DGS curve evaluation applied to ultrasonic phased array testing

The application of phased array to the ultrasonic testing of components such as forged or plate products, with the longitudinal wave arranged in a sectorial scan centred at zero degrees, can be very attractive because of the possibility, due to the electronic sectorial scan of the ultrasonic beam, of producing a complete and documented volume inspection with a fewer number of scan lines than with using a standard probe. The problem is that, in this inspection technique, defect estimation is carried out, normally, by the use of a Distance Gain Size (DGS(dagger)) set of curves([1,4,5]). Such curves are easily available for standard probes of circular shape, but not for phased array probes whose active area is a function of the number of active elements chosen and which can be strongly rectangular. In order to avoid such difficulty, we have developed a computer model that is capable of generating the DGS curves from an input of the actual phased array parameters. This computer model has been assessed using some calibration blocks containing flat-bottomed holes. The results are very encouraging, showing good performance when defects are in the far field of the actual probe configuration, while in the near-field region the generated DGS curves lead to a defect overestimation.