Application of ultrasonic phased array total focusing method in weld inspection using an inclined wedge

To improve the sensitivity for small defects in weld inspection using ultrasonic phased array, total focusing method (TFM) has been studied and applied when an inclined wedge is used during detection. Firstly, the data set is captured by the approach of full matrix capture. Secondly, the propagation paths which the ultrasonic wave takes from a transmit element to a certain scatter source and then back to a receiver element are determined, and the time of flight of each echo for any possible transmitter-receiver pair is calculated for every pixel in target area. Then coherent superposition is carried out over all the echoes. Experiments are carried out on phased-array block with side-drilled holes and on butt weld with natural flaws, and the results using TFM and conventional fixed-focus method (FFM) are compared. Experimental results show that TFM outperforms FFM in resolution and has improved the recognition ability for small defects. Therefore TFM can be used as an effective post-processing method to improve sensitivity for small defects in weld detection involving inclined wedges.