A sweep outlet is a type of  integrally reinforced branch connection used to facilitate radiography, one or many non-destructive tests (NDT) used to inspect welds.
This type of NDT uses Gamma or X-rays to penetrate material. The rays are then passed through film on the opposite side .the exposed film is examined as a negative and displays the internal features The thickness of the weld is shown through lighter or darker areas on the film.