GTAW (GAS TUNGSTEN ARC WELDING)/(TUNGSTEN INERT

GAS WELDING)

Kunal Parikh, SEPL,Vadodara

Contents
1. Process Description
2. Principle of Operation
3. Process Advantages
4. Process Limitations
5. Process Variables
6. Shielding Gases
7. Use of Filler Metals
8. Specifications of GTAW filler Metals
9. Welding Equipment for GTAW
10.Welding Defects in GTAW
11.SEPL’s Scope for FY 2020-21
12.Packaging
13.Business Segments & Applications
1. Process Description
 Gas tungsten arc welding (GTAW) is an arc welding
process that uses an arc between a tungsten
electrode (non consumable) and the weld pool. The
process is used with shielding gas and without the
application of pressure. The process may be used
with or without the addition of filler metal
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2. Principle of Operation
 Shielding gas is fed through the torch to protect the electrode, molten weld
pool, and solidifying weld metal from contamination by the atmosphere. The
electric arc is produced by the passage of current through the conductive,
ionized shielding gas. The arc is established between the tip of the electrode
and the work. Heat generated by the arc melts the base metal. Once the arc
and weld pool are established, the torch is moved along the joint and the
arc progressively melts the faying surfaces. Filler wire, if used, is usually
added to the leading edge of the weld pool to fill the joint. Four basic
components are common to all GTAW set ups.
1.Torch
2. Electrode
3. Welding Power Source
4. Shielding Gas
3. Process Advantages
 3.1 Produces superior quality of welds, generally free of defects
 3.2 Free of the spatter which occurs with other arc welding processes.
 3.3 Can be used with or without filler metal as required for the specific
application.
 3.4 Allows excellent control of root pass weld penetration.
 3.5 It can use relatively inexpensive power supplies.
 3.6 Allows precise control of the welding variables.
 3.7 It can be used to weld almost all metals, including dissimilar metal joints.
 3.8 It allows the heat source and filler metal additions to be controlled
independently.
4.Process Limitation
 4.1 Deposition rates are lower than the rates possible with
consumable electrode arc welding processes.
 4.2 Less economical than the consumable electrode arc welding
processes for thicker sections greater than 10mm.
 4.3 There is a difficulty in shielding the weld zone properly in
drafty environments.
 4.4 There is a need for slightly more dexterity and welder
coordination than GMAW & SMAW.
5. Process Variables
 The primary variables in GTAW are
 5.1 Arc Current (Welding Current)
 5.2 Arc Voltage (Arc Length)

 5.3 Travel Speed

 5.4 Wire Feed

 5.5 Shielding Gas

The amount of the energy produced by the arc is

proportional to the current and voltage. The amount
transferred per unit length or weld is inversely
proportional to the travel speed.
 6. Shielding Gases
 Shielding gas is directed by the torch to the arc and weld pool to protect the
electrode and molten weld metal from atmospheric contamination. Back up
purge gas can also be used to protect the underside of the weld and its
adjacent base metal surfaces from oxidation during welding. Uniformity of
root bead contour, freedom from undercutting, and the desire amount of root
bead reinforcement are more likely to be achieved when using gas backup
under controlled conditions. In some materials, gas backup reduces root
cracking and porosity in the weld.
 Types of gases
 6.1 Argon ( Having moleculer weight 40, Purity is 99.95 %acceptable for most metals except reactive and
refractory metals where purity required 99.997%)
 6.2 Helium ( It is light one having atomic wt 4,obtained by separation from natural gas, welding grade He
is refined to a purity of at least 99.99%
 6.3 Mixture of Argon and Helium
 6.4 Mixture of Argon and Hydrogen for special applications. (It employed in special cases such as
mechanized welding of light gauge SS tubing where the hydrogen does not cause adverse metallurgical
effects such as porosity and hydrogen induced cracks. The most commonly used argon-hydrogen mixture
contains 15% Hydrogen.
7. Use of Filler Metals

 The filler metal composition is adjusted to match the properties of the base
metal in its welded condition. Such filler metals are produced with closer
control on chemistry, purity and quality than are base metals. Deoxidizers
are frequently added to ensure weld soundness. Further modifications are
made of some filler metal compositions to improve response to post weld
heat treatments.
 The choice of filler metal are dependent on
following.
 A. The tensile and impact properties.
 B. Corrosion resistance.

