Method and device for detecting circumferential weld micro-defects of high attenuation material pipe

Abstract

The application discloses a kind of high attenuation material pipeline circumferential weld microdefect detection method and device, adopt PVDF comb flexible piezoelectric sensor, to meet the universality of the geometric shape of pipeline circumferential weld.Its detection method includes: through the geometric shape and material attribute of the pipeline circumferential weld to be detected, based on semi-analytical finite element method, the dispersion curve is calculated;Based on the nonlinear static component theory, the ultrasonic mode pair of group velocity mismatch is selected.Processing and FFT filtering processing are carried out to the ultrasonic detection receiving signal based on wavelet change noise reduction, and the stress concentration phenomenon, microdamage degree and position in the high attenuation material pipeline circumferential weld are judged based on FFT filtering processing result.The application adopts the above scheme, realizes the nondestructive testing of stress concentration phenomenon and microdamage of high attenuation material pipeline circumferential weld, solves the problem that existing circumferential weld microdamage nondestructive testing method cannot meet the efficient detection of the sample to be detected and the high-precision microdefect positioning requirement.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing technology and relates to a technique for non-destructive defect detection of test samples using ultrasonic waves. Specifically, it is a method and device for detecting micro-defects in the circumferential welds of high-attenuation material pipes. Background Technology

[0002] Pipeline transportation is widely used in various industries. Compared to other modes of transportation, pipeline transportation has advantages such as high efficiency, low consumption, safety, and stability. High-attenuation materials, such as polyethylene, polybutene, and ABS, have excellent thermoplasticity, flexibility, corrosion resistance, and low cost. Therefore, high-attenuation material pipelines are gradually replacing metal pipelines and becoming the preferred choice for medium and low-pressure pipelines such as urban gas pipelines and sewage pipelines. The main connection method for high-attenuation material pipelines is butt welding. The main process of butt welding is as follows: first, the two ends of the pipe are heated by a heating plate; then, a certain pressure is applied to press the ends of the pipes together; finally, pressure is maintained and cooled to form a circumferential weld that meets the requirements. Butt welding is a complex thermo-coupling process. Because the thermal expansion and contraction of high-attenuation materials is more pronounced than that of metal materials, excessive thermal stress is easily generated during butt welding, leading to stress concentration and micro-defects such as micro-cracks. Stress concentration and micro-defects can easily develop into macro-defects during pipeline service and seriously affect the safety of pipeline operation. Furthermore, during the service life of pipelines made of high-attenuation materials, these materials undergo aging under the influence of factors such as temperature, stress, microorganisms, and chemical degradation. Aging leads to embrittlement, discoloration, and microcrack formation in the high-attenuation materials, which also contributes to affecting the safety of pipeline operation. Currently, commonly used non-destructive testing methods are insufficient to detect stress concentration and micro-defects such as microcracks within the tested samples. Therefore, non-destructive testing of micro-defects in the circumferential welds of high-attenuation material pipelines is essential.

[0003] Currently, the commonly used non-destructive testing methods for circumferential welds of pipes made of high-attenuation materials include the following:

[0004] X-ray inspection: X-ray inspection technology utilizes the principle that the intensity of X-rays gradually weakens as they penetrate the object being inspected due to attenuation. If a defect exists at a pipe joint, the intensity of the X-rays attenuates differently after passing through the defect location, resulting in varying density on the film. Based on the position, shape, size, and density of the image on the film, the presence, nature, type, and quantity of defects can be determined. However, X-ray inspection technology is limited by equipment and is not suitable for on-site inspection. X-rays are harmful to the human body, requiring certain protective measures. Furthermore, X-ray inspection cannot effectively detect micro-defects such as stress concentrations and microcracks in circumferential welds.

[0005] Infrared thermal imaging detection technology utilizes the principle that an object's surface radiates heat in the infrared spectrum. If a defect exists in the circumferential weld, the thermal radiation energy at different locations along the circumferential weld will vary, resulting in different colors on the thermal image. Infrared thermal imaging detection technology features non-contact detection, large detection area, high speed, and long distance. However, it can only detect larger defects within fused weld joints and is difficult to detect defects parallel to the surface of the inspected pipe.

[0006] Conventional ultrasonic testing methods and ultrasonic phased array testing methods: Ultrasonic defect detection is based on the interaction between ultrasonic waves and defects, including reflection, penetration, and diffraction, as well as the attenuation of ultrasonic energy. Ultrasonic testing technology is well-suited for pipes made of high-attenuation materials and is the earliest developed and most widely used non-destructive testing technique. However, conventional ultrasonic testing methods have low detection efficiency, and the acoustic attenuation of high-attenuation materials is much greater than that of metals. Ultrasonic waves at higher frequencies have extremely limited propagation distances, while those at lower frequencies, due to their longer wavelengths, cannot effectively detect defects within fused weld joints. Ultrasonic phased array testing, on the other hand, consists of multiple piezoelectric crystals arranged in a specific pattern. Each crystal is excited sequentially with a predetermined delay time, and the ultrasonic waves emitted by all the crystals form a unified wavefront, thus enabling beam scanning, deflection, and focusing of the ultrasonic waves. Compared to conventional ultrasonic testing methods, ultrasonic phased array testing offers advantages such as a larger detection range, higher signal-to-noise ratio, and narrower beam. However, the scanning range of ultrasonic phased array testing is still limited each time, making it unable to detect some inaccessible areas, and it is also insensitive to stress concentrations and micro-defects within the material. Therefore, existing non-destructive testing (NDT) methods cannot meet the demand for high-precision and high-efficiency detection of micro-damage in high-attenuation material pipelines, especially for minute defects such as internal stress concentrations and internal microcracks in welds. Conventional ultrasonic testing relies on scattered or reflected waves from defects for detection, and the minimum size of the defect it can detect is related to the wavelength of the ultrasonic wave used, typically half the wavelength. For micro-defects like microcracks, the defect size is too small to produce significant scattered waves or defect echoes. Defects such as internal stress concentrations mainly involve changes in the internal microstructure of the material, and these defects also do not produce scattered waves or defect echoes. Conventional ultrasonic testing is not sensitive to changes in the internal microstructure of materials; localized changes in the microstructure are unlikely to cause significant changes in ultrasonic wave velocity and attenuation. Therefore, conventional ultrasonic testing cannot detect these micro-defects. Summary of the Invention

