Possessed of a laser-like focus, good welders control weld beads. A depth-regulated seam progresses between two joint zones. As the filler metals and weld pool cool behind the travelling electrode, it produces a solid joint that’s just the right width. This seam is smooth and free of excess weld metal. From the smooth, clean joint face to the root and toe, the weld bead hardens into an imperfection-free join.
Talking About Weld Bead Size Issues
At least that’s what should be happening. Every time a skilled welder lays down a weld bead
that should be the final result, a smooth joint that penetrates to the core of the two intersecting metal surfaces. If the fusion line isn’t wide enough, then the weld depth ratio is going to suffer. Without full penetration, the joint weakens. For a small weld bead, multi-pass welding can fix this issue. If the bead is too broad, however, then a void could form between the weld filler and the root of the joint. Again, the jointed plates end up weak because the filler hasn’t penetrated deep enough into the joint interface.
Weld Shape and Width: Analyzing Weldment Geometry
Using two plates to illustrate the next set of welding challenges, the two workpieces are cleaned and placed at ninety-degrees to one another. Using a GMAW (Gas Metal Arc Welding) rig, a properly sized weld bead is applied. A triangular fusion line follows closely behind the powered arc as it melts the filler material. The metal melts then cools. In reality, it’s more of a wedge-shaped joint. The face is visible as a slightly rippled metal line, which joins the two metal parts. With the equipment charge and feed rate adjusted, the desired weld bead size has been achieved. Now, the geometry of the bead is maintained by keeping the electrode at a set angle, unless the welder suddenly develops a nervous tic.
It’s not just the electrode angle that creates weld bead discontinuities; the equipment voltage and amperage settings also require attention. Welders should confirm the viability of those settings by working on a waste piece of metal. Then, with the arc length consistent and the power supply settings adjusted just-so, the rest is up to the welder, so no nervous tics, please. To keep things flowing smoothly, the equipment operator should find a comfortable position, take a cleansing breath, and then adopt a moderately fast travel rate. If it’s too fast, though, the depth and shape of the weld bead won’t form as a clean, consistent seam. Fast travel speeds also cause bead-corrupting problems.
To Welding Inspectors, acid etching kits are just another tool. That box of cushioned vials fits snugly in with an extensive range of joint examining instruments. True, these substances are a lot more energetic than a dye penetrant. Acids are designed to be corrosive, after all. But these aren’t any old volatile chemicals. On the contrary, they’re specially formulated so that they’ll dissolve boundary obscuring slag inclusions.
It’s a Defect Clarifying Mechanism
Acid etch examinations dissolve weld slag. The test emphasizes the boundaries between welds and base metal edges. In other words, the test emphasizes the topographical anatomy of a weld. Otherwise, the anticipated demarcation zones around each weld section would be impossible to make out. Unlike the age revealing rings inside a felled tree, those boundary lines aren’t instantly recognizable, not unless a weld is treated with an acid etching solution. However, like that tree, this inward-looking perspective can’t be viewed until a weld cross-section is taken. Polished and acid-etched, the sliced away transverse section is prepped so that it’ll reveal its secrets.
A Destructive and Corrosive Weld Examining Ordeal
No doubt, the examination process can only be described as an ordeal. After an inspectors’ cushioned examination box opens up, a hydrochloric or nitric acid solution is cautiously applied. The test cross-sectional sample has been cut away from a suspect weld, and now it’s sitting in a dish full of acid. The corrosive compound eats its way into the sample. Soon after, a very revealing chemical action takes place. Weld-to-base metal boundaries are highlighted, slag inclusion deposits dissolve, hidden gas pockets are exposed, and all once masked weld defects become much easier to recognize.
Employed as a Soundness Determining Device
Weld integrity is severely tested by this destructive joint torturing regimen. With slag inclusion melted away, weld defects stand exposed. If a weld boundary can be highlighted in this manner, think how cracks will come to light. Porosity issues, poor fusion difficulties, hairline fractures and all other forms of fusion degradation, they can’t hide from a chemical attack that’s designed to dissolve all opportunistic flaw-masking weld detritus.
If a weld defect is buried deep inside the cooled metal, it’s nigh-on impossible to spot that flaw. Even dyes and microscopes can miss tiny porosity blemishes and other welder or equipment applied imperfections. Once missed, the flaws worsen over time, a weld causes a structural flaw to appear, and a construct suffers. Weld Inspectors can’t abide such quality and safety impacting matters, which is why an acid etch test examinations is so important. Used to destructively bring out concealed joint defects, the corrosive substance exposes the tiniest weld discontinuities for all to see.
