How does shielding gas purity relate to porosity in GMAW?

• A. Gas purity has no effect on porosity.
• B. Moisture or contamination in shielding gas increases porosity; ensure clean gas, proper flow.
• C. Porosity is only caused by arc length.
• D. Porosity improves with purer gas.

Answer: (B)

Shielding gas purity directly affects porosity because any moisture or contaminants in the shielding gas can enter the weld zone and form gas pockets as the metal solidifies. The shielding gas is there to shield the molten weld from the atmosphere; if it carries water vapor, oxygen, or other impurities, those elements can become trapped as the weld solidifies, creating porosity. Hydrogen-rich moisture, in particular, tends to produce hydrogen porosity, weakening the weld.

To prevent this, use clean, dry shielding gas and maintain proper flow. Check gas lines, regulators, and hoses for moisture, leaks, or contamination, and purge the system before starting to weld. Use an appropriate shielding gas mixture for the material and process, ensure the gas is flowing at the correct rate, and minimize drafts and turbulence around the arc. Porosity is reduced by keeping the shielding gas pure and consistently shielding the molten pool.

Other statements miss the mark because porosity is not immune to gas purity, and simply using purer gas does not worsen porosity—the opposite is true.