[0007] A brief overview of embodiments of the invention is provided below to provide a basic understanding of certain aspects of the invention. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0008] According to one aspect of this application, a method for detecting micro-defects in circumferential welds of pipes made of high-attenuation materials is provided, comprising the following steps:

[0009] Step 1: Select the inspection location on the surface of the circumferential weld of the pipeline to be inspected; based on the ultrasonic nonlinear static component theory, select an ultrasonic guided wave mode pair that does not satisfy the group velocity matching condition. The fundamental frequency of this ultrasonic guided wave mode pair is... The frequency of the quasi-static component is ;

[0010] Step 2: Excite the selected ultrasonic fundamental frequency signal to the circumferential weld of the pipe being inspected. The fundamental frequency of this ultrasonic fundamental frequency signal is... The received ultrasonic characteristic guided wave detection signal is locally truncated, and the truncated result is subjected to wavelet packet denoising and FFT filtering.

[0011] Step 3: Based on the FFT filtering results obtained in Step 2, determine whether there are micro-defects in the detection path; if there are micro-defects, accurately locate the micro-defects based on the time of abrupt change in the time domain signal after FFT filtering and the group velocity of the quasi-static component of the ultrasonic characteristic guided wave propagation.

[0012] Furthermore, step 1 specifically includes: calculating the dispersion curve of the circumferential ultrasonic guided wave of the circumferential weld using a semi-analytical finite element method based on the geometry and material properties of the circumferential weld of the pipeline being inspected; selecting ultrasonic guided wave mode pairs that do not satisfy the group velocity matching condition based on the dispersion curve, and the quasi-static component frequency... The following conditions must be met: ( ), where d is the wall thickness of the pipe containing the high-attenuation material being tested.

[0013] Furthermore, in step 1, selecting ultrasonic guided wave mode pairs that do not meet the group velocity matching condition specifically includes: the fundamental frequency being... The group velocity is Quasi-static component frequency The group velocity is The group velocity matching condition is not satisfied if the following conditions are met: .

[0014] Furthermore, in step 2, the ultrasonic fundamental frequency signal selected for excitation of the circumferential weld of the inspected pipe has a fundamental frequency of [missing information]. Specifically, this includes: selecting a PVDF comb-shaped flexible piezoelectric sensor with a matching geometry based on the geometry of the circumferential weld of the inspected pipe; the PVDF comb-shaped flexible piezoelectric sensor includes comb-shaped electrodes, and the dimensions of the comb-shaped electrodes are designed based on the wavelength of the fundamental frequency: finger width a, finger spacing width b, finger length L, and number of fingers N; the dimensions a and b of the comb-shaped electrodes satisfy: , The wavelength (mm) of the fundamental frequency is given; the fundamental frequency is excited to the circumferential weld of the inspected pipe by a PVDF comb-shaped flexible piezoelectric sensor. The ultrasonic fundamental frequency signal has a period number of c, and the period number c of the ultrasonic fundamental frequency excitation signal satisfies: .

[0015] Furthermore, in step 2, the received ultrasonic characteristic guided wave detection signal is locally truncated, and the truncated result is subjected to wavelet packet denoising and FFT filtering. Specifically, this includes receiving the ultrasonic guided wave detection time-domain signal through a PVDF comb-shaped flexible piezoelectric sensor. The obtained time-domain signal is further truncated, and the truncated time window is [ - , + ], To receive time domain signals The time at which the absolute value of the amplitude reaches its maximum. The total duration of the fundamental frequency excitation signal is used to obtain the time-domain signal. ; By analyzing the time-domain signal Wavelet packet denoising is performed to obtain the denoised time-domain signal. .

[0016] Furthermore, the wavelet packet denoising process includes the following steps: 1. Selecting a wavelet function and determining the decomposition level to perform wavelet packet decomposition on the time-domain signal; 2. Selecting a suitable threshold and threshold function to perform global processing on the wavelet packet coefficients; 3. Superimposing the processed wavelet packet coefficients to reconstruct the signal using wavelet packets; wherein, the wavelet function selected in the wavelet packet denoising process is the coif3 wavelet function, and the decomposition level is 4 levels.

[0017] Furthermore, the FFT filtering process involves: processing the time-domain signal... Perform FFT filtering to obtain the filtered time-domain signal. The FFT filtering process is a low-pass filter, and the low-pass filter range is... .

[0018] The time-domain signal obtained after FFT filtering This allows for the determination of stress concentration and early micro-damage in the circumferential weld of the inspected pipeline, and the location of micro-damage can be determined by using quasi-static component time-of-flight.

