A pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology

Abstract

The present invention discloses a pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology, wherein pipeline cracks are detected by a balanced electromagnetic detection device; the detection of pipeline cracks by the balanced electromagnetic detection device includes detecting the deflection angle of the pipeline crack, wherein the deflection angle is the angle between the line between the two magnetic feet of the balanced electromagnetic detection device and the crack direction of the pipeline crack; the range of the deflection angle detected by the method is 0° to 90°. The present invention uses a balanced electromagnetic detection device to detect pipeline cracks, and the recognition range of the deflection angle of the pipeline crack is 0° to 90°, with a wide recognition range and high recognition accuracy, thereby realizing full-angle detection of pipeline cracks and improving the efficiency and effect of detection.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic nondestructive testing of pipeline defects, and in particular to a pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology. Background Art

[0002] More than 3.5 million kilometers of pipelines in the world are responsible for the distribution of more than 70% of the world's oil and gas resources. Compared with road, rail, air and sea transportation, pipeline oil and gas transportation is the most efficient mode of transportation. In recent years, with the deterioration of resource quality and the adjustment of energy structure, the operation and maintenance of oil and gas pipeline networks are faced with the dilemma of working in extreme operating environments such as ultra-large pipe diameters, ultra-large wall thicknesses, high temperatures, high pressures, and complex corrosion. During the service process, long-distance oil and gas pipelines are subject to the combined effects of the internal transmission medium and the external load-bearing environment. Fatigue cracks are easily generated on the inner and outer surfaces of the pipelines, which then develop into corrosion defects. The accumulation of defects seriously affects the reliability of the pipeline system and may even lead to system failure and unexpected downtime.

[0003] The existing AC magnetic leakage detection can usually detect pipeline crack deflection angles in the range of 30° to 90°, and the AC electromagnetic detection can detect pipeline crack deflection angles in the range of 0° to 60°. Both methods cannot achieve full-angle identification of pipeline cracks. Therefore, there is an urgent need to develop an efficient and reliable full-angle surface crack detection method. Summary of the invention

[0004] In view of this, the present invention provides a pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology.

[0005] The specific technical solutions are:

[0006] A pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology.

[0007] Detect pipeline cracks using a balanced electromagnetic detection device;

[0008] The method includes that the detection of pipeline cracks by a balanced electromagnetic detection device includes detecting a deflection angle of the pipeline crack, wherein the deflection angle is an angle between a line connecting two magnetic feet of the balanced electromagnetic detection device and a crack direction of the pipeline crack;

[0009] The deflection angle detected by the method ranges from 0° to 90°.

[0010] Optionally, the method includes performing AC magnetic flux leakage detection and AC electromagnetic detection on the pipeline crack by using the balanced electromagnetic detection device;

[0011] The method further comprises determining the deflection angle of the pipeline crack according to the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection;

[0012] When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in a first preset state, the method determines that the deflection angle of the pipeline crack is 90°, in which the voltage signal is detected during the AC magnetic flux leakage detection and the voltage signal is not detected during the AC electromagnetic detection;

[0013] When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in a second preset state, the method determines that the deflection angle range of the pipeline crack is greater than 60° and less than 90°, and in the second preset state, the voltage signal detected during the AC magnetic flux leakage detection is greater than the voltage signal detected during the AC electromagnetic detection;

[0014] When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in the third preset state, the method determines that the deflection angle range of the pipeline crack is greater than or equal to 30° and less than or equal to 60°, the voltage signal detected during the AC magnetic flux leakage detection in the third preset state is less than the voltage signal detected during the AC magnetic flux leakage detection in the second preset state and is greater than the voltage signal detected during the AC magnetic flux leakage detection in the fourth preset state, and at the same time, the voltage signal detected during the AC electromagnetic detection in the third preset state is less than the voltage signal detected during the AC electromagnetic detection in the fourth preset state and is greater than the voltage signal detected during the AC electromagnetic detection in the second preset state;

[0015] When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in a fourth preset state, the method determines that the deflection angle range of the pipeline crack is greater than 0° and less than 30°, and in the fourth preset state, the voltage signal detected during the AC magnetic flux leakage detection is less than the voltage signal detected during the AC electromagnetic detection;

[0016] When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in a fifth preset state, the method determines that the deflection angle of the pipeline crack is 0°, and in the fifth preset state, the voltage signal is not detected during the AC magnetic flux leakage detection, and the voltage signal is detected during the AC electromagnetic detection.

[0017] Optionally, the method includes generating a main circuit magnetic field and a magnetic circuit eddy current field in the pipeline wall of the pipeline by the balanced electromagnetic detection device, and performing AC magnetic leakage detection on the pipeline crack based on the main circuit magnetic field and performing AC electromagnetic detection on the pipeline crack based on the magnetic circuit eddy current field;

[0018] The main circuit magnetic field and the magnetic circuit eddy current field are excited by an alternating current source.