Conductivity headaches are bad news, especially since arc welding equipment relies upon electrical charges to generate metal-to-metal jointing heat. If a welder, while holding an equipment electrode, can’t generate enough heat to carry out a high-quality weld, then the joint site is weakening the circuit somehow. There’s something resisting the energy flow. Not to worry, a few minutes of prep work should take care of this current attenuating effect.
Checking Weld Site Resistivity
Right to the point, is the weld area clean? Dirt or paint, rust or oily film, any of these conductivity-impeding surface contaminants could be obstructing what would otherwise be a high conductivity weld zone. Before switching on what’s essentially a highly charged electrical circuit, the weld area must be cleaned. Wire brushes to hand, a welder soon takes care of such current resisting coatings. Likewise, looking at the grounding clamp this time, the welder should inspect this mechanical linkage to see if it’s behaving as a current bottleneck. Clean the weld zone and the circuit grounding clamp before picking up the handheld electrode.
Tracing the Fault Back Further
If the weld metal is clean, try taking another approach. Look for a maintenance sticker and check to see whether the gear has been inspected recently. Are the leads and electrodes securely fastened to the equipment terminals? What if the electrode includes a consumable filler rod or wire? Alternatively, the electrode might use TIG (Tungsten Inert Gas) technology, so carefully trace out the connection between the non-consumable tungsten rod and the handheld electrode. Electrical currents can’t flow easily if they’re impeded by a loose electrode connection. What’s more, contact tips experience wear over time. Generating that much heat and focused energy, the inner circuit elements within welding equipment electrodes do require periodic replacements.
Far from being helpless, welders can take affirmative action. Besides the weld area cleaning, there are other steps that can be taken. A welder checks the condition of the work leads and electrodes every time a new job is undertaken. Also, using the gear, an experienced welder doesn’t yank the cables around, nor does he bend and twist the leads when attempting to get at an awkward jointing area. That’s a strictly amateurish move, one that will cause cable fraying and terminal damage. Remember, the goal is high conductivity, the formation of a low-resistance circuit. The smallest loose connection will undermine this goal. Like a clog in a high-pressure water line, loose or damaged connections form attenuated contact points. Typically, it’s a dirty work area that’ll cause the current inhibiting effect, but lead cable issues are common too.
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.
Welding inspectors tend to be highly experienced team members. They’re reliable, task-oriented, and capable of recalling all kinds of welding codes. Really, just check out a job listing on the internet to see how much an employer expects of a welding inspector. Essentially, employers demand accomplished staff members. Welding experience is the key, as are the credentials that guarantee joint integrity.
Welding Inspectors Are Project Failsafes
Skilled welders do their job. If that job is done ineptly, the results can’t escape the expert attention of an alert inspector. Alternatively, even if the welder seems to have concluded the job properly, seems to have applied a perfectly finished weld, an experienced and accredited joint assessor sees matters differently. Carrying special dyes and inspection tools, that walking job safeguard is there to make sure all project welds are free of concealed discontinuities. Structured as a “push-pull” program, weld inspectors gain their qualifications by taking two different career paths.
A Discipline That Applies an Adjustable Career Path
Experience is the first of the two job prerequisites. If a prospective company employee has years of engineering and welding experience, they’re already halfway there, at least as long as that experience can be verified by a past employer. Then there’s the second half of the job path, which takes qualifications and special credentials. Featured prominently among those competency-based qualifications, the CSWIP 3.1 Certificate is a highly sought after credential. With a Certification Scheme for Welding and Inspection Personnel in pocket, a welding inspector demonstrates a broad spectrum of knowledge. Yes, welding codes and standards are covered here, plus a tested ability to visually assess a range of joint discontinuities. Just as importantly, at least in Australia, WTIA (Welding Technology Institute of Australia) credentials are always in high demand.
Using that push-pull approach, a job holder could have years of practical experience, then there’d be several years of theoretical knowledge to add to their abilities. Alternatively, many years of engineering theory could combine with several years of practical welding work. Either way, it’s not enough to be an expert office worker, nor can the job be done by someone who’s only worked in the field. Basically, a degree is desirable, but years of onsite experience are every bit as valuable. At any rate, after the experience-to-theory balance is worked out, there are these WTIA credentials and/or CSWISP qualifications, which can take weld inspectors overseas. At minimum, a candidate should hold an AS1796 Certificate 10 ticket. Incidentally, that prerequisite is also covered by the WTIA.