CN105301117B - A kind of method that hollow cylinder circumferential defect is detected with ultrasonic frequency dispersion compensation principle - Google Patents

Abstract

The invention discloses a method for detecting circumferential defects of a hollow cylinder by using the principle of ultrasonic dispersion compensation. The steps are: 1) Excite the ultrasonic guided wave in the hollow cylinder, and use the guided wave receiver to measure the reference signal s _ref (θ,t) and the circumferential defect echo signal s _obj (θ,t); 2 ) Calculate the position of the circumferential defect according to the time difference between the two signals and the sound velocity; 3) Perform two-dimensional Fourier transform on s _ref (θ,t) and s _obj (θ,t), apply phase shift, and perform n-θ transformation on The one-dimensional inverse Fourier transform of gets the distribution on the (θ,ω) domain with 4) to for reference Perform Wiener filtering; 5) Calculate the distribution A(θ) of the amplitude of s _dec (θ,t) along the circumferential rotation angle θ of the hollow cylinder and the full width at half maximum of A(θ), which is the circumference of the hollow cylinder defect to size. The invention realizes the measurement of the position and size of the circumferential defect of the hollow cylinder, and has high precision.

Description

A Method of Detecting Circumferential Defects of Hollow Cylinder Using the Principle of Ultrasonic Dispersion Compensation

technical field

The invention relates to the non-destructive detection of the circumferential defect of the hollow cylinder, in particular to a method for detecting the position and size of the circumferential defect of the hollow cylinder by using a guided wave dispersion compensation algorithm.

Background technique

Nowadays, pipelines are used more and more in the transportation industry, and pipeline accidents also increase accordingly, which has brought huge losses to the national economy and threatened people's lives. Therefore, it is particularly important to carry out economical, applicable, simple and effective non-destructive testing on pipelines. The technology of non-destructive detection of pipeline defects using ultrasonic guided wave technology has also attracted more and more attention.

In the existing research, Gazis et al. gave the calculation expression of hollow cylinder dynamic analysis under the assumption of linear isotropic elasticity. Their work made it possible to calculate the dispersion curve of the pipeline with given geometric and mechanical parameters. . Alleyne and Cawley et al. excited and received axisymmetric longitudinal guided waves in a pipe with circumferential grooves, and they studied the echo coefficients of grooves with different depths and lengths. Lowe and Cawley et al. developed the finite element method to simulate the low-order echo reflected from the groove, and compared the simulation results with the experimental results, and achieved a relatively good agreement. The groove depth and length are related to the guided wave echo coefficient, which provides guidance for flaw characterization. However, for most cases, the signal-to-noise ratio of the echo signal from the defect is relatively low. Therefore, guided-wave focusing techniques were developed to enhance the ability to identify defects.

Guided wave focusing can be achieved in two ways. First, phased-array excitation technology can emit focused energy to a defined area in a given direction and distance. John and Joseph proposed the NME (NME, Normal mode expansion) technique to determine the amplitude of guided waves of any mode generated by a specified surface load. By arranging a phased array on the circumference of the pipeline, using appropriate voltage and phase delay, the angular distribution of the excited vibration energy can be focused at a specified circumferential position. Takahiro Hayashi calculated the angle Pu of an element using the semi-analytical finite element method (SAFE). Using phased array excitation technology and appropriate excitation voltage and phase delay can generate a focused sound field, which greatly improves the signal-to-noise ratio. Phased array ultrasonic technology has important applications in the field of pipeline non-destructive testing, but the cost is also very expensive.

In addition to phased array technology, guided wave signals can also be focused by dispersion subtraction. Takahiro Hayashi et al. used a magnetostrictive transmitter to generate T(0,1) mode vibration, and then used 8 uniformly distributed sensors in the pipeline circumferential direction to receive vibration signals. The vibration components of different orders in the circumferential direction are separated by a mode extraction technique, and the dispersion subtraction technique is used to realize the reconstruction of the defect image. Higher ultrasonic frequencies allow for higher resolution both circumferentially and axially in the pipe. Jacob Davies and Peter Cawley used an analog technique called synthetic focusing to image defects in pipes. In the work of Cawley et al., images of circumferential crack-like defects of different depths and lengths were obtained, and at the same time, it was demonstrated that the focusing system can be capable of detecting circumferential defects with a size greater than _1.5λS . But this requires completely symmetrical excitation of the T(0,1) mode on the pipe, which is difficult to achieve in practice. In addition, improving the resolution of detecting defects often requires a higher center frequency, which, however, results in a loss of effective detection range.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for detecting circumferential defects of a hollow cylinder using the principle of ultrasonic dispersion compensation. The specific plan is as follows:

