Guided wave testing uses a low-frequency ultrasound operating between 20-100kHz compared to the conventional ultrasonics MHz frequency range used for thickness checks. This allows the ultrasound to be broadcast away from the tool and axially along the pipe in GWT. When this broadcast ultrasound encounters a change in cross-section, the change in acoustic impedance of this region causes an echo of sound to return to the tool for detection. Using the welds on a pipe for calibration and comparing amplitudes of other signals to these welds, it is possible to indicate the severity of any corrosion detected. Furthermore, using additional advanced methods such as C-scan imaging techniques and, in Eddyfi Technologies’ case, a unique secondary focusing method, it is possible to give angular positioning and circumferential extent. However, even with all this post-processing currently, minimum remaining wall loss is not possible using GWT.

https://blog.eddyfi.com/en/how-guided-wave-testing-fits-into-a-pipeline-inspection-program

blog.eddyfi.com