Define root opening in a groove weld.

• A. The gap between the edges of the base metals at the joint root.
• B. The depth of the groove required for full penetration.
• C. The distance from weld face to root along the joint axis.
• D. The width of the welded joint at the surface.

Answer: (A)

Root opening is the gap between the edges of the base metals at the joint root in a groove weld. This distance is measured where the two pieces meet at the bottom of the groove and before filling. It matters because it directly influences fusion at the root and how easily the weld penetrates; too large a gap can hinder complete fusion and require more filler metal, while too small a gap can lead to lack of fusion at the root.

The other concepts are not root opening: estimating the groove depth corresponds to groove depth needed for full penetration, not the gap at the root; the distance from the weld face to the root along the joint axis describes a different dimension (often related to throat or leg geometry), not the opening at the root; and the width of the welded joint at the surface refers to the surface weld width, not the root gap.