.10.4.LRMMAH2, ml/100 g
Hydrogen pick-up from SAW fluxH2, ml/100 gSAW
Hydrogen pick up from shielding gas at TIG weldingShielding gasAr + 5% H2Shielding gasAr + 10% H2TIG - no root gasH2, ml/100 g
Hydrogen pick up from shielding gasand root gas at TIG weldingTIG - with root gasH2, ml/100 gShielding gas ArRoot gas ArShielding gas ArRoot gas 90% N2 + 10% H2
ConclusionsKey Areas
Good WeldabilityUses Conventional Welding ProcessesJoint DesignRole of NitrogenHeat Input ImportantInterpass Temperature
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