5 Welding Processes

5 Welding Processes

Equipments & Piping

Equipments & Piping 

http://www.heatecholdings.com/business_pipingSystem_oil.html

Equipments & Piping

Equipments & Piping

Equipments & Piping

Equipments & Piping

Equipments & Piping

5.1 GENERAL 

The inspector should understand the basic arc welding processes most 

frequently used in the fabrication and repair of refinery and chemical process 

equipment. These processes include shielded metal arc welding (SMAW), gas 

tungsten arc welding (GTAW), gas metal arc welding (GMAW), flux cored arc 

welding (FCAW), submerged arc welding (SAW), and stud arc welding (SW). 

Descriptions of less frequently used welding process are available in the 

referenced material. 

Each process has advantages and limitations depending upon the application 

and can be more or less prone to particular types of discontinuities. 

http://www.substech.com/dokuwiki/doku.php?id=shielded_metal_arc_welding_smaw

5.2 SHIELDED METAL ARC WELDING (SMAW) 

SMAW is the most widely used of the various arc welding processes. SMAW 

uses an arc between a covered electrode and the weld pool. It employs the 

heat of the arc, coming from the tip of a consumable covered electrode, to 

melt the base metal. Shielding is provided from the decomposition of the 

electrode covering, without the application of pressure and with filler metal 

from the electrode. Either alternating current (ac) or direct current (dc) may be 

employed, depending on the welding power supply and the electrode 

selected. A constant-current (CC) power supply is preferred. SMAW is a 

manual welding process. See Figures 1 and 2 for schematics of the SMAW 

circuit and welding process.

5.2.1 Electrode Covering 

Depending on the type of electrode being used, the covering performs one or 

more of the following functions: 

a. Provides a gas to shield the arc and prevent excessive atmospheric 

contamination of the molten filler metal. 

b. Provides scavengers, deoxidizers, and fluxing agents to cleanse the weld 

and prevent excessive grain growth in the weld metal. 

c. Establishes the electrical characteristics of the electrode. 

d. Provides a slag blanket to protect the hot weld metal from the air and 

enhances the mechanical properties, bead shape, and surface cleanliness 

of the weld metal. 

e. Provides a means of adding alloying elements to change the mechanical 

properties of the weld metal.

5.2.2 Advantages of SMAW 

Some commonly accepted advantages of the SMAW process include: 

a. Equipment is relatively simple, inexpensive, and portable. 

b. Process can be used in areas of limited access. 

c. Process is less sensitive to wind and draft than other welding processes. 

d. Process is suitable for most of the commonly used metals and alloys. 

5.2.3 Limitations of SMAW 

Limitations associated with SMAW are: 

a. Deposition rates are lower than for other processes such as GMAW. 

b. Slag usually must be removed at stops and starts, and before depositing a 

weld bead adjacent to or onto a previously deposited weld bead.

Shielded metal arc welding

Shielded metal arc welding

SMAW

SMAW

SMAW

SMAW- Underwater Welding

SMAW- Underwater Welding

SMAW- Qualification of Underwater Welders

SMAW- Structural Welding

SMAW- Structural Welding

SMAW- WPQ Welder Performance Qualification

SMAW- Transmission Pipeline Welding

Equipment is relatively 

simple, inexpensive, and 

portable.

SMAW- Weld Profile

SMAW- Weld Profile

SMAW- Weld Profile

SMAW- Weld Profile

SMAW- Weld Profile

SMAW- Weld Profile

SMAW- Weld Profile

SMAW- Weld Profile

SMAW- Grinding at Start-Stop

SMAW- Tack Welding

SMAW- Root Pass + Hot Pass

SMAW- Large Tack Weld for Thick Welding

SMAW- Pipeline Tie-in Joint

SMAW- Pipeline Welding

SMAW- WPQ Test Coupon



SMAW- AWS Test Positions

SMAW- Smiling Experts at Work

5.3 GAS TUNGSTEN ARC WELDING (GTAW) 

GTAW is an arc welding process that uses an arc between a nonconsumable 

tungsten electrode and the weld pool. The process is used with 

shielding gas and without the application of pressure. GTAW can be used 

with or without the addition of filler metal. 

