The Affection of Pipes Characteristics to Exciting Frequency for Guided Waves NDT

In the application of guided waves NDT, the selection of exciting frequency is not only related with the setup of sensor, but also with the characteristics of pipe’s structure and material. In this paper, the characteristic of guided waves propagation in pipes that L(0,1) and L(0,2) have a cutoff frequency are respectively discussed, and the calculation formulas of their cutoff frequency are given. The varied relationship between the cutoff frequency of L(0,1) and L(0,2) mode guide waves, the outer diameter and wall thickness of pipes are discussed, respectively. For a given steel pipe, experiments are carried out by selection of different exciting frequency. The results show that the “low-pass” type cutoff frequency of L(0,1) and “high-pass” type cutoff frequency of L(0,2) are reduced with increasing of outer diameter of pipes, and the “low-pass” type cutoff frequency of L(0,1) and “high-pass” type cutoff frequency of L(0,2) are initially increased with increasing of wall thickness of pipes, but the increased amplitude is slowly changed a little. When the outer diameter of pipes is more than 351mm, both of the cutoff frequencies are not changed with varied of wall thickness of pipes. The experimental results are well agreed with theoretical computation of selected exciting frequency for pipes guided waves NDT.