Posted by: heatsschoolofweldingtechnology | January 9, 2009

TIG (GTAW) WELDING


Gas Tungsten Arc Welding

Gas Tungsten Arc Welding

TIG is Tungsten Inert Gas, and GTAW is Gas Tungsten Arc Welding. These two terms are just the same. This is the most commonly used in welding of piping for Oil and Gas Industry.

Advantages of TIG Welding

High quality welds, low distortion
Easy to mechanize and automate
Flexibility and ease of heat control
All metals, all positions

Limitations of TIG Welding
Lower deposition rates
Good skills required
Sensitive to cleanliness and contamination
Arc blow sensitive

Polarity
The Tungsten Electrode in Gas Tungsten Arc Welding (GTAW or Tig) can make contact with a Direct Current (DC) power supply either at the positive (+) or at the negative (-) terminal. In the first case the connection is for DCEP (electrode positive) or reverse polarity. In the second one for DCEN (electrode negative) or straight polarity.

DCEP:
30% of the heat is concentrated in the workpiece
70% of the heat in concentrated in the tungsten electrode
Shallow penetration
Wide weld area

DEN:
70% of the heat is concentrated in the workpiece
30% of the heat is concentrated in the tungsten electrode
Deep penetration
Narrow weld area

Tungsten Electrodes
A few tungsten alloys are used as electrodes for GTAW (tig welding). They are non consumable as they do not enter, intentionally, in the composition of the weld pool. Their function is limited to carry the currents employed, to stand the heat of the arc without melting and to provide electrons by thermionic emission.

Filler Wire
Manual GTAW is often performed autogenously (without added filler metal) when the joint requires only fusion of the abutting ends. However when needed, filler material can be added manually from the side, right in the weld puddle, by alternatively introducing the wire tip into the arc and withdrawing it.

Shielding Gases
The shielding gas is provided continuously through the torch to protect the molten weld metal, the tungsten electrode and the filler wire tip, if used, from air contamination. Backup shielding gas may be provided if necessary on the underside of the weld to purge and displace surrounding air.

Shielding is always needed but it may be critical especially for highly reactive metals like titanium that would be promptly oxidized and ruined if heated in air. To weld titanium by GTAW use is made of glove boxes purged with shielding gas of the highest purity before weld start or of trailing shields, specially designed accessories that provide a sufficient gas trail to protect the welded surface until cool enough.

The gases uses are mostly Argon and Helium or mixtures of the two. Argon is the standard shielding gas. Helium, which is lighter than air, must be supplied with a higher flow than argon because it tends to rise. It transfers more heat than argon for the same current and voltage. Thus it may be needed to join metals of higher conductivity or heavy plates.

When extinguishing the arc at the end of the weld, it is important to let the gas flow for a certain time to shield the hot metal from air. Equipment provides a delay before shutting off the gas flow, but the welder must linger with the torch upon the weld as long as needed.

Materials
Most weldable metals can be welded by the GTAW process. It is adaptable to thin and delicate joints but also to thick and demanding applications, always of good quality although possibly not the most fast and economic process.

Aluminum alloys of the weldable kinds are among those for which GTAW is most suited. One should always remember that not all aluminum alloys can be welded successfully or with the same ease. For a reminder of the reasons making some of the strongest alloys non readily weldable by fusion processes see Aluminum Welding.

Joining is made difficult by the surface formation of tenacious refractory aluminum oxides of melting point much higher than that of aluminum metal. The oxides though are broken up by the cathodic cleaning action of the Electrode Positive part of the alternating current cycle. Once broken they may float upon the molten metal and they no longer interfere with the welding process. Therefore high frequency stabilized alternating current power supply is the most used GTAW process for aluminum with pure tungsten electrodes. Exceptionally, for thin sections, DCEP can be used with thoriated tungsten. Argon is the most used shielding gas.

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Responses

  1. tig filler material used for all uses for all typs of steel ,low alloy steel,carbon steel,etc

  2. i need data for this typs

  3. Hi thabat, thanks for coming by. as far as I know, there is no such filler metal that can be used for all types of steel. It is very clear in ASME IX that there are different classification and types of filler metal in accordance to their uses.

    Pls check the following section of ASME IX
    QW 432.1 – Steel and Steel Alloys
    QW 432.2 – Aluminum and Aluminum – Base Alloys
    QW 432.3 – Copper and Copper – Base Alloys
    QW 432.4 – Nickel and Nickel Base Alloys
    QW 432.5 – Titanium and Titanium Base Alloys
    QW 432.6 – Zirconium and Zirconium Base Alloys
    QW 432.7 – Hard Surfacing Weld Metal Overlay

    I hope the above information answers your query.

