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

摘要： 常规超声导波回波信号处理是基于A扫描分析，存在易漏检、无法定位缺陷周向位置等不足，选用L（0，2）模态中心频率为48kHz的导波进行管道检测实验，通过对A扫描检测回波与腐蚀缺陷的对比分析，提出了对A扫描检测回波先进行小波变换处理，再进行log线性化处理，最后使用C扫描显示管道腐蚀检测结果的回波信号处理方法。实验表明，所提方法可有效地检测各类管道腐蚀缺陷，并准确地定位缺陷的轴向和周向位置，为导波技术的实际工程应用提供简单有效的方法。

关键词: 超声导波, 管道, 腐蚀, C扫描