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K-TIG vs Plasma Keyhole TIG and Plasma Arc Welding Compared
K-TIG vs PlasmaKeyhole TIG and Plasma Arc Welding Compared
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 savings generated by the process areextraordinary. I can’t think of a material, thickness or weld geometrywhere plasma arc welding would be chosen over K-TIG.
What is K-TIG?Keyhole GTAW explained
Attila Szabo, Principal Joining Engineer, GE
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PENETRATION Up to 16mm Up to 10mm
SPEED Up to 1000mm/min Up to 500mm/min
COMPLEXITY Extremely simpleHighly complex,numerous criticalparameters
TOLERANCE Tolerant to jointimperfections
Requires very precisefit-up
KEYHOLE STABILITY High inherent stability,self-correcting keyhole
Inherently unstable dueto plasma gas flow
KEYHOLE CLOSE-OUT Very simple, just slopedown, no voids
Extremely difficult,plasma gas often leavesvoids, defects in close-out region of weld
PROCESS CONSISTENCY Very consistent keyhole,no process drift
Inconsistent due toorifice erosion
MAINTENANCE COSTS Very low High
CONSUMABLES COSTS Very low, long electrodelife
High, nozzles/orificeerode quickly, needreplacement
SKILL OF OPERATOR Low High
ELECTRODE ALIGNMENT Not significant Critical, frequentintervention required
CONSTRICTION OF ORIFICE No orifice Critical, limited life dueto erosion from plasma
PILOT ARC STARTING No pilot arc required 3 to 15 amp pilot arcstarting system required
DUTY CYCLE 100% Typically 60%
K-TIG vs PAWKeyhole TIG and Plasma Arc Welding Compared
K-TIG PAW
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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 up to 9mm in ferriticsteels & carbon steels.
Up to 10mm
Claims for the penetration capabilities ofPAW vary. The practical upper limit forsingle pass PAW welding is generallyconsidered to be 8 -10mm. PAW istypically used for root passes of 4-6mm,followed by filler passes using TIG.
SPEED
Up to 1000mm/min
K-TIG welding is typically twice the speedof PAW. Typical speeds are:• 3mm material at up to 1000mm/min• 4mm material at up to 750 mm/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 500mm/min
PAW welding is significantly slower thanK-TIG. Typical speeds are:• 3mm material at up to 500mm/min• 4mm material at up to 400 mm/min• 6mm material at up to 300mm/min• 8mm materials at up to 200mm/min• 12mm material – n/a• 14mm material – n/a• 16mm material – n/a
COMPLEXITY
Extremely simple
K-TIG is very simple to operate. The arcstructure and keyhole developspontaneously and are maintainedautomatically by the controllerthroughout the weld. There is no plasmanozzle or orifice, no precise electrodealignment is required, only one weldinggas is used, flow rate is not critical, andthe torches are very robust. All standardGTAW welding gases can be used withthe K-TIG process.
Highly complex, numerous criticalparameters
PAW is widely regarded as the mostcomplex of the arc welding processes.The constricted, high energy densityplasma jet is produced by maintaining acritical balance between plasma gas flowrate, shielding gas flow rate, current,orifice diameter and the alignmentbetween the electrode and the orifice.This requires meticulous set-up andfrequent maintenance.
KEYHOLE STABILITY
High inherent stability, self-correctingkeyhole
K-TIG keyholes have extremely highstability. The K-TIG keyholes have arelatively wide opening relative to theirdepth, and the front face opening isconsiderably wider than that in the root.Surface tension alone renders the K-TIGkeyhole very stable. As a result, there isno requirement to seek a balancebetween arc forces and surface tension -the nature of the keyhole surface is suchthat it naturally and dynamically self-corrects for fluctuations in the arc forcesand material / fitup imperfections.
Inherently unstable keyhole
PAW keyholes are inherently unstable.The keyhole must be held open againstgravity & surface tension by acombination of gas pressure & recoilpressure from metal evaporating fromthe walls of the keyhole. Since theenergy density & the plasma pressureare in turn dependent on many otherprocess variables (gas flow rates,electrode-orifice alignment, current andorifice diameter being the most critical),the keyhole is highly sensitive to changesin welding parameters, making it difficultto control.
K-TIG vs PAWKeyhole TIG and Plasma Arc Welding Compared
K-TIG PAW
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TOLERANCE
Tolerant to imperfections
Moderately tolerant to imperfectionsin fit-up due to non-constricted, lowerenergy-density, conical-shaped arc.
