CN100344968C

CN100344968C - Excitation of single non-axial-symmetric pipe line guide mode and pipeline no-demaged detection method

Info

Publication number: CN100344968C
Application number: CNB2004100142935A
Authority: CN
Inventors: 程建春; 汤立国
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2004-03-12
Filing date: 2004-03-12
Publication date: 2007-10-24
Anticipated expiration: 2024-03-12
Also published as: CN1560619A

Abstract

A method for using piezoelectric transducers to excite relatively simple non-axisymmetric guided wave F(1,3) modes in pipelines and for non-destructive detection of pipelines: place a piezoelectric transducer symmetrically on the top and bottom of the outer wall of the pipeline The circumferential expansion angle of the transducer is 120 degrees, and the two transducers are excited in opposite phases along the axial direction, and at the same time, the excitation frequency is controlled within the range of weak dispersion and fast propagation speed on the group velocity dispersion curve. The pure F(1,3) mode excited is used for non-destructive detection of pipelines. The present invention first proposes a method for using a piezoelectric transducer to excite relatively simple non-axisymmetric guided wave F(1,3) modes. Similar to the L(0,2) mode, the F(1,3) mode is also within a certain frequency band, with small dispersion and fast propagation speed, so its waveform reflected by the defect is simple, which is beneficial for analyzing and characterizing defects.

Description

A method for non-destructive detection of pipelines using the excitation of a single non-axisymmetric pipeline guided wave mode

一、技术领域1. Technical field

本发明涉及一种管道无损探伤的方法，尤其是激发利用单个非轴对称管道导波模式F(1，3)进行管道无损探伤的方法。The invention relates to a method for pipeline nondestructive flaw detection, in particular to a method for stimulating and utilizing a single non-axisymmetric pipeline guided wave mode F(1, 3) for pipeline nondestructive flaw detection.

二、背景技术2. Background technology

与传统的单点超声检测或成像方法相比，超声导波探伤具有高效，实施方便且代价低等优点。利用超声导波进行管道缺陷探测的研究是无损检测领域一个热门课题。Compared with traditional single-point ultrasonic detection or imaging methods, ultrasonic guided wave flaw detection has the advantages of high efficiency, convenient implementation and low cost. The research of pipeline defect detection by ultrasonic guided wave is a hot topic in the field of non-destructive testing.

目前，利用轴对称纵振导波模式进行管道缺陷检测的研究已经取得很大进展。其核心思想是将压电换能器沿管道一周放置，从而激发单纯的轴对称L(0，2)模式探测管道缺陷，因为该模式在频率较低的某频带内，非色散且传播速度最快，故其经缺陷反射后的波形简单利于分析定征缺陷。但该方法存在以下两个主要缺陷：(a)在现场检测时，对于并排放置且间距较小的管道，往往无法沿管道一周放置换能器，从而难以激发出单纯的L(0，2)模式；(b)L(0，2)模式只对沿环向分布的管道缺陷比较敏感，对沿轴向分布的管道缺陷不敏感。At present, great progress has been made in the research of pipeline defect detection using axisymmetric longitudinal vibration guided wave mode. The core idea is to place the piezoelectric transducer along the pipeline to excite the pure axisymmetric L(0,2) mode to detect pipeline defects, because this mode is non-dispersive and has the fastest propagation speed in a certain frequency band with a lower frequency. Fast, so the waveform reflected by the defect is simple and easy to analyze and characterize the defect. However, this method has the following two main defects: (a) During on-site detection, for pipelines placed side by side and with small spacing, it is often impossible to place transducers along the pipeline, so it is difficult to excite a simple L(0,2) mode; (b) L(0, 2) mode is only sensitive to pipeline defects distributed along the circumferential direction, but not sensitive to pipeline defects distributed along the axial direction.

由于非轴对称模式在管道内呈螺旋形向前传播，故与轴对称模式相比，其对沿轴向分布的缺陷更加敏感。但是利用非轴对称模式进行管道缺陷检测的研究长期以来没有大的进展，其原因之一在于难以象激发轴对称导波一样，激发出比较单纯的非轴对称模式，否则激发出的波形复杂，难以分析。Since the non-axisymmetric mode propagates forward in a helical shape in the pipe, it is more sensitive to defects distributed along the axial direction than the axisymmetric mode. However, the research on pipeline defect detection using non-axisymmetric modes has not made great progress for a long time. One of the reasons is that it is difficult to excite relatively simple non-axisymmetric modes like exciting axisymmetric guided waves, otherwise the excited waveforms will be complicated. Difficult to analyze.

