K-TIG vs SAWKeyhole TIG and Submerged Arc Welding Compared

What is K-TIG?Keyhole GTAW explained

Overview

A high energy density variant of GTAW, K-TIG (Keyhole TIG) is a high speed, single pass,full penetration welding technology that welds up to 100 times faster than TIG welding inmaterials up to 5/8in (16mm) in thickness, and typically operates at twice the speed ofplasma welding.

K-TIG works across a wide range of applications, and is particularly well suited to lowerconductivity materials such as stainless steels, nickel alloys, titanium alloys and mostcorrosion resistant and exotic materials. It easily handles longitudinal and circumferentialwelds on pipe, plate, spooling, vessel, tank and other materials in a single pass:

Titanium at 3mm to 16mm (1/8 to 5/8 inch) Stainless steel at 3mm to 13mm (1/8 to 1/2 inch) Carbon steel at 3mm to 9mm (1/8 to 11/32 inch)

K-TIG’s extremely fast welding times result in dramatic reductions in labor costs, weldingcycle times, rework and repair costs, gas and power usage. K-TIG’s single pass, fullpenetration welds significantly reduce or eliminate grinding and reworking. The K-TIGprocess dramatically reduces or eliminates the need for wire, eliminates edge bevelling,and requires only a square butt joint, but can also weld into all standard GTAWpreparations. No root gap is required.

The Process

Keyhole TIG is not a Plasma welding process. It is a much simpler, high productivity GTAWvariant developed by the Australian Government’s Commonwealth Scientific & IndustrialResearch Organisation (CSIRO), in conjunction with the Cooperative Research Centre forWelded Structures before being acquired and commercialised by K-TIG.

The System

The K-TIG 1000 System has been precision engineered to deliver the Keyhole GTAWprocess in a robust, intelligent and user friendly form. The K-TIG 1000 System ismanufactured in Adelaide, South Australia, is being used by many of the world’s mostproductive fabricators and has been exported to 18 countries.

K-TIG welding is a new productivity benchmark.The speed, penetration, quality and overall savingsgenerated by the process are extraordinary.

Attila Szabo, Principal Joining Engineer, GE

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PENETRATION Up to 16mm Up to 4mm

SPEED Up to 1000mm/min Up to 600mm/min

WELD QUALITY Very high due to benefits fromkeyhole mode

Reasonably good, porosity and lackof fusion are the main types ofdefects. Active flux scavenges thelarge weld pool for oxygen, otherundesirable elements and floatsthem to surface as slag

JOINT PREPARATION Very low cost, simple square buttdesign

High, due to V- or J-groovepreparation for any thickness over4mm, due to limited penetration andlarge weld pool that can drop out dueto gravity

WELDING CYCLE TIMES Very fast, high speed and deeppenetration

Very slow, medium travel speed andthe need for multiple weldpasses. Slag from the flux must beremoved by chipping or grinding,otherwise will cause lack of fusion;this is very time consuming

KEYHOLE STABILITY High inherent stability, self-correctingkeyhole

No keyhole; slow, multi-passpenetration and fill passes

CIRCUMFEREN-TIALWELD OVERLAP TIE-IN

Very simple, just slope down, novoids

Often experience lack of fusion orincomplete penetration @ overlapdue to weld metal build up from startof weld, limited pen capability

WELD APPEARANCEVery smooth and good contour; nodressing or grinding required oneither crown or root

Reasonably good contour with slag(from the flux) that must be removedby chipping away or grinding

DISTORTIONVery low overall distortion due tohigh energy density, low heat input,and high travel speeds

Very high overall distortion due tolow energy density, high heat input,and slow travel speeds

PROCESSCONSISTENCY

Very consistent keyhole, no processdrift

Good consistency, no keyhole, multi-pass welding that must be monitoredto avoid lack of fusion and otherdefects

CONSUMABLES COSTS Very low, long electrode lifeHigh, large diameter filler wire andflux that must be added to cover andprotect weld pool

SKILL OF OPERATOR Very low High

DUTY CYCLE 100% Typically 60%

K-TIG SAW

K-TIG vs SAWKeyhole TIG and Submerged Arc Welding Compared

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PENETRATION

Up to 16mm

K-TIG comfortably performs single passwelds in 16mm thick titanium, 13mmaustenitic stainless steels, Hastelloys,Inconels and a wide range of nickel andcobalt alloys, and 9mm in conductivematerials such as ferritic steels & carbonsteels.

Up to 4mm

The practical upper limit for single passSAW welding is generally considered to be4mm. Beyond this thickness, a V-grooveroot pass is normally applied, followed byfiller passes.

SPEED

Up to 1000 mm/min

Typical speeds are:• 3mm material at up to 1000mm/min• 4mm material at up to 750mm/min• 6mm material at up to 600mm/min• 8mm material at up to 500mm/min• 12mm material at up to 350mm/min• 14mm material at up to 250mm/min• 16mm material at up to 200mm/min

Up to 600 mm/min

SAW welding is significantly slower than K-TIG. Typical speeds are:• 1mm material - N/A• 2mm material - N/A• 6mm material – multipass• 8mm materials – multipass• 12mm material – multipass• 14mm material – multipass• 16mm material – multipass

WELDQUALITY

Very high

One of the benefits of keyhole welding isthe exit path available for any vaporizedimpurities to leave the weld through theback of the keyhole. This prevents theevolved gases from becoming trapped asporosity in the solidifying weld. Anotherbenefit is the simple square butt jointdesign, which eliminates the possibility of"bridging" during fill passes and resultantlack of fusion.

