What does it mean if a weld must be completely removed and re-welded from the start?

When a weld must be completely removed and re-welded from the start, it indicates a significant defect known as a lack of fusion. This term refers to a situation where the molten filler metal does not adequately bond with the base metal or the previous layers of weld metal. As a result, the weld does not achieve the necessary strength and integrity required for the structural application. A lack of fusion can compromise the overall performance of the weld and could lead to structural failure under load.

In practice, addressing a lack of fusion often necessitates complete removal of the deficient weld and re-welding to ensure that the joint meets the required standards for strength and quality. This type of defect is particularly critical, as it can arise from various factors, including improper welding technique, insufficient heat, or contamination at the weld interface. Thus, the need to remove and re-weld reflects the seriousness of the defect and the importance of achieving a proper bond in the weld joint.