[0019] According to one aspect of this application, a device for detecting micro-defects in the circumferential welds of high-attenuation material pipelines is provided. This device includes an ultrasonic excitation transducer, a high-energy nonlinear ultrasonic signal generator / receiver, a first signal amplifier (power amplifier), a second signal amplifier, a bandpass filter, a low-pass filter, a PVDF comb-shaped flexible piezoelectric sensor, an oscilloscope, and a computer. The ultrasonic excitation transducer is implemented using a PVDF comb-shaped flexible piezoelectric sensor, which is fixedly placed at the detection position of the circumferential weld of the pipeline being inspected and is positioned relative to the circumferential weld of the pipeline being inspected. The weld seam is fitted; the high-energy nonlinear ultrasonic signal generator / receiver is used to excite a high-power ultrasonic guided wave signal at a suitable frequency. After the signal is amplified by the first signal amplifier and filtered by the bandpass filter, it is connected to a PVDF comb-shaped flexible piezoelectric sensor, so that the ultrasonic guided wave signal is introduced into the circumferential weld seam of the pipe being tested. The PVDF comb-shaped flexible piezoelectric sensor is also used to receive the propagating ultrasonic signal. After the signal is amplified by the second signal amplifier and filtered by the low-pass filter, it is sent to the high-energy nonlinear ultrasonic signal generator / receiver. At the same time, the received signal is sent to an oscilloscope and a computer for signal analysis. The nonlinear ultrasonic signal generator / receiver can excite high-power ultrasonic pulses. The signal generated by the nonlinear effect is often several orders of magnitude smaller than the linear signal and is easily masked by noise. Nonlinear testing requires the excitation of a signal with a large amplitude in the sample.

[0020] Furthermore, the high-energy nonlinear ultrasonic signal generator / receiver is used to excite ultrasonic guided wave signals at a suitable frequency, specifically including: selecting ultrasonic guided wave mode pairs that do not satisfy the group velocity matching condition based on the ultrasonic nonlinear static component theory, wherein the fundamental frequency of the ultrasonic guided wave mode pair is... The frequency of the quasi-static component is The fundamental ultrasonic frequency is selected by exciting the circumferential weld of the inspected pipe using a high-energy nonlinear ultrasonic signal generator / receiver. (That is, based on the theory of ultrasonic nonlinear static components, ultrasonic guided wave mode pairs that do not satisfy the group velocity matching condition are selected, and the fundamental frequency of the ultrasonic guided wave mode pairs is selected).

[0021] Furthermore, the bandpass range of the bandpass filter includes the selected fundamental frequency. Furthermore, the center frequency of the bandpass filter is the same as the selected fundamental frequency. Approximately; the filtering range of the low-pass filter includes the selected quasi-static component frequency. .

[0022] Furthermore, the PVDF comb-shaped flexible piezoelectric sensor is fixedly placed at the detection position of the circumferential weld of the pipeline being inspected. Specifically, based on the geometry of the circumferential weld of the pipeline being inspected, a PVDF comb-shaped flexible piezoelectric sensor with matching geometry is selected.

[0023] Furthermore, the PVDF comb-shaped flexible piezoelectric sensor includes comb-shaped electrodes, and the dimensions of the comb-shaped electrodes are designed based on the wavelength of the fundamental frequency: finger width a, finger spacing width b, finger length L, and number of fingers N; the dimensions a and b of the comb-shaped electrodes satisfy the following conditions: , The wavelength (mm) of the fundamental frequency of the ultrasound;

[0024] Furthermore, to ensure consistent ultrasonic signal coupling conditions and avoid the coupling conditions affecting the detection results, an ultrasonic coupling agent is filled between the PVDF comb-shaped flexible piezoelectric sensor and the circumferential weld of the pipe being inspected.

[0025] This invention provides a method and apparatus for detecting micro-defects in circumferential welds of high-attenuation material pipelines through the aforementioned scheme. Compared with existing technologies, this invention has the following advantages: It calculates the dispersion curve of the circumferential weld based on the geometry and material properties of the weld, using a semi-analytical finite element method; it selects ultrasonic mode pairs with group velocity mismatch based on nonlinear static component theory; it performs wavelet packet denoising and FFT filtering on the received ultrasonic signal, and determines the stress concentration phenomenon, degree of micro-damage, and location within the weld joint of the high-attenuation material pipeline based on the FFT filtering results. Based on ultrasonic nonlinear static component theory, this invention solves the problems of low detection accuracy, poor efficiency, and high cost of current methods for detecting micro-defects in circumferential welds of high-attenuation material pipelines, enabling high-accuracy non-destructive testing and location of micro-defects. The use of ultrasonic characteristic guided waves for detection increases efficiency and enables rapid, real-time on-site detection of micro-defects within pipe welded joints. Utilizing static components overcomes the limitations imposed by high-attenuation materials on ultrasonic wave propagation distance. Furthermore, static components are highly sensitive to stress concentrations and micro-cracks, detecting defects undetectable by conventional ultrasound, thus increasing the reliability and signal-to-noise ratio of the results. Employing group velocity mismatched ultrasonic characteristic guided wave mode pairs, based on the plateau-shaped wave packet of the generated static component and the abrupt signal changes caused by micro-defects, high-precision detection and location of micro-defects within pipe welded joints are achieved. Moreover, the geometry of circumferential welds in pipes is not fixed; pipe diameter, pipe material, and welding process significantly affect the weld joint's geometry. This invention employs a PVDF comb-shaped flexible piezoelectric sensor, overcoming the limitation of geometric universality, enabling non-destructive testing of circumferential welds in pipes of arbitrary geometries, saving costs and increasing detection efficiency. Attached Figure Description