A method for detecting circumferential defects of a hollow cylinder using the principle of ultrasonic dispersion compensation, the steps are as follows:

1) A magnetostrictive material is pasted around the outer circumference of one end of the target hollow cylinder with a circumferential defect, and an excitation coil is wrapped around the magnetostrictive material, and then a magnetostrictive material is pasted around the circumferential defect and the excitation coil. Materials; connect the excitation coil to the magnetic field excitation controller, and connect the receiving coil to the oscilloscope through the guided wave signal receiver;

2) Control the magnetic field. The excitation controller sends a voltage pulse signal to the excitation coil. An alternating magnetic field is generated on the surface of the magnetostrictive material under the excitation coil, and then the ultrasonic guided wave signal is excited in the hollow cylinder. The receiving coils respectively receive the first The reference signal s _ref (θ, t) transmitted from the exciting coil and the echo signal s _obj (θ, t) reflected from the circumferential defect, where θ is the angle variable along the circumference of the hollow cylinder, and t is time variable;

3) According to the arrival time difference Δt of the reference signal s _ref (θ, t) and the echo signal s _obj (θ, t) at the receiving coil, and the propagation velocity c of the guided wave mode T(0,1) in the hollow cylinder Calculate the axial distance z _x of the circumferential defect relative to the excitation coil, the calculation formula is:

In the formula, z ₀ is the distance between the receiving coil and the exciting coil;

4) Carry out two-dimensional Fourier transform on the reference signal s _ref (θ, t) and the echo signal s _obj (θ, t) respectively, and obtain the reference signal s _ref (θ, t) in the (n, ω) domain The distribution s _ref (n, ω), and the distribution s _obj (n, ω) of the echo signal s _obj (θ, t) in the (n, ω) domain, where n is the circumferential order of the guided wave mode in the hollow cylinder number, ω is the angular frequency;

5) Add a phase shift to the distribution s _ref (n, ω) Add a phase shift to the distribution s _obj (n, ω) And do the inverse Fourier transform of the n-θ transform pair on the phase-shifted result, and get the distribution of s _ref (n, ω) in the (θ, ω) domain and the distribution of s _obj (n, ω) in the (θ, ω) domain in k _n (ω) is the wave number of the nth order mode at a certain frequency ω;

6) to as a reference signal, the Perform Wiener filtering to get Filtered distribution

In the formula for Conjugate of , Q ² (θ) is the noise reduction factor, and for different variables ω Sum;

7) yes Perform the inverse Fourier transform on the ω-t transform pair to get The distribution s _dec (θ, t) in the domain (θ, t);

8) Calculate the distribution A(θ) of the magnitude of s _dec (θ, t) along the circumferential rotation angle θ of the hollow cylinder:

A(θ)＝max|s _dec (θ,t)|

In the formula, max|s _dec (θ, t)| is the maximum value of |s _dec (θ, t)| about the variable θ

9) Calculate the full width at half maximum of A(θ), which is the circumferential dimension of the hollow cylinder defect.

In the described step 4), the calculation formulas of s _ref (n, ω) and s _obj (n, ω) are:

s _ref (n, ω) = FFT ² [s _ref (θ, t)]

s _obj (n, ω) = FFT ² [s _obj (θ, t)]

Where FFT ² [] is a two-dimensional Fourier transform.

In the described step 5), with The calculation formula is:

where IFFT ^nθ [] is the inverse Fourier transform of the n-θ transform pair.

In the step 7) described where IFFT ^ωt [] is the inverse Fourier transform of the ω-t transform pair.

The magnetostrictive material is any one of nickel-cobalt-chromium alloy, iron-aluminum alloy, and iron-cobalt-vanadium alloy.