[0019] Optionally, the method includes detecting the pipeline crack by using a quasi-square wave excitation signal through the balanced electromagnetic detection device, the waveform of the quasi-square wave excitation signal changes periodically, and the waveform of the quasi-square wave excitation signal in each cycle includes a rising edge, a constant current high level interval, a falling edge and a zero level interval;

[0020] The method comprises generating a main circuit magnetic field in the pipeline wall of the pipeline by the balanced electromagnetic detection device during the rising edge and the constant current high level interval and performing AC magnetic leakage detection on the pipeline crack;

[0021] The method further comprises exciting a magnetic circuit eddy current field in a pipeline wall of the pipeline by the balanced electromagnetic detection device at the falling edge and the zero level interval after the AC magnetic flux leakage detection and performing AC electromagnetic detection on the pipeline crack.

[0022] Optionally, the method includes forming the quasi-square wave excitation signal by connecting a plurality of groups of harmonic signals in series;

[0023] The multiple groups of harmonic signals include a first group of harmonic signals and a second group of harmonic signals, the first group of harmonic signals is composed of a plurality of first harmonic signals superimposed, and the second group of harmonic signals is composed of a plurality of second harmonic signals superimposed;

[0024] The method includes using the first group of harmonic signals to form the rising edge and the constant current high level interval, and using the second group of harmonic signals to form the falling edge after the constant current high level interval.

[0025] Optionally, the number of the second harmonic signals is less than the number of the first harmonic signals.

[0026] Optionally, the pipeline crack includes multiple defect types, and the method includes determining the frequencies and amplitudes of multiple second harmonic signals according to the multiple defect types.

[0027] Optionally, the AC electromagnetic detection includes a primary AC electromagnetic detection and a secondary AC electromagnetic detection, and the primary AC electromagnetic detection and the secondary AC electromagnetic detection are performed sequentially.

[0028] Optionally, the method includes, after exciting the magnetic circuit eddy current field in the pipe wall of the pipe, performing the primary AC electromagnetic detection on the pipe crack in the falling edge and part of the zero level interval by the balanced electromagnetic detection device, and performing the secondary AC electromagnetic detection on the pipe crack in part of the zero level area after the primary AC electromagnetic detection.

[0029] Optionally, the method includes demagnetizing the pipeline in a portion of the zero-level interval after the secondary AC electromagnetic detection is completed.

[0030] The beneficial effects of the technical solution provided by the embodiment of the present invention include at least:

[0031] The present invention utilizes a balanced electromagnetic detection device to detect pipeline cracks. The recognition range of the deflection angle of pipeline cracks is 0° to 90°. The recognition range is wide and the recognition accuracy is high. The full-angle detection of pipeline cracks is realized, and the detection efficiency and effect are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 This is a schematic diagram of the principle of multi-frequency homologous balanced electromagnetic detection of the present invention;

[0034] Figure 2 This is a schematic diagram of the multi-frequency homologous balanced electromagnetic time-sharing excitation principle of the present invention;

[0035] Figure 3 This is a schematic diagram of the multi-frequency homologous balanced electromagnetic detection process of the present invention;

[0036] Figure 4 It is a schematic diagram of signal transmission of the multi-frequency homologous balanced electromagnetic detection system of the present invention;

[0037] Figure 5 It is the voltage waveform for full-angle identification of pipeline cracks under single-frequency excitation of the present invention;

[0038] Figure 6 The voltage waveform for full-angle identification of pipeline cracks under multi-frequency excitation of the present invention;

[0039] Figure 7 It is the voltage peak value for full-angle identification of pipeline cracks in the present invention.

[0040] The reference numerals in the figures represent respectively:

[0041] 1-excitation coil; 2-magnetic sensor; 3-pipeline; 4-U-shaped iron yoke; 5-crack defect;

[0042] B a -AC leakage magnetic field; B p -Magnetic pole eddy current J p The induced magnetic field; B d -Magnetic circuit eddy current Jd The induced magnetic field;

[0043] J p - magnetic pole eddy current; J d - eddy current in magnetic circuit; B- synthetic magnetic field formed by superposition of AC leakage magnetic field and eddy current induced magnetic field.

[0044] The above drawings have shown clear embodiments of the present invention, which will be described in more detail below. These drawings and text descriptions are not intended to limit the scope of the present invention in any way, but to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] Before further describing the embodiments of the present invention in detail, the directional nouns involved in the embodiments of the present invention, such as "upper part", "lower part", "side part", etc., are Figure 1 The directions shown in the figure are for reference only and do not limit the protection scope of the present invention.

[0047] To make the technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0048] This implementation introduces a pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology, the method includes detecting pipeline cracks through a balanced electromagnetic detection device; detecting pipeline cracks through a balanced electromagnetic detection device includes detecting the deflection angle of the pipeline crack, the deflection angle is the angle between the line between the two magnetic feet of the balanced electromagnetic detection device and the crack direction of the pipeline crack; the range of the deflection angle detected by the method is 0°~90°.

