Abstract: An apparatus for inspecting a pipe comprising a body adapted for passage through the bore of a pipe to be inspected, a main transducer array comprising a plurality of circumferentially spaced transducers for transmitting ultrasound energy, the transducers being mounted on the body for movement between a retracted position, wherein the body can freely move through the bore of the pipe, and an extended position wherein the plurality of transducers are pressed into operative contact with the inner wall of the pipe. An actuator selectively urges the plurality of transducers to their extended positions. A control transmits ultrasound energy into the pipe to propagate a guided wave within the pipe walls in at least one longitudinal direction along the pipe when the transducers are in their operative position and receives the propagated wave and analyzes the wave to determine the presence or absence of defects in the pipe wall.