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NARROW GAP TIG WELDING AND DEVELOPMENT OF FILLER WIRES OF RAFMS FOR WELDING G. SRINIVASAN SHAJU K. ALBERT A.K. BHADURI Materials Technology Division Indira.

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Presentation on theme: "NARROW GAP TIG WELDING AND DEVELOPMENT OF FILLER WIRES OF RAFMS FOR WELDING G. SRINIVASAN SHAJU K. ALBERT A.K. BHADURI Materials Technology Division Indira."— Presentation transcript:

1 NARROW GAP TIG WELDING AND DEVELOPMENT OF FILLER WIRES OF RAFMS FOR WELDING G. SRINIVASAN SHAJU K. ALBERT A.K. BHADURI Materials Technology Division Indira Gandhi Centre for Atomic Research Kalpakkam , India

2 Background RAFM steels are the candidate structural materials for TBM to be installed in the ITER Fusion Reactor.RAFM steels are the candidate structural materials for TBM to be installed in the ITER Fusion Reactor. RAFM steels have a chemical composition similar to modified 9Cr-1Mo steel.RAFM steels have a chemical composition similar to modified 9Cr-1Mo steel. Mo and Nb that produce long living radioactive isotopes in the reactor environment are replaced with W and Ta.Mo and Nb that produce long living radioactive isotopes in the reactor environment are replaced with W and Ta. Temperature window for use of these steels are presently about 350–550°CTemperature window for use of these steels are presently about 350–550°C Lower value being limited by irradiation-induced embitterment effectsLower value being limited by irradiation-induced embitterment effects Upper value by a strong reduction in mechanical strength.Upper value by a strong reduction in mechanical strength.

3 Objectives To develop and qualify procedures for joining of various components of TBM using RAFM steelTo develop and qualify procedures for joining of various components of TBM using RAFM steel –Narrow Gap TIG –Laser –Electron Beam –Hybrid Laser –Diffusion bonding To develop consumables for NG-TIG and hybrid laserTo develop consumables for NG-TIG and hybrid laser To choose suitable joining process based onTo choose suitable joining process based on –Joint Design –Accessibility –Assembly sequence

4 Requirements of Weld Joints in TBM Fabrication Microstructure of the joint shall be resistant to the effects of neutron irradiation in the temperature range of °CMicrostructure of the joint shall be resistant to the effects of neutron irradiation in the temperature range of °C –No significant shift in Ductile Brittle Transistion Temperature Joint should possess required strength, fracture toughness, creep and fatigue resistance to ensure adequate structural stability throughout the serviceJoint should possess required strength, fracture toughness, creep and fatigue resistance to ensure adequate structural stability throughout the service Fusion welds on the first wall facing plasma is not acceptableFusion welds on the first wall facing plasma is not acceptable

5 Other Considerations in the Choice of the Welding Process Minimize the size of the fused metal zone and heat affected zone in the fabricated componentsMinimize the size of the fused metal zone and heat affected zone in the fabricated components Minimum distortion and low residual stress in the weldMinimum distortion and low residual stress in the weld Minimize the use of edge preparation and filler wiresMinimize the use of edge preparation and filler wires Suitable for the joint configuration and assembly sequence chosenSuitable for the joint configuration and assembly sequence chosen

6 TIG Arc welding process, uses a nonconsumable tungsten electrode to produce the weld.Arc welding process, uses a nonconsumable tungsten electrode to produce the weld. Weld area is protected from atmospheric contamination by an inert gas and a filler metal is normally usedWeld area is protected from atmospheric contamination by an inert gas and a filler metal is normally used Autogenous welds do not require FMAutogenous welds do not require FM Most commonly used to weld thin sections of SS and light metalsMost commonly used to weld thin sections of SS and light metals

7 NG-TIG NG-TIG is an advanced technique for higher productivity in the manufacture of thick-walled componentsNG-TIG is an advanced technique for higher productivity in the manufacture of thick-walled components Developed to achieve similar corrosion and fatigue properties for both weld and base metals without porosity or inclusionsDeveloped to achieve similar corrosion and fatigue properties for both weld and base metals without porosity or inclusions Electrode will be oscillated in the narrow groove by twisting the torch tip in which the tungsten electrode tilted and the pulse energizes and preheats the filler wire prior to its contact the weld puddle.Electrode will be oscillated in the narrow groove by twisting the torch tip in which the tungsten electrode tilted and the pulse energizes and preheats the filler wire prior to its contact the weld puddle.

8 NG-TIG Excellent mechanical properties- comparable to BMExcellent mechanical properties- comparable to BM Ensures high weld quality and high efficiencyEnsures high weld quality and high efficiency Volume of weld metal deposited and total heat input teo the weld are lower than in conventional TIGVolume of weld metal deposited and total heat input teo the weld are lower than in conventional TIG Results in a favorable residual stress profile in the HAZResults in a favorable residual stress profile in the HAZ NG-TIG technique is considered for the fabrication of the various components of TBM especially in site welding where other joining techniques cannot used.NG-TIG technique is considered for the fabrication of the various components of TBM especially in site welding where other joining techniques cannot used. –For PFBR steam generator fabrication this welding process is chosen by the fabricators instead of a combination of TIG and shielded metal arc welding (SMAW) proposed. Ease of AutomationEase of Automation