The CC type power supply can be used with either dc or ac, the choice 

depends largely on the metal to be welded. Direct current welding is typically 

performed with the electrode negative (DCEN) polarity. DCEN welding offers 

the advantages of deeper penetration and faster welding speeds. Alternating 

current provides a cathodic cleaning (sputtering) that removes refractory 

oxides from the surfaces of the weld joint, which is necessary for welding 

aluminum and magnesium. The cleaning action occurs during the portion of 

the ac wave, when the electrode is positive with respect to the work piece. 

See Figures 3 and 4 for schematics of the GTAW equipment and welding 

process.

Gas tungsten arc welding

Gas tungsten arc welding 

http://www.substech.com/dokuwiki/doku.php?id=tungsten_inert_gas_arc_welding_tig_gtaw

Gas tungsten arc welding

The cleaning action occurs during the portion of the ac 

wave, when the electrode is positive with respect to the 

work piece.

GTAW

GTAW

5.3.1 Advantages of GTAW 

Some commonly accepted advantages of the GTAW process include: 

a. Produces high purity welds, generally free from defects. 

b. Little post-weld cleaning is required. 

c. Allows for excellent control of root pass weld penetration. 

d. Can be used with or without filler metal, dependent on the application. 

5.3.2 Limitations of GTAW 

Limitations associated with GTAW process are: 

a. Deposition rates are lower than the rates possible with consumable 

electrode arc welding processes. 

b. Has a low tolerance for contaminants on filler or base metals. 

c. Difficult to shield the weld zone properly in drafty environments.

GTAW / TIG Welding

GTAW / TIG Weld 

a. Produces high purity welds, generally free from defects.

TIG weld without 

addition of filler 

metal- autogenous 

weld.

GTAW / TIG Weld

TIG – Gas Nozzles

Tungsten 

Electrodes

Tungsten 

Electrodes

Tungsten 

Electrodes

Tungsten 

Electrodes

Tungsten- Automation

5.4 GAS METAL ARC WELDING (GMAW) 

GMAW is an arc welding process that uses an arc between continuous filler 

metal electrode and the weld pool. The process is used with shielding from an 

externally supplied gas and without the application of pressure. GMAW may 

be operated in semiautomatic, machine, or automatic modes. It employs a 

constant voltage (CV) power supply, and uses either the (1) short circuiting, 

(2) globular, or (3) spray methods to transfer metal from the electrode to the 

work: The type of transfer is determined by a number of factors. The most 

influential are: 

a. Magnitude and type of welding current. 

b. Electrode diameter. 

c. Electrode composition. 

d. Electrode extension. 

e. Shielding gas. 

See Figures 5 and 6 for schematics of the GMAW equipment and welding 

process. 

CV

Gas metal arc welding 

GMAW / MIG (metal 

inert gas) 

CV

Flux cored arc welding (FCAW) 

CV

GMAW 

http://www.docslide.com/gmaw-fundamentals/

GMAW 

CV

GMAW 

CV

Gas metal arc welding 

GMAW / MIG (metal inert 

gas)

5.4.1 Short Circuiting Transfer (GMAW-S) 

GMAW-S encompasses the lowest range of welding currents and electrode 

diameters associated with GMAW process. This process produces a fast 

freezing weld pool that is generally suited for joining thin section, out-of 

position, or root pass. Due to the fast-freezing nature of this process, there is 

potential for lack of sidewall fusion when welding thickwall equipment or a 

nozzle attachment. 

