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February 2008 This Presentation is provided to you by: WPSAmerica.com Industry Standard Welding Procedures Software for AWS and ASME Codes.

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Presentation on theme: "February 2008 This Presentation is provided to you by: WPSAmerica.com Industry Standard Welding Procedures Software for AWS and ASME Codes."— Presentation transcript:

1 February 2008 This Presentation is provided to you by: WPSAmerica.com Industry Standard Welding Procedures Software for AWS and ASME Codes

2 February 2008 Effect of Gas selection on arc stability, chemistry, mechanical properties and diff. H2 contents of FCAW, MCAW, GMAW weldmetals Viwek Vaidya February 12 th 2008 CWA Toronto Chapter conference

3 February 2008 The GMAW Set-up Wire Feeder Power Source Water Cooler (optional) Regulator / Flow meter Shielding Gas Welding Gun Work Ground Clamp Work piece (Base Material) Wire

4 February 2008 FCAW, MCAW, GMAW Contact tube Base metal Electrode stick out Arc length Shielding gas Gun Nozzle Electrode wire Welding Arc

5 February 2008 Observation of the welding arc Video of metal transfers in – GMAW steel Please note: Members will receive above video by request. It include other processes as well. (SAW, SMAW, FCAW, GMAW, PULSE MIG) Thank You for Your Support!

6 February 2008 The functions of shielding gases are Protect the weld pool from atmosphere Provide a gas plasma - ionized gas Support metal transfer and bead wetting

7 February 2008 Thermal conductivity and plasma shape Thermal Conductivity is the ease with which the gas will dissipate heat Argon has low thermal conductivity It is used for superior R-Value windows Helium has high thermal conductivity, CO2 also has high thermal conductivity than Argon Argon

8 February 2008 Thermal conductivity and plasma shape : Globular transfer Consider energy flow through He and CO2, both characterised with Higher thermal conductivity than Argon Narrow plasma column CO2 and Helium produce globular transfer cannot produce spray transfer!

9 February 2008 Penetration profiles Argon has a finger nail penetration profile consistent with spray transfer CO2 and He have elliptical penetration consistent with the globular transfer

10 February 2008 Thermal conductivity and plasma shape : Spray Transfer Low thermal conductivity Expanded plasma column Electron condensation heating

11 February 2008 Thermal conductivity and plasma shape : Spray Transfer Wire melts in a fast fine droplet stream Wire end becomes pointed Spray transfer results in high deposition and good penetration Argon gives spray transfer!

12 February 2008 Penetration profiles Argon has a finger nail penetration profile consistent with spray transfer CO2 and He have elliptical penetration consistent with the globular transfer

13 February 2008 GMAW single wire deposition rates ( 0.045& )

14 February 2008 Pulsed arcSpray modulated 10 drops /pulse 1 drop /pulse (interrupted spray) GMAW – Aluminum welding – modulated pulse Pollution of gas Porosity level spray pulse Modulated spray

15 February 2008 Introduction of oxygen through the contact tip in GMAW Aluminium + 20 % Annular gas: Argon + 1,5%O2 Annular gas: Argon + contact tip: +0,3 l/min O2 Dark deposited removed with rag or by brushing or final degreasing Addition of Oxygen to argon increases arc speed by 20%

16 February 2008 Ar Ar+ % CO2 Ar+He+ % CO2 Ar+H2+ % CO2 Ar+ He+ CO2 NICKEL BASE ALLOYS GMAW NICKEL BASE ALLOYS GMAW Appearance of the weld and stability of the pulsed transfer greatly improved with CO2 additions

17 February 2008 NICKEL BASE ALLOYS GMAW NICKEL BASE ALLOYS GMAW Influence of CO2 addition on the pulse transfer stability U peak U droplet detachment Argon Argon+ CO2 Ar+ H2 + CO2

