What is slag inclusion?

• A. Gas pockets trapped in the weld metal.
• B. Nonmetallic slag trapped within the weld metal due to improper slag control.
• C. An opening at the root due to insufficient fusion.
• D. A crack that propagates through the weld.

Answer: (B)

Slag inclusion is nonmetallic slag trapped in the weld metal. It happens when flux slag from the welding process isn’t properly controlled or removed, allowing chunks of slag to become embedded as the weld solidifies. This creates internal defects that can weaken the weld and may require grinding or reworking to fix. To prevent slag inclusions, thoroughly remove slag between passes, keep slag on the surface by maintaining proper travel speed and electrode angle, use the correct flux or coating, and clean the weld area before continuing.

Gas pockets in the weld are porosity, not slag, and indicate shielding or process issues. An opening at the root from insufficient fusion describes lack of fusion, a different defect. A crack is a fracture that propagates through the weld, also a separate defect.