How to Weld Stainless Steel with Keyhole TIG

Stainless steel is known for its resistance to corrosion. It is used in many different fields such as food and dairy, chemical, power, cryogenic, nuclear and many other industry sectors.

K-TIG welding technology combines the high-quality and cleanliness of GTAW with a depth of penetration that is unmatched by conventional gas-tungsten arc, gas metal arc or plasma welding processes.

 
Bill Kelly, Senior Sales & Commissioning Engineer talks welding stainless steel with K-TIG

How does K-TIG’s Keyhole Work?

K-TIG (Keyhole TIG) is a highly refined version of TIG/GTAW developed by the Australian Government’s Commonwealth Science & Industrial Research Organisation (CSIRO). The patented technology is a result of extensive, scientific study of the gas-tungsten-arc process, and is the result of many innovations in arc characteristics, weld pool stabilisation, heat removal and process efficiency. This welding process has been quietly adopted by some of the world’s largest and most productive stainless steel fabricators and is also ideally suited to lower conductivity materials such as duplex, super duplex, nickel alloys, titanium alloys and most corrosion resistant and exotic materials.

K-TIG has 8x the penetration of GTAW, allowing it to perform x-ray quality welds in materials up to 5/8 inch (16mm) thick in a single pass, without the need for edge bevelling. The resulting welds are performed at up to 100x the speed of conventional TIG/GTAW. Gas consumption is reduced by more than 90%, and wire consumption is reduced by in excess of 90% or eliminated entirely.

The physics of the K-TIG process create high energy density in the welding arc, allowing it to open up a ‘keyhole’ and fully penetrate the material being welded and weld at high speed.

The unique nature of the keyhole geometry and the relatively unrestricted egress of the arc gases combine to produce an extremely stable and benign weld pool. The molten metal within the weld pool is prevented from falling from the root face by surface tension created by the process.

The K-TIG torch is engineered to convert a high current arc into a plasma jet which fully penetrates the material and creates a high surface tension weld pool on the underside of the material. By managing the surface tension, K-TIG can hold and stabilise the weight of the molten material while welding.

The penetration capabilities of K-TIG varies from material to material. It can achieve full penetration and single-pass welding on austenitic stainless steel of ½ inch (13mm) thickness. A key advantage of this impressive penetration is that there is no need for edge bevelling or a gap. All that is required is a simple square butt presentation, and you’ll be ready to complete single pass stainless steel welding.

Stainless Steel welding applications for K-TIG

The material range of K-TIG keyhole welding for stainless steel is between 3mm (1/8’’) and 13mm (1/2”). K-TIG can weld these thicknesses in stainless steel without any need for edge bevelling or a gap. Within this thickness range a full penetration butt weld is achievable in a single pass.

K-TIG can perform full penetration butt welds in both 1G and 2G positions, as well as longitudinal and circumferential welding. Stainless steel pressure vessels and tanks are ideally suited to the K-TIG process.  K-TIG has been replacing plasma keyhole welding technology for several years, and there are no issues with closing out or tying in on circumferential welding with K-TIG. This is an enormous advantage for stainless steel welding.

how-to-weld-stainless-steel-with-keyhole-tig.jpg

Why is K-TIG so beneficial for Stainless Steel Welding?

Exceptional Speed & Productivity

K-TIG performs single pass, full penetration welds both longitudinally and circumferentially at speeds as high as 1,000mm/m in stainless steel. Speed itself however, is only part of the story – it is the combination of full penetration with high speed that delivers the extreme productivity gains typical of the K-TIG process.