Compared with the prior art, the present invention has the beneficial effects of: overcoming the deficiency of existing pipeline or other hollow cylinder defect detection technology, and using signal For reference, the use of Wiener filtering to eliminate the influence of unavoidable asymmetric excitation greatly improves the accuracy of measurement results, which is of positive significance for the detection of the position and circumferential size of circumferential defects in pipes or other hollow cylinders.

Description of drawings

Fig. 1 is a schematic diagram of a hollow cylinder circumferential defect detection system detected by a guided wave dispersion compensation algorithm;

Fig. 2 is a schematic cross-sectional view of a hollow cylinder where the excitation coil of the detection system is located;

Fig. 3 is a schematic cross-sectional view of a hollow cylinder where the receiving coil of the detection system is located;

Fig. 4 is a normalized amplitude diagram of time-domain signals received at different circumferential positions of the hollow cylinder before and after dispersion compensation.

In the figure, excitation coil controller 1, guided wave signal receiver 2, oscilloscope 3, hollow cylinder 4, excitation coil 5, receiving coil 6, circumferential defect 7 and magnetostrictive material 8.

detailed description

The present invention will be further elaborated below in conjunction with the accompanying drawings and specific embodiments.

A method for detecting circumferential defects of a hollow cylinder using the principle of ultrasonic dispersion compensation, the steps are as follows:

1) A magnetostrictive material 8 is pasted around the periphery of one end of the target hollow cylinder 4 with circumferential defects, and the magnetostrictive material 8 can be any one of nickel-cobalt-chromium alloy, iron-aluminum alloy or iron-cobalt-vanadium alloy . Surround the excitation coil 5 outside the magnetostrictive material 8, then surround and paste the magnetostrictive material 8 between the circumferential defect 7 and the excitation coil 5; the excitation coil 5 is connected with the magnetic field excitation controller 1, and the receiving coil 6 is passed through The guided wave signal receiver 2 is connected to the oscilloscope 3 (as shown in Figures 1-3);

2) Turn on the magnetic field excitation controller 1, the guided wave signal receiver 2 and the oscilloscope 3. Control the magnetic field excitation controller 1 to transmit a voltage pulse signal to the excitation coil 5, an alternating magnetic field is generated on the surface of the magnetostrictive material 8 below the excitation coil 5, and then an ultrasonic guided wave signal is excited in the hollow cylinder 4, and the receiving coil 6 respectively The reference signal s _ref (θ, t) transmitted from the exciting coil 5 for the first time and the echo signal s _obj (θ, t) reflected from the circumferential defect 7 are successively received, where θ is the The angle variable of , t is the time variable;

3) According to the time difference Δt of the reference signal s _ref (θ, t) and the echo signal s _obj (θ, t) reaching the receiving coil 6, and the propagation speed of the guided wave mode T(0,1) in the hollow cylinder c Calculate the axial distance z _x of the circumferential defect 7 relative to the excitation coil 5, the calculation formula is:

In the formula, _z0 is the distance between the receiving coil 6 and the exciting coil 5;

4) Carry out two-dimensional Fourier transform on the reference signal s _ref (θ, t) and the echo signal s _obj (θ, t) respectively, and obtain the reference signal s _ref (θ, t) in the (n, ω) domain The distribution s _ref (n, ω), and the distribution s _obj (n, ω) of the echo signal s _obj (θ, t) in the (n, ω) domain, the calculation formula is:

s _ref (n, ω) = FFT ² [s _ref (θ, t)]

s _obj (n, ω) = FFT ² [s _obj (θ, t)]

In the formula, FFT ² [] is a two-dimensional Fourier transform, where n is the circumferential order of the guided wave mode in the hollow cylinder, and ω is the angular frequency;

5) Add a phase shift to the distribution s _ref (n, ω) Add a phase shift to the distribution s _obj (n, ω) And do the inverse Fourier transform of the n-θ transform pair on the phase-shifted result, and get the distribution of s _ref (n, ω) in the (θ, ω) domain and the distribution of s _obj (n, ω) in the (θ, ω) domain in with The calculation formula is:

where IFFT ^nθ [] is the inverse Fourier transform of the n-θ transform pair, k _n (ω) is the wave number of the nth order mode at a certain frequency ω;

6) to as a reference signal, the Perform Wiener filtering to get Filtered distribution

In the formula for Conjugate of , Q ² (θ) is the noise reduction factor, and for different variables ω Sum;

7) yes Perform the inverse Fourier transform on the ω-t transform pair to get The distribution s _dec (θ, t) in the domain (θ, t), where

where IFFT ^ωt [] is the inverse Fourier transform of the ω-t transform pair.

