Abstract: An apparatus for detecting defects comprises a pair of ultrasonic probes which are gimballed onto a pair of elongate members. A pair of yokes are gimballed onto the elongate members. Springs cause an interaction between the yokes and the ultrasonic probes such that the ultrasonic beams travel in a plane parallel to the longitudinal direction of the elongate members. The elongate members are slidably mounted on a carriage and the elongate members are arranged apart at a predetermined angle. The carriage is mounted to travel on an arcuate member to scan the corner of joint between a pressure vessel and a nozzle in a direction radially with respect to the axis of the nozzle. The arcuate member is rotatably mounted to a support member to scan the corner or the joint circumferentially with respect to the axis of the nozzle.