Long range ultrasonic guided wave focusing in pipe for small defect detection, location and circumferential length analysis

Ultrasonic guided wave focusing techniques in steel pipe are used to detect and measure the axial as well as circumferential locations of three differently shaped defects (planar saw cuts, a volumetric through-wall hole, and a volumetric elliptical corrosion). The axial location of a defect was obtained by measuring the arrival time of the defect echo. Defect circumferential location was determined by focusing at 44 circumferential positions around the pipe at a specific distance. The maximum amplitude of the defect echo was recorded with respect to each circumferential focal position in producing an angular profile of the reflected wave. The maximum amplitude of this experimental angular profile occurs at the angle of the defect circumferential location. The energy impingement onto the defect for each focusing position can be calculated from the focused angular profile and the defect cross sectional area. Comparison between the experimental angular profiles and the theoretical ones provides us with a good estimate of the defect circumferential size.