[0026] The present invention can be better understood by referring to the description given below in conjunction with the accompanying drawings, in which the same or similar reference numerals are used throughout the drawings to denote the same or similar parts. These drawings, together with the following detailed description, are incorporated in and form part of this specification, and are used to further illustrate preferred embodiments of the invention and explain the principles and advantages of the invention. In the drawings:

[0027] Figure 1 This is a schematic diagram of the non-destructive testing device for circumferential welds of high-attenuation material pipes according to Embodiment 1 of the present invention;

[0028] Among them, 1—high-energy nonlinear ultrasonic signal generator / receiver, 21—first signal amplifier, 22—second signal amplifier, 3—bandpass filter, 4—low-pass filter, 5—sample under test, 6—PVDF comb-shaped flexible piezoelectric sensor, 7—oscilloscope, 8—computer;

[0029] Figure 2 This is a schematic diagram of a PVDF comb-shaped flexible piezoelectric sensor and its comb-shaped electrodes;

[0030] Figure 3 This is a flowchart illustrating the non-destructive testing method for circumferential welds of high-attenuation material pipes according to Embodiment 2 of the present invention.

[0031] Figure 4 This is the result of Fourier filtering of the ultrasonic received signal in the non-destructive testing method for circumferential welds of high-attenuation material pipes in Embodiment 2 of the present invention when there are no micro-defects.

[0032] Figure 5 This is the result of Fourier filtering processing of the ultrasonic received signal when micro-defects exist in the non-destructive testing method for circumferential welds of high-attenuation material pipes in Embodiment 2 of the present invention. Detailed Implementation

[0033] Embodiments of the present invention will now be described with reference to the accompanying drawings. Elements and features described in one drawing or embodiment of the invention may be combined with elements and features shown in one or more other drawings or embodiments. It should be noted that, for clarity, representations and descriptions of components and processes known to those skilled in the art that are unrelated to the invention have been omitted from the drawings and description. In the description of the invention, it should be understood that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] Micro-damage and stress concentration at the circumferential weld of high-attenuation material pipes are highly concealed, making them difficult to detect accurately and efficiently using conventional non-destructive testing methods. Compared to metallic materials, high-attenuation materials have a higher attenuation coefficient, limiting the propagation distance of ultrasonic waves. Traditional ultrasonic testing cannot meet the requirements for high efficiency and accuracy. Furthermore, the geometry of the circumferential weld of a pipe is not unique. Therefore, this invention provides a method and apparatus for detecting micro-defects in the circumferential weld of high-attenuation material pipes, employing a PVDF comb-shaped flexible piezoelectric sensor to accommodate the universality of geometric shapes. The non-destructive evaluation method involves exciting ultrasonic characteristic guided waves at a specific frequency in the high-attenuation material pipe under test using the PVDF comb-shaped flexible piezoelectric sensor, and receiving the ultrasonic signal through the PVDF comb-shaped flexible piezoelectric sensor. The received ultrasonic detection signal is then subjected to wavelet packet denoising and FFT filtering. Based on the FFT filtering results, the stress concentration phenomenon and the degree and location of micro-damage within the weld joint of the high-attenuation material pipe are determined. This invention overcomes the problems of low detection efficiency, low signal-to-noise ratio of detection results, and inability to locate micro-damage in conventional non-destructive testing methods for circumferential welds of pipes made of high-attenuation materials. It achieves high-precision non-destructive testing of circumferential welds of pipes made of high-attenuation materials, improves detection efficiency and accuracy, and enables the location of micro-damage.

[0035] Example 1

[0036] This embodiment provides a non-destructive testing device for circumferential welds of high-attenuation material pipes, the structure of which is shown in the figure below. Figure 1 As shown, the system includes a high-energy nonlinear ultrasonic signal generator / receiver 1, a first signal amplifier 21 (power amplifier), a first signal amplifier 22 (power amplifier), a bandpass filter 3, a low-pass filter 4, a circumferential weld seam of the pipe to be inspected 5, a PVDF comb-shaped flexible piezoelectric sensor 6, an oscilloscope 7, and a computer 8. The PVDF comb-shaped flexible piezoelectric sensor 6 is placed and attached to the circumferential weld seam 5 of the pipe to be inspected. A schematic diagram of the PVDF comb-shaped flexible piezoelectric sensor 6 and its comb-shaped electrodes is shown below. Figure 2 As shown. In this embodiment, two PVDF comb-shaped flexible piezoelectric sensors 6 are provided, one for transmitting ultrasonic signals and the other for receiving ultrasonic signals.

[0037] A high-energy nonlinear ultrasonic signal generator / receiver 1 excites an ultrasonic signal of a suitable frequency. After the excitation signal is purified by a bandpass filter 3 and amplified by a second signal amplifier 22, it is connected to a PVDF comb-shaped flexible piezoelectric sensor 6 at one end of the detection area, guiding the ultrasonic signal into the circumferential weld 5 of the pipe being inspected. Another PVDF comb-shaped flexible piezoelectric sensor 6 is placed above the other end of the detection area. The PVDF comb-shaped flexible piezoelectric sensor includes comb-shaped electrodes, and the dimensions of the comb electrodes, including the finger width a, finger spacing width b, finger length L, and number of fingers N, are designed based on the wavelength of the ultrasonic excitation signal. The detected propagation signal is amplified by a first signal amplifier 21 and filtered by a low-pass filter 4 to remove noise and clutter signals before being sent to the high-energy nonlinear ultrasonic signal generator / receiver 1. Simultaneously, the received signal is sent to an oscilloscope 7. The signal received by the high-energy nonlinear ultrasonic signal generator / receiver 1 is further input to a computer 10 for signal analysis. Furthermore, the bandpass filter 3 used has a bandpass range covering the selected ultrasonic excitation frequency. Furthermore, the center frequency of the bandpass filter is related to the selected ultrasonic excitation frequency. Approximately; the low-pass filter 4 used has a filtering range that includes the selected ultrasonic quasi-static component frequency. To ensure consistent ultrasonic signal coupling conditions, an ultrasonic coupling agent is filled between the PVDF comb-shaped flexible piezoelectric sensor 6 and the test specimen; in addition, the PVDF comb-shaped flexible piezoelectric sensor 6 and the test specimen remain fixed during testing.

