On Circumferential Disposition of Pipe Defects by Long-Range Ultrasonic Guided Waves

Ultrasonic guided waves have been used extensively for long-range pipe inspections. The technique is based on detecting the guided wave echoes reflected from pipe defects located at a remote distance. The axial location of the defect from the transducer can be determined by the arrival time of the echo. However, further information about the defect, such as the circumferential size or distribution of the defect, is hard to obtain with conventional guided waves. This problem will be a critical issue for applications, such as discriminating the pipe corrosion defects from pipe welds. In this paper, a circumferential guided wave array is built for sending and receiving guided waves along the pipe. All of the elements are connected to a single channel pulser/receiver through multiplexers. An algorithm based on two-dimensional (2D) blind deconvolution is developed to process the guided wave echoes acquired by the multiplexed circumferential transducer array. The output of the algorithm can be utilized for evaluating the circumferential distributions and geometry of the defects. The processing algorithm is verified via both numerical simulations and experiments in the paper. This circumferential sizing algorithm can serve as an effective postanalysis tool for most available guided wave pipe inspection systems.