[0049] Furthermore, the multi-frequency balanced electromagnetic technology is a new electromagnetic composite detection method based on multi-frequency AC signal excitation. The main circuit magnetic field and magnetic circuit eddy current field are generated in the pipe wall of the pipeline 3. The voltage signal generated by the electromagnetic disturbance caused by the pipeline crack on the pipeline 3 can realize full-angle crack detection. The detection principle is as follows: Figure 1As shown. The balanced electromagnetic detection device includes an excitation coil 1, a magnetic sensor 2 and a U-shaped yoke 4. The excitation coil 1 is wound on the U-shaped yoke 4 and arranged in the middle of the U-shaped yoke 4. After the quasi-square wave excitation signal is passed into the excitation coil 1, the main circuit magnetic field generated in the U-shaped yoke 4 enters the pipe wall of the pipe 3 along the magnetic feet of the U-shaped yoke 4, and then forms a magnetic circuit eddy current field in the pipe wall of the pipe 3. The magnetic sensor 2 is arranged in the middle position of the two magnetic feet of the U-shaped yoke 4. The magnetic sensor 2 is used for voltage signals during AC leakage magnetic detection and AC electromagnetic detection. When there is no crack defect 5 on the pipeline 3, the magnetic lines of force are bound in the skin layer of the pipe wall, the leakage magnetic field can be regarded as zero, and the induced eddy current is distributed in a direction perpendicular to the magnetic lines of force. Since the balanced electromagnetic detection device has a symmetrical structure, the induced voltages generated on both sides of the magnetic sensor 2 are equal in magnitude and opposite in direction. At this time, the voltage detected by the magnetic sensor 2 is zero, which is defined as an electromagnetic equilibrium state. When there is a crack defect 5 on the pipeline 3, the existence of the crack defect 5 will destroy the original electromagnetic balance, causing the voltage signal received by the magnetic sensor 2 to be non-zero, which can intuitively reflect whether there is a crack defect 5 in the pipeline 3. When the direction of the crack defect 5 is at an angle with the magnetic field line, the magnetic field will be magnetically refracted at the crack defect interface, and part of the magnetic flux will leak from the surface of the pipeline 3 to form a leakage magnetic field, and the voltage signal can be detected by the magnetic sensor 2; when the direction of the crack defect 5 is parallel to the magnetic field line, because the main circuit magnetic field and the magnetic circuit eddy current field distribution are perpendicular to each other, the crack defect 5 will cause the magnetic circuit eddy current field to be distorted, and the magnetic sensor 2 can detect the voltage signal.

[0050] In this embodiment, a balanced electromagnetic detection device is used to detect pipeline cracks. The recognition range of the deflection angle of the pipeline crack is 0° to 90°. The recognition range is wide and the recognition accuracy is high. The full-angle detection of pipeline cracks is achieved, and the detection efficiency and effect are improved.

[0051] The method includes performing AC magnetic flux leakage detection and AC electromagnetic detection on pipeline cracks by using a balanced electromagnetic detection device;

[0052] The method also includes determining the deflection angle of the pipeline crack based on the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection;

[0053] When the voltage signal detected during AC magnetic flux leakage detection and the voltage signal detected during AC electromagnetic detection are in a first preset state, the method determines that the deflection angle of the pipeline crack is 90°, in which the voltage signal is detected during AC magnetic flux leakage detection and the voltage signal is not detected during AC electromagnetic detection;

[0054] When the voltage signal detected during AC magnetic flux leakage detection and the voltage signal detected during AC electromagnetic detection are in a second preset state, the method determines that the deflection angle range of the pipeline crack is greater than 60° and less than 90°, and in the second preset state, the voltage signal detected during AC magnetic flux leakage detection is greater than the voltage signal detected during AC electromagnetic detection;

[0055] When the voltage signal detected during AC magnetic flux leakage detection and the voltage signal detected during AC electromagnetic detection are in the third preset state, the method determines that the deflection angle range of the pipeline crack is greater than or equal to 30° and less than or equal to 60°, the voltage signal detected during AC magnetic flux leakage detection in the third preset state is less than the voltage signal detected during AC magnetic flux leakage detection in the second preset state and is greater than the voltage signal detected during AC magnetic flux leakage detection in the fourth preset state, and at the same time, the voltage signal detected during AC electromagnetic detection in the third preset state is less than the voltage signal detected during AC electromagnetic detection in the fourth preset state and is greater than the voltage signal detected during AC electromagnetic detection in the second preset state;

[0056] When the voltage signal detected during AC magnetic flux leakage detection and the voltage signal detected during AC electromagnetic detection are in a fourth preset state, the method determines that the deflection angle range of the pipeline crack is greater than 0° and less than 30°, and in the fourth preset state, the voltage signal detected during AC magnetic flux leakage detection is less than the voltage signal detected during AC electromagnetic detection;

[0057] When the voltage signal detected during AC magnetic flux leakage detection and the voltage signal detected during AC electromagnetic detection are in the fifth preset state, the method determines that the deflection angle of the pipeline crack is 0°, in which the voltage signal is not detected during AC magnetic flux leakage detection and the voltage signal is detected during AC electromagnetic detection.

