High-Resolution Ultrasonic NDE Imaging Method with Virtually Expanded Circumferential Aperture in Small-Diameter Cylindrical Oil/Gas Pipes
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In the nondestructive evaluation (NDE) of a shell structure, the locations of structural defects can be identified by exciting the structure with a guided ultrasonic wave (GUW), measuring the waves reflected from the defects, and constructing an image of reflected wave sources from the measured signals. However, the NDE of a small-diameter circular pipe has been challenging, due to the small curvature in the circumferential direction. Then, the axial locations of the structural defects are dominantly determined by axially-propagating, planar GUW components, making it difficult to locate the defects axially with a single array. For the accurate identification of the axial locations, it is proposed to place dual ultrasonic transducer arrays at the ends of a scanning pipe section. Generally, a high resolution NDE image can be obtained by increasing the aperture size of a sensor array. However, it is not physically possible to increase the circumferential aperture size in the small-diameter pipe. A novel method is proposed to improve the spatial resolution by virtually increasing the circumferential aperture size. It has been numerically shown that the proposed array configuration and the virtual aperture expansion method can be used to accurately identify the structural defects in the small-diameter pipe.