三、发明内容3. Contents of the invention

本发明提出了一种利用压电换能器激发比较单纯的非轴对称导波F(1，3)模式的方法，并将此方法用于管道无损探伤。The invention proposes a method of using a piezoelectric transducer to excite relatively simple non-axisymmetric guided wave F(1,3) modes, and uses the method for non-destructive flaw detection of pipelines.

与轴对称纵振导波L(0，2)模式类似，F(1，3)模式亦在一定的频带内，色散小且传播速度快，故其经缺陷反射后的波形简单，利于分析定征缺陷。Similar to the L(0,2) mode of the axisymmetric longitudinal vibration guided wave, the F(1,3) mode is also within a certain frequency band, with small dispersion and fast propagation speed, so the waveform reflected by the defect is simple, which is beneficial for analysis and determination. defect.

本发明目的是这样实现的：在管道外壁顶端和底端对称地各放置一压电换能器，换能器的环向展开角度为120度，且两换能器沿轴向反相激发，同时将激发频率控制在F(1，3)模式的群速度色散曲线上色散弱而传播速度快的范围内，从而激发出单纯的F(1，3)模式。本发明利用激发出的单纯的F(1，3)模式进行管道无损探伤。The object of the present invention is achieved in this way: a piezoelectric transducer is symmetrically placed on the top and bottom of the outer wall of the pipeline, the circumferential expansion angle of the transducer is 120 degrees, and the two transducers are excited in opposite phases along the axial direction, At the same time, the excitation frequency is controlled within the range of weak dispersion and fast propagation speed on the group velocity dispersion curve of the F(1,3) mode, thereby exciting the pure F(1,3) mode. The invention utilizes the excited pure F (1, 3) mode to carry out non-destructive flaw detection of pipelines.

1.单个非轴对称管道导波模式F(1，3)的激发1. Excitation of a single non-axisymmetric pipe guided wave mode F(1,3)

当压电换能器置于管道外壁且轴向振动以激发导波，管道外壁所受力可写成下面的形式When the piezoelectric transducer is placed on the outer wall of the pipe and vibrates axially to excite the guided wave, the force on the outer wall of the pipe can be written in the following form

s(b，θ，z，t)|_r＝b＝b^-1f(θ)g(z)T(t)e_z (1)s(b, θ, z, t)| _r=b ＝b ^-1 f(θ)g(z)T(t)e _z (1)

当管道无限长时，管外壁上各点的轴向振动位移为When the pipe is infinitely long, the axial vibration displacement of each point on the outer wall of the pipe is

${u u}_{z z} ((b b,, θ θ,, z z,, t t)) = = {&Integral; &Integral;}_{00}^{\infty \infty} dξ dξ \underset{nm nm}{Σ Σ} \frac{{{ϵ ϵ}_{11} {ϵ ϵ}_{22} [[{R R}_{nm nm}^{z z} ((b b,, ξ ξ,, {ω ω}_{nm nm}))]]}^{22}}{{ω ω}_{nm nm}^{22} {M m}_{nm nm}} - - - - - - ((22))$

$\cdot \cdot {&Integral; &Integral;}_{00}^{t t} T T ((τ τ)) sin sin {ω ω}_{nm nm} ((t t - - τ τ)) dτ dτ \cdot &Center Dot; cos cos nθ nθ \cdot &Center Dot; cos cos ξz ξz$

其中b为外半径，θ与z分别为环向及轴向坐标分量，t为时间，ξ为波数，ω为圆频率，n为环向阶数，m为给定n后模式的阶数，T(t)为管外壁所受力随时间的变化，且Where b is the outer radius, θ and z are the circumferential and axial coordinate components respectively, t is time, ξ is the wave number, ω is the circular frequency, n is the order of the circle, m is the order of the mode after a given n, T(t) is the change of force on the outer wall of the tube with time, and

${M m}_{nm nm} = = π π {&Integral; &Integral;}_{a a}^{b b} ρ ρ [[{R R}_{nm nm}^{r r}^{22} + + {R R}_{nm nm}^{θ θ}^{22} + + {R R}_{nm nm}^{z z}^{22}]] rdr rdr - - - - - - ((33))$

${ϵ ϵ}_{11} = = {&Integral; &Integral;}_{00}^{22 π π} f f ((θ θ)) cos cos nθdθ nθdθ - - - - - - ((44))$

${ϵ ϵ}_{22} = = {&Integral; &Integral;}_{- - \infty \infty}^{\infty \infty} g g ((z z)) cos cos ξzdz ξzdz - - - - - - ((55))$

R_nm ^r，R_nm ^θ与R_nm ^z分别为本征位移分量的幅度。f(θ)，g(z)分别代表外力沿环向及轴向的分布。R _nm ^r , R _nm ^θ and R _nm ^z are the amplitudes of the intrinsic displacement components respectively. f(θ), g(z) respectively represent the distribution of external force along the ring direction and the axial direction.

