An apparatus is provided for external inspection of a pipeline circumferential weld. This comprises a radiation source (5) and radiation detector (3). Both units are controllably movable around a drive band or track (7) which is fitted around the circumferential weld. To align the source with the detector the source and detector are moved with respect to each other clockwise and anticlockwise around an initial position whilst sampling the radiation detected at a number of positions. A position of maximum strength of the radiation signal detected can then be determined such that the centre point of the radiation source may be located. The source and detector are then substantially aligned with each other and means are provided to move the source and detector circumferentially around the weld whilst remaining substantially in alignment.
