How can porosity form in a GMAW weld and what steps minimize it?

• A. Porosity can form from moisture in filler, moisture on base metal, and improper shielding gas coverage or arc length; minimize by drying filler, cleaning base metal, ensuring shielding gas, and appropriate travel speed and technique.
• B. Porosity forms from excessive current; minimize by reducing current.
• C. Porosity forms only from base metal oxidation; minimize by heating.
• D. Porosity is not relevant to GMAW.

Answer: (A)

Porosity in a GMAW weld happens when gas becomes trapped in the weld metal as it cools and solidifies. In short, the molten pool must be shielded from air by the shielding gas, and any intrusion of moisture or interruptions in shielding can form gas pockets inside the solidifying weld.

The steps to minimize it address the main culprits: keep everything dry and clean, ensure solid shielding coverage, and maintain good arc control. Dry the filler wire and remove moisture from the base metal so hydrogen- or moisture-related porosity isn’t introduced. Clean and prepare the joint to remove oils, rust, and contaminants that can outgas during welding. Ensure the shielding gas is flowing correctly and reaching the weld zone without leaks or turbulence, and use proper travel speed and technique to keep the shield close and stable over the weld pool. Together these actions keep the molten metal protected and reduce the chances of gas being trapped as it solidifies. Excessive current, base metal oxidation alone, or the idea that porosity isn’t relevant to GMAW do not capture the primary causes or the practical fixes for porosity.