Which term describes a weld that does not fully penetrate the joint thickness as required by the spec?

• A. Lack of fusion
• B. Hot cracking
• C. Cold cracking
• D. Lack of penetration

Answer: (D)

Penetration is about how deep the weld metal fuses into the joint. When a weld is tested or inspected, full penetration means the weld goes through the entire joint thickness to the opposite side as required by the spec. If it does not reach that far, it’s called lack of penetration—the root isn’t fused through to the far side, so the weld is not as strong as required.

Lack of fusion, by contrast, means the weld metal didn’t fuse to the base metal (or to a previous weld pass) at the joint, which is a different defect from insufficient depth. Hot cracking occurs during welding as the metal solidifies and can develop cracks in the weld metal, while cold cracking happens after welding due to hydrogen-assisted cracking or residual stresses at lower temperatures.