Defect circumferential sizing by using long range ultrasonic guided wave focusing techniques in pipe

Abstract

Ultrasonic guided waves have the advantage of propagating over very long distances due to their natural ability of following differently shaped wave guides. This advantage makes guided waves a good candidate for long range non-destructive evaluation (NDE). The recently developed guided wave focusing techniques in pipes employ a circumferentially distributed phased array. By applying different amplitude and time-delay inputs to the phased array, guided wave energy can be successfully focused at any predetermined locations in pipes. Guided wave focusing techniques improve penetration power and circumferential resolution. As a result, excellent defect detection and accurate axial and circumferential location have been achieved. In addition, defect circumferential sizing in pipes is realized by doing circumferential scans at defect distances. A circumferential scan is accomplished by focusing at 44 angles around the circumference of a pipe at a specific axial distance. In a circumferential scan, the maximum amplitude of the defect echo was recorded and then plotted with respect to each focal angle. This produces an experimental angular profile of the reflected wave. The theoretical angular profiles of the reflected wave is obtained by calculating the focused guided wave energy impinged onto defects with different cross sectional areas (CSA). By comparing the theoretical and experimental profiles, the circumferential extent of the defect can be effectively measured.

Keywords:

• Guided wave
• Circumferential sizing
• Phased array
• Focusing
• Pipe

Acknowledgement

We would like to thank Peter Mudge of Plant Integrity for the use of a TeleTest^® focus system and Jack Spanner at EPRI for partial support of this work.