Application of TFM for defect sizing in welded joints.
These below pictures show T-joints at the offshore windmill construction. The material thickness to inspect is 40 mm to 60 mm. Here the TFM remote scan has been shown as the most effective inspection technique, first for safety reasons, and second because of the wide scan width required for the scan path and coupling control. Typical scan lengths of the T-joint sections are ~5m, both when testing from the top side, and the bottom side. The 64-element, 5 MHz probe is fixed in a probe holder for direct coupling via a 3mm water gap, and has a cable length of 30m. The remote controlled Scanner (Jireh: Navic) moves the probe, allowing additional transverse shift for correctly guiding the probe along the scan path. The scanning speed is 17 mm/s (~1 m/minute) providing a scan resolution of 1 mm, and additionally 4 video cameras are used to control the test procedure.