Two of the most common root defects are ____?

• A. Grapes and Porosity
• B. Slag Inclusions and Suck Back
• C. Porosity and Slag Inclusions
• D. Incomplete Fusion and Concave Root Surface

Answer: (D)

Root defects are problems that occur at the weld root where the weld metal meets the base metal. Two of the most common root defects are incomplete fusion and a concave root surface. Incomplete fusion means the weld metal did not fully fuse with the base metal at the root, leaving unmelted areas or a narrow region where fusion did not occur. This weakens the joint and is usually caused by insufficient heat input, too-fast travel speed, improper torch angle, or poor joint fit-up. A concave root surface happens when the root bead does not fill the root cavity adequately, creating an inward dip at the weld bottom. This results from too little filler metal, excessive travel speed, or insufficient heat at the root, and it reduces root reinforcement and can lead to leakage or reduced load-bearing capacity. These two conditions specifically target the root region and are therefore the most common root defects. Porosity and slag inclusions can occur in welds, but they are not characteristic root defects in GTAW, and slag is not produced in this process.