What causes porosity in a weld, and how can it be prevented?

• A. Gas entrapment from moisture, oil/grease, rust, or improper shielding; prevented by clean surfaces, dry electrodes, proper shielding gas coverage, correct travel speed, and proper technique.
• B. Porosity is caused by high travel speed.
• C. Porosity is unaffected by shielding gas.
• D. Porosity is prevented by using salty water.

Answer: (A)

Porosity in a weld happens when gas gets trapped in the molten weld metal as it cools and solidifies. This usually comes from moisture or contaminants on the workpiece or electrode (water, oil/grease, rust) or from inadequate shielding gas coverage, which allows air to enter the weld pool. Prevent it by cleaning and drying surfaces and electrodes, removing oil, grease, and rust, and by ensuring complete and stable shielding gas coverage with proper flow. Use the right travel speed and technique to keep a stable puddle and minimize turbulence. While travel speed can influence heat and bead shape, the primary prevention is keeping the joint clean and ensuring proper shielding. Using salty water would contaminate the weld, not prevent porosity, and shielding gas quality or cleanliness is essential—porosity is not avoided by ignoring shielding gas.