Porosity in the weld metal can lead to overall strength reduction in the weld. Luckily, porosity can be prevented most of the time. There are a good number of causes of weld metal porosity, and a few of the important ones are mentioned below.
- Diminished shielding gas can cause dilution with the atmosphere due to an empty gas cylinder, a pinched gas hose, a restricted gas nozzle, the gas nozzle being too far from the weld pool, as well as many other reasons.
- Contaminants such as anti-spatter compound, grease, paint, oil, glue and moisture can also cause porosity. Consumables (nozzles, tips, liners) and other welding equipment that might be near the weld pool should be checked and cleaned.
- Air can enter the weld in various ways, and can also lead to weld porosity. If shielding gas flow speed is too high it can suck air into the mixture. A draft or air current can also push air into the weld. If the weld joint is open at the root it could suck air in from the back end. Damaged o-ring seals can also introduce air into the shielding gas.
Although certain levels of weld porosity are acceptable under some welding codes or standards, it should still be actively prevented to ensure a high quality weld.