The major problems encountered are beam skewing and distortion, high and variable attenuation, and high background noise.

For many inspection problems involving austenitic components, the best examination performance has been achieved using broadband twin-crystal compression wave (TRL) angle beam probes, due to pseudo-focusing effect resulting from the convolution of the transmitter and receiver beams. Recently, the use of curved piezo-electrical elements, providing an additional optical focusing effect, has been observed to considerably enhance the signal-to-noise ratio in the focal zone of the transducer.

On the other hand, the phased array technology has already demonstrated its advantages in various industrial applications: the possibility to apply various examination angles during a scanning sequence while using one single probe, and its ability to electronically focus the acoustic beam at one or more given depths.

This paper shall present an innovating phased array transducer design for the examination of cast stainless steel components, combining the intrinsic advantages of conventional highly-damped low-frequency TRL transducers and the versatility offered by the phased array technology.

Various aspects of the twin side-by-side array design, as well as the dedicated procedures that were developed for the characterization of the probes shall be addressed

Practical trials were performed on artificial flaws in thick wall cast stainless steel specimens, to illustrate the excellent performance of the prototypes in terms of signal-to-noise ratio and lateral resolution. The examination data shall be analyzed, and the UT capability of the twin side-by-side phased arrays shall be compared to the results obtained with conventional TRL transducers on the one hand and single-crystal phased arrays on the other hand.