What is interpass cleaning and why is it important in multi-pass GMAW?

• A. Cleaning oxidation and contaminants between passes; ensures proper fusion and prevents porosity.
• B. Cleaning oxidation only from the surface after welding.
• C. Cleaning the gas nozzle between passes.
• D. Cleaning the base metal before starting the weld.

Answer: (A)

Interpass cleaning means removing oxidation, scale, spatter, oil, moisture, and other contaminants from the weld surface between each pass. In a multi-pass GMAW weld, every new pass must fuse properly to what’s already welded. If an oxide film or debris remains, it acts like a barrier and can prevent good wetting, leading to lack of fusion and porosity at the interfaces. Cleaning between passes ensures the next pass can metallurgically bond to the previous weld and to the base metal, producing a sound weld with proper fusion and reduced defects. This is different from cleaning the base metal before starting or cleaning the gas nozzle between passes, which are not interpass cleaning.