关键词: 超声导波, 管道, 腐蚀, C扫描

Abstract: Ultrasonic guided-wave detection of pipeline corrosion is an important pipeline inspection technology.Conventional ultrasonic guided-wave echo signal processing is based on A-scan, which easily misses defects and is unable to locate defects, such as circumferential position.L (0,2) modal of center frequency 48 kHz guide-wave was used to detect pipeline.According to comparison of A-scan result and artificial defects, it was suggested that wavelet transform was used to process data, then log linearization was made, and finally C-scan was used to display pipeline corrosion.Since echo signal of gradational or large corrosion defect was gentle, and could be easily missed, so correlation analysis was used to choose sym5 wavelet transform processing.It could clearly show the defect location and determine the basic direction of defects.Because guided-wave propagation energy decayed exponentially, linear representation of the extent of corrosion defects could be achieved by log linearization of echo amplitude.Based on A-scan collected from the pipe cross-sectional distribution of echo signals from 120 probes,the pipeline was circumferentially unfolded 360°, and colors represented the extent of corrosion.C-scan could not only accurately scan the axial position of defect but also display the distribution of defects in the circumferential direction.The experiments on corrosion detection of a ±6m long pipeline showed that the proposed method could accurately detect and locate the locations, sizes, and shapes (rectangles, circles, ellipses) of pipeline corrosion defects.C-scan ultrasonic guided-wave detection provided a simple and effective method for application of guided-wave to locate defects.

Key words: ultrasonic guided wave, pipeline, corrosion, C-scan