[0038] Example 2

[0039] This embodiment provides a non-destructive testing method for circumferential welds of high-attenuation material pipes. The dispersion curve of the circumferential weld of the pipe under test is calculated by semi-analytical finite element method. Based on the nonlinear static classification theory of ultrasonic guided waves, ultrasonic guided wave mode pairs with group velocity mismatch are selected. The received ultrasonic detection signal is subjected to wavelet packet denoising and FFT filtering. Based on the FFT filtering results, the stress concentration phenomenon and the degree and location of micro-damage inside the weld joint of high-attenuation material pipes are determined, so as to realize the non-destructive testing and positioning of micro-damage inside the weld joint of high-attenuation material pipes. The implementation of this method is based on: (1) When a beam of single-frequency ultrasonic waves propagates in an isotropic, weakly nonlinear solid, it will not only generate second (higher) harmonics, but also be accompanied by a component with a frequency close to zero, namely the static component. The carrier frequency of the static component is almost zero, and the attenuation is not serious even under high attenuation and high frequency excitation. (2) Using a group velocity mismatched ultrasonic mode pair, since the fundamental frequency group velocity is different from the quasi-static component group velocity, the quasi-static component is manifested in the time domain as the wave packet of the ultrasonic guided wave being stretched. If an additional nonlinear source is encountered, such as stress concentration or micro-cracks and other micro-damage, the quasi-static component will have a significant abrupt change in the time domain, thereby achieving precise positioning of micro-damage.

[0040] For details, see Figure 3 The flowchart of the non-destructive testing method for circumferential welds of high-attenuation material pipes in this embodiment includes the following processes:

[0041] Process 1) Based on the geometry and material properties of the circumferential weld of the pipeline under inspection, the dispersion curve of the circumferential ultrasonic guided wave of the circumferential weld of the high-attenuation material pipeline is calculated using the semi-analytical finite element method.

[0042] Step 2) Using the aforementioned dispersion curve, select ultrasonic guided wave mode pairs that do not meet the group velocity matching condition (fundamental frequency is...). The frequency of the quasi-static component is ), Quasi-static component frequency The following conditions must be met: ( ), where d is the wall thickness of the pipe of the high-attenuation material being tested, and the group velocity of the fundamental frequency is The group velocity of the quasi-static component is The group velocity matching condition is not met as follows: The following conditions must be met. ;

[0043] Step 3) Based on the geometry of the circumferential weld of the pipe being inspected, a PVDF comb-shaped flexible piezoelectric sensor with matching geometry is selected; the PVDF comb-shaped flexible piezoelectric sensor includes comb-shaped electrodes, and the relevant dimensions of the comb-shaped electrodes, namely, finger width a, finger spacing width b, finger length L, and number of fingers N, are designed based on the wavelength of the fundamental frequency; the relevant dimensions a and b of the comb-shaped electrodes satisfy the following conditions: , The wavelength (mm) of the fundamental frequency;

[0044] Process 4) Excite the fundamental frequency of ultrasound using an ultrasonic excitation transducer. The number of cycles of the ultrasonic fundamental frequency excitation signal, c, satisfies the following condition: The ultrasonic guided wave detection time-domain signal is received through the ultrasonic receiving transducer. ;

[0045] Step 5) Further truncate the obtained time-domain signal, with the truncation time window being [ - , + ], To receive time domain signals The time at which the absolute value of the amplitude reaches its maximum. The total duration of the fundamental frequency excitation signal is used to obtain the time-domain signal. ;

[0046] Process 6) By analyzing the time-domain signal Wavelet packet denoising is performed to obtain the denoised time-domain signal. The wavelet packet denoising process is as follows: 1. Select a wavelet function and determine the decomposition level to perform wavelet packet decomposition on the time-domain signal; 2. Select a suitable threshold and threshold function to perform global processing on the coefficients of the wavelet packet; 3. Superimpose the processed wavelet packet coefficients to reconstruct the signal using wavelet packets; furthermore, the wavelet function selected in the wavelet packet denoising process is the coif3 wavelet function, and the decomposition level is 4 levels.

[0047] Process 7) By analyzing the time-domain signal Perform FFT filtering to obtain the filtered time-domain signal. ;

[0048] Furthermore, the FFT filtering process is converted to low-pass filtering, with a low-pass filtering range of [range missing]. ;

[0049] Step 8) The time-domain signal obtained after the FFT filtering process described above The system determines the stress concentration phenomenon and micro-damage of the circumferential weld of the inspected pipeline, and locates the micro-damage by using the quasi-static component time of flight.

