K-TIG vs Plasma Arc Welding

Process Comparison

How do K-TIG and PAW compare?

Plasma Arc Welding (PAW) was developed in the 1960s, and until recently was the only practical choice where deep penetration welds were required. While good quality welds can be achieved, the practical upper limit for full penetration PAW welding is 8mm to 10mm (5/16 to 13/32 inch), and is more typically used for root passes of 4mm to 6mm (5/32 to 1/4 inch), followed by filler passes using TIG.

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PAW is characterised by an orifice to pinch the arc, accurate alignment with the electrode, frequent maintenance, high level of complexity, the need for both plasma and shield gases to form the jet and protect the orifice, very accurate determination and maintenance of flow rates.

As well as low inherent stability of the keyholes due to reliance on a combination of gas pressures and energy density to achieve penetration, high degree of sensitivity to the many parameters involved, highly precise fit-up and high degree of operator skill to set up, operate and maintain.

By contrast, K-TIG can weld materials up to 16mm (5/8 inch) in thickness, and typically operates at twice the travel speed of PAW.

K-TIG is very simple to operate. The arc structure and keyhole develop spontaneously and are maintained automatically by the controller throughout the weld.

There is no plasma nozzle or orifice, no precise electrode alignment is required, only one welding gas is used, flow rate is not critical, and the torches are very robust.

K-TIG is a much simpler, more robust process than plasma arc welding.
Attila Szabo, Principal Joining Engineer, GE

 

K-TIG is a much faster, deeper penetrating and simpler process than PAW. Some key differences include:

  • Penetration:
    The upper limit for PAW is 10mm, but it is typically used for root passes of 4 to 6mm, followed by TIG filler passes. 
    K-TIG comfortably performs single pass welds in 16mm thick titanium, 14mm zirconium, 13mm austenitic stainless steels, Hastelloys, Inconels and a wide range of nickel and cobalt alloys, and 9mm in conductive materials such as ferritic steels and carbon steels.

  • Speed:
    PAW’s typical welding speed is up to 500mm per minute.
    K-TIG’s is significantly faster than this at 1,000mm per minute.

  • Complexity:
    PAW is the most complex of all the arc welding processes, with critical balance required between plasma and shielding gas flow rates, as well as the current, orifice diameter and alignment.
    K-TIG is extremely simple. Arc structure and keyhole develop spontaneously and are maintained automatically. There is no plasma nozzle, orifice, or electrode alignment required. Only one welding gas is used and flow rate is not critical.

  • Tolerance:
    PAW requires very precise fit-up due to its highly constricted, energy-density columnar-shaped arc.
    K-TIG is tolerant to imperfections in fit-up as it has a non-constricted, lower energy density, conical shaped arc.

  • Keyhole Stability:
    PAW keyholes are inherently unstable, and highly sensitive to changes in welding parameters, making control difficult.
    K-TIG keyholes are highly stable, with a relatively wide opening relative to their depth, and the front face opening is considerably wider than that in the root. There is no need to balance arc forces and surface tension – the keyhole surface naturally and dynamically self-corrects for fluctuations in the arc forces.

  • Keyhole Close-Out:
    PAW keyhole close-out is extremely difficult, with plasma gas often leaving porosity, voids and even cracks.
    Due to its high-energy density arc and patented torch design, K-TIG keyhole close-out is extremely simple—just slope down to end the weld.

  • Consistency:
    In PAW, there is a tremendous amount of heat at the torch nozzle, which quickly erodes the orifice. The process loses its stability, consistency and control once the orifice elongates or loses its shape.
    K-TIG’s high-energy density arc produces a smooth, consistent keyhole through the joint, with very little variation. The process is so simple that erosion (and process drift) are negligible.

  • Maintenance Costs:
    PAW systems incur the highest maintenance costs of any arc welding process due to their complexity. K-TIG welding systems incur very low maintenance costs due to their simplicity.
    K-TIG systems have few consumable components, are robust and extremely reliable.

  • Consumables Costs:
    Plasma torches and nozzles and orifices erode quickly, and need frequent replacement, making consumable costs high.
    K-TIG’s consumables costs are very low, with its long electrode life, absence of erosion and wear in other parts, and 100% duty cycle power supply.

  • Skill of Operator:
    PAW requires extensive, in-depth operator training due to its complexity, and all the variables involved. Training usually takes up to 2 weeks.
    K-TIG is so simple that minimal training is required. Operator training takes just 3 hours, and supervisor training 1 to 2 days.

  • Pilot Arc Starting:
    PAW requires a 3 to 15 amp pilot starting system, increasing equipment costs and the likelihood of potential problems.
    K-TIG requires no pilot starting system, instead using the standard high frequency arc start used by conventional TIG systems.

  • Duty Cycle:
    PAW welding systems are typically rated for 60% duty cycle. K-TIG uses a 100 amp power supply, considerably more than is required for any keyhole process, and is rated for 100% duty cycle.

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If you’re welding vessels, tanks or pipe using Plasma Arc Welding, you're probably experiencing unacceptable defect rates and are struggling with thicker materials and close outs.

I’m currently using Plasma Arc Welding. Can I switch to K-TIG?

Yes, and the switch is straightforward.

If you are currently using Plasma Arc Welding (PAW) you are almost certainly a model K-TIG customer.

You will probably be welding stainless steel, duplex or super duplex of between 3mm and 10mm (1/8 to 13/32 inch). You will have already invested in automation equipment to provide a consistent travel speed, typically a positioner, rotator, seamer or column & boom. Your application is probably pressure vessels, cryogenic vessels, tanks or you're a tube mill.

K-TIG has vast experience in these applications and can transition you to K-TIG very quickly and simply.

A fabricator who is currently using Plasma Arc Welding (PAW) will find upgrading to KTIG to be straightforward. The existing welding automation system can continue to be used. Setting up is typically as simple as swapping over to the K-TIG torch. If desired, the K-TIG controller can also easliy be integrated with the existing welding automation system to provide highly automated welding procedures.

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Download a Case Study

K-TIG has a number of case studies which do a deep-dive into our customer's applications,
how they've used K-TIG and the results they've achieved.

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