  4. sir gud pm..ask ko lng kung pwede ko na agad kunin ung GTAWII na course…thanks

  5. sir may mig welding po ba kau na course dyan?? if possible sana gtawII na agad kunin ko na course wag na ung smawI&II

  6. Hi Ian, pwede po ninyong i take agad ang GTAW NCII kung may SMAW NCII na po kayo or experienced na kayo sa pipewelding (SMAW). Yun po kasi ang pre-requisite nya. Thanks

  7. Hi Ian, sorry ti inform you that we do not have MIG yet. coming soon. Thanks

  8. Hi! Just a question, what does “SA” stand for inm the accronym GTAW_SA?

    Thank you so much

  9. Sir im gonna ask if anu po ba requirements para sa tig welding course and available po ba ngaun yan,how many months it will take and how much it will cost..salamat po

  10. Hi, the pre-requisite of TIG is SMAW NCII and the pre-requisite of SMAW NCII is SMAW NCI or Basic Welding. Pero kung may experience ka na sa Pipe Welding, pwede ka ng mag directs TIG Course. Yes, available po and course namin all year round. Our course starts every monday. regards.

  11. ilang days po ang training ng tig welder po?at magkanu po ang bayad lahat lahat po,,actual po ba ang training o me lecture din po??slamat po,,

  12. GTAW NCII is 34 days, theory plus practical more on practical. P34,000 tuition fee.
    TIG Course – 6 days – P16,000 pure practical

    requirements:
    you must be graduate of SMAW NCII or Pipe Welding Course or Experienced pipe welder

  13. gud evening sir kung skaling mg training ako sa inyo basic smaw. smawnc11 ska gtawnc11 meron po ba kayong boarding house dyan na pwedeng tuluyan. d2 kasi aq sa QC nkatira ngayon..

  14. Meron po sa harap namin. P1,500 po one month

  15. Sir pwede po ba akong kumuha ng courde na tig welding kht po ang ntapos q lng ay fcaw welding,meron po ba kaung brance dto sa batanggas?at mgkanu po kya ang aabotin ng tuition lhat lhat ksama po actual training!

  16. Sir ilang days po ba ang aabutin pg ng training po sa inyo ng tid welder?

  17. ang pre-requisite kasi ng TIG ay SMAW NCII, kasi yun ang nag co combine sa work. I suggest, kuha ka muna ng SMAW NCII. regards

  18. GTAW NCII – P34,000 – 34 days (theory and practical)
    or
    TIG welding Course – P16,000 – 6 days (practical only)
    or
    TIG Welding Course – P26,666 – 10 days (practical only)

  19. sir anu po bang kaibahan sa TIG welding course na 6 days compare sa 10 days , meron po ba kyu schedule sakali the month of august 2013. tanz po

  20. sir la pa po ako certificate about sa basic welding katulad ng SMAW, pro my idea n po ako sa stick welding at sa tig welding , ilang tao po b ang minimum nyu bago kyu sakali mag start ang traning.? at bukod po ba sa amount n 16,000thu for 6 days or sa 26,666thu sa 10 days, may iba pa bang mga charge yan during training, at ung certificate makuha po kaagad? tanx…

  21. Number of training days lng po difference so mas mahaba ang exposure. Anytime po may schedule kami except sundays and holidays

  22. Enroll now you can start the next day. Inclusive na po lahat dun

  23. Good day !
    Gusto ko pong mag aral ng tig ..
    Kaya po ba yung ng 1 month ?

  24. Pwede po. May smaw n kyo?

  25. yes po

  26. i already have SMAW NC II and plan to get my Tig Welding this coming last week of april to may..pwedi po bah?

  27. You can take (GTAW) even you are not graduated a high school?

  28. Blessed day! No. You must at least be a high school graduate.

  29. Sir ako po ay currently working in a taiwanese owned company dito sa cavite bilang tig welder, I worked for about 2yrs and several months and I know how to weld well as a tig welder, I had an SMAW NC2 but I dont have GTAW NC2, gusto ko po sanang kumuha ng assestment for the certification of GTAW, mgkano po b ang bayad? Pls response. Tnx.

  30. We cant send you for assessment directly po. You need to enroll our course kahit yungshort course lang po so we can send you for tesda assessment. Alternatively, hanap po kayo assessment center na nag aasses directly without training. Kasi di po kami gumagawa ng ganun. Thanks


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