[0050] The verification principle of this invention is as follows: In recent years, scholars have discovered a special type of guided wave—the characteristic guided wave—exists in waveguide structures (characteristic structures) with local geometrical variations. Ultrasonic characteristic guided waves, with energy concentrated in the characteristic structure, have broad application prospects for long-distance detection in characteristic regions because their concentrated energy allows for a longer propagation distance. Compared to traditional ultrasonic point-to-point detection and ultrasonic phased array local area scanning detection, ultrasonic characteristic guided waves propagating along the characteristic structure have higher detection efficiency. Furthermore, due to the energy trapping effect, the energy of the characteristic guided wave is more concentrated in the characteristic region, improving the sensitivity and signal-to-noise ratio of the detection results. When a single-frequency ultrasonic wave propagates in an isotropic, weakly nonlinear solid, it not only generates second (higher) harmonics but also a component with a frequency close to zero, namely the static component, also known as the DC component. The acoustic attenuation coefficient of high-attenuation materials is much greater than that of metallic materials, thus limiting the propagation distance of ultrasonic waves within high-attenuation materials. Moreover, when the ultrasonic frequency is high, the sound wave undergoes severe attenuation, which is very unfavorable for practical ultrasonic detection applications. However, the carrier frequency of the static component is almost zero, and even in highly attenuated materials, the attenuation is not severe under high-frequency excitation. Since the carrier frequency of the static component is almost zero, ultrasonic transducers cannot receive its signal. However, like other ultrasonic signals, the static component of an ultrasonic signal also has a certain bandwidth. Within a certain range, a relatively strong static component signal can be received by an ultrasonic transducer; that is, the static component of the ultrasonic signal is characterized by receiving the quasi-static component. In ultrasonic guided waves, the dispersion characteristics make the nonlinear effects more complex, requiring specific conditions to be met to generate nonlinear characteristic quantities that accumulate with propagation distance. The static component of ultrasound can be understood as a self-interaction product of ultrasonic waves; the accumulation effect is no longer constrained by specific synchronicity conditions (because its own characteristics satisfy the phase velocity matching condition). When the ultrasonic mode pair satisfies the group velocity matching condition, the quasi-static component of the ultrasound accumulates continuously with the propagation distance. At this time, the quasi-static component of the ultrasound represents the nonlinear information along the entire propagation path, making it impossible to accurately locate the source of nonlinearity along the path. When the selected ultrasonic mode pair does not satisfy the group velocity matching condition, the ultrasonic quasi-static component manifests as an elongated wave packet in the time domain due to the group velocity difference. In this case, if an additional nonlinear source is encountered in the propagation path, the ultrasonic quasi-static component will experience abrupt changes in the time domain. Based on the time of this abrupt change and the group velocity of the ultrasonic characteristic guided wave quasi-static component, the source of nonlinearity can be accurately located. Researchers have also conducted extensive studies on ultrasonic stress detection. Studies have shown that nonlinear ultrasound can effectively and accurately detect the internal stress of the tested material. When stress concentration exists inside the circumferential weld of a pipe, it significantly alters the nonlinearity of the ultrasound. Besides stress, microcracks can also significantly alter the nonlinearity of ultrasound.Scholars have established a nonlinear model for acoustic contact. When ultrasound propagates through a microcrack, the microcrack exhibits a "breathing" phenomenon: the crack opens when the wave stretches and closes when the wave compresses. When the crack opens, the ultrasonic guided wave cannot pass through, resulting in nonlinearity. Both localized stress concentration and micro-damage such as microcracks alter the nonlinearity of the ultrasonic guided wave; therefore, the aforementioned nonlinear ultrasonic detection methods can be effectively used for detection.

[0051] When applying the ultrasonic guided wave-based micro-defect detection method of this invention, before the actual detection process, it is necessary to calculate the dispersion curve of the circumferential weld of the high-attenuation material pipe based on the material and geometric dimensions of the weld. Based on the dispersion curve, ultrasonic mode pairs with group velocity mismatch are selected, including the ultrasonic guided wave mode and frequency. The phase velocity and wave structure of the ultrasonic guided wave are different under different modes and frequencies. Directly exciting the selected specific ultrasonic guided wave on the surface of the circumferential weld using an ultrasonic transducer cannot excite the selected specific ultrasonic guided wave. Therefore, to achieve the excitation of ultrasonic guided waves under specific modes, this invention employs a PVDF comb-shaped flexible piezoelectric sensor. The PVDF comb-shaped flexible piezoelectric sensor can be fitted to the circumferential weld being detected, easily maintaining ultrasonic coupling conditions. The comb-shaped electrodes of the PVDF comb-shaped flexible piezoelectric sensor are associated with the fundamental frequency mode of the excited ultrasonic wave. The comb-shaped electrodes of the PVDF comb-shaped flexible piezoelectric sensor are designed according to the wavelength of the required ultrasonic mode. The use of PVDF comb-shaped flexible piezoelectric sensors overcomes the problem of varying ultrasonic coupling due to different weld joint geometries, increasing the universality of the detection method and enhancing the accuracy and robustness of the detection results. Furthermore, a prior patent application (CN202211428588.1) disclosed a high-resolution imaging detection method and device for micro-defects at the mesoscale. The detection device in this application is similar in hardware to that patent, but this application improves upon it by using PVDF comb-shaped flexible piezoelectric sensors, eliminating the need for variable-angle wedges and avoiding their slotted design. PVDF is a flexible sensor that can conform to welds of different geometric dimensions, further increasing the universality of the detection method.

[0052] Figure 4 and Figure 5The figures show the FFT filtering results of the received ultrasonic signal under the conditions of no micro-defects and with micro-defects, respectively. As can be seen from the figures, without micro-defects, the quasi-static component of the ultrasonic wave exhibits an elongated wave packet in the time domain due to group velocity mismatch. The envelope of the overall wave packet is rectangular, and its length increases with increasing propagation distance, but the overall shape of the envelope does not change significantly. When a micro-defect (at x=160mm) exists in the propagation path of the ultrasonic characteristic guided wave, the nonlinearity of the micro-defect manifests as a significant abrupt change in the quasi-static component of the ultrasonic wave in the time domain. Based on the time-domain signal change of this quasi-static component and its group velocity, the micro-defect can be located with high precision.

