[3A5] Comparison between PAUT and TFM techniques for inspections of welds on coarse-grained materials

Olivier Roy, Guillaume Neau and Frederic Reverdy
Eddyfi Europe, France 

TFM imaging is increasingly recognized in the field of non-destructive testing for its qualities: realistic images over an extended region with optimized resolution, facilitating the analysis and interpretation of results. These techniques also allow for simplified setup of control configurations for faster and safer inspection work. Standards development is underway in the ASME and IIW working groups to qualify these techniques, and as a consequence, the number of successful applications in different industrial fields is steadily increasing.

Despite these qualities, TFM imaging must respect the physics of ultrasound to produce relevant images. Components with a coarse or attenuative material and large thickness require the use of large transducers to increase the energy transmitted into the material and to increase the focusing capacity to detect small defects. A large aperture also improves the signal-to-noise ratio in the presence of structural noise by multiplying the ultrasound paths between the transducer and the target defect. Large aperture can be reinforced with TRL or dual transducers that can improve defect detection at chosen depth, reducing disturbance from other areas.

This article compares weld inspection applications achieved with PAUT techniques and TFM imaging, using appropriate transducers and TFM options. The combination of dual transducers with the TFM method produces high quality imaging with all the additional benefits. TFM imaging can be enhanced by using a different excitation mode, PWI, transmitting more energy to increase sensitivity and detection capability.

In particular, we study the capabilities of TFM applied with PWI to reduce grain noise compared to PA focusing using the same large aperture transducers.

Experimental results are presented to illustrate the pros and cons of TFM and PAUT techniques for weld inspections on complex material components. These results were achieved using a field portable device applying standard PAUT techniques and different options of TFM techniques.