8) Calculate the distribution A(θ) of the magnitude of s _dec (θ, t) along the circumferential rotation angle θ of the hollow cylinder:

A(θ)＝max|s _dec (θ,t)|

In the formula, max|s _dec (θ, t)| is the maximum value of |s _dec (θ, t)| about the variable θ

9) Calculate the full width at half maximum (FWHM, Full width at half maximum) of A(θ), which is the circumferential dimension of the hollow cylinder defect.

Example

A certain 304 stainless steel pipe is detected by the above method. The length of the pipe is 1500mm, the outer diameter is 101mm, and the wall thickness is 1mm. A magnetostrictive material 8 with a thickness of 0.1mm and a width of 10mm is pasted on one end of the pipe. The magnetostrictive material 8 is iron cobalt-vanadium alloy, and the excitation coil 5 is surrounded by the magnetostrictive material 8. Then between the circumferential defect 7 and the excitation coil 5, the magnetostrictive material 8 is also affixed at the place where the distance from the excitation coil 5 is 322 mm; then the magnetic field excitation controller 1 is controlled to transmit a voltage pulse signal to the excitation coil 5, and the receiving coil 6 The reference signal s _ref (θ, t) transmitted from the excitation coil 5 for the first time and the echo signal s _obj (θ, t) reflected from the circumferential defect 7 are respectively successively received, along the circumference of the pipeline, every 11° 15' collects data once, and collects 32 sets of data in total. The data processing process is as described above, and finally A(θ) is the normalized amplitude of the rotation angle θ along the circumference of the hollow cylinder (as shown in Figure 4).

The final measurement results and their relative errors are shown in the table below:

It can be seen from the table that the relative error of the present invention for the detection of the position and the circumferential dimension of the circumferential defect of the pipeline is within 1%, and has very high precision. The invention greatly improves the detection of the position and the circumferential dimension of the circumferential defect of the hollow cylinder.

Claims (5)

