What does the term "overlap" refer to in welding defects?

The term "overlap" in welding defects specifically refers to a defect where weld metal has flowed over the base metal without forming a proper bond. This occurs when the weld metal does not fully penetrate or fuse the surfaces of the base metal, leading to a situation where the weld appears to be sitting on top, rather than being integrated within the base material. This type of defect is characterized by the surface having a smooth, rounded appearance, which often indicates a lack of proper thermal input or technique during the welding process.

Proper bonding is critical in welding to ensure the strength and integrity of the joint. When overlap occurs, it compromises the mechanical properties of the weld, making it weaker and potentially leading to failure when the component is put under stress. Understanding this defect is crucial for welders, as it helps them to identify improper techniques and refine their skills to achieve better quality welds.

The other choices refer to different types of defects or issues in welding, but they do not accurately define what overlap specifically is, focusing instead on other forms of bonding problems or joint preparation issues.