[0053] This invention, based on nonlinear ultrasonic theory, develops a method and device for detecting micro-defects in the circumferential welds of high-attenuation material pipes. This technology is highly sensitive to micro-defects in the circumferential welds of the pipes being inspected, enabling high-efficiency and high-precision non-destructive testing of micro-defects. When using ultrasonic characteristic guided wave modes with group velocity mismatch for detection, if an additional nonlinear source is encountered in the propagation path, the quasi-static component of the ultrasound will exhibit abrupt changes in the time domain. By analyzing the time of this abrupt change and the group velocity of the quasi-static component of the ultrasonic characteristic guided wave, the source of nonlinearity can be accurately located.

[0054] Unlike higher harmonic nonlinear parameters such as the second harmonic, static components can be generated without satisfying the phase velocity matching condition. Currently, nonlinear ultrasonic testing methods based on static components all use ultrasonic guided wave mode pairs with group velocity matching for detection. The energy generated by the static component comes from the fundamental frequency. In this case, since the fundamental frequency and the static component have the same group velocity, they will propagate together, and the amplitude of the static component will continuously accumulate. During the detection process, the signal shape of the received static component is similar to the envelope shape of the fundamental frequency signal. Therefore, this signal only contains all the nonlinear information along the entire detection path and cannot reflect whether there is nonlinear damage in the path, let alone locate these micro-damages. Traditional detection methods require the detection signal of an undamaged sample as a baseline, and the detection path is judged by comparing it with the baseline, but this also cannot achieve localization. The group velocity of the static component can be approximated as the group velocity of the L0 mode at low frequencies, which is faster than the group velocity of most guided wave modes. Therefore, we propose a detection method using mode pairs with mismatched group velocities. In other nonlinear ultrasonic testing methods, none employ mismatched modes for detection. When group velocities are mismatched, the group velocity of the fundamental frequency is lower than the velocity of the static component. When the static component is generated, it propagates faster than the fundamental frequency, and the fundamental frequency cannot provide energy to the generated static component. Therefore, in this case, the shape of the received static component is drastically different from that when the group velocity is matched, exhibiting an overall plateau shape, such as... Figure 4 If nonlinear damage (an additional source of nonlinearity) exists along the path, then a significant abrupt change will occur in the static component waveform, such as... Figure 5 As shown in the figure, this method overcomes the limitations of traditional nonlinear ultrasonic testing methods in determining the source and location of nonlinearity, enabling the identification and location of nonlinear micro-damage in the detection path without a baseline. Another advantage of using static components to detect high-attenuation pipes is that the frequency of the static component is very low. The lower the ultrasonic frequency, the smaller the attenuation, and compared to conventional ultrasonic waves, the static component can propagate further.

[0055] Furthermore, the method of the present invention is not limited to being executed in the chronological order described in the specification, but may also be executed in other chronological orders, in parallel, or independently. Therefore, the execution order of the method described in this specification does not constitute a limitation on the technical scope of the present invention.

[0056] Although the invention has been disclosed above through the description of specific embodiments, it should be understood that all the embodiments and examples described above are exemplary and not restrictive. Those skilled in the art can design various modifications, improvements, or equivalents to the invention within the spirit and scope of the appended claims. These modifications, improvements, or equivalents should also be considered to be included within the protection scope of the invention.

Claims

1. A method for detecting micro-defects in circumferential welds of high-attenuation material pipelines, characterized in that: Includes the following steps: Step 1: Select the inspection location on the surface of the circumferential weld of the pipeline to be inspected; Select an ultrasonic guided wave mode pair that does not satisfy the group velocity matching condition. The fundamental frequency of this ultrasonic guided wave mode pair is... The frequency of the quasi-static component is ; Step 2: Excite the selected ultrasonic fundamental frequency signal to the circumferential weld of the pipe being inspected. The fundamental frequency of this ultrasonic fundamental frequency signal is... The received ultrasonic characteristic guided wave detection signal is locally truncated, and the truncated result is subjected to wavelet packet denoising and FFT filtering. Step 3: Based on the FFT filtering results obtained in Step 2, determine whether there are micro-defects in the detection path; if there are micro-defects, accurately locate the micro-defects based on the time of abrupt change in the time domain signal after FFT filtering and the group velocity of the quasi-static component of the ultrasonic characteristic guided wave. In step 2, the ultrasonic fundamental frequency signal selected to excite the circumferential weld of the inspected pipe is [missing information]. Specifically, this includes: selecting a PVDF comb-shaped flexible piezoelectric sensor with a matching geometry based on the geometry of the circumferential weld of the inspected pipe; the PVDF comb-shaped flexible piezoelectric sensor includes comb-shaped electrodes, and the dimensions of the comb-shaped electrodes are designed based on the wavelength of the fundamental frequency: finger width a, finger spacing width b, finger length L, and number of fingers N; the dimensions a and b of the comb-shaped electrodes satisfy: , The wavelength of the fundamental frequency is given; the fundamental frequency is excited to the circumferential weld of the pipe being inspected by a PVDF comb-shaped flexible piezoelectric sensor. The ultrasonic fundamental frequency signal has a period number of c, and the period number c of the ultrasonic fundamental frequency excitation signal satisfies: ; In step 2, the received ultrasonic characteristic guided wave detection signal is locally truncated, and the truncated result is subjected to wavelet packet denoising and FFT filtering. Specifically, this includes receiving the ultrasonic guided wave detection time-domain signal through a PVDF comb-shaped flexible piezoelectric sensor. The obtained time-domain signal is further truncated, and the truncated time window is [ - , + ], To receive time domain signals The time at which the absolute value of the amplitude reaches its maximum. The total duration of the fundamental frequency excitation signal is used to obtain the time-domain signal. ; By analyzing the time-domain signal Wavelet packet denoising is performed to obtain the denoised time-domain signal. ; The FFT filtering process is as follows: by processing the time-domain signal... Perform FFT filtering to obtain the filtered time-domain signal. The FFT filtering process is a low-pass filter, and the low-pass filter range is... .

