Enhanced sizing for surface cracks in welded tubular joints using ultrasonic phased array and image processing

Abstract

This study presents an approach, which couples the ultrasonic wave reflection principle and image processing for the ultrasonic phased array, to enhance the sizing surface cracks in welded tubular joints. Ultrasonic phased array, as one of the non-destructive techniques, has wide applications in detecting and sizing of cracks in engineering structures. In detecting surface cracks in a welded tubular joint and potentially other types of welded components, however, the focused emitting ultrasonic wave, which is not normal to the surface crack plane, can create ultrasonic S-scan images with an inaccurate crack size and incorrect orientation. This study aims to improve the accuracy of the ultrasonic measurement through, 1) capturing multiple S-scan ultrasonic images by emitting the ultrasonic waves at different distances from the surface crack location; and 2) developing the algorithm based on the principle of ultrasonic wave reflections to improve the crack sizing and orientation from the ultrasonic S-scan images. Combined with the real-time crack monitoring during the low-cycle fatigue tests of tubular joints, the proposed scheme and algorithm achieves an enhanced agreement with other crack sizing approaches including the Alternating Current Potential Drop and measurements on the reproduced fracture surface using silicone-replica.