To indicate variation from the thickness of the tube wall of a steam generator by providing a partial load tone burst active system comb type ultrasonic transducer, transmitting an axially asymmetric ultrasonic wave through steam generator piping and detecting the reflected ultrasonic wave.

The steam generator piping inspection system comprises a comb type transducer 12, a tone burst power amplifier 14, a sweep frequency generator 16, and an ultrasonic inspector 18. The transducer 12 is molded according to the shape of steam generator piping 10 on the inner circumferential direction thereof. In the operation, sweep frequency range is selected to maximize the sound field in material. The transducer is located at the end of opening of the steam generator piping disposed in the tube plate of a steam generator. Defect in the steam generator piping partially reflects a waveguide signal which is received by the comb type transducer thus indicating effective defect data.