Which weld quality issue is caused by shielding gas not turned on or base metal contamination?

Which weld quality issue is caused by shielding gas not turned on or base metal contamination?

• A. Porosity
• B. Distortion
• C. Penetration
• D. Burn through

Answer: (A)

Shielding gas protects the molten weld pool from the atmosphere. When the shielding gas isn’t flowing or the base metal is contaminated, atmospheric gases (like air oxygen and moisture) can become trapped as the metal solidifies, forming tiny gas pockets known as porosity. Contaminants such as oil, grease, rust, or moisture on the metal surface worsen this effect by releasing additional gases or creating uneven surfaces that disrupt shielding. Porosity weakens the weld and can lead to leaks or reduced corrosion resistance, so the cure is to ensure the shielding gas is flowing properly and the metal surface is clean and dry before welding. Other defects relate to different issues: distortion comes from heat input and restraint, penetration describes how deeply the weld fuses into the base metal, and burn-through occurs when there’s excessive heat on thin material. These are not directly caused by shielding gas being off or by surface contamination in the same way porosity is.

Shielding gas protects the molten weld pool from the atmosphere. When the shielding gas isn’t flowing or the base metal is contaminated, atmospheric gases (like air oxygen and moisture) can become trapped as the metal solidifies, forming tiny gas pockets known as porosity. Contaminants such as oil, grease, rust, or moisture on the metal surface worsen this effect by releasing additional gases or creating uneven surfaces that disrupt shielding. Porosity weakens the weld and can lead to leaks or reduced corrosion resistance, so the cure is to ensure the shielding gas is flowing properly and the metal surface is clean and dry before welding.

Other defects relate to different issues: distortion comes from heat input and restraint, penetration describes how deeply the weld fuses into the base metal, and burn-through occurs when there’s excessive heat on thin material. These are not directly caused by shielding gas being off or by surface contamination in the same way porosity is.