Which statement is true about porosity?

Which statement is true about porosity?

• A. Cavities occur on the surface only
• B. Porosity consists of cavity-type discontinuities formed by gas entrapment during solidification
• C. Root cracks are easily detected
• D. The primary causes of porosity are dirt, rust, and moisture on the base metal surface

Answer: (B)

Porosity is about small gas-filled voids that appear in weld metal as it solidifies. These cavities form when gas dissolved in the molten metal (like hydrogen, oxygen, or nitrogen) or gas from the shielding atmosphere gets trapped and cannot escape before the metal cools and becomes solid. That is exactly what the statement describes: cavity-type discontinuities formed by gas entrapment during solidification. The other options miss the essence—porosity isn’t limited to surface cavities, it’s not about cracks, and while contaminants can contribute, porosity centers on gas entrapment during solidification rather than being caused solely by dirt or moisture.

Porosity is about small gas-filled voids that appear in weld metal as it solidifies. These cavities form when gas dissolved in the molten metal (like hydrogen, oxygen, or nitrogen) or gas from the shielding atmosphere gets trapped and cannot escape before the metal cools and becomes solid. That is exactly what the statement describes: cavity-type discontinuities formed by gas entrapment during solidification. The other options miss the essence—porosity isn’t limited to surface cavities, it’s not about cracks, and while contaminants can contribute, porosity centers on gas entrapment during solidification rather than being caused solely by dirt or moisture.