摘要
采用周向导波用于厚壁管道中的缺陷扫描检测。基于连续小波变换提取特定频率下小波系数包络信号用于厚壁管道缺陷成像。试验中斜探头以步长为2 mm轴向扫描检测轴向缺陷,得到斜探头晶片覆盖轴向缺陷不同程度时的检测信号。截取包含缺陷回波和周向回波的信号并得到频率点500 kHz的小波变换系数包络信号,与频散曲线对比分析得到检测信号主要为周向类Lamb波模态CL3。进一步利用不同扫描点处检测信号的连续小波变换系数包络信号并进行幅值包络成像。利用该幅值包络成像重构得到轴向缺陷并有效确定该缺陷的长度。基于连续小波变换得到的特定频率点处幅值包络信噪比较好,且成像结果具有较高的聚焦性。因此,利用基于连续小波变换的幅值包络成像方法可提高检测信号识别以及缺陷识别能力。
Circumferential guided waves are used for scanning detection of defects in thick wall pipes. Wavelet transform coefficients at a certain frequency point are extracted for imaging defect in thick wall pipe by using continuous wavelet transform. In experiments, the angle beam probe is used to scan the axial defect in the step of 2 mm in the axial direction and inspection signals are obtained when the element of angle beam probe covers the axial defect with different coverage extents. The signals containing defect echoes and circumferential echoes are intercepted and their continuous wavelet transform coefficient envelope signals at 500 kHz are extracted. According to the comparison of these envelop signals and dispersion curves, received inspection signals are confirmed to be mainly circumferential Lamb wave mode CL3. Furthermore, continuous wavelet transform coefficient envelopes of inspection signals at different scanning points are used for amplitude envelop imaging. The defect is reconstructed based on this amplitude envelope image and its axial length can be confirmed efficiently. The signal to noise ratio of amplitude envelopes at a certain frequency point is greatly better based on continuous wavelet transform and imaging results show high focus performance. Therefore, amplitude envelop imaging method can be used for enhancing inspection signal identification and defect recognition based on continuous wavelet transform.
出处
《机械工程学报》
EI
CAS
CSCD
北大核心
2013年第2期14-19,共6页
Journal of Mechanical Engineering
基金
国家自然科学基金(51235001
50975006
11272021)
北京市自然科学基金(1122007)
北京市教委科技计划(KM201010005003)
北京市科技新星计划(2008A015)资助项目
关键词
周向导波
厚壁管道
轴向缺陷
连续小波变换
幅值包络成像
Circumferential guided waves Thick wall pipe Axial defect Continuous wavelet transformAmplitude envelop imaging
