What is the main benefit of cleaning metal surfaces before welding?

• A. It prevents defects and improves penetration
• B. It increases bead width
• C. It reduces protective coating
• D. It changes metal composition

Answer: (A)

Cleaning metal surfaces before welding is crucial because contaminants such as oil, grease, rust, paint, and oxide films can prevent proper fusion and trap gases in the weld. When the base metal is clean, the molten filler metal wets and bonds to it more effectively, leading to better penetration and a stronger, defect-free joint. The other ideas aren’t the primary outcome of cleaning: bead width is mainly affected by welding parameters and joint design, coatings aren’t the goal to reduce (they’re simply removed to allow welding), and cleaning does not change the metal’s composition. So the main benefit is preventing defects and improving penetration.