[0058] Furthermore, eddy current has the characteristic of skin effect. The eddy current density is mainly distributed on the surface of the pipe, and diffuses and decays rapidly outward and downward. The position where the surface eddy current density decays to 1 / e in the depth direction is called skin depth δ, which is the reference value for effective defect detection depth. The specific skin effect calculation formula is:

[0059]

[0060] Where: μ, σ are the magnetic permeability and electrical conductivity of the pipeline respectively, f is the excitation frequency, and π is a constant.

[0061] There are many triggering schemes for the multi-frequency excitation signal s(t). This paper adopts synchronous addition synthesis, as shown in formula (2).

[0062]

[0063] Where: n is the number of harmonic components, A iis the amplitude of the harmonic component, ω i is the angular frequency of the harmonic component, is the initial phase of each harmonic component, and t represents time.

[0064] Under the excitation of multi-frequency AC signal, the detection voltage signal is shown in formula (3):

[0065]

[0066] After superposition summation and trigonometric function transformation, formula (3) can be rewritten as:

[0067]

[0068] In the formula,

[0069] From the analysis of formula (4), it can be seen that the balanced electromagnetic technology combines the advantages of AC electromagnetic detection and AC magnetic flux leakage detection, and uses the main circuit magnetic field leakage and magnetic circuit eddy current field distortion caused by the crack defect 5 to identify the deflection angle of the pipeline crack. In this embodiment, the deflection angle is the angle between the line between the two magnetic feet of the balanced electromagnetic detection device and the crack direction of the pipeline crack. It is assumed that the deflection angle of the pipeline crack is θ. When 0°≤θ<30°, the current distortion mechanism is dominant, that is, the voltage signal detected during AC electromagnetic detection is greater than the voltage signal detected during AC magnetic flux leakage detection, which can be specifically divided into: 0°<θ<30° in the fourth preset state, and θ=0° in the fifth preset state; when 60°<θ≤90°, the magnetic field disturbance mechanism is dominant, that is, the voltage signal detected during AC magnetic flux leakage detection is greater than the voltage signal detected during AC electromagnetic detection, which can be specifically divided into: θ=90° in the first preset state, and 60°<θ<90° in the second preset state; when 30°≤θ≤60°, the current distortion and magnetic field disturbance mechanisms work together, that is, the voltage signal detected during AC magnetic flux leakage detection is less than the voltage signal detected during AC magnetic flux leakage detection in the second preset state and is greater than the voltage signal detected during AC magnetic flux leakage detection in the fourth preset state, and at the same time, the voltage signal detected during AC electromagnetic detection in the third preset state is less than the voltage signal detected during AC electromagnetic detection in the fourth preset state and is greater than the voltage signal detected during AC electromagnetic detection in the second preset state, which is the fourth preset state.

[0070] Further, according to formula (1), the penetration depth of the electromagnetic field is inversely proportional to the electrical / magnetic permeability of the pipeline and the frequency of the detection signal. According to formula (2), the frequency combination technology can provide multiple detection signals, and each detection signal determines the penetration depth of the corresponding electromagnetic field. Therefore, this embodiment can realize the identification of pipeline cracks located at different positions (inside or outside the pipeline or at different wall thicknesses of the pipeline). Figure 5 and Figure 6The figure shows the identification of the deflection angle of pipeline cracks based on the same depth. In this embodiment, the identification of the deflection angle in the first preset state, the second preset state, the third preset state, the fourth preset state and the fifth preset state is also based on the pipeline cracks at the same depth.

[0071] Furthermore, the multi-frequency balanced electromagnetic technology can detect the deflection angle of the pipeline crack at different depths of the pipeline 3, and can also detect the depth of the pipeline crack itself, thereby realizing full-angle, full-position, and full-depth blind-spot identification of the pipeline crack on the pipeline 3.

[0072] The method includes generating a main circuit magnetic field and a magnetic circuit eddy current field in the pipeline wall of the pipeline by a balanced electromagnetic detection device, and performing AC magnetic leakage detection on pipeline cracks based on the main circuit magnetic field and performing AC electromagnetic detection on pipeline cracks based on the magnetic circuit eddy current field; the main circuit magnetic field and the magnetic circuit eddy current field are excited by an AC current source.

[0073] Furthermore, in this embodiment, the main circuit magnetic field and the magnetic circuit eddy current field are excited by an AC current source. After analyzing the principle commonality, technical complementarity and process feasibility of various existing technologies, in order to reduce the secondary design cost of the probe, the balanced electromagnetic detection device designed in this embodiment has a structure homogeneous with the existing AC magnetic flux leakage detector. It can be directly improved and applied on the basis of the existing AC magnetic flux leakage detector, and has strong promotional potential.

[0074] The method includes detecting pipeline cracks by using a quasi-square wave excitation signal through a balanced electromagnetic detection device, wherein the waveform of the quasi-square wave excitation signal changes periodically, and the waveform of the quasi-square wave excitation signal in each cycle includes a rising edge, a constant current high level interval, a falling edge, and a zero level interval;

[0075] The method includes generating a main circuit magnetic field in a pipeline wall of a pipeline by a balanced electromagnetic detection device during a rising edge and a constant current high level interval and performing AC magnetic leakage detection on pipeline cracks; the method also includes exciting a magnetic circuit eddy current field in a pipeline wall of a pipeline by a balanced electromagnetic detection device during a falling edge and a zero level interval after the AC magnetic leakage detection and performing AC electromagnetic detection on pipeline cracks.

