What does root opening refer to in groove welds?

• A. The gap at the root between the base metals that is necessary to achieve proper joint penetration.
• B. The outermost edge of the weld bead.
• C. The thickness of the filler metal.
• D. The color of the weld.

Answer: (C)

Root opening is the gap between the base metals at the root of a groove weld. This space allows the weld metal to penetrate and fuse the two pieces of metal at the root, which is essential for a sound joint. The size of the root opening influences penetration and fusion quality—too small can prevent full root fusion, while too large can complicate control and increase reinforcement. It isn’t the outer edge of the weld bead, nor the thickness of the filler metal deposited, and it has nothing to do with weld color. The exact dimension is specified in the joint design or welding procedure.