中文摘要：

频散是长距离管道导波检测中影响检测频率选择的重要因素。通过分析空心圆管中纵向模态导波的频散特性，探讨导波检测常用模态L（0,2）和L（0,1）的频率选择问题。根据导波频散现象，建立缺陷回波分辨距离与激励信号参数间的量化关系，分析检测频率优化选择问题。以导波频散引起的信号分辨距离为依据，计算不同几何尺寸管道中L（0,2）和L（0,1）导波非频散段的限制频率。结果表明，限定或最小化缺陷回波分辨距离，可获得最佳的导波激励信号周期及检测频率或频段。随着管道几何尺寸变化，得到L（0,2）和L（0,1）导波频散特性变化的几个重要结论。当管道内径壁厚比不小于4时，L（0,2）导波低限频率与管道直径的乘积约为4.0 MHz·mm，高限频率与壁厚的乘积约为1.06 MHz·mm。对于小口径管中的L（0,1）导波，其高限频率与直径的乘积约为0.81 MHz·mm。这些简单的函数关系为管道检测时快速确定非频散段频率范围提供参考。

英文摘要：

The dispersion of guided waves is an important factor that affects the frequency selection in long range pipe inspection. By analyzing the dispersion characteristics of longitudinal guided waves in hollow cylinders, the selection of inspection frequencies for the commonly used modes L（0,2） and L（0,1） is studied. According to the dispersion phenomenon, the quantitative relationship between defect echo resolvable distance and excitation signal parameters is established, and then the problem of frequency optimization selection is analyzed. A distance parameter caused by dispersion of guided waves is defined, and basis on this, the limiting frequencies of L（0,2） and L（0,1） modes in non-dispersive region are calculated. It is shown that the optimized cycles of tone burst and frequencies can be selected by restricting and minimizing the defect echo resolvable distance. Along with the variation of pipe geometry, several important conclusions are drawn about the change rules of the L（0,2） and L（0,1） modes dispersion characteristics. For the L（0,2） mode, when the pipe inner-radius-thickness ratio is great than or equal to 4, the lower limiting frequencies diameter product is about 4.0 MHz·mm, and the upper limiting frequencies thickness product is about 1.06 MHz·mm. For the L（0,1） mode in small tubes the upper limiting frequencies diameter product is about 0.81MHz·mm. These simple function relationships provide reference for quickly determining the frequencies of non-dispersive region in pipe inspection.