Heavy flakes and large deposits of oxides are signs of what?

• A. Overheating
• B. Porosity
• C. Under filler deposition
• D. Root surface contamination

Answer: (D)

Root surface cleanliness is essential for a sound GTAW root pass. Heavy flakes and large deposits of oxides indicate the root face was contaminated before welding. Oils, grease, moisture, rust, or oxide scale on the root metal will oxidize when heated, forming oxide layers that can spall off as flaky deposits and get trapped in the weld area. Even with shielding gas, these oxides hinder proper fusion and can lead to weak weld root quality. The proper approach is thorough cleaning of the root surface—degreasing, solvent wiping, and mechanical cleaning to remove oxide and scale, followed by ensuring the surface is completely dry before welding.