18 February 2008 NICKEL BASE ALLOYS GMAW NICKEL BASE ALLOYS GMAW welding speed Ar + CO2 +He+ CO2 +H2+ %CO2 Welding speed (cm/mn) +26% +17% +12% stability of the pulse transfer transfer stability energy distribution & transfer stability Influence of CO2 addition on Welding speed

19 February 2008 INCONEL 625 INCONEL 600 Ar+ H2 + CO2 improvement in bead appearance NICKEL BASE ALLOYS GMAW NICKEL BASE ALLOYS GMAW

20 February 2008 Two-wire GMAW welding process can double productivity! Extremely fast response power sources needed Two wires fed simultaneously into the same weld pool Wires powered to operate with peak pulses: Perfectly in phase = twin wire technique Perfectly out of phase = tandem wire technique

21 February 2008 GMAW Dual wire process Automatic GMAW with dual wires: thickness: mm Carbon steel, stainless steels and aluminium alloys 2 wires connected at the same electrical potential Each wire connected at the different electrical potential Twin wireTandem Technique

22 February 2008 Metal sheath - outer envelope Metallic and non Metallic Fluxes & powders Joint FCAW & MCAW wire cross section

23 February 2008 FCAW weld with slag formation

24 February 2008 Observation of the welding arc Video of Ar-CO2 systems - FCAW To see above video, click hereclick here

25 February 2008 Improved weld profile with FCAW+GMAW combination, due to better wetting. Presence of oxidizing species through the FCAW wire 5/16 inch single pass fillet weld : 35 ipm dual wire as opposed to 16 ipm with single wire systems.

26 February 2008 GMAW chemistry variation with Ar-O2 mixes. Wire Chemistry : C=0.1%, Si=0.9%, Mn=1.48%

27 February 2008 GMAW chemistry variations : Ar-CO2 system Wire: Mn=1.25%, Si=0.73% C =0.08%,

28 February 2008 Mechanical properties : 1% Ni MCAW all tests with same lot Shielding gasUTS MPa YS MPa % EImpacts C v -51ºC 100% CO ,62,64,49,69 Argon +15% CO ,62,68,82,45 Argon+10% He + 15% CO ,72,95,92,79

29 February 2008 Classification of metal cored and FCAW wires in Canada and US METAL CORED ; CSA W48-01/W48-06, CLASS E491C-6-H4/E491C-6M-H4 AWS A /ASME SFA 5.18, Class E70C-6-H4/E70C-6M-H4 FLUX CORED CSA W48-01/W48-06, Class E491T-1-H8/T-1M-H8, E491T-9- H8/T-9M-H8 AWS A /ASME SFA 5.20, Class E71T-1-H8/T-1M-H8, E71T-9-H8/T-9M-H8 CSA W48-01/W48-06, Class E492T-9-H8/T-9M-H8 AWS A /ASME SFA 5.20, Class E70T-1-H8/T-1M-H8, E70T-9-H8/T-9M-H8

30 February 2008 Weldmetal chemistries – E491 C6-H4 Shielding gasOxidation potential % Carbon% Manganese% Silicon Ar+2%O2 2% Ar+5%O2 5% Ar+10%CO2 5% Ar+25%CO2 12.5% Ar+4%O2+ 5%CO2 6.5% CSA W48 = %O2 + ½ % CO2 N/R1.75 max0.90 max

31 February 2008 Weldmetal mechanical property variation – E491 C6-H4 Shielding gasUTS MPaYS Mpa%EImpacts C v -30ºC Ar+2%O Ar+5%O Ar+10%CO Ar+25%CO Ar+4%O2+ 5%CO CSA W min 410 min22 min27

32 February 2008 Carbon pick up in stainless steel weld deposits Ar-CO2 Wire Carbon = 0.012%

33 February 2008 Effect of ambient humidity on diffusible H2 contents-SMAW Location + (Diff H2 ml/100g) ScotlandZurichTokyoRioNew Orleans Cape Town January August Same electrode lot, sealed in vacuum packed condition was shipped to various locations below and tested at different times of the year!

