Metal Weld Porosity in Mig Welding: What is it all About?20 March 2019
Pinholes can form inside welds. There’s no two ways about it, that’s a patently shoddy example of welding workmanship. The joint isn’t solid. Just as one adverse effect, the strength of a metal-bonded joint diminishes when tiny cavities accumulate inside welds. Okay, having identified the defect, what’s causing this fusion-undermining porosity in the first place? Stopping to look at a MIG welding operation, an inspector ponders this question.
Shield Gas Inadequacies
There’s something wrong with the CO2 gas that’s meant to protect the HAZ (Heat-Affected Zone) from the oxygen and nitrogen-rich atmosphere that we all breathe. Sure, air is a life-sustaining gas for biological entities, for plants and people alike, but that invisible atmospheric stuff is bad for MIG welded joins. That’s where the shielding gas comes in, as a barrier between the air and the weld site. One likely problem here is a lack of CO2, the most common shielding gas in the MIG welding industry. Another possible issue is the presence of a force that’s hampering the formation of the gas cloud. In essence, a strong wind is blowing away the gas.
Craters and wormholes are developing on what should be a smooth joint. The gas is flowing, a shelter has been raised around the worksite, so what’s up here? To correct this frustrating problem, stop for a moment. Take a look around. Is the worksite wet or cold? Perhaps one of the work surfaces is dirty or layered with greasy deposits? After raising the wind shelter, let’s take the time to prep the worksite. Clean the surfaces. Are they free of dirt and oil? That’s good, but the prep work isn’t finished yet. If it’s a cold day and the job is being done on an offshore oil rig, humidity is going to impact the work. Try preheating the metal, for that’ll eject the moisture.
MIG (Metal Inert Gas) welders are expected to adopt a forward-thinking mindset. To prevent pinholes, craters, and general porosity issues, this expertly trained individual plans out his job. There’s the proper formation of that gas shielding cloud to ensure. Getting down close to the weld surfaces, the welder checks out the join sites for dirt and oily deposits. Scrubbed clean, there’s still that last potential pinhole causative factor to deal with, so the metal is warmed until all the moisture is evaporated. Needless to say, this approach becomes a reflex action after a while. It’s a course of action that’s taken alongside an exhaustive equipment check. After all, there’s still a chance a simple hose pinch is hampering the CO2 flow.
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