 C. Electrical or thermal conductivities.

8. Specification of GTAW filler metals

 The specifications establish filler metal classifications based on

the mechanical properties or chemical compositions,or both, of
each filler metal. They also set forth the conditions under which
the filler metals must be tested.
 Filler metals for GTAW are available in most alloys in the form
of straightened and cut lengths (rods),usually 36 in. long for
manual welding, and spooled or coiled for continuous wire for
machine or automatic welding. The filler metal diameters
range from about 0.5mm for fine and delicate work to about
5 mm for high current manual welding or surfacing.
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AWS SPECIFICATIONS FOR FILLER METASL SUITABLE FOR
GAS TUNGSTEN ARC WELDING
Specification no. Title
AWS SFA A 5.2 Iron and Steel Gas-welding Rods

AWS SFA A 5.7 Copper & Copper Alloy bare welding rods and electrodes
Corrosion resisting chromium and chromium-nickel steel bare and composite metal cored
AWS SFA A 5.9 and stranded arc
welding rods and bare electrodes
Aluminum and Aluminum Alloy welding rods and bare electrodes ( ER 4043,ER4047,ER 5183,
AWS SFA A 5.10 ER 5356 etc.)
AWS SFA A 5.13 Surfacing welding rods and electrodes

AWS SFA A 5.14 Nickel and Nickel Alloy bare welding rods and electrodes

AWS SFA A 5.16 Titanium and Titanium alloy bare welding rods and electrodes

AWS SFA A 5.18 Mild Steel Electrodes for Gas Metal Arc Welding ( ER 70S2,ER 70S G,ER 70S6 etc.)

AWS SFA A 5.19 Magnesium-Alloy welding rods and bare electrodes

AWS SFA A 5.21 Composite surfacing welding rods and electrodes

AWS SFA A 5.22 Stainless Steel Electrodes for FCAW & GTAW (ER308L,ER309L,ER316L,ER 347 etc.)

AWS SFA A 5.24 Zirconium and Zirconium alloy bare welding rods and electrodes
Low alloy steel electrodes and rods for Gas Shielded Arc Welding (ER 80S B2,ER 90S B3,
AWS SFA A 5.28 ER 80 SG,ER 90S G,ER 80S D2,ER 80SB6)
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Example:- AWS SFA/A 5.18 ER 70 S 2

AWS= American Welding Society

5.18 = Specification of carbon steel electrode rods

ER = ER indicates filler metal may be used as either an

electrode or rod
70 = Indicates tensile strength of the weld metal in 10000 psi
S = Indicates that the filler metal wire is solid.

2 = Indicates the chemical composition of the solid filler metal wire

9. Welding Equipment GTAW
 10.Weld Defects in GTAW
 Discontinuities are interruptions in the typical structure of welment, and they
may occur in the base metal, weld metal, and heat affected zones.
Discontinuities in a weldment that do not satisfy the requirements of an
applicable fabrication code or specification are classified as defects, and are
required to be removed because they could impair the performance of the
weldment in service.
 Problems and Corrections
A. Tungsten Inclusions:-One discontinuity found only in gas tungsten arc
welds is tungsten inclusions. Particles of tungsten from the electrode can be
embedded in a weld then improper welding procedure are used with the
GTAW process. Probable causes for the same are as follows.
A1. Contact of electrode tip with molten weld pool
A2. Contact of filler metal with hot tip of electrode
A3. Contamination of the electrode tip by spatter from the weld pool.

A4. Exceeding the current limit for a given electrode size or type.
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 B. Lack of Shielding:- In adequate shielding gas
flow rates or excessive wind drafts resulting in
oxidation of the electrode tip. The mechanical
properties of titanium,aluminum,nickel, and high
strength steel alloys can be seriously impaired with
loss of inert gas shielding. Gas shielding effectiveness
can be often evaluated prior to production welding
by making a spot weld and continuing gas flow until
the weld has cooled to a low temperature A bright,
silvery spot will be evident if shielding is effective.
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C. Welding Problems & Remedies:- Following is the trouble shooting guide for GTAW