1. A method for detecting hollow cylinder circumferential defects with the principle of ultrasonic dispersion compensation, characterized in that the steps of the method are as follows: 1) Paste the magnetostrictive material (8) around the periphery of one end of the target hollow cylinder with the circumferential defect, and surround the excitation coil (5) outside the magnetostrictive material (8), and then place the magnetostrictive material (8) on the circumferential defect ( 7) Surround and paste the magnetostrictive material (8) between the excitation coil (5); connect the excitation coil (5) to the magnetic field excitation controller (1), and pass the receiving coil (6) through the waveguide signal receiver (2 ) is connected with the oscilloscope (3); 2) Controlling the magnetic field excitation controller (1) transmits a voltage pulse signal to the excitation coil (5), an alternating magnetic field is generated on the surface of the magnetostrictive material (8) below the excitation coil (5), and then the hollow cylinder (4) The ultrasonic guided wave signal is excited in the center, and the receiving coil (6) respectively receives the reference signal s _ref (θ,t) transmitted from the exciting coil (5) for the first time and the echo signal reflected from the circumferential defect (7) s _obj (θ,t), where θ is the angular variable along the circumference of the hollow cylinder, and t is the time variable; 3) According to the time difference Δt of the reference signal s _ref (θ,t) and the echo signal s _obj (θ,t) reaching the receiving coil (6), and the guided wave mode T(0,1) in the hollow cylinder The propagation speed c calculates the axial distance z _x of the circumferential defect (7) relative to the excitation coil (5), and the calculation formula is: <mrow><msub><mi>z</mi><mi>x</mi></msub><mo>=</mo><mi>c</mi><mo>&amp;CenterDot;</mo><mfrac><mrow><mi>&amp;Delta;</mi><mi>t</mi></mrow><mn>2</mn></mfrac><mo>+</mo><msub><mi>z</mi><mn>0</mn></msub></mrow> In the formula, _z0 is the distance between the receiving coil (6) and the exciting coil (5); 4) Perform two-dimensional Fourier transform on the reference signal s _ref (θ,t) and the echo signal s _obj (θ,t) respectively, and obtain the reference signal s _ref (θ,t) in the (n,ω) domain The distribution s _ref (n,ω), and the distribution s _obj (n,ω) of the echo signal s _obj (θ,t) in the (n,ω) domain, where n is the circumferential order of the guided wave mode in the hollow cylinder number, ω is the angular frequency; 5) Add a phase shift to the distribution s _ref (n,ω) Add a phase shift to the distribution s _obj (n,ω) And do the inverse Fourier transform of the n-θ transform pair on the phase-shifted result, and get the distribution of s _ref (n, ω) in the (θ, ω) domain and the distribution of s _obj (n, ω) in (θ, ω) domain in k _n (ω) is the wave number of the nth order mode at a certain frequency ω; 6) to as a reference signal, the Perform Wiener filtering to get Filtered distribution <mrow><msub><mover><mi>s</mi><mo>&amp;OverBar;</mo></mover><mrow><mi>d</mi><mi>e</mi><mi>c</mi></mrow></msub><mrow><mo>(</mo><mi>&amp;theta;</mi><mo>,</mo><mi>&amp;omega;</mi><mo>)</mo></mrow><mo>=</mo><mfrac><mrow><msubsup><mover><mi>s</mi><mo>&amp;OverBar;</mo></mover><mrow><mi>o</mi><mi>b</mi><mi>j</mi></mrow><mi>exp</mi></msubsup><mrow><mo>(</mo><mi>&amp;theta;</mi><mo>,</mo><mi>&amp;omega;</mi><mo>)</mo></mrow><mo>&amp;CenterDot;</mo><msubsup><mover><mi>s</mi><mo>&amp;OverBar;</mo></mover><mrow><mi>r</mi><mi>e</mi><mi>f</mi></mrow><mrow><mi>exp</mi><mo>*</mo></mrow></msubsup><mrow><mo>(</mo><mi>&amp;theta;</mi><mo>,</mo><mi>&amp;omega;</mi><mo>)</mo></mrow></mrow><mrow><msup><mrow><mo>|</mo><msubsup><mover><mi>s</mi><mo>&amp;OverBar;</mo></mover><mrow><mi>r</mi><mi>e</mi><mi>f</mi></mrow><mi>exp</mi></msubsup><mrow><mo>(</mo><mi>&amp;theta;</mi><mo>,</mo><mi>&amp;omega;</mi><mo>)</mo></mrow><mo>|</mo></mrow><mn>2</mn></msup><mo>+</mo><msup><mi>Q</mi><mn>2</mn></msup><mrow><mo>(</mo><mi>&amp;theta;</mi><mo>)</mo></mrow></mrow></mfrac></mrow> In the formula for Conjugate of , Q ² (θ) is the noise reduction factor, and for different variables ω Sum; 7) yes Perform the inverse Fourier transform on the ω-t transform pair to get The distribution s _dec (θ,t) in the (θ,t) domain; 8) Calculate the distribution A(θ) of the magnitude of s _dec (θ,t) along the circumferential rotation angle θ of the hollow cylinder: A(θ)＝max|s _dec (θ,t)| In the formula, max|s _dec (θ,t)| is the maximum value of |s _dec (θ,t)| about the variable θ; 9) Calculate the full width at half maximum of A(θ), which is the circumferential dimension of the hollow cylinder defect. 2. The method according to claim 1, characterized in that: in the described step 4), the calculation formulas of s _ref (n, ω) and s _obj (n, ω) are: s _ref (n,ω)=FFT ² [s _ref (θ,t)] s _obj (n,ω)=FFT ² [s _obj (θ,t)] Where FFT ² [] is a two-dimensional Fourier transform. 3. method as claimed in claim 1, is characterized in that: in described step 5) with The calculation formula is: where IFFT ^nθ [] is the inverse Fourier transform of the n-θ transform pair. 4. The method according to claim 1, characterized in that: s _dec (θ, t)= in the described step 7) where IFFT ^ωt [] is the inverse Fourier transform of the ω-t transform pair. 5. The method according to claim 1, characterized in that: the magnetostrictive material (8) is any one of nickel-cobalt-chromium alloy, iron-aluminum alloy, and iron-cobalt-vanadium alloy.