若在管道外壁顶端和底端各放置一压电换能器，换能器的环向展开角度为120°，且两换能器沿轴向反相激发，则有If a piezoelectric transducer is placed on the top and bottom of the outer wall of the pipeline, the circumferential expansion angle of the transducer is 120°, and the two transducers are excited in opposite phases along the axial direction, then there is

将式(6)代入式(4)可得Substituting formula (6) into formula (4), we can get

由式(7)可知，轴对称导波模式以及n＝2k，3k(k为正整数)的非轴对称导波模式已经完全被抑制，故管道中被激发导波的模式数显著减少。若进一步控制压电换能器的激发频率，则可以只激发出几个低阶非轴对称导波模式。若换能器轴向激发，则F(1，3)模式的能量在激发出的波形中占主要。It can be seen from formula (7) that the axisymmetric guided wave mode and n=2k, 3k (k is a positive integer) non-axisymmetric guided wave mode have been completely suppressed, so the number of excited guided wave modes in the pipeline is significantly reduced. If the excitation frequency of the piezoelectric transducer is further controlled, only a few low-order non-axisymmetric guided wave modes can be excited. If the transducer is excited axially, the energy of the F(1,3) mode dominates the excited waveform.

将8个周期65kHz的正弦脉冲加海宁窗处理后所得波形作为压电换能器的激发信号，从式(7)和群速度色散曲线图可判断，此时只能激发出F(1，1)，F(1，2)，F(1，3)及F(5，1)这几个模式。为了更好地抑制F(1，1)，F(1，2)及F(5，1)等无用模式，采用两组压电换能器并控制换能器的宽度及两组换能器的间距。从有限元法模拟的结果可发现激发出的波形为相当单纯的F(1，3)模式。The waveform obtained by processing 8 periods of 65kHz sinusoidal pulses with a Haining window is used as the excitation signal of the piezoelectric transducer. It can be judged from the formula (7) and the group velocity dispersion curve that only F(1,1 ), F(1,2), F(1,3) and F(5,1) modes. In order to better suppress unwanted modes such as F(1,1), F(1,2) and F(5,1), two sets of piezoelectric transducers are used and the width of the transducers and the two sets of transducers are controlled Pitch. From the simulation results of the finite element method, it can be found that the excited waveform is a fairly simple F(1,3) mode.

2.F(1，3)模式在管道无损检测中应用2. Application of F(1,3) mode in pipeline non-destructive testing

数值实验中的管道总长17m，外径OD＝88.7mm，壁厚h＝5.5mm，泊松比γ＝0.28，拉密常数μ＝8.4×10¹⁰N/m²，密度ρ＝7.8×10³kg/m³，激发换能器中心距离管道左端8cm，接收换能器中心距离管道左端9m，缺陷距离管道左端15m，换能器宽度皆为5.2cm。换能器激发频率f＝65kHz，管道左端采用对称边界条件，右端采用约束边界条件。The total length of the pipeline in the numerical experiment is 17m, the outer diameter OD=88.7mm, the wall thickness h=5.5mm, Poisson’s ratio γ=0.28, the Lami constant μ=8.4×10 ¹⁰ N/m ² , and the density ρ=7.8×10 ³ kg/m ³ , the center of the exciting transducer is 8cm away from the left end of the pipe, the center of the receiving transducer is 9m away from the left end of the pipe, the defect is 15m away from the left end of the pipe, and the width of both transducers is 5.2cm. The excitation frequency of the transducer is f=65kHz, the left end of the pipeline adopts symmetrical boundary conditions, and the right end adopts constrained boundary conditions.

