Porosity in welds is primarily caused by what?

• A. Trapped gas
• B. Slag inclusions
• C. Incomplete fusion
• D. Surface contamination

Answer: (A)

Porosity shows up as tiny gas pockets inside the weld metal as it solidifies. The main reason these pockets form is gas getting trapped in the molten metal, typically because shielding isn’t perfect. If shielding gas coverage is inadequate, leaks in the hose, or drafts blow away the shielding, air—and any moisture it carries—can reach the weld pool and create porosity. Hydrogen porosity specifically often comes from moisture in flux coatings, damp electrodes, or moisture on the workpiece. Surface contamination can contribute by adding gases that are released when heated, but the defining issue is gas that becomes trapped in the weld as it cools.

Slag inclusions and incomplete fusion describe different defects—solid slag trapped in the weld and lack of bonding between weld metal and base or filler metal, respectively—not gas pockets. To prevent porosity, maintain proper shielding gas flow and system integrity, keep consumables dry, and clean surfaces to minimize moisture and contamination.