What is the purpose of interpass cleaning and why is slag removal important in multi-pass welding?

• A. To comply with color coding; cosmetic only.
• B. To prevent contamination and ensure proper fusion; cleaning maintains weld quality and penetration.
• C. To increase slag thickness; to protect weld.
• D. To save time; slag removal not necessary.

Answer: (B)

Interpass cleaning and slag removal are about making sure each new weld pass fuses properly to the previous one. After a pass, slag, oxides, and other contaminants can form on the weld surface. If these are not cleaned off between passes, the next bead may not bond cleanly to the underlying metal, which can cause lack of fusion, porosity, and slag inclusions, weakening the weld.

Removing slag before the next pass exposes a clean metal surface, allowing the arc and molten metal to penetrate and fuse correctly with the previous layer. This keeps penetration consistent and preserves weld quality and strength in a multi-pass weld.

So, the purpose is to prevent contamination and ensure proper fusion, maintaining overall weld quality and penetration.