激发换能器的环向展开角度为120°，共两组，被对称地置于管道外壁顶段及底段，控制换能器沿轴向反相振动，并将激发频率控制在F(1，3)模式色散曲线上色散弱，传播速度快且与其它模式相距较远的区域内，如对于上述几何及材料参数的管道，可选激发频率范围为60-90kHz，在下面的模拟中，选取激发频率f＝65kHz。若管道中存在缺陷，激发出的单纯的F(1，3)模式在传播过程中与其发生相互作用产生发射波，反射波形可利用接收换能器接收到。The circumferential expansion angle of the excitation transducer is 120°, and there are two groups in total, which are symmetrically placed on the top and bottom sections of the outer wall of the pipeline to control the anti-phase vibration of the transducer along the axial direction, and control the excitation frequency at F(1 , 3) On the mode dispersion curve, the dispersion is weak, the propagation speed is fast and the distance from other modes is far away, such as for the pipeline with the above geometric and material parameters, the optional excitation frequency range is 60-90kHz. In the following simulation, Select the excitation frequency f = 65kHz. If there is a defect in the pipeline, the excited pure F(1,3) mode interacts with it during the propagation process to generate a transmitted wave, and the reflected waveform can be received by the receiving transducer.

由模拟得到的F(1，3)模式经不同环向长度缺陷反射后的波形可观察到，随着环向长度的增加，反射F(1，3)模式的波形幅度变大。另外，还可明显观察到缺陷导致的模式转换现象，经环向延伸角度θ₀＝90°的缺陷反射后出现了L(0，2)，F(1，3)及F(2，3)等模式，由于其它转换产生的模式传播速度比较慢，故可不予考虑，当缺陷环向延伸角度θ₀增大到180°，反射波中不出现F(2，3)模式，若缺陷环向延伸角度θ₀继续增大到360°，即缺陷是轴对称的，反射波中不会转换产生轴对称波。由F(1，3)模式经不同深度的轴对称缺陷反射后的波形可发现，随着缺陷深度的增加，反射波形的幅度逐渐变大。It can be observed from the simulated waveforms of the F(1,3) mode reflected by defects of different circumferential lengths that the waveform amplitude of the reflected F(1,3) mode becomes larger as the circumferential length increases. In addition, the mode conversion phenomenon caused by the defect can also be clearly observed, and L(0,2), F(1,3) and F(2,3) appear after the reflection of the defect with a circular extension angle θ ₀ =90° and other modes, because the propagation velocity of the modes generated by other transformations is relatively slow, so they can be ignored. When the defect circumferential extension angle θ ₀ increases to 180°, the F(2, 3) mode does not appear in the reflected wave. If the defect circumferential The extension angle θ ₀ continues to increase to 360°, that is, the defect is axisymmetric, and the reflected wave will not be transformed to generate an axisymmetric wave. From the waveforms of the F(1,3) mode reflected by the axisymmetric defects of different depths, it can be found that with the increase of the defect depth, the amplitude of the reflected waveform gradually increases.

当频率给定时，各模式具有一相应的传播速度，因此通过分析反射波形中各导波模式到达接收点的时间，可对缺陷在轴向的位置作出判断。如由上述的数值实验可知，当缺陷呈轴对称分布时，接收换能器于t≈1.84ms时接收到入射F(1，3)模式的波峰，于t≈4.21ms时接收到反射F(1，3)模式的波峰，时间差Δt≈2.37ms，而中心频率为65kHz时，F(1，3)模式的群速度C_g≈5082m/s，根据l＝C_g*Δt，可得接收换能器距缺陷的距离1/2约为6.02m，与实际模拟距离6.00m非常接近，误差仅为0.3％，实际测量时，可进行多次测量取平均以减小误差。又由上面的数值模拟可知，F(1，3)模式经不同环向长度的缺陷反射后，反射波中各模式的反射系数不一样，因此对反射波中各模式的反射系数进行分析可对缺陷的环向大小作出定征。When the frequency is given, each mode has a corresponding propagation velocity, so by analyzing the time when each guided wave mode in the reflected waveform reaches the receiving point, the position of the defect in the axial direction can be judged. As can be seen from the above numerical experiments, when the defects are axisymmetrically distributed, the receiving transducer receives the peak of the incident F(1,3) mode at t≈1.84ms, and receives the reflected F( 1, 3) mode peak, the time difference Δt≈2.37ms, and when the center frequency is 65kHz, the group velocity C _g ≈5082m/s of the F(1,3) mode, according to l=C _g *Δt, the receiving conversion can be obtained The distance 1/2 between the energy device and the defect is about 6.02m, which is very close to the actual simulation distance of 6.00m, and the error is only 0.3%. In actual measurement, multiple measurements can be averaged to reduce the error. It can also be seen from the above numerical simulation that after the F(1, 3) mode is reflected by defects with different circumferential lengths, the reflection coefficients of each mode in the reflected wave are different, so the analysis of the reflection coefficient of each mode in the reflected wave can be The circumferential size of the defect is characterized.

