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.