CV

Short Circuit mode 

http://www.ualberta.ca/~ccwj/videos/files/01_Fundamental%20GMAW%20Metal%20Transfer%20Modes/GMAW_Steel_8 

5Ar-15CO2_Short-Circuit_001/GMAW_Steel_85Ar-15CO2_Short-Circuit_001.mp4

Short Circuit mode 

http://www.ualberta.ca/~ccwj/videos/files/05_Tubular%20Wires/GMAW_Ni-WC_70Ar-30CO2_Short- 

Circuit_001/GMAW_Ni-WC_70Ar-30CO2_Short-Circuit_001.mp4

Conceptual schematic of 

metal transfers in GMAW: 

(a) short circuit, (b) 

globular, (c) pulse and (d) 

spray

5.4.2 Globular Transfer 

This process encompasses relatively low current (below 250 A). The globular 

transfer mode is characterized by a drop size with a diameter greater than 

that of the electrode. In general, this process is limited to the flat position and 

can produce spatter. 

CV

Globular transfer mode 

http://www.ualberta.ca/~ccwj/videos/pages/Intro%20High%20Speed/ 

CV




5Ar-15CO2_Globular_001/GMAW_Steel_85Ar-15CO2_Globular_001.mp4



http://www.ualberta.ca/~ccwj/videos/files/05_Tubular%20Wires/GMAW_Ni-WC_85Ar-15O2_Globular_001/GMAW_Ni- 

WC_85Ar-15O2_Globular_001.mp4


http://www.weldsmith.co.uk/dropbox/cranu/110523_wavefor 

ms_GMAW_steel/waveforms_GMAW_steel.html


CV

5.4.3 Spray Transfer 

The spray transfer mode results in a highly directed stream of discrete drops 

that are accelerated by arc forces. Spatter is negligible. Due to its high arc 

forces with high current, applying this process to thin sheets may be difficult. 

The thickness limitation of the spray arc transfer has been overcome by the 

use of pulsed GMAW. Pulsed GMAW is a variation of the GMAW in which the 

current is pulsed to obtain the advantage of spray transfer at the less average 

currents than that of spray transfer mode. 

CV

Spray transfer mode 


5Ar-15CO2_Spray_001/GMAW_Steel_85Ar-15CO2_Spray_001.mp4

5.4.4 Advantages of GMAW 

Some commonly accepted advantages of the GMAW process include: 

a. The only consumable electrode process that can be used to weld most 

commercial metals and alloys. 

b. Deposition rates are significantly higher than those obtained with SMAW. 

c. Minimal post-weld cleaning is required due to the absence of a slag. 

5.4.5 Limitations of GMAW 

Limitations associated with GMAW are: 

a. The welding equipment is more complex, more costly, and less portable 

than that for SMAW. 

b. The welding arc should be protected from air drafts that will disperse the 

shielding gas. 

c. When using the GMAW-S process, the weld is more susceptible to lack of 

adequate fusion. 

CV

Pulsed GMAW – Modified Spray Mode 

CV

Pulsed GMAW – Modified Spray Mode 

http://www.millerwelds.com/resources/articles/Pulsed-MIG-gmaw-aluminum/ 

CV

Pulse Spray transfer mode 

http://www.ualberta.ca/~ccwj/videos/files/05_Tubular%20Wires/GMAW_Ni-WC_95Ar-5CO2_Pulsing_001/GMAW_Ni- 

WC_95Ar-5CO2_Pulsing_001.mp4

GMAW-MIG 

CV

GMAW-MIG 

CV

GMAW-MIG 

CV

GMAW-MIG 

CV

GMAW-MIG 

CV

GMAW-MIG 

CV

GMAW- Automation

GMAW- Automation

GMAW- Automation

GMAW- Branch Pipe Welding

GMAW- Stainless Steel Piping

GMAW- Stainless Steel Piping

5.5 FLUX CORED ARC WELDING (FCAW) 

FCAW is an arc welding process that uses an arc between continuous tubular 

filler metal electrode and the weld pool. The process is used with shielding 

gas evolved from a flux contained within the tubular electrode, with or without 

additional shielding from an externally supplied gas, and without the 

application of pressure. Normally a semiautomatic process, the use of FCAW 

depends on the type of electrodes available, the mechanical property 

requirements of the welded joints, and the joint designs and fit-up. 