本发明首次提出了一种利用压电换能器激发出比较单纯的非轴对称导波F(1，3)模式的方法。类似于L(0，2)模式，F(1，3)模式亦在一定的频带内，色散小且传播速度快，故其经缺陷反射后的波形简单，利于分析定征缺陷。但与L(0，2)模式相比，F(1，3)模式对某些管道缺陷，如沿轴向分布的管道缺陷，更加敏感。从有限元法模拟得到的结果可判断，利用非轴对称管道导波模式F(1，3)探测管道缺陷是完全可行的。The present invention firstly proposes a method of using a piezoelectric transducer to excite a relatively simple non-axisymmetric guided wave F(1,3) mode. Similar to the L(0,2) mode, the F(1,3) mode is also within a certain frequency band, with small dispersion and fast propagation speed, so its waveform reflected by the defect is simple, which is beneficial for analyzing and characterizing defects. However, compared with the L(0,2) mode, the F(1,3) mode is more sensitive to some pipeline defects, such as those distributed along the axial direction. From the results of the finite element method simulation, it can be judged that it is completely feasible to use the non-axisymmetric pipeline guided wave mode F(1,3) to detect pipeline defects.

四、附图说明4. Description of drawings

图1并排放置的管道示意图Figure 1 Schematic diagram of pipes placed side by side

图2(a)L(0，2)模式与沿轴向分布的缺陷相互作用示意图；(b)F(1，3)模式与沿轴向分布的缺陷相互作用示意图Figure 2 (a) Schematic diagram of the interaction between the L(0,2) mode and the axially distributed defects; (b) the schematic diagram of the interaction between the F(1,3) mode and the axially distributed defects

图3管道导波传播的群速度色散曲线，OD＝88.7mm，h＝5.5mm，γ＝0.28，μ＝8.4×10¹⁰N/m²，ρ＝7.8×10³kg/m³ Figure 3 Group Velocity Dispersion Curve of Pipe Guided Wave Propagation, OD=88.7mm, h=5.5mm, γ=0.28, μ=8.4×10 ¹⁰ N/m ² , ρ=7.8×10 ³ kg/m ³

图4(a)压电换能器放置示意图；(b)压电换能器振动示意图Figure 4(a) Schematic diagram of piezoelectric transducer placement; (b) Schematic diagram of piezoelectric transducer vibration

图5(a)压电换能器径向振动时，F(1，1)，F(1，2)和F(1，3)模式的瞬态径向位移幅度与频率的关系；(b)压电换能器轴向振动时，F(1，1)，F(1，2)和F(1，3)模式的瞬态轴向位移幅度与频率的关系Figure 5(a) The relationship between the transient radial displacement amplitude and frequency of the F(1,1), F(1,2) and F(1,3) modes when the piezoelectric transducer vibrates radially; (b ) when the piezoelectric transducer vibrates axially, the relationship between the transient axial displacement amplitude and frequency of F(1,1), F(1,2) and F(1,3) modes

图6为8个周期65kHz的正弦脉冲加海宁窗处理后所得波形Figure 6 is the waveform obtained after 8 periods of 65kHz sinusoidal pulse plus Haining window processing

图7两组宽度为5.2cm，中心间距为16cm的换能器激发出的波形，z＝9m，θ＝0°Fig.7 Waveforms excited by two sets of transducers with a width of 5.2cm and a distance between centers of 16cm, z=9m, θ=0°

图8F(1，3)模式激发及回波接收模型Figure 8F(1,3) mode excitation and echo reception model

图9缺陷横截面示意图。Figure 9. Schematic diagram of defect cross-section.

