In-line apparatus for inspecting pipes using ultrasonic guided waves

摘要

A pig (A, B, C, D, E, fig. 1) for inspecting a pipe has a main transducer array comprising a plurality of circumferentially-spaced ultrasonic shear piezoelectric transducers 1 moveable between a retracted position, allowing the pig to move freely, and an extended position in which the transducers are pressed into operative contact with the inner wall of the pipe. Control means is provided for transmitting ultrasonic energy into the pipe to propagate a guided wave (e.g. a torsional-mode, Lamb-type or flexural-mode wave) within the pipe walls in at least one longitudinal direction along the pipe and for analysing the wave to determine the presence or absence of defects in the pipe wall. Each transducer element may also comprise a doubled-curved alumina faceplate 2, acting as a contact head, that isolates the transducer electronically from the pipe. The shape of the faceplate is the intersection of a rectangular parallelepiped and the edge of a toroid.