Electromagnetic ultrasonic transducers and systems for in-service inspection of gas pipelines

Electromagnetic ultrasonic transducers (EMUS) do not need liquid couplants; they can be designed to operate at elevated temperatures; they can be scanned at high speeds; and they can be designed and fabricated for a much wider variety of wave modes than piezoelectric probes, especially for modes with tangential polarisation. A disadvantage is the larger insertion loss than that of piezoelectric transducers. However, using an optimised layout of probes and transmitting and receiving electronics yields sufficient power and signal/noise ratio for pipe testing and many other industrial applications. The paper describes the general state of the art and the results of optimisation for in-service inspection of gas pipelines. In particular, the optimisation of linearly polarised shear-wave transducers for vertical and oblique incidence is presented. (IZFP)