[0076] The AC electromagnetic detection includes primary AC electromagnetic detection and secondary AC electromagnetic detection, and the primary AC electromagnetic detection and the secondary AC electromagnetic detection are performed sequentially.

[0077] The method includes: after the magnetic circuit eddy current field is excited in the pipeline wall of the pipeline, an AC electromagnetic detection is performed on the pipeline crack at the falling edge and part of the zero level interval by a balanced electromagnetic detection device, and a secondary AC electromagnetic detection is performed on the pipeline crack in the part of the zero level area after the first AC electromagnetic detection.

[0078] The method includes demagnetizing the pipeline in a partial zero-level interval after the secondary AC electromagnetic detection is completed.

[0079] Furthermore, the waveform of the quasi-square wave excitation signal in this embodiment is as follows: Figure 2 As shown, the timing characteristics are used to reduce the time overlap and mutual interference between AC magnetic flux leakage detection and AC electromagnetic detection. The implementation strategy is as follows:

[0080] 1) Pipeline magnetization: During the period t0-t1, a main circuit magnetic field is established in the pipe wall of the pipe 3 by a balanced electromagnetic detection device. The degree of magnetization of the pipe wall determines the detection sensitivity of the crack defect 5;

[0081] 2) AC magnetic flux leakage detection: During the period t1-t2, the pipeline 3 is subjected to AC magnetic flux leakage detection by a balanced electromagnetic detection device. At this time, the voltage signal detected during the AC magnetic flux leakage detection can be obtained by the magnetic sensor 2;

[0082] 3) Excitation of magnetic circuit eddy current field: t2-t3 period. This period is not conducive to overlapping field decoupling due to the hysteresis effect and is only used for the excitation of magnetic circuit eddy current field.

[0083] 4) Primary AC electromagnetic detection: During the period t3-t4, the eddy current field excitation of the magnetic circuit and the eddy current induction field (primary AC electromagnetic detection) overlap linearly;

[0084] 5) Secondary AC electromagnetic detection: During the period t4-t5, the excitation magnetic field disappears completely, and the eddy current induction field without overlap can be detected (secondary AC electromagnetic detection);

[0085] 6) Pipeline demagnetization: The period t5-t6 serves as preparation before the next detection cycle.

[0086] Furthermore, in this embodiment, a common set of AC current sources is used to generate the main circuit magnetic field and the magnetic circuit eddy current field, and the waveform characteristics of the quasi-square wave excitation signal are used to perform AC leakage magnetic detection and AC electromagnetic detection in a time-sharing manner. This idea not only simplifies the structure of the detection device, but also improves the degree of overlapping interference between the leakage magnetic field and the eddy current field in principle.

[0087] Furthermore, the primary AC electromagnetic detection signal mainly contains high-frequency components, the signal is strong, but the effective penetration depth is shallow, and it can only be used to identify cracks on the surface of the pipeline; the secondary AC electromagnetic detection signal mainly contains low-frequency components, the signal is weak, but the signal penetration ability is strong, and it can be used to identify deep cracks in the pipeline.

[0088] Further, if Figure 2As shown, this embodiment uses a quasi-square wave adjustable current source to replace the traditional permanent magnet excitation, and by constructing a quasi-square wave excitation signal with a specific timing, the characteristics of the quasi-square wave constant current high-level interval equivalent to the permanent magnet excitation are used to perform AC magnetic leakage detection on the pipeline 3; and the harmonic signals in the constant current high-level interval are screened, and the harmonic signals insensitive to the pipeline cracks are deleted, and the harmonic signals sensitive to the pipeline cracks are retained to construct the falling edge of the quasi-square wave excitation signal for the excitation of the magnetic circuit eddy current field, and then the pipeline 3 is subjected to AC electromagnetic detection after the magnetic circuit eddy current field excitation is completed. Traditional pulse eddy current detection often uses a standard square wave excitation signal, and its rich harmonic signals are not all sensitive to the crack defect 5, and even insensitive harmonic signals will become interference sources. For this reason, it is necessary to screen the harmonic signals with high sensitivity to the detection of the crack defect 5 to reconstruct the magnetic circuit eddy current excitation, and the frequency combination technology is the key to improving the sensitivity of AC electromagnetic detection.

[0089] The method includes forming a quasi-square wave excitation signal by connecting multiple groups of harmonic signals in series; the multiple groups of harmonic signals include a first group of harmonic signals and a second group of harmonic signals, the first group of harmonic signals is composed of a plurality of first harmonic signals superimposed, and the second group of harmonic signals is composed of a plurality of second harmonic signals superimposed; the method includes using the first group of harmonic signals to form a rising edge and a constant current high level interval, and using the second group of harmonic signals to form a falling edge after the constant current high level interval.

[0090] The number of the second harmonic signal is smaller than the number of the first harmonic signal.

[0091] Pipeline cracks include multiple defect types, and the method includes determining frequencies and amplitudes of multiple second harmonic signals according to the multiple defect types.