2. The method for detecting micro-defects in circumferential welds of high-attenuation material pipelines according to claim 1, characterized in that: Step 1 specifically includes: calculating the dispersion curve of the circumferential ultrasonic guided wave of the circumferential weld seam using a semi-analytical finite element method based on the geometry and material properties of the circumferential weld seam of the inspected pipeline; selecting ultrasonic guided wave mode pairs that do not satisfy the group velocity matching condition based on the dispersion curve, and determining the quasi-static component frequency. The following conditions must be met: , where d is the wall thickness of the pipe containing the high-attenuation material being tested.

3. The method for detecting micro-defects in circumferential welds of high-attenuation material pipelines according to claim 1, characterized in that: In step 1, selecting ultrasonic guided wave mode pairs that do not meet the group velocity matching condition specifically includes: the fundamental frequency is The group velocity is Quasi-static component frequency The group velocity is The group velocity matching condition is not satisfied if the following conditions are met: .

4. The method for detecting micro-defects in circumferential welds of high-attenuation material pipelines according to claim 1, characterized in that: The wavelet packet denoising process is as follows:

1. Select a wavelet function and determine the decomposition level to perform wavelet packet decomposition on the time-domain signal; 2. Select a suitable threshold and threshold function to perform global processing on the coefficients of the wavelet packet; 3. Superimpose the processed wavelet packet coefficients to reconstruct the signal using wavelet packets; wherein, the wavelet function selected in the wavelet packet denoising process is the coif3 wavelet function, and the decomposition level is 4 levels.

5. A device for detecting micro-defects in circumferential welds of high-attenuation material pipelines, characterized in that: The system includes an ultrasonic excitation transducer, a high-energy nonlinear ultrasonic signal generator / receiver, a first signal amplifier, a second signal amplifier, a bandpass filter, a low-pass filter, a PVDF comb-shaped flexible piezoelectric sensor, an oscilloscope, and a computer. The ultrasonic excitation transducer is implemented using a PVDF comb-shaped flexible piezoelectric sensor, which is fixedly placed at the detection position of the circumferential weld of the pipe being inspected and is in close contact with the weld. The high-energy nonlinear ultrasonic signal generator / receiver is used to excite an ultrasonic guided wave signal at a suitable frequency. After the signal is amplified by the first signal amplifier and filtered by the bandpass filter, it is connected to the PVDF comb-shaped flexible piezoelectric sensor, allowing the ultrasonic guided wave signal to be introduced into the circumferential weld of the pipe being inspected. The PVDF comb-shaped flexible piezoelectric sensor is also used to receive the propagating ultrasonic signal. After the signal is amplified by the second signal amplifier and filtered by the low-pass filter, it is sent to the high-energy nonlinear ultrasonic signal generator / receiver. Simultaneously, the received signal is sent to the oscilloscope and computer for signal analysis. The high-energy nonlinear ultrasonic signal generator / receiver is used to excite a high-power ultrasonic guided wave signal at a suitable frequency. Specifically, it includes selecting an ultrasonic guided wave mode pair that does not satisfy the group velocity matching condition, wherein the fundamental frequency of the ultrasonic guided wave mode pair is... The frequency of the quasi-static component is The fundamental ultrasonic frequency selected by exciting the circumferential weld of the pipe under inspection via a high-energy nonlinear ultrasonic signal generator / receiver; This device realizes the method for detecting micro-defects in circumferential welds of high-attenuation material pipelines as described in any one of claims 1-4.

6. The device for detecting micro-defects in circumferential welds of high-attenuation material pipelines according to claim 5, characterized in that: The pass range of the bandpass filter includes the selected fundamental frequency. Furthermore, the center frequency of the bandpass filter is the same as the selected fundamental frequency. Approximately; the filtering range of the low-pass filter includes the selected quasi-static component frequency. .

7. The device for detecting micro-defects in circumferential welds of high-attenuation material pipelines according to claim 5, characterized in that: The PVDF comb-shaped flexible piezoelectric sensor is fixedly placed at the detection position of the circumferential weld of the pipeline being inspected. Specifically, a PVDF comb-shaped flexible piezoelectric sensor with a matching geometry is selected based on the geometry of the circumferential weld of the pipeline being inspected.

8. The device for detecting micro-defects in circumferential welds of high-attenuation material pipelines according to claim 5, characterized in that: The PVDF comb-shaped flexible piezoelectric sensor includes comb-shaped electrodes. The dimensions of the comb-shaped electrodes are designed based on the wavelength of the fundamental frequency: finger width a, finger spacing width b, finger length L, and number of fingers N. The dimensions a and b of the comb-shaped electrodes satisfy the following conditions: , The wavelength is the fundamental frequency of the ultrasound.

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