The recommended power source is the dc constant-voltage type, similar to 

sources used for GMAW. Figures 7 and 8 show a schematic of FCAW 

equipment and welding process with additional gas shielding. Figure 9 shows 

a schematic of the self-shielded FCAW process where no additional gas is 

used. 

CV

Flux cored arc welding (FCAW)

FCAW 

CV

FCAW 

CV

FCAW-Self shield 

CV

FCAW-Self shield 

CV

FCAW

FCAW

FCAW

FCAW

3G FCAW WPQT

FCAW 

CV

FCAW 

http://www.brewerweldingandfabrication.com/OrbitalWelding.htm

5.5.1 Advantages of FCAW 

Some commonly accepted advantages of the FCAW process include: 

a. The metallurgical benefits that can be derived from a flux. 

b. Slag that supports and shapes the weld bead. 

c. High deposition and productivity rates than other processes such as 

SMAW. 

d. Shielding is produced at the surface of the weld that makes it more 

tolerant of stronger air currents than GMAW. 

5.5.2 Limitations of FCAW 

Limitations associated with FCAW process are: 

a. Equipment is more complex, more costly, and less portable than that for 

SMAW. 

b. Self-shielding FCAW generates large volumes of welding fumes, and 

requires suitable exhaust equipment. 

c. Slag requires removal between passes. 

d. Backing material is required for root pass welding. 

CV

5.6 SUBMERGED ARC WELDING (SAW) 

Submerged arc welding is an arc welding process that uses an arc or arcs 

between a flux covered bare metal electrode(s) and the weld pool. The arc 

and molten metal are shielded by a blanket of granular flux, supplied through 

the welding nozzle from a hopper. The process is used without pressure and 

filler metal from the electrode and sometimes from a supplemental source 

(welding rod, flux, or metal granules). SAW can be applied in three different 

modes: semiautomatic, automatic, and machine. It can utilize either a CV or 

CC power supply. SAW is used extensively in shop pressure vessel 

fabrication and pipe manufacturing. Figure 10 shows a schematic of the SAW 

process. 

Manual 

Semiautomatic 

Automatic 

Machine 

CV

5.6.1 Advantages of SAW 

Some commonly accepted advantages of the SAW process include: 

a. Provides very high metal deposition rates. 

b. Produces repeatable high quality welds for large weldments and repetitive 

short (defective) welds. 

5.6.2 Limitations of SAW 

Limitations associated with SAW are: 

a. A power supply capable of providing high amperage at 100% duty cycle is 

recommended. 

b. Weld is not visible during the welding process. 

c. Equipment required is more costly and extensive, and less portable. 

d. Process is limited to shop applications and flat position. 

CV

SAW 

CV

Submerged arc welding (SAW)








SAW Twin electrodes in tandem with guider

SAW- Triple Electrodes Set-up (tilted)

SAW- Portable single Electrode Unit

SAW – Experts at Work

Spiral welding SAW- API 5LS

Spiral Welded SAW Pipes

SAW- Pressure Vessel Conical Head Welding

SAW- Vessel Internal Welding

2G SAW – Tank Semi-Automatic Welding

SAW- Spiral Welded Pipes

SAW 

SAW- Internal Welding Leg Cane

SAW- Serious Experts at Work

SAW- Welding on a Rotorary Wheel Set-up

SAW- Vessel Ellipsoidal Disk Head

SAW- Pressure Vessel

SAW- Pipe Can Welding

SAW- Structural Mud Mats

SAW- Structural Welding

5.7 STUD ARC WELDING (SW) 

SW is an arc welding process that uses an arc between a metal stud or 

similar part and the work piece. Once the surfaces of the parts are properly 

heated, that is the end of the stud is molten and the work has an equal area 

of molten pool, they are brought into contact by pressure. Shielding gas or 

flux may or may not be used. The process may be fully automatic or 

semiautomatic. A stud gun holds the tip of the stud against the work. Direct 

current is typically used for SW with the stud gun connected to the negative 

terminal (DCEN). The power source is a CC type. SW is a specialized 

process predominantly limited to welding insulation and refractory support 

pins to tanks, pressure vessels and heater casing.

