On a radiograph, what does undercut appear as?

In radiography, undercut appears as a dark line or area on the radiograph. This phenomenon occurs due to the way X-rays penetrate the material. When there is an undercut, it indicates that there is a groove or notch in the weld or base material. This groove allows for more radiation to pass through and be absorbed by the film, leading to a darker density on the radiograph.

The appearance of a dark line is significant because it provides essential information about the welding quality. Undercuts can lead to stress concentration points, which might compromise the integrity of the weld or the overall structure. Thus, identifying undercuts on a radiograph is crucial for assessing the quality of welds during inspection and ensuring adherence to safety and performance standards in welding processes.