The invention relates to an acoustic sensor system (1) for detecting a defect (2) of a pipeline wall (3), having: at least one transmitter unit (4) which is configured to emit ultrasound in the direction of a pipeline wall (3) and detect an ultrasound echo reflected by the pipeline wall (3); and a control unit (5) which is connected to the at least one transmitter unit (4) for signaling purposes and which is configured to detect a defect (2) of the pipeline wall (3) using a present change in the ultrasound echo. The invention additionally relates to an in-line inspection device comprising the sensor system (1), to a method for detecting a defect (2) in a pipeline wall (3), to a computer program, to a data carrier signal, and to a data storage unit.

A sonic inspection device of an embodiment includes: a sonic probe including a transducer configured to execute at least one of transmission and reception of a sound wave; and a contact member including: a first sheet-like member containing an elastomer and having a first surface that comes into contact with a sonic function surface of the sonic probe directly or with an intermediate member therebetween and a second surface opposite the first surface; and a second sheet-like member having a plurality of openings and provided in contact with the second surface of the first sheet-like member. The second sheet-like member includes a high-hardness member provided in at least a part in contact with the second surface and containing at least one selected from a polymer, a metal member, and a ceramic member higher in Young's modulus at room temperature than the first sheet-like member.