Article Article
Live imaging using TFM in a 30-inch forged steel block

Phased array ultrasonic inspection of large forged steel blocks (more than 30 inches in each direction) is very challenging because of the long propagation distances and the variations in the material properties along the propagation axis. In addition, common phased array ultrasonic testing methods such as beam focusing are not suitable because the size of the focused area is very small compared with the dimension of the part under inspection. The Total Focusing Method (TFM) associated with the Full Matrix Capture (FMC) acquisition scheme is therefore appropriate in this scenario. In this work, the material properties were studied and used to design a transducer optimized for the inspection large parts. Elements size and number was a strong concern because of the natural focus of FMC and the large amount of data generated and treated for TFM reconstruction. The aim was to minimize the amount data to be processed in order to perform live imaging with a minimal compromise on the resolution. Emission sequences and reconstructions were optimized to increase Signal to Noise Ratio (SNR). Finally, live imaging of 1/16” Side Drilled Holes in a 30-inch forged steel block was performed. For each reflector, the 6-dB drop extent was lower than 0.2” in the axial direction and 0.5” in the lateral direction. The SNR was more than 32 dB and the maximum value of 54 dB was measured at the middle of the block also corresponding to the natural focus of the probe in elevation.


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