Slag Inclusion in Welding: Causes and Prevention16 July 2019
Do weld inspectors ever come upon joint flaws that are unquestionably blemished? Certainly, and slag inclusion defects fall nicely into this category. Just by looking at a weld that’s scarred like this, it’s easy to see something has gone wrong. A vitreous deposit is trapped in the fused metal. Clearly, a weld inspector must look carefully at this linear defect to see if it’ll undermine joint integrity.
Slag Inclusion Causative Factors
The defect can arise when flux-cored or stick welding equipment goes awry. Either the arc welding gear is malfunctioning or a welder’s technique is lacking. In all probability, the flux has melted and found its way into the weld pool. As a weld pass comes to an end, the oxidized slag becomes trapped underneath the next pass. Let’s go over the sequence again. The flux becomes an undesirable weld byproduct, which oxidizes when it reacts to the surrounding environment and weld surface heat. Forming a vitreous barrier, a film that hardens between two weld passes, the slag becomes trapped in the cooling metal. Equipment sorts that are susceptible to this defect type include flux-cored arc welding gear and stick welding systems. Also, since the slag trapping occurs between two separate passes, operator error is another contributing factor.
Employing Preventative Actions
For substandard technique problems, the solution is clear. A welder must take steps as the job progresses. The equipment operator should select a superior flux coating, a high-quality material that won’t leave any waste behind. Cleaning the weld site, each pass proceeds steadily and carefully, with no sign of dirt or vitreous waste getting into the inter-run overlap. Sticking with weld pass issues, the torch head moves slowly forward, then the weld pool is allowed to cool without any interference. Keeping these actions in mind, no oxidizing films or flux byproducts are allowed to become trapped between weld passes. If slag does form on top of a cooling layer of welded metal, it must be cleaned off before the job can proceed. Again, it’s the job of an ever-aware welder to look out for such process defects.
And what happens if a welder doesn’t correct a slag inclusion obstacle? Out comes a wire brush, which means the job suffers interminable stoppages. If the site welding inspector doesn’t give the joint a passing grade, a grinder is pulled from a toolbox. The slag is abraded away until the weld area is clean. Otherwise, especially when slag inclusion is detected close to a weld root, structural integrity issues could ensue. An oxidized linear defect could very well separate. Microfissures and porous discontinuities are also credible threats when slag inclusions are bad enough. To judge such issues, weld inspectors call upon their every resource.
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