5.7.1 Advantages of SW 

Some commonly accepted advantages of the SW process include: 

a. High productivity rates compared to manually welding studs to base metal. 

b. Considered an all-position process. 

5.7.2 Limitations of SW 

Limitations of SW are: 

a. Process is primarily suitable for only carbon steel and low alloy steels. 

b. Process is specialized to a few applications.

Stud arc 

welding (SW)

Stud arc welding (SW)




Welding Transfer Modes: 

SMAW - CC 

TIG - CC 

SW - CC 

SAW - CC or CV 

GMAW - CV 

FCAW - CV

Further Reading: (Non Examination) 

1. GMAW Welding 1 

2. GMAW Welding 2 

3. CV & CC Welding Modes 

4. Other Interesting Readings

1. Reading 1 

Considering the benefits of pulse spray transfer GMAW 

PRACTICAL WELDING TODAY® SEPTEMBER/OCTOBER 2001 

October 25, 2002 

By: Paul Niskala 

http://www.thefabricator.com/article/arcwelding/considering-the-benefits-of-pulse-spray-transfer-gmaw

1.0 General 

Pulse spray gas metal arc welding (GMAW) is a versatile welding process. 

Sometimes welding suppliers and welding managers don't want to try it, 

because they don't want to change the process they're using, train users, 

adjust welding processes, or spend money on new equipment. While any 

pulse spray machine can perform short-circuit transfer, each type of transfer 

has distinct differences and benefits. 

1.1 Three Common Types of Transfer for GMAW 

Short-circuit ,spray transfer and pulse-spray are the three most common 

types of GMAW metal transfer.

1.3 The short-circuit process 

In the short-circuit process, when the wire touches the base metal, it causes a 

short circuit. The base metal and wire become molten at the point where the 

wire touches the base metal, and the wire is pinched off. Spatter, in the form 

of round, molten balls that stick to the base metal, is a result of the sudden 

separation, or transfer, of the wire. 

The Short Circuit process can weld sheet metal and commonly is used for 

joining materials 1/4 in. (6mm) thick or less. Its fast-freezing puddle 

characteristic makes welding in all positions simple.

Short-circuiting is a low-heat-input process, generally less than 20 volts and 

200 amps (4000 Volt-Ampere – Apparent Power) using small-diameter 

welding wires no larger than 0.045 in. (1mm) The short-circuit process can 

weld materials that fit poorly. Besides shielded metal arc welding, it's probably 

the least expensive GMAW process because of the low welding currents 

involved, which require smaller, less expensive equipment. 

Short-circuit also is the most abused process because welders use it 

frequently for jobs that the process was not designed for, such as welding 

metals thicker than the process reasonably allows.

The short-circuit process is not a deep-penetrating process and is not suited 

for welding thick materials. It also lacks penetration at the toes of the weld, 

especially in out-of-position welding, causing cold laps (lack of fusion). 

Disadvantages of short-circuit include excessive spatter and low deposition 

rates. It generally is not recommended for aluminum or other alloys, which 

typically require higher heat input to obtain proper fusion. 

short-circuiting can be beneficial because: 

■ 

■ 

■ 

■ 

■ 

It can be used for welding sheet metal. 

It can weld materials 1/4 in. (6mm) thick or less. 

It can be used to weld in all positions. 

It uses low heat input, generally less than 20 V and 200 amps, using 

small-diameter welding wires no larger than 0.045 in. (1.2mm) 

It can weld materials that fit poorly.

1.4 The Spray Transfer Mode 

Spray transfer uses higher voltage and higher percentages of argon mixtures, 

80 percent or better, mixed with carbon dioxide or small amounts of oxygen. 

This high-energy output causes the droplets to be very small and burn off the 

wire before short-circuiting occurs. This small stream of droplets creates a 

fluid spray, which melts the base metal. Using higher operating parameters 

results in deeper penetration. The biggest benefit of the spray transfer 

process is its ability to make high-deposition welds on thick carbon steels, 

stainless steels, aluminum, and other alloys using large-diameter welding 

wires (0.052 in. and 0.062 in.) (1.3mm – 1.6mm) with very little spatter and no 

cleanup.

