Post-processing of guided wave array data for high resolution pipe inspection

This paper describes a method for processing data from a guided wave transducer array on a pipe. The raw data set from such an array contains the full matrix of time-domain signals from each transmitter-receiver combination. It is shown that for certain configurations of an array, the total focusing method can be applied, which allows the array to be focused at every point on a pipe in both transmission and reception. The effect of array configuration parameters on the sensitivity of the proposed method to random and coherent noise is discussed. Experimental results are presented using electromagnetic acoustic transducers for exciting and detecting the S-0 Lamb wave mode in a 12-in. diameter steel pipe at 200 kHz excitation frequency. The results show that using the imaging algorithm, a 2-mm (0.08 wavelength) diameter half-thickness hole can be detected.