The production of high quality, highly repeatable welds is the priority of any fabricator or workshop. The importance of welding quality control cannot be underestimated—it is often a question of structural and public safety rather than mere aesthetics. In some instances, the failure of a poor quality weld can result in damage to property, injuries, and even fatalities.
We take a look at the top 8 quality issues commonly found by welding inspectors, and delve into how K-TIG can help overcome these issues.
1. Weld Porosity
Porosity occurs when excess gas is trapped inside the weld, which creates cavity formation, reducing the overall strength of the join and therefore the quality of the weld. While not all forms of weld porosity can be detected by a welding inspector (many forms require non-destructive testing techniques), porosity that is visible on the surface of the weld presents as small round holes. There are several reasons that surface porosity forms:
- Electrodes and filler metals may had been handled improperly during preparation or the welding process itself
- Shielding gas may be contaminated or its flow may be restricted
- Welders may be using an incorrect welding technique
K-TIG offers a simple fix to weld porosity. K-TIG's keyhole creates an exit point for the welding gases to pass through. So, instead of becoming trapped in the weld as porosity, they exit through the keyhole, leaving the weld free from impurity. In addition, the K-TIG system ensures consistent application and execution of the weld procedure. The K-TIG Controller monitors, automates and reports on all aspects of your welding operations.
Capable of reducing complex weld procedures involving multiple plant automation sequences to single push-button operations, the K-TIG Controller consistently delivers repeatability, conformity and productivity.
2. Lack of Fusion
Lack of fusion occurs when the weld metal does not fully fuse with base metal during welding. This is especially prevalent at the overlap and slope out of a circumferential weld. For example, when completing a circumferential weld overlap tie-in with a conventional GTAW process, the lack of penetration makes it challenging to create a good fuse; the metal at the beginning of the weld can act as a barrier against full penetration at the point of overlap.
As there is no metallurgical bond between the weld and base metal, incomplete fusion drastically reduces weld strength. It can also cause higher localized rates of corrosion.
Lack of fusion can be caused by many variables, including the use of incorrect welding parameters and an incorrect welding technique.
K-TIG, on the other hand, offers keyhole penetration, delivered via a patented torch design and a high energy density arc. No complex constricted arc of plasma gas is required, and the process of sloping down and closing out is straightforward.
On top of this, K-TIG’s increased penetration greatly reduces the possibility of lack of fusion.
Finally, the K-TIG Controller offers comprehensive, highly accurate, real-time data logging that enables you to quickly and easily measure, document and record any and every weld parameter you could ever need.
A standard welding problem for processes like GMAW and GTAW is distortion. Both of these processes offer low energy density and slow travel speeds while requiring high heat input to create the weld. This high heat input can distort the metal and compromise the overall quality of the weld.
K-TIG offers very low distortion rates, thanks to its low heat input. This decreased heat input doesn't come at the expense of either energy density or travel speed, meaning welding inspectors notice significantly improved welding quality. In fact, K-TIG operates at 100x the speed of conventional GTAW processes.
K-TIG reduces angular, longitudinal and transverse distortion, not just by lessening the heat input, but also by providing full penetration welding and eliminating root gaps. This reduction in distortion is evident even in materials that are highly susceptible to distortion, such as duplex, super duplex and stainless steel.
Inclusions occur more commonly when welding thick materials (that require several passes), particularly when using flux coated cored rods. Each weld pass generates slag that covers the weld pool. If this slag is not removed before additional passes are made, it can enter the weld. When slag enters a weld, it can cause contamination and therefore weakness.
Some of the more common causes of inclusions are: a failure to clean a weld pass before applying the next pass; use of too much flux; welding at an incorrect angle; and use of an amperage that is too low. As K-TIG is an automated system, these causes are eradicated, helping to keep welds free from inclusions.
A weld undercut is an erosion of the base metal, which causes a surface discontinuity at the toe of the weld. The erosion is caused by energy being focused on an area where filler metal has not been deposited. A weld undercut is sharp in shape, which leaves it prone to stress (if not treated) and can lead to premature structural failure.
Excess energy is often caused by the arc voltage being too high, or an overly-long arc. Incorrect angle and usage of electrodes or using a travel speed that is too quick can also cause this issue.
K-TIG is an automated system. The arc and the keyhole are created simultaneously, and the weld moves at a constant speed. This removes the need for the welder to monitor speed. In addition, the arc and the sophistication of the K-TIG Controller mean all other variables are easy to control.
6. Process Inconsistency
Welding inspectors often encounter inconsistency in the use of welding processes, which impact negatively on the final quality of the weld. Process consistency is possible to achieve with PAW, GMAW and GTAW, although there are many variables at play.
With PAW, a smooth and consistent keyhole can be created at a low power level, but if the power has to be dialled up to weld thicker sections, the process can drift due to thermal distortion and lens contamination.
The need for a root pass and multiple fill passes, as well as tungsten tip erosion and sensitivity to parameter variation also makes GTAW susceptible to process inconsistency.
The simplicity of the K-TIG process, with its large electrode and the high-energy density arc of its keyhole, ensure process consistency, as well as negligible process drift throughout the weld.
7. Arc Strikes
Created by the rapid (often accidental) discharge of an electrical arc, an ark strike is a mark on the component or structure being welded located outside the weld zone. If an arc strike occurs, the base material will heat and then cool rapidly, which can form a hard, brittle microstructure prone to cracking. An ark strike usually leaves a dent on the base material, reducing its original thickness and, therefore, strength.
Arc strikes are usually caused by the use of incorrect welding techniques or improper grounding.
Welding is an extremely technical trade. PAW, SAW, GTAW, and GMAW forms of welding, are all notoriously difficult processes to master, requiring expert tradesmen. The K-TIG system is simple to use, while the automation takes much of the responsibility off the shoulders of the welder.
8. Poor Preparation
While poor preparation is not an issue that welding inspectors will face specifically, it does cause quality issues that welding inspectors regularly deal with. Unfortunately, GTAW, GMAW and SAW all require extensive joint preparation, which adds to the cost and time of each welding project. As the demand for productivity, efficiency and cost-cutting measures increases, preparation can be neglected. The result? Weld quality suffers.
K-TIG addresses this issue by reducing preparation requirements. For example, a SAW welding preparation requires a costly V-groove or J-groove preparation. This adds significantly to materials costs, as filler metal must be used to replace the removed joint metal. Manually bevelling joints also leads to inconsistency in welding results.
To prepare for a K-TIG weld, the welder only has to create a low-cost and straightforward square butt design, and no edge bevelling is required. There is also no groove to fill for materials slimmer than 14mm to 16mm. So, not only does K-TIG reduce preparation time, but it also cuts down on materials costs.
K-TIG greatly reduces the potential for porosity, lack of fusion, distortion, undercut and other welding quality issues commonly found by welding inspectors.
K-TIG welds meet US, European and Australasian welding standards (including ASME IX), and have been subjected to exhaustive Lloyds-witnessed and certified testing. K-TIG delivers highly repeatable, x-ray quality welds with superb cap and root aesthetics.
The ability to weld in a single, full penetration pass virtually eliminates the potential for lack of fusion and inclusions, and dramatically reduces the potential for porosity and other defects typical of multi-pass welding processes.
K-TIG is a low distortion process, with heat inputs well within normal ranges. As a result, transverse shrinkage and distortion are greatly reduced. K-TIG’s weld pool provides an exceptional quality cap and root that requires no back-gouging, finishing, cleaning or interpass grinding.