[0092] Further, if Figure 3 There are many types of crack defects 5, and factors affecting the defect type include the position of the crack defect 5, the deflection angle of the crack defect 5, the depth of the crack defect 5, etc. For example, defect type 1 is a deflection angle of 0°, defect type 2 is a deflection angle of 30°, and defect type 3 is a crack defect 5 located on the inner wall of the pipe 3, etc. Each defect type corresponds to multiple harmonic signals. By performing frequency sensitivity analysis on the defect type, the harmonic signal most sensitive to the defect type detection is screened out.

[0093] Further, if Figure 2 As shown, in this embodiment, the amplitudes of the multiple harmonic signals in the falling edge are the same, but the frequencies are different; or, in other implementation schemes, the amplitudes of the multiple harmonic signals are different, but the frequencies are the same; or, in other implementation schemes, the amplitudes and frequencies of the multiple harmonic signals are different.

[0094] Further, if Figure 1As shown in the figure, the U-shaped yoke 4 is placed directly above the crack defect 5 of the pipeline 3. The excitation coil 1 is wound around the center of the U-shaped yoke 4, and the magnetic sensor 2 is placed on the crack defect 5. After a quasi-square wave excitation signal is applied to the excitation coil 1, a change in magnetic flux will be generated in the U-shaped yoke 4, and the changing magnetic flux will cause an induced electromotive force in the excitation coil 1; a leakage magnetic field and a magnetic circuit eddy current field will be generated above the crack defect 5, and the magnetic sensor 2 can move along the x direction (-20mm < x < 20mm) to detect the leakage magnetic field strength and the magnetic circuit eddy current field strength.

[0095] The detection method includes the following steps: Step 1: Set the probe of the balanced electromagnetic detection device in the axial direction of the pipeline for scanning; Step 2: Apply a quasi-square wave excitation signal to the excitation coil 1; Step 3: Scan the pipeline 3 along the axial direction of the pipeline 3. A voltage signal is detected in the magnetic sensor 2, and the crack conditions at different depths and different deflection angles of the pipeline can be determined by analyzing the amplitude and phase characteristics of the voltage signal.

[0096] As Figure 4 shown, the quasi-square wave excitation signal generated by the function generator is converted into a voltage signal, amplified by a power amplifier, and then input into the excitation coil 1. Under the action of the excitation coil 1, a magnetic flux is generated in the U-shaped yoke 4. The two magnetic feet of the U-shaped yoke 4 are in contact with the pipeline 3, and then a main circuit magnetic field and a magnetic circuit eddy current field are generated in the pipeline wall of the pipeline 3. The magnetic sensor 2 is in contact with the pipeline 3. The voltage signal detected by the magnetic sensor 2 is transmitted to a multifunctional filter for amplification, filtering, and comparison, and then the signal is processed and digitally displayed by a high-precision oscilloscope to obtain all the information of the pipeline crack.

[0097] The detection method in this embodiment integrates the technical advantages of alternating current magnetic flux leakage detection and alternating current electromagnetic detection, and can mutually supplement the effective ranges of alternating current magnetic flux leakage detection and alternating current electromagnetic methods for identifying cracks. In addition, in the detection range overlap area, the simultaneous use of magnetic flux leakage and eddy current signals can greatly improve the crack identification accuracy. The group frequency signal can flexibly screen frequencies according to the detection task requirements, improve the identification accuracy of pipeline surface cracks, and improve the anti-interference ability of the signal.

[0098] The crack identification capabilities of the balanced electromagnetic detection device corresponding to different excitation parameters are different. Therefore, to achieve blind spot-free identification of cracks in all directions (surface, deep layer) and all angles (0° to 90°) of the pipeline, multiple second harmonic signals in the second group of harmonic signals at the falling edge have multiple frequency components and different amplitudes, and have both the anti-interference ability of high-frequency signals and the strong penetration of low-frequency signals.

[0099] When the method is used for crack identification, since the magnetic lines of force and current lines on the pipeline surface are perpendicular to each other and intertwined into a mesh distribution, any form of crack will cause the deflection of the current lines or magnetic lines of force, resulting in changes in the magnetic field on the pipeline surface. The present invention integrates the technical advantages of AC magnetic leakage and AC electromagnetic detection, and the range of the angle of pipeline crack identification by the balanced electromagnetic detection device is 0° to 90°, solving the technical problem of blind spots when traditional magnetic leakage detection is used for multi-directional and full-angle crack detection of pipelines.

[0100] Embodiment 2

[0101] This embodiment specifically introduces a pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology.

[0102] Constructed in the laboratory Figure 4 A multi-frequency homologous balanced electromagnetic detection system is built based on the principle of signal transmission, which mainly includes a function generator, a power amplifier, an electromagnetic balancing device, a multi-function filter, a high-precision oscilloscope and a pipeline to be tested.