By using 0.035- and 0.045-in.-dia. (0.9mm – 1.2mm) welding wires, you can 

weld a range of thinner materials with the spray transfer process. It is not 

recommended for metals 1/8 in. (3mm) or less. Other benefits include no 

spatter, good fusion, a smooth bead, and weld appearance 

The biggest drawback of spray transfer is that it can be used only in the flat 

position because the puddle is so fluid. Both processes can be accomplished 

with a basic constant-voltage welding power source. 

Manufacturers have been able to design equipment that controls the weld 

puddle. Amperage is pulsed from a specified high-low current at 

predetermined frequencies to control the puddle better and thus allow for outof-position 

welding.

1.5 Pulse-Spray Transfer Mode 

As with any welding process, short-circuit and spray transfer methods of 

metal transfer in GMAW have their pros and cons. Pulse spray GMAW can be 

useful for the following reasons: 

• It can weld a variety of metals. 

• It has good penetration. 

• It can weld a wide range of thicknesses. 

• It provides good fusion at the toes of the weld. 

• It can weld faster than short-circuit and globular transfer. 

• It has 90 percent less spatter than short-circuit transfer. 

• It can be used to weld in all positions. 

• It reduces the number of ASME and AWS certifications required.

1.6 Summary 

Equipment for short-circuit welding can be less expensive than for spray 

transfer. Any spray machine can perform short-circuit transfer as well, but 

cost differences exist primarily in the type of gas used. Short-circuit uses less 

argon and more carbon dioxide, while spray transfer requires more argon and 

less carbon dioxide. Argon is one of the most expensive industrial welding 

gases used in GMAW, while carbon dioxide is the least expensive. While any 

pulse spray machine can perform short-circuit transfer, each type of transfer 

has distinct differences and benefits.

Equipment for short-circuit welding can be less expensive than for spray 

transfer. Any spray machine can perform short-circuit transfer as well, but 

cost differences exist primarily in the type of gas used. Short-circuit uses less 

argon and more carbon dioxide, while spray transfer requires more argon and 

less carbon dioxide. Argon is one of the most expensive industrial welding 

gases used in GMAW, while carbon dioxide is the least expensive. 

By considering the cost, the benefits of short-circuit and spray transfer 

processes, and your product line, you can decide the best mode of transfer 

for you.

2. Reading 2 

Understanding transfer modes for GMAW 

How they affect filler metal selection 

PRACTICAL WELDING TODAY® NOVEMBER/DECEMBER 2008 

DECEMBER 14, 2008 

BY: JERRY MATHISON 

http://www.thefabricator.com/article/consumables/understanding-transfer-modes-for-gmaw

2.0 General 

The gas metal arc welding (GMAW) process uses four basic modes to 

transfer metal from the electrode to the workpiece. Each mode of transfer 

depends on the welding process, the welding power supply, and the 

consumable, and each has its own distinct characteristics and applications. 

Several variables dictate the type of transfer you use, including the amount 

and type of welding current, the electrode chemistry, electrode surface, 

electrode diameter, shielding gas, and the contact tip-to-work distance. 

Transfer mode also affects your choice of filler metal used. Choosing wisely 

can greatly affect your efficiencies and productivity. 

■ 

■ 

■ 

■ 

Short Circuit 

Globular 

Spray 

Pulse-Spray

2.1 Short-circuit Transfer 

In short-circuit transfer, the electrode touches the work and short circuits, 

causing the metal to transfer as a result of the short. This happens at a rate of 

20 to more than 200 times per second. 

The advantage of the short-circuit transfer is its low energy. This method is 

normally used on thin material ¼ (6.3mm) inch or less, and for root passes on 

pipe with no backing. It can be used to weld in all positions. 

