Guided wave testing, or GWT, uses low-frequency ultrasound operating between 20-150kHz compared to the MHz frequency range for conventional ultrasonics 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. Moreover, using additional advanced methods such as C-scan imaging techniques and, in Eddyfi Technologiesí case, a unique secondary focusing method, it is possible to give angular positioning and circumferential extent.
Read the full blog at Eddyfi.com.