[0103] In the experiment, the function generator (Tektronix Corporation AFG31000) generates a quasi-square wave voltage signal with an amplitude of 1V. After the voltage signal is amplified by a constant voltage power amplifier (Aigtek Corporation ATA-3080), it is connected to the excitation coil 1 of the balanced electromagnetic detection device for excitation current loading; the voltage signal detected by the magnetic sensor 2 of the balanced electromagnetic detection device is processed and adjusted by a multi-function filter (NF Corporation 3611), and then connected to a high-precision oscilloscope (Tektronix Corporation MSO508) for corresponding processing as needed. The oscilloscope can realize the extraction and analysis of the characteristic quantity of the detection signal, and can perform real-time waveform display and data storage. In the experiment, the group frequency signal contains two frequencies of 20Hz and 400Hz. The superposition of 1-channel and 2-channel sine signals can be realized through the "add in" interface of the function generator, and the group frequency signal is output through the "output" interface. The amplification factor of the power amplifier is set to 15. The cutoff frequency and gain of the filter can be configured as needed. In the experiment, the cutoff frequency and gain of the filter are set to 0.4kHz and 20dB respectively. Add a set of comparative experiments, with other parameters being the same and the excitation frequency being adjusted to a single frequency of 400 Hz.

[0104] The tested piece is a carbon steel Q235 straight pipe with a measured wall thickness of 10mm. A crack was machined on the inner surface of the pipe. The actual size of the crack is 8mm×1mm×4mm (length×width×depth). The angles between the crack direction and the pipe axis are 0°, 30°, 45°, 60° and 90° respectively. The geometric parameters of the probe are shown in Table 1. The excitation coil is wound with 1mm diameter enameled wire and 540 turns. The magnetic sensor is wound with 0.1mm enameled wire and 900 turns.

[0105] Table 1 Experimental parameters

[0106]

[0107] Figure 5 and Figure 6 It is the voltage waveform of balanced electromagnetic detection of full-angle surface cracks. It can be seen from the figure that no matter single-frequency excitation or multi-frequency excitation is used, the induced voltage signal changes significantly when the crack deflection angle increases from 0° to 90°, which verifies the effectiveness of the balanced electromagnetic detection method in realizing blind-spot identification of pipeline cracks.

[0108] Further extraction Figure 5 and Figure 6 The signal peak in the image is analyzed to analyze the relationship between the crack deflection angle and the voltage peak, such as Figure 7 As shown. It can be seen from the figure that the voltage peak of single-frequency balanced electromagnetic detection increases with the increase of crack deflection angle. When the crack deflection angle is in the range of 0°-30°, the peak value change gradient is small. In the range of 30°-90°, the voltage peak increases approximately linearly with the increase of crack deflection angle. Analysis of the voltage peak change of multi-frequency balanced electromagnetic detection shows that multi-frequency excitation can increase the peak value of voltage, but the peak value increase is different in different crack deflection angle ranges. When the crack deflection angle is in the range of 0°-30°, the voltage peak increases slightly. This is because the induced current is dominant at this time, and the current distortion caused by the low-frequency component is small; when the crack deflection angle is in the range of 30°-90°, the voltage peak increases significantly. This is because the leakage magnetic field gradually dominates at this time, and the magnetic field disturbance caused by the low-frequency component is large.

[0109] Based on the above analysis, the proposed method is compared with the traditional AC magnetic flux leakage detection and alternating electromagnetic method in terms of the ability to detect internal and external surface defects and identify full-angle cracks on pipelines. The results are shown in Table 2:

[0110] Table 2 Comparison of detection capabilities of different methods

[0111]

[0112] In this embodiment, when the crack on the pipeline surface changes from 0° to 90°, the balanced electromagnetic signal successively goes through five stages: independent action of induced current, dominant action of induced current, joint action of leakage flux and induced current, dominant action of leakage flux, and independent action of leakage flux. Characterized by the peak value of the balanced electromagnetic signal, it is possible to realize the blind spot identification of cracks on the pipeline surface at all angles, and the multi-frequency balanced electromagnetic method is used to identify cracks, which can significantly increase the peak value of the voltage signal.

[0113] In the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "plurality" refers to two or more than two, unless otherwise clearly defined.

[0114] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The description and examples are to be considered exemplary only.