This mode of transfer generally calls for smaller-diameter electrodes, such as 

0.6mm,0.8mm, 0.9mm, 1.0mm, and 1.1mm. The welding current must be 

sufficient to melt the electrode, but if it is excessive, it can cause a violent 

separation of the shorted electrode, leading to excessive spatter. Using 

adjustable slope and inductance controls can enhance the transfer to 

minimize spatter and promote a flatter weld profile. Slope adjustment limits 

the short-circuit amperage, while inductance adjustments control the time it 

takes to reach maximum amperage. Proper adjustment of these two factors 

can produce excellent bead appearance and is essential for short-circuit 

transfer with stainless steel electrodes.

The most predominant solid stainless steel electrodes are ER 308L, ER 309L, 

and ER 316L. These electrodes are also available in the Si type, such as 

308LSi. The LSi types contain more silicon, which increases puddle fluidity 

and helps the weld puddle to wet out better than the standard alloys. While 

minor power source adjustments may be needed, both types can be used 

successfully as long as the specification for the welding consumables permits. 

For carbon steel electrodes, the electrode classification dictates the silicon 

level. ER 70S-3 and ER 70S-6 are the most widely used. For pipe 

applications, ER 70S-2, ER7 0S-4, and ER 70S-7 are sometimes used for 

open-root work because they offer lower silicon levels. The lower silicon 

produces a stiffer puddle and gives you more control of the back bead profile. 

In an open-root weld, you may use an S-6 type electrode with less inductance 

than an S-2 type electrode because the S-6 type has a higher level of silicon 

and the puddle is more fluid.

Maintaining a constant contact tip-to-work distance in short-circuit transfer is 

important to maintain a smooth transfer. 

The most common shielding gas for the short-circuit transfer mode for carbon 

steel electrodes is: 75 percent argon/25 percent CO2. 

Numerous three-part shielding gas mixes are also available for carbon steel 

and stainless steel for this mode of transfer.

2.2 Globular Transfer 

Globular transfer means the weld metal transfers across the arc in large 

droplets, usually larger than the diameter of the electrode being used. 

This mode of transfer -generally is used on carbon steel only and uses 100 

percent CO 2 shielding gas. 

The method typically is used to weld in the flat and horizontal positions 

because the droplet size is large and would be more difficult to control if used 

in the vertical and overhead positions compared to the short-circuit arc 

transfer. This mode generates the most spatter; however, when higher 

currents are used with CO 2 shielding and a buried arc, spatter can be greatly 

reduced. You must use caution with a buried arc because this can result in 

excessive reinforcement if travel speed isn't controlled.

Stainless steel GMAW electrodes normally aren't used in this mode of 

transfer because their nickel and chrome content (9 to 14 percent nickel and 

19 to 23 percent chromium) creates a higher electrical resistance than carbon 

steel electrodes. In addition to the electrical resistance differences, the use of 

100 percent CO 2 as a shielding gas could be detrimental to the corrosion 

resistance of the stainless steel electrodes. Carbon steel ER 70S-3 and ER 

70S-6 generally are the electrodes of choice.

2.3 Spray Transfer Mode 

Spray transfer is named for the spray of tiny molten droplets across the arc, 

similar to spray coming out of a garden hose when the opening is restricted. 

Spray transfer usually is smaller than the diameter of the wire and uses 

relatively high voltage and wire feed speeds or amperage. Unlike short-circuit 

transfer, once the arc is established, it is on at all times. This method 

produces very little spatter and is most often used on thick metals in the flat 

and horizontal positions.

Spray Transfer Mode 

Shield Gas & Transition 

Current

Spray transfer is achieved with high percentages of argon in the shielding gas, 

generally a minimum of 80 percent. 

Also called axial spray, this mode uses a current level above what is 

described as the transition current. The transition current will vary depending 

on the electrode diameter, shielding gas mixture percentages, and contact tipto-work 

distance. When the current level is higher than the transition current, 

the electrode transfers to the work in very small droplets that can form and 

detach at the rate of several hundreds per second. Sufficient arc voltage is 

required to ensure that these small droplets never touch the work, achieving a 

spatter-free weld. Spray transfer also produces a fingerlike penetration profile.

