How is the depth of root penetration measured?

• A. top of the metal to the root face (bottom)
• B. from the surface to the filler bead
• C. from the bottom to the root
• D. from the root to the crown

Answer: (A)

Root penetration depth is measured from the exposed surface of the weld up to the deepest point where the weld has fused with the base metal at the root. In a butt joint, that means from the top surface down to the bottom of the root fusion line (the root face). This vertical measurement shows how far the weld has penetrated into the joint, which is what determines the joint’s strength and integrity. Measuring from the surface to the filler bead, or from bottom to root, or from root to crown, would not accurately reflect how deeply the weld metal has fused into the base metal.