[0115] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology, characterized in that: The method comprises detecting cracks in the pipeline by means of a balanced electromagnetic detection device, wherein the balanced electromagnetic detection device comprises an excitation coil, a magnetic sensor and a U-shaped yoke, the excitation coil is wound around the U-shaped yoke and arranged in the middle of the U-shaped yoke, after a quasi-square wave excitation signal is introduced into the excitation coil, a main circuit magnetic field generated in the U-shaped yoke enters into the pipe wall of the pipeline along the magnetic feet of the U-shaped yoke, and then forms a magnetic circuit eddy current field in the pipe wall of the pipeline, the magnetic sensor is arranged in the middle of two magnetic feet of the U-shaped yoke, and the magnetic sensor is used for voltage signals during AC magnetic leakage detection and AC electromagnetic detection; The detecting of pipeline cracks by the balanced electromagnetic detection device includes detecting a deflection angle of the pipeline crack, wherein the deflection angle is an angle between a line connecting two magnetic feet of the balanced electromagnetic detection device and a crack direction of the pipeline crack; The deflection angle detected by the method ranges from 0° to 90°; The method comprises performing AC magnetic leakage detection and AC electromagnetic detection on the pipeline crack by using the balanced electromagnetic detection device; The method further comprises determining the deflection angle of the pipeline crack according to the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection; When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in a first preset state, the method determines that the deflection angle of the pipeline crack is 90°, in which the voltage signal is detected during the AC magnetic flux leakage detection and the voltage signal is not detected during the AC electromagnetic detection; When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in a second preset state, the method determines that the deflection angle range of the pipeline crack is greater than 60° and less than 90°, and in the second preset state, the voltage signal detected during the AC magnetic flux leakage detection is greater than the voltage signal detected during the AC electromagnetic detection; When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in the third preset state, the method determines that the deflection angle range of the pipeline crack is greater than or equal to 30° and less than or equal to 60°, the voltage signal detected during the AC magnetic flux leakage detection in the third preset state is less than the voltage signal detected during the AC magnetic flux leakage detection in the second preset state and is greater than the voltage signal detected during the AC magnetic flux leakage detection in the fourth preset state, and at the same time, the voltage signal detected during the AC electromagnetic detection in the third preset state is less than the voltage signal detected during the AC electromagnetic detection in the fourth preset state and is greater than the voltage signal detected during the AC electromagnetic detection in the second preset state; When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in a fourth preset state, the method determines that the deflection angle range of the pipeline crack is greater than 0° and less than 30°, and in the fourth preset state, the voltage signal detected during the AC magnetic flux leakage detection is less than the voltage signal detected during the AC electromagnetic detection; When the voltage signal detected during the AC magnetic flux leakage detection and the voltage signal detected during the AC electromagnetic detection are in a fifth preset state, the method determines that the deflection angle of the pipeline crack is 0°, and in the fifth preset state, the voltage signal is not detected during the AC magnetic flux leakage detection, and the voltage signal is detected during the AC electromagnetic detection.

2. According to claim 1, a pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology is characterized by: The method comprises generating a main circuit magnetic field and a magnetic circuit eddy current field in the pipeline wall of the pipeline by the balanced electromagnetic detection device, and performing AC magnetic leakage detection on the pipeline crack based on the main circuit magnetic field and performing AC electromagnetic detection on the pipeline crack based on the magnetic circuit eddy current field; The main circuit magnetic field and the magnetic circuit eddy current field are excited by an alternating current source.

3. The pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology according to claim 1 is characterized in that: The method comprises detecting the pipeline crack by using a quasi-square wave excitation signal through the balanced electromagnetic detection device, wherein the waveform of the quasi-square wave excitation signal changes periodically, and the waveform of the quasi-square wave excitation signal in each cycle comprises a rising edge, a constant current high level interval, a falling edge and a zero level interval; The method comprises generating a main circuit magnetic field in the pipeline wall of the pipeline by the balanced electromagnetic detection device during the rising edge and the constant current high level interval and performing AC magnetic leakage detection on the pipeline crack; The method further comprises exciting a magnetic circuit eddy current field in a pipeline wall of the pipeline by the balanced electromagnetic detection device at the falling edge and the zero level interval after the AC magnetic flux leakage detection and performing AC electromagnetic detection on the pipeline crack.

4. The pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology according to claim 3 is characterized in that: The method comprises forming the quasi-square wave excitation signal by connecting a plurality of groups of harmonic signals in series; The multiple groups of harmonic signals include a first group of harmonic signals and a second group of harmonic signals, the first group of harmonic signals is composed of a plurality of first harmonic signals superimposed, and the second group of harmonic signals is composed of a plurality of second harmonic signals superimposed; The method includes using the first group of harmonic signals to form the rising edge and the constant current high level interval, and using the second group of harmonic signals to form the falling edge after the constant current high level interval.

5. The pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology according to claim 4 is characterized in that: The number of the second harmonic signals is smaller than the number of the first harmonic signals.

6. The pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology according to claim 4 is characterized in that: The pipeline cracks include multiple defect types, and the method includes determining the frequencies and amplitudes of multiple second harmonic signals according to the multiple defect types.

7. The pipeline crack detection method based on multi-frequency balanced electromagnetic technology according to claim 3 is characterized in that: The AC electromagnetic detection includes a primary AC electromagnetic detection and a secondary AC electromagnetic detection, and the primary AC electromagnetic detection and the secondary AC electromagnetic detection are performed sequentially.

8. The pipeline crack detection method based on multi-frequency balanced electromagnetic technology according to claim 7 is characterized in that: The method includes, after exciting the magnetic circuit eddy current field in the pipeline wall of the pipeline, performing the primary AC electromagnetic detection on the pipeline crack in the falling edge and part of the zero level interval by the balanced electromagnetic detection device, and performing the secondary AC electromagnetic detection on the pipeline crack in part of the zero level area after the primary AC electromagnetic detection.

9. The pipeline crack detection method based on multi-frequency homologous balanced electromagnetic technology according to claim 8 is characterized in that: The method includes demagnetizing the pipeline in a portion of the zero-level interval after the secondary AC electromagnetic detection is completed.

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