图10F(1，3)模式经不同环向长度缺陷反射后的波形，缺陷深度与壁厚比为50％：(a)缺陷环向长度与管周长比为25％；(b)缺陷环向长度与管周长比为50％；(c)缺陷环向长度与管周长比为100％Figure 10F (1, 3) mode after reflection by defects of different circumferential lengths, the ratio of defect depth to wall thickness is 50%: (a) the ratio of defect circumferential length to pipe circumference is 25%; (b) defect ring The ratio of the circumferential length to the pipe circumference is 50%; (c) the ratio of the circumferential length of the defect to the pipe circumference is 100%

图11F(1，3)模式经轴对称缺陷反射后的波形：(a)缺陷深度与壁厚比为36％；(b)缺陷深度与壁厚比为64％Figure 11F(1, 3) mode reflected by the axisymmetric defect: (a) the ratio of defect depth to wall thickness is 36%; (b) the ratio of defect depth to wall thickness is 64%

具体实施方式：Detailed ways:

采用两组环向展开角度为120°的压电换能器，将其对称地置于管道外壁顶段及底段，控制换能器沿轴向反相振动，并将激发频率控制在F(1，3)模式的群速度色散曲线上色散弱，传播速度快且与其它模式相距较远的区域内，如对于几何及材料参数分别为OD＝88.7mm，h＝5.5mm，γ＝0.28，μ＝8.4×10¹⁰N/m²，ρ＝7.8×10³kg/m³的管道，可选激发频率范围为60-90kHz。若管道中存在缺陷，激发出的单纯的F(1，3)模式在传播过程中与其发生相互作用产生发射波，反射波可利用接收换能器接收到。Two sets of piezoelectric transducers with a circumferential expansion angle of 120° are used, which are symmetrically placed on the top and bottom sections of the outer wall of the pipeline, and the transducers are controlled to vibrate in anti-phase along the axial direction, and the excitation frequency is controlled at F( 1, 3) On the group velocity dispersion curve of the mode, the dispersion is weak, the propagation speed is fast and the area is far away from other modes, such as the geometric and material parameters are OD=88.7mm, h=5.5mm, γ=0.28, For pipes with μ=8.4×10 ¹⁰ N/m ² and ρ=7.8×10 ³ kg/m ³ , the optional excitation frequency range is 60-90kHz. If there is a defect in the pipeline, the excited pure F(1,3) mode interacts with it during the propagation process to generate a transmitted wave, and the reflected wave can be received by the receiving transducer.

当频率给定时，各模式具有一相应的传播速度，因此通过分析反射波形中各导波模式到达接收点的时间，可对缺陷在轴向的位置作出判断。又F(1，3)模式经不同深度及环向长度的缺陷反射后，反射波中各模式的反射系数不一样，因此对反射波中各模式的反射系数进行分析可对缺陷的深度及环向长度作出定征。When the frequency is given, each mode has a corresponding propagation velocity, so by analyzing the time when each guided wave mode in the reflected waveform reaches the receiving point, the position of the defect in the axial direction can be judged. After the F(1,3) mode is reflected by defects with different depths and circumferential lengths, the reflection coefficients of each mode in the reflected wave are different. Determine the length.

Claims

1, a kind of pipeline nondestructive means of single non-rotational symmetry pipeline guided wave mode: utilize piezoelectric transducer to excite simple non-rotational symmetry guided wave F (1,3) pattern, and the method is used for the pipeline nondestructive examination; It is characterized in that respectively placing a piezoelectric transducer symmetrically on pipeline outer wall top and bottom, the hoop start point of transducer is 120 degree, and two transducers are anti-phase vertically to be excited, and simultaneously stimulating frequency is controlled on the GVD (Group Velocity Dispersion) curve a little less than the chromatic dispersion and in the fast scope of velocity of propagation, utilizes the simple F (1 that inspires, 3) the non-rotational symmetry guided wave of pattern carries out the pipeline nondestructive examination, for pipeline length overall 17m, external diameter OD=88.7mm, h=5.5mm, γ=0.28, μ=8.4 * 10 ¹⁰N/m ², ρ=7.8 * 10 ³Kg/m ³Pipeline, excite transducer centre distance pipeline left end 8cm, receiving transducer centre distance pipeline left end 9m, the transducer width is all 5.2cm; If have defective in the pipeline, simple F (1, the 3) pattern that inspires produces transmitted wave with its generation interaction in communication process, and reflection configuration can utilize receiving transducer to receive; Along with the increase of hoop length, the wave-shape amplitude of reflection F (1,3) pattern becomes big; By F (1,3) the non-rotational symmetry guided wave of pattern will interact with defective in communication process and produce reflection wave, and meeting emergence pattern conversion phenomena, utilize piezoelectric transducer can receive reflection configuration, analyze the time of each pattern arrival acceptance point in the reflection configuration and the reflection coefficient of each pattern, then the position and the size of defective are made sign.