Experimental study of guided wave propagation and damage detection in large diameter pipe ﬁlled by different ﬂuids Zhenhua Song a, * , Xiangshang Qi b , Zenghua Liu c , Hongwei Ma b a School of Engineering, Sun Yat-sen University, Guangzhou 510006, China b College of Science & Engineering, Jinan University, Guangzhou 510632, China c College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 100124, China ARTICLE INFO Keywords: Guided waves Liquid-ﬁlled pipe Mode conversion Attenuation Damage detection ABSTRACT A series of experiments on damage detection of large-diameter (88 mm diameter) pipe with and without liquid by guided waves have been conducted. Two types of liquid as water and machine oil are chosen to ﬁll in pipe for detecting the inﬂuence of ﬁller. The inﬂuences of liquid types on guided wave propagation, dispersion and attenuation characteristics have also been studied. The mode conversion phenomenon of reﬂection waves exists regardless ﬁlling state of pipe, but it is most serious in water-ﬁlled pipe, and weakest in vacant pipe. The defect wave signal could be distinguished from converted wave mode by time-frequency analysis, and the time- frequency distributions of the two type signals are different. The relationship between defect length and defect reﬂect signal strength is linear in vacant pipe and nonlinear in liquid-ﬁlled pipe. With the defect length increasing, the defect signals of liquid-ﬁlled pipe increase too, but the rate of increment are reduced. 1. Introduction Industrial and civil life pipes for ﬂuids transporting, such as gas, water and oil, have been widely distributed all over the world. The pipelines are the third major transport method in the world. However, for some exceptional cases, such as nuclear steam generator tubing [1] and un- derground buried pipes [2], it is uneasy to use traditional ultrasonic A-scan to scan defect of the pipe by point-to-point way on the outline of pipe. The guided waves are a series of longitudinal propagation wave packets, which different from the traditional ultrasonic wave mainly focus on local area in depth direction, could be excited in a local section of pipe wall to detect defect of pipe in longitudinal direction [3]. Lowe et al. [4] employ the long-range guided waves to detect defects in unﬁlled pipe ﬁrstly. It reveals the potential application prospects of guided wave on damage detection. Then, the dispersion curves and wave modes analysis of unﬁlled pipe have been conducted by Wilcox et al. [5]. They notice that there are several types of wave modes exist in pipes when guided wave propagating. Therefore, the existence of mode con- version and the occurrence pattern of it become a focus of current research. The mode conversion of notch echo has also been studied by them in succession [6,7]. Their research shows that the reﬂect mode F(1, 3) as strongly as the axially symmetric L(0,2) mode when the notch length is short, and the F(2,3) also received in reﬂection. On the other hand, the pipes inevitably ﬁlled with liquids in practice. Thus, there are many researchers have studied the dispersion characteristics of guided waves in water-ﬁlled cylindrical pipe by theoretical analysis [8,9] and numerical calculations [10,11]. They conclude that the dispersion curves of water-ﬁlled pipe are very different from the unﬁlled one. The guided waves in water are approximate plane-wave motion. The research of Aristegui et al. [12] indicate that there is a α mode exists in water-ﬁlled pipe as the water mode which generated by leaked guided waves [13] from pipe wall. And the experiments of guided waves propagate in small diameter (6.8 mm) and thin thickness (0.7 mm) copper pipe with different liquids inside and outside of pipe have been done by them. Their research results show that α mode is nearly a constant in water ﬁlled pipe at low frequencies, the guided waves decrease more rapid than outer wall at high frequencies due to wave leakage into inside and surrounding water. The pipe ﬁlled by viscosity ﬂuid (castor oil) and signal attenuation of it have also been discussed in their report. It could conclude that the guided waves in liquid-ﬁlled pipes are very different from that of vacant pipes. And the mode characteristics of guided wave in liquid-ﬁlled pipe are inﬂuenced by several factors. Long et al. [2] make experimental and numerical analysis investigate on symmetric (longitudinal) and non-axis-symmetric (ﬂexural) modes attenuation of guided wave in * Corresponding author. School of Engineering, Sun Yat-sen University, No.132 Waihuan East Rd. of University Town, Guangzhou 510006, China. E-mail address: songzhenhua@mail.sysu.edu.cn (Z. Song). Contents lists available at ScienceDirect NDT and E International journal homepage: www.elsevier.com/locate/ndteint https://doi.org/10.1016/j.ndteint.2017.10.002 Received 8 March 2017; Received in revised form 26 September 2017; Accepted 3 October 2017 Available online 4 October 2017 0963-8695/© 2017 Elsevier Ltd. All rights reserved. NDT and E International 93 (2018) 78–85