Complete Joint Penetration describes a weld that:

• A. Penetrates through the full thickness of the joint
• B. Uses complete joint fit-up
• C. Has no porosity
• D. Is used only in fillet welds

Answer: (A)

Complete joint penetration means the weld metal fuses through the entire thickness of the joint, from one face to the opposite face. This level of penetration provides full structural continuity across the thickness, so the weld can carry stresses as effectively as the base metals. It’s typically associated with groove welds where the groove depth is designed to allow the weld to reach the far side, often checked by root fusion and full-weld penetration.

A joint being well fit up involves aligning the parts and controlling gaps, but it doesn’t by itself guarantee that the weld will fuse through the full thickness. Porosity is a defect related to gas pockets in the weld, not how deeply the weld penetrates. Fillet welds, by design, do not achieve full penetration through the joint thickness like groove welds can, so they’re not described as having complete joint penetration.