Reasonably good

SAW is a high wire deposition weldingprocess, so the weld quality can beacceptable but not so easy to control. Itcan only be run in 1G position in semi-automatic mode. Penetration is achievedby melting through the joint thickness, anddue to the high amount of molten fillermetal being added to the pool, porosity isoften trapped in the solidifying weld. Lackof fusion is also a significant concern, asbridging a V-groove occurs regularlywithout properly fusing the joint sidewalls. Active flux scavenges the large weldpool for oxygen, other undesirableelements and floats them to surface asslag.

JOINT PREPARATION

Low cost, simple square butt design

A simple square butt joint design isrequired, no groove to fill (unless greaterthan 14-16mm thick).

Costly V- or J-groove preparation

Groove preparation is required, whichadds cost, and the removed joint metalmust be replaced with fillermetal. Manually beveled joints often leadto inconsistent welding results. The fluxproduces a slag layer that must beremoved by grinding or chipping to avoidlack of fusion in subsequent weld passes.

K-TIG SAW

K-TIG vs SAWKeyhole TIG and Submerged Arc Welding Compared

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WELDING CYCLETIMES

Very fast

The high energy density keyhole permitssingle pass penetration of thick joints at avery high travel speed, resulting inminimal weld passes accomplished in veryshort time.

Rather slow

The low energy density arc has limitedpenetration capability, and the root and fillpasses are performed at moderate travelspeeds, resulting in numerous weld passesaccomplished in fairly lengthy weldingtimes. Inter-pass removal of slag isrequired (after every weld pass).

KEYHOLE STABILITY

High inherent stability, self-correctingkeyhole

K-TIG keyholes have extremely highstability, due to the high travel speeds andsurface tension in the weld pool. As aresult, there is no requirement to seek abalance between arc force (plasmacolumn) and surface tension - the natureof the keyhole surface is such that itnaturally and dynamically self-corrects forfluctuations in the arc forces.

No keyhole; pen + fill passes

There is no keyhole, simply a "meltthrough" approach. Beyond 4mmthickness, a V-groove root pass is normallyapplied, followed by filler passes. Thisapproach takes much longer, costs more interms of labor and consumables, and isprone to welding defects.

CIRCUMFEREN-TIALWELD OVERLAP TIE-IN

Very simple, just slope down, no voids

The K-TIG keyhole is produced from a highenergy density arc and patented torchdesign, without any plasma gas or complexconstricted arc required. As a result, atthe overlap and slope out of acircumferential weld, the process isextremely simple to slope down to closeout the keyhole and end the weld.

Potential for Lack of Fusion at overlap

Due to the limited penetration capabilityof the process, the overlap can be difficultto "tie in" or fuse properly, as the weldmetal from the original start of the weld(with considerable filler wire added) canbe a barrier to full penetration at theoverlap point.

WELD APPEARANCE

Very good and smooth contour

With proper gas shielding of the face androot sides of the weld, the K-TIG processinherently produces a very smooth anduniform weld appearance that requires nofurther grinding or dressing.

Good appearance, reasonable contourdue to flux protection

There is no gas shielding of the weld, theSAW process relies on a layer of flux tocover and protect the weld pool. Theresulting weld appearance can havemoderately good contour, as the slag layerprotects the weld surface. The slag mustbe removed, which requires grinding ordressing.

DISTORTION

Very low

Due to the high energy density of theprocess, the high travel speeds that can beachieved with single pass penetrationresult in remarkably low weld shrinkageand distortion.

Very high

Due to the low energy density of theprocess, the slow travel speeds that aretypical with multiple weld passes result insubstantial weld shrinkage and distortion.

K-TIG SAW

K-TIG vs SAWKeyhole TIG and Submerged Arc Welding Compared

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PROCESSCONSISTENCY

Very high

The high energy density arc from K-TIGproduces a smooth and consistent keyholethrough the joint, with very little variationfor the duration of the weld. The processis simple enough, and the electrode islarge enough, that erosion (and processdrift) are negligible.

High

The SAW process can be "dialed in" toachieve sound welds in a mechanizedmode, with a root pass followed bymultiple fill passes. However, the weldcan vary to some degree, the slag thatforms during welding must be removedbetween weld passes, and the transfer oflarge amounts of filler wire to the weldpool creates a level of inconsistency.

CONSUMABLES COSTS

Very low

Long electrode life, nothing else erodes orwears, 100% duty cycle power supply.

High

The SAW process utilizes high volumes oflarge diameter filler wire and activatedflux. Due to high welding amperage, torchparts often need replacement.

SKILL OF OPERATOR

Very low

K-TIG requires minimal training due to thesimplicity of the process and thesophistication of the K-TIG controller. Anunskilled operator is sufficient.

High

SAW requires extensive operator training,as lack of fusion can form easily in theweld and must be avoided with propertechniques.

DUTY CYCLE

100 %

K-TIG utilises a 1000 amp power supply,which is considerably more than isrequired for any keyhole process, and israted for 100% duty cycle.

Typically 60%

Submerged arc welding systems aretypically provided with power supplies inthe range of 400-1000 amps, and aretypically only rated for 60% duty cycle.

K-TIG SAW

K-TIG vs SAWKeyhole TIG and Submerged Arc Welding Compared

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