Before welding the joint surface shall be free of which contaminants?

Before welding the joint surface shall be free of which contaminants?

• A. Mill scale
• B. Moisture
• C. Oil and Grease
• D. Mill scale, Moisture, Oil and Grease

Answer: (D)

Before welding, the joint surface must be completely clean, because any contaminant can prevent proper fusion and create defects. Mill scale is an oxide that doesn’t melt smoothly and can become trapped under the weld, leading to lack of fusion and porosity. Moisture adds hydrogen when heated, which can cause porosity and hydrogen-induced cracking in the weld. Oil and grease leave residues that burn and release gases, also promoting porosity and weakening the weld. Because each of these contaminants can cause problems, the best practice is to have the joint surface free of mill scale, moisture, oil, and grease. Clean thoroughly with brushing or grinding to remove scale, wipe with a solvent to remove oil/grease, and ensure the surface is dry before welding.

Before welding, the joint surface must be completely clean, because any contaminant can prevent proper fusion and create defects. Mill scale is an oxide that doesn’t melt smoothly and can become trapped under the weld, leading to lack of fusion and porosity. Moisture adds hydrogen when heated, which can cause porosity and hydrogen-induced cracking in the weld. Oil and grease leave residues that burn and release gases, also promoting porosity and weakening the weld. Because each of these contaminants can cause problems, the best practice is to have the joint surface free of mill scale, moisture, oil, and grease. Clean thoroughly with brushing or grinding to remove scale, wipe with a solvent to remove oil/grease, and ensure the surface is dry before welding.