34 February 2008 FCAW wire storage conditions and worm tracking

35 February 2008 FCAW wire storage conditions and worm tracking

36 February 2008 Wire closing seam configuration Typical FCAW/MCAW wire cross sections

37 February 2008 FCAW wires – Hydrogen pick up susceptibility

38 February 2008 Variation of diffusible hydrogen content and shielding gases Parameters100% CO2Argon+15%CO2Argon + 5% CO2 Wire dia.1/16" Amps Volts E.S.O3/4" Diffusible Hydrogen7.5ml/100g9.5ml/100g10.4ml/100g R.H/Temp45%/22.6'C

39 February 2008 Diffusible Hydrogen variation with oxidation potential

40 February 2008 FCAW/diffusible hydrogen and electrical stick out Wire A Wire B 1.2mm dia. 1.6mm dia. 230 amps 285 amps 26 volts 28 volts 14 ipm ESO 10mmESO 20mm ESO 10 mm ESO 20 mm 8.1ml/100g5.5ml/100g10.0ml/100g9.0ml/100g

41 February 2008 FCAW wire storage conditions and worm tracking To avoid worm tracking and porosity store the wire properly Use shielding gas with higher oxidation potential Reduce welding amperage Weld with a longer stick out to preheat the wire Discard two layers of the spool and retry If possible recondition the wire – not generally recommended

42 February 2008 Deleterious effect of Nitrogen on impact energy: carbon steels

43 February 2008 Nitrogen additions to shielding gas for Duplex stainless Up to 2 % additions of N2 advantageous for duplex stainless steel GMAW welding: Reduction of 10-15% ferrite improving ferrite/austenite balance 10% improvement in strength Better performance against pitting corrosion Beyond 6% Nitrogen in the gas will produces weld porosity..

44 February 2008 Choice of Shielding gases Too many to choose from Too complex for users Too complex for producers ALMIG ALTIG ALFLUX

45 February 2008 Conclusions Video imaging of the welding arc shows that progressive increase in oxidation potential of the shielding gas, stabilizes the arc for GMAW welds in stainless and mild steel welds Fumes also increase with increasing CO2 content of the shielding gases Addition of 1-2% Oxygen to Argon seems to improve arc stability and arc speeds for Aluminum GMAW process Micro additions of CO2 to Argon + H2 or Argon+He mixtures improves stability of the GMAW welding of Inconel 625 alloys GMAW, FCAW, MCAW deposits in mild steel loose strength and alloying elements with increasing oxidation potential of the shielding gases Increasing CO2 content of the shielding gas may contribute to increased pick up of carbon in extra low carbon stainless steels GMAW deposits.

46 February 2008 Conclusions - continued Diffusible hydrogen of a FCAW weld deposit increases with higher levels of Argon contents in the shielding gas Improper storage of FCAW consumable can result in substantial increase in diffusible hydrogen content, causing worm tracking porosity. Some remedies have been suggested An addition of up to 2% Nitrogen to an Argon+Helium+CO2 mixture shows improved control on ferrite content of the weldmetal, about 10% increase in strength and improved pitting corrosion resistance in case of duplex stainless steel GMAW welds.

47 February 2008 Acknowledgements The author would like to thank the research staff at the Air Liquide World Headquarters in Paris for providing guidance and stimulating discussions while the manuscripts were being drawn up. Thanks are also due to technical experts at Air Liquide Canada and data obtained from the certification center in Boucherville. Photographic support came from several CAP Audit reports, performed at various customer locations in Canada. Dr. Christian Bonnet, Dr. P. Rouault, Mr. J. M. Fortain, Mr. Pierre Geoffroy, Mr. Joe Smith and Mr. Jean Venne provided valuable technical support for this paper and are being recognized for their contribution.

48 February 2008 Thank you!


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