Sr.No. Problem Cause Remedy

1.1 Inadequate gas flow 1.1 Increase gas flow
1.2 Operating on reverse polarity 1.2 Use larger electrode or change to straight polarity
1.3 Improper Size electrode for current required 1.3 Use larger electrode
Excessive 1.4 Excessive heating in holder 1.4 Check for proper collect contact
1 electrode
consumption 1.5 Remove contaminated portion. Erratic results will continue
1.5 Contaminated electrode
as long as contaminatin exists.
1.6 Keep gas flowing after stopping are for at least 10 to 15
1.6 Electrode oxidation during cooling
seconds
1.7 Using gas containing oxygen or Co2 1.7 Change to proper gas

2.1 Base metal is dirty, greasy 2.1 Use appropriate chemical cleaners, wire brush, or abrasives
2.2 Open joint groove, bring electrode closer to work; decrease
2.2 Joint too narrow
2 Erratic Arc voltage.
2.3 Electrode is contaminated 2.3 Remove contaminated portion of electrode
2.4 Arc is too long 2.4 Bring holder closer to work to shorten arc.
3.1 Blow out air from all lines before striking arc; remove
3.1 Entrapped gas impurities ( Hydrogen,Nitrogen,Air, Water
condensed moisture from lines; use welding grade (99.99%)
Vapour)
inert gas.
3 Porosity
3.2 Defective gas hose or loose hose connections 3.2 Check nose and connections for leaks
3.3 Clean with chemical cleaner not prone to break up in arc; Do
3.3 Oil film on base metal
Not weld while base metals is wet
4.1 Contact starting with electrode 4.1 Use high frequency starter; use copper strike plate.
Tungsten
4.2 Use less current or larger electrode;use thoriated or
4 contamination of 4.2 Electrode melting and alloying with base metal
zirconium-tungsten electrode.
Workpiece
4.3 Touching tungsten to molten pool 4.3 Keep tungsten out of molten pool
 11.SEPL’s Scope for FY2020-21
Product Family Product Types/Grades AWS Classification Product Family Product Types/Grades AWS Classification
ER 70S G ER 308/308L

ER 70S 2, ER 70S 2 (spl) ER 309/309L

Mild Steel AWS SFA/A 5.18
ER 70S 6 ER 310
ER 70S 6 ER 316/316L
ER 70S A1 ER 347
ER 80S B2 Stainless Steel ER 309LMo AWS SFA/A5.9
ER 90S B3 ER 309LSi
ER 90S G ER 347Si
Low Alloy ER 80S D2 AWS SFA/A 5.28 ER 385
ER 110S G ER 2209
ER 120S G ER 2509
ER 80S Ni1 ER 2594
ER 80S Ni2 ER 1100
ER Ni1 ER 4043
ER NiCr3 ER 4047
Aluminium AWS SFA/A5.10
ER NiCrMo14 ER 5183
Nickel alloy AWS SFA/A5.14
ER NiCrMo3 ER 5356
ER NiCrMo4 ER 5556 A
ER NiCu7
12.Packaging
AWS ER 70S2 AWS ER 70S2
Ø 2.40mm
FABTIG FABTIG

1000 mm

Ø x L in mm Primary Box/Tube in kg No. of Primary Boxes/Tubes in Net Weight 1 No. of Outer Box
one outer box in kg

1.60x1000 5 4 20

2.00x1000 5 4 20

2.40x1000 5 4 20

3.20x1000 5 4 20

4.00x1000 5 4 20
 13.Business Segments & Applications

Product
Product Types/Grades AWS Classification Application/Segment
Family

General structural Steel fabrication, Thick plates

ER 70S G & Thick Pipeline.

For non-alloyed & Micro alloyed structural steel

up to 520 Mpa used for Boiler,pressure vessel &
ship building. Also used for high quality pipe
welding of mild and medium tensile steels.
ER 70S 2, ER 70S 2 (spl)

Mild Steel AWS SFA/A 5.18

Root pass of pipe welding,thin sheet,Metal

autobody,farm implements,steel casing,collision
repairs,Pressure vessel,high pressure piping for
ship building,Petro Chemical and Nuclear power
ER 70S 6 plant.
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Product Family Product Types/Grades AWS Classification Application/Segment