Full Penetration

Penetration is the key to K-TIG’s dramatic impact on welding productivity. The ability to achieve full penetration without the need for edge bevelling saves considerable time and resources, which reduces costs and increases profits. By contrast, conventional TIG and MIG welding processes require costly V- or J- groove preparations, with the metal removed during the groove preparation replaced with expensive filler metal, and to ensure consistency the preparations must be machine-prepared.

stainless-welding-how-to-keyhole-tig.jpg

Reduced Distortion and Shrinkage

Stainless steel is known for its high propensity to distort when welding. K-TIG’s ability to fully penetrate material and weld in a single pass means shrinkage and distortion are dramatically reduced. This is particularly beneficial for pipe spooling, when multiple joints are needed for a spool and overall length dimensions are critical for site fit up.

How to get the most out of your K-TIG system when welding Stainless Steel

Automation

K-TIG is intended to be used with welding automation which delivers a consistent travel speed. The requirements for automation are very simple - stable and consistent travel speed and a rigid torch mount. K-TIG can integrate with existing equipment such as seamers, rollers, rotators, manipulators, column and booms and robots.

The sophistication of the K-TIG system and controller, combined with the consistent quality of an automated process means both productivity and quality will typically increase significantly when you transition to the K-TIG process.   

Edge Preparation and Set-Up

In a perfect world, every square butt joint would have zero gap, but this is challenging to achieve in production fabrication environments. K-TIG has the ability to maintain a stable weld pool with gaps and misalignment tolerances unmatched by other keyhole welding processes such as plasma arc welding and laser welding. Additions of filler wire can also be added to the full penetration keyhole pass to increase fitup tolerance further.

stainless-steel-welding-how-to-keyhole-tig.jpg

Purging

Purging requirements for K-TIG are typical of GTAW welding. In stainless steel, purge gas is necessary to ensure a clean root bead. Many purge systems have been used with K-TIG welding, from an engineered purge dam that can regulate pressure and back pressure, right down to simply using masking tape and cardboard to blank off the ends with a hole poked through. When welding stainless steel with K-TIG we recommend to purge with 100% Argon.

This makes K-TIG purging familiar and further adds to the ease with which workshop supervisors can make the switch and transfer their existing knowledge to the new set –up for an incredibly easy and fast transition period.

Shielding Gas

The preferred shielding gas for K-TIG welding with stainless steel is 95% Argon and 5% Hydrogen. This has proven to be the most efficient gas for many welding processes and when it comes to welding stainless steel, K-TIG is no different. K-TIG can weld with 100% Argon, Hydrogen gas mixes and any welding gas used in GTAW welding processes. When welding duplex and super duplex, nitrogen additions help maintain a phase balance between the austenite and ferrite within the material.

Consumables

Filler wire can be added to the keyhole penetration pass, which helps maintain a stable weld pool when welding with slight gaps or mismatch in alignment. If filler wire is added the amount of filler material is greatly reduced – typically by more than 95%. Gas consumption is also reduced due to the speed at which K-TIG can weld. Consumables for all exotic materials are costly, meaning this reduction in consumables can be enormously helpful in improving your bottom line.

Bilfinger saved 92% welding stainless steel with K-TIG.

Bilfinger Case Study Brochure

What Training or Knowledge Do I Require?

You’ll be surprised to learn that an operator doesn’t require years of welding training and practical skills to perform quality stainless welding with K-TIG. Although background knowledge of welding is preferred, the simplicity of the system allows operators to be trained typically in under 3 hours, while workshop supervisors can receive comprehensive training in one to two days.

K-TIG’s simple, yet highly effective welding system can help address the chronic skills shortage in the welding and fabrication trade. Fewer and fewer young people are deciding to take up the trade, which has led to a situation in which the average age of UK and Australian welder is over 55, while in the US the average age of a welder is now 57.

To find out more about how K-TIG can help you and your stainless steel welding production, contact the team at K-TIG.

Related Posts

How does K-TIG compare?

K-TIG is a high performance, full penetration variant of the TIG/GTAW process which delivers productivity previously only possible with expensive laser, hybrid laser and electron beam processes.

Unlike plasma arc welding, there is only one welding gas and no orifice, making the process exceptionally robust and welding procedures highly repeatable in a wide range of materials, thicknesses and applications.