Which statement correctly describes a common weld discontinuity and its cause?

Which statement correctly describes a common weld discontinuity and its cause?

• A. Porosity is caused by slag being trapped in the weld
• B. Slag inclusion is caused by large filler metal diameter
• C. Undercut is caused by excessive shielding gas flow
• D. Porosity is caused by trapped gas in the weld metal

Answer: (D)

Porosity is gas pockets that form in the weld metal as it cools and solidifies. When gas gets trapped instead of escaping, tiny voids remain in the weld, weakening it. The most common cause is inadequate shielding of the weld pool—shielding gas leaks, too high a flow, being too far from the joint, wind, or contaminants like oil, moisture, or rust on the base metal or filler material. Keeping the area clean and dry, maintaining proper shielding gas coverage and nozzle distance, and avoiding drafts helps prevent porosity. Other discontinuities have different causes: slag inclusion happens when slag is trapped in the weld, often due to insufficient slag removal between passes or overly thick slag; undercut occurs from too much current or too fast a travel speed, not from shielding gas. Porosity arises specifically from trapped gas, making the stated cause the correct one.

Porosity is gas pockets that form in the weld metal as it cools and solidifies. When gas gets trapped instead of escaping, tiny voids remain in the weld, weakening it. The most common cause is inadequate shielding of the weld pool—shielding gas leaks, too high a flow, being too far from the joint, wind, or contaminants like oil, moisture, or rust on the base metal or filler material. Keeping the area clean and dry, maintaining proper shielding gas coverage and nozzle distance, and avoiding drafts helps prevent porosity.

Other discontinuities have different causes: slag inclusion happens when slag is trapped in the weld, often due to insufficient slag removal between passes or overly thick slag; undercut occurs from too much current or too fast a travel speed, not from shielding gas. Porosity arises specifically from trapped gas, making the stated cause the correct one.