This transfer mode is used mostly in the flat and horizontal positions because 

it produces a large weld puddle. High deposition rates can be achieved 

compared to the other transfer modes. 

Because of the arc length used, it is also more easily influenced by magnetic 

fields. If this is not controlled, penetration profile, bead appearance, and 

spatter levels can be negatively affected.

The major factor in choosing a carbon steel electrode is sometimes the 

amount of silicate islands that remain on the weld bead surface. This is 

especially the case if you need to minimize postweld cleaning time or if the 

finished product will be painted. For this reason, you might choose an ER 

70S-3, ER 70S-4, or ER 70S-7 electrode. With stainless steel electrodes, 

there is little difference in the bead appearance in the Si types because of the 

higher energy used in this mode of transfer. The wetting action advantage of 

the Si types is not necessary, and if they are used it usually is a matter of 

preference. The effect of the chemistry on the transition current is minimal, 

but a higher voltage may be required with one alloy compared to another to 

achieve a true spray.

2.4 Pulse-Spray Transfer Mode 

In the pulse-spray transfer mode, the power supply cycles between a high 

spray transfer current and a low background current. This allows for super 

cooling of the weld pool during the background cycle, making it slightly 

different than a true spray transfer. Ideally, in each cycle one droplet transfers 

from the electrode to the weld pool. Because of the low background current, 

this mode of transfer can be used to weld out of position on thick sections 

with higher energy than the short-circuit transfer, thus producing a higher 

average current and improved side-wall fusion. Additionally, it can be used to 

lower heat input and reduce distortion when high travel speeds are not 

needed or cannot be achieved because of equipment or throughput 

limitations.

Generally, the same shielding gases used for spray transfer are also used for 

pulsed-spray mode. 

The electrodes you can use include all the standard carbon steel and 

stainless steel types, along with some of the specialty alloys such as 

INCONEL® (625), duplex (2209), and superduplex (2509). With a 

programmable pulse power supply, most solid-wire alloys can be used with a 

customized pulse waveform. 

With all modes of transfer, the wire type will have some effect on the machine 

settings. In addition, the wire surface will affect the transfer. Manufacturers 

use different types of arc stabilizers on the wire surface to enhance a smooth 

transfer. This is why small adjustments must be made when welding with the 

same type of electrode from different manufacturers.

3. CV Transfer Mode 

A CV power source delivers constant voltage by varying the current to 

maintain a constant arc length. In this mode, the operator is able to adjust 

wire feed speed and arc voltage. CV is considered the conventional way to 

weld aluminum, and fabricators today still choose CV for its simplicity and 

lower capital cost over other GMAW methods. Welding aluminum with either 

CC or CV power sources requires high-energy axial spray transfer to melt the 

base metal and ensure good fusion. 

To obtain spray arc transfer—a steady stream of molten metal that sprays 

across the arc—the welding current must be above a certain minimum 

“transition” current. For example, using CV spray transfer with 3⁄64-inch 

aluminum GMAW wire requires a minimum of 135 amps. 

http://www.thefabricator.com/article/aluminumwelding/tackling-aluminum-gmaw

CV/CC Current Transfer Modes: 

Voltage, V 

Constant Current 

Power Source 

Operating 

point 

Voltage, V 

Constant Voltage 

Power Source 

Operating 

point 

Current, A 

Current, A 

http://www.lincolnelectric.com/en-us/support/process-and-theory/Pages/constant-current-vs-constant-coltage-output.aspx

Current Transfer Modes: CC 

http://www.lincolnelectric.com/en-us/support/process-and-theory/Pages/constant-current-vs-constant-coltage-output.aspx

4. Other Interesting Reading: 

3.1 

Choosing the right shielding gas and supply system for GMAW 

WWW.THEFABRICATOR.COM JANUARY 2002 

July 26, 2001 

By: David Bell 

http://www.thefabricator.com/article/consumables/choosing-the-right-shielding-gas-and-supply-system-for-gmaw

5 Welding Processes

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