Requires very precise fit-up
Intolerant to imperfections in fit-updue to highly constricted, high energy-density, columnar-shaped arc.
KEYHOLECLOSE-OUT
Very simple, just slope down
The K-TIG keyhole is produced from ahigh energy density arc and patentedtorch design, without any plasma gasor complex constricted arcrequired. As a result, at the overlapand slope out of a circumferentialweld, the process is extremely simpleto slope down to close out the keyholeand end the weld, leaving no voids orporosity.
Extremely difficult, often leavesdefects in close-out region of weld
Highly dependent on a constricted arcwith recessed electrode, fixeddiameter nozzle orifice & concentratedflow of a plasma gas. To close out thekeyhole in a circumferential weld,multiple parameters must bemanipulated in a small area of theweld, often leaving porosity & voids inthe resulting weld termination.
PROCESSCONSISTENCY
Highly consistent, no process drift
The high energy density arc from K-TIGproduces a smooth and consistentkeyhole through the joint, with verylittle variation for the duration of theweld. The simplicity of the process,extremely robust torch design and sizeof the electrode result in a highlyconsistent process with negligibleprocess drift, ensuring high processconsistency for very extended periods.
Inconsistent due to orifice erosion
Because the plasma process dependson the introduction and control of aplasma gas through an orifice whichconstricts the arc, there is atremendous amount of heat at thenozzle end of the torch. The orificeerodes quickly and in less than onehour of welding time the process canlose its stability and control once theorifice elongates or loses its shape.
MAINTENANCECOSTS
Very low
K-TIG welding systems incur very lowmaintenance costs due to theirsimplicity. K-TIG systems have fewconsumable components, are robustand extremely reliable. Maintenancerequirements are negligible.
High
PAW systems incur the highestmaintenance costs of any arc weldingprocess due to their complexity. PAWsystems require frequent maintenanceby skilled operators in order to ensureparameters remain within tolerance.
CONSUMABLESCOSTS
Very low
K-TIG uses low cost electrodes, theelectrode have extremely long life,nothing else erodes or wears, 100%duty cycle power supply.
High
Plasma torches and nozzles/orificeserode quickly, and need frequentreplacement. As they are specializeditems, replacement costs can be high.
DUTY CYCLE
100%
K-TIG utilises a 1000 amp powersupply, which is considerably morethan required for any keyhole process,and is rated for 100% duty cycle.
Typically 60%
PAW welding systems are typicallyprovided with power supplies in therange of 300-500 amps, and aretypically only rated for 60% duty cycle.
K-TIG vs PAWKeyhole TIG and Plasma Arc Welding Compared
K-TIG PAW
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SKILL OF OPERATOR
Low
K-TIG requires minimal training due tothe simplicity of the process and thesophistication of the K-TIG controller. Anunskilled operator is sufficient.
High
PAW requires extensive operatortraining due to its complexity andsensitivity to the many critical variablesinvolved. Operators must be skilled inmaintenance of these parameters. Askilled operator is required.
ELECTRODEALIGNMENT
No alignment required
As K-TIG requires no plasma nozzle ororifice, no precise electrode alignment orassociated maintenance is required.
Critical, frequent intervention required
The alignment of the electrode is one ofseveral critical parameters and requiresfrequent attention.
CONSTRICTION OFORIFICE
No orifice required
The K-TIG process uses natural arc forcesto achieve keyhole penetration, does notrequire a plasma nozzle, does not havean orifice (therefore no orifice diameterneeds to be set/maintained) and doesnot impinge on or constrict the arc in anyway.
Critical
The plasma nozzle orifice diameter iscritical and has a limited life, often as lowas 1-2 hours, due to high temperatureplasma erosion and elongation of thenozzle orifice. The life of the nozzle isfurther reduced if helium or hydrogenare utilized for plasma gas.
PILOT ARCSTARTING
No pilot required
K-TIG does not require a pilot arc startingsystem, just a standard high frequencyarc start used by conventional TIGsystems, which is built into the K-TIGpower supply.
3 to 15 amp pilot required
PAW requires a separate pilot arcstarting system/circuit, addingcomplexity, equipment cost, and thepotential for problems such as a non-transferred plasma arc.
K-TIG
K-TIG vs PAWKeyhole TIG and Plasma Arc Welding Compared
PAW
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