Creep resistance steel for pipes in pressure vessels and boilers with a working
ER 70S A1 temperature of up to about 500°C
Welding of dissimilar combination of Cr.Mo & Carbon steels for pipes,plates
and castings.Elevated temperature and corrosive service applications in
ER 80S B2
refineries,petrochemical and fertilizer plant. Also can be used for the root
pass as a part of WPS where E 8018 class of electrodes are being used.
With high% of Cr & Mo low alloy steel for petrochemical,refineries and
fertilizer plant. It can be also used to join P5A material ,german steels and for
ER 90S B3 and up to higher temperatures. This can be best choice for the root pass of E
9018 types of electrodes.
Welding of 0.5Mo steel in pipeline and pressure vessel with operating temp
ER 80S G of about 500°C. Welding of medium steel casting etc.
Welding of sulphur heating free mechanism steels used for pipe line,pressure
ER 90S G vessel for and up to 500°C temperature. Repairs of medium steel
castings,pipe,fittings,flanges and valves.

Suitable for weldin gof Sailma450/450H steels used for manufacturing of

ER 90S D2 CONCOR WAGONS.

Welding of 0.5% molysteel in oil process,pipe work and fittings where sulphur
ER 80S D2
induced stress corrosion cracking is more important.
Low Alloy AWS SFA/A 5.28 For welding of 1 % Ni steels,fine grained and low alloyed Ni Steels at sub zero
ER 80S Ni 1 temperature mostly in offshore industry.
For welding of 2.5% Ni Steels,fine grained and low alloyed Ni Steels at sub
ER 80S Ni 2 zero temperature mostly in pressure vessel,pipes,offshore indutry and
storage tanks.
Welding of 5 Cr-0.5Mo creep resistant steels and equivalen grades.
ER 80S B6 Application in power generation,ammonia synthesis plant and in
petrochemical. Widely used in joining P5/T5 materials or similar composition.

Welding of 9 Cr 1 Mo type or equivalent material in pipe and tube form

wedling of ferritic,martensitc,chrome steels for general corrosion and heat
ER 80S B8 resistance application. For joining of P9/T9 material of similar composition
getting used in power plant,Oil Refineries and petrochemical.
Suitable for Cr,Mo,V,Nb steels such as P91,T91,F91 for heavy wall
ER 90S B9 composnents such as headers,main steam piping and turbine rotors in power
generating plants.
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Product Family Product Types/Grades AWS Classification Application/Segment

Corrosion resistant CrNi Tig Wire for welding of austenitic CrNi Alloys of 18Cr-
8Ni type having good corrosion resisting properties. It is widely used in
ER 308/308L chemical plant,food processing plant,Paint machinery,as well as for
pipes,tubes and boiler SS piping in refineries,oil and gas industries.
Fabrication of boilers,reactors,turbines,pipes and tubes.
Widely used for dissimilar joints between stainless steel and low alloy carbon
steels. Joining of corrosion resistant clad steel.Buffer layers on low alloy and
ER 309/309L
carbon steel.

This CrNiMo wire is having excellent corrosion resistance against acid and
chlorinated environment. This is being widely used in food processing
ER 316/316L industries,shipbuilding,various types of architectural structure,textile
processing,Naval and Chemical environments. Also used in paper,pulp and
dying industries with a special application of cladding stainless steel spares.
It is having Nb Stabilize content hence it gives highest resistance against
IGC.Used for refineries,power plant,centrifugal pump,impellers
Staniless Steel AWS SFA/A5.9 and shafts,valve faces and seats. Recommended to use at high
ER 347
temperature like fabrication of boilers ang gas turbine,welding of
stainless steel tanks,pipes,valves in food chemical and
petrochemical plants.
Especially designed to weld 309Mo,316/316L to dissimilar metal like low alloy
ER 309LMo and/or carbon Mn steel.
Welding of duplex stainless steel and similar grades.Specially designed for
pipeline transporting chloride bearing products and sour gases. Cladding of
ER 2209 carbon and low alloy steel. Cast Pump industries,valve bodies and sea water
handling requirement for chemical equivalents,heat exchangers,off shore
platform etc.
This wire belongs to super duplex series of stainless steel and it is used for to
weld the similar grade. Applications where it is being used are pipeline
ER 2594 system,flow lines,risers,manifolds,pumps and valves,process equipments in
offshore,oil and gas industries,petrochemical plant etc.
TOGETHER
EACH Working Together for a
Common Goal
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