9 Schematic of hot wire NG-TIG Oscillation of the torch tip to ensure side wall fusion Avoiding use of SMAW process, which has low weld metal toughness

10 TIG (Eurofer) TIG JOINT DESIGN FOR HORIZONTAL/VERTICAL STIFFEENING PLATES

11 TIG (Eurofer) FZ: Equiaxed grains of martensite lathsFZ: Equiaxed grains of martensite laths No δ ferriteNo δ ferrite G/size µG/size µ No defects like cracks and inclusionsNo defects like cracks and inclusions Cross Section view of TIG weld

12 Improvisations in TIG Welding – Penetration Enhancing Flux Assisted (PEFA) TIG Welding (Patented) PEFA-TIG flux developed for single-pass autogenous welding –Weld bead penetration of upto 12 mm achieved Specific Advantages –Upto 50%  in welding costs  in bevel preparation  in no. of weld passes  in welding times  in filler wire consumption –  Distortion  in heat input Straight edges –No back gouging or grinding Full penetration in single pass Diffused arc in Normal-TIG Constricted arc in PEFA-TIG Weld bead shape in Normal TIG Weld bead shape in PEFA-TIG 12mm

13 Multi-pass TIG Vs. PEFA-TIG

14 PEFA-TIG Welded 9 mm thick 316LN SS Square-Butt Joint Top faceBottom face

15 PEFA-TIG Welding Implemented at CWD/IGCAR

16 TIG – Comparison with other Processes HAZ width is high - 3mmHAZ width is high - 3mm Distortion noticedDistortion noticed Filler addition is required for more than 3mm thicknessFiller addition is required for more than 3mm thickness Preheating and post heating generally employedPreheating and post heating generally employed Residual stress would be highResidual stress would be high Very low welding speedVery low welding speed Suitable for site weldingSuitable for site welding All position weldingAll position welding Wide experience is availableWide experience is available

17 Concerns with respect to Joint Design and Assembly Sequence

18 Other Concerns with respect to Joining Use of preheating and post heatingUse of preheating and post heating Post Weld Heat Treatment ( /2h)Post Weld Heat Treatment ( /2h) –It is essential, but extreme care shall be taken to ensure dimensional stability of the components and cooling channels For hybrid welding, solid state laser welding machine with fiber delivery may be requiredFor hybrid welding, solid state laser welding machine with fiber delivery may be required Dissimilar welds involving RAFMS and 316L will have microstructure and properties different from the base metalsDissimilar welds involving RAFMS and 316L will have microstructure and properties different from the base metals

19 Development of RAFMS Filler Wires Requirements: Sound structural weldsSound structural welds Free from cracksFree from cracks High joint efficiencyHigh joint efficiency Low pore levelsLow pore levels Amenable to automationAmenable to automation –in a spool form for both NG-TIG & Hybrid Laser welding

20 Characterisation Required Tests: Chemical CompositionChemical Composition Soundness as per AWS SFA 5.28Soundness as per AWS SFA 5.28 Mechanical Property All Weld Tensile at RT and at 550°CAll Weld Tensile at RT and at 550°C DBTT <-45°CDBTT <-45°C

21 Chemical Composition ElementsWt.%ElementsWt.% Cr W C Ta Mn N V O<0.01 Nb<0.001Ni<0.005 Mo<0.002Cu<0.002 Co<0.005P<0.002 Si<0.05S<0.002 Al<0.005As+Sn+Sb+Zr<0.03

22 Mechanical Properties (RT) Tensile Property BMEurofer*BMIGCARWMEurofer*WMIGCAR UTS - MPa YS - MPa Elongation % Reduction in Area % 80 To be reporte d * Achieved

23 Mechanical Properties Mechanical Properties (550°C) Tensile Property BMEurofer*BMIGCARWMEurofer*WMIGCAR UTS - MPa YS - MPa Elongation % 22 To be reporte d 22 Reduction in Area % 9078 * Achieved

24 DBTT WM <-45°CWM <-45°C BM <-70°CBM <-70°C EUROFEREUROFER Below RT <-50°C (for both BM&WM)Below RT <-50°C (for both BM&WM)

25 Summary It is possible to develop welding procedure to produce defect free welds of RAFMS using any of the processes considered for TBM fabrication.It is possible to develop welding procedure to produce defect free welds of RAFMS using any of the processes considered for TBM fabrication. Indigenous development of filler wire is feasible and M/s MIDHANI has the technology for melting and wire drawingIndigenous development of filler wire is feasible and M/s MIDHANI has the technology for melting and wire drawing Challenge would be actual fabricationChallenge would be actual fabrication –Joint design –Assembly sequence –PWHT –Distortion Mock up trails shall be carried out for actual joint configuration and fabrication procedure established before component fabrication is taken up (including heat treatment)Mock up trails shall be carried out for actual joint configuration and fabrication procedure established before component fabrication is taken up (including heat treatment) Weld joints needs to be characterised in detail for dissimilar joints involving austenitic stainless steels and RAFMS and produced by EB or Laser Welding without filler addition.Weld joints needs to be characterised in detail for dissimilar joints involving austenitic stainless steels and RAFMS and produced by EB or Laser Welding without filler addition.

26 THANK YOU


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