A Method and System for Detecting the Location of Welds in Covered Pipes Based on Magnetic Field Attenuation Characteristics

Abstract

This application provides a method and system for detecting the location of welds in coated pipelines based on magnetic field attenuation characteristics. The method includes: applying pulsed eddy current excitation to the coated pipeline, wherein the pulsed eddy current excitation uses a square wave or step wave signal; arranging multiple magnetic field sensors along the circumference of the pipeline and receiving voltage signals induced in the pipeline by the pulsed eddy currents, which include secondary magnetic field decay signals; measuring the magnetic field decay rate of the voltage signal received by each magnetic field sensor, wherein the magnetic field decay rate is characterized by the attenuation slope of the secondary magnetic field decay signal; superimposing the attenuation rate slope values ​​of the multiple magnetic field sensors in the later stage of magnetic field decay to obtain a superimposed attenuation rate slope value; and determining the presence and location of the weld based on a comparison between the superimposed attenuation rate slope value and a preset threshold, wherein the preset threshold is set based on the attenuation rate slope value of the weldless region.

Description

Technical Field

[0001] This application relates to the technical field of measuring electromagnetic variables, specifically to a method and system for detecting the location of weld seams in covered pipelines based on magnetic field attenuation characteristics. Background Technology

[0002] Metal pressure pipelines are widely used in industries such as petroleum, chemical, and power, often operating in harsh environments with high temperatures, high pressures, and corrosive media. To reduce heat loss from the internal media and prevent corrosion failure, the pipeline is typically covered with a cladding layer, generally consisting of insulation materials (such as high-temperature glass wool or polyurethane foam) and an external metal protective layer (such as aluminum or stainless steel). Welding is the primary form of pipeline connection, but the weld area is more susceptible to corrosion due to the material difference between the weld and the pipe body, becoming a weak point in the pipeline structure. Therefore, after long-term pipeline operation, it is crucial to conduct presence detection and precise location of the welds, and then selectively open the cladding layer for detailed inspection.

[0003] Currently, common weld location methods mainly include the drawing and data tracing method, hammer impact and sound listening method, ultrasonic guided wave method, X-ray imaging method, and electromagnetic induction method. The drawing method relies on existing data and is low in cost, but is limited by the completeness and accuracy of the data, and is prone to errors introduced by pipeline modifications; the hammer impact method is simple to operate and low in cost, and can be used for coarse location, but it is highly subjective, has limited accuracy, and is not effective for welds with thick cladding or reinforcing rings; the ultrasonic guided wave method has high accuracy, but requires local peeling of the cladding to set up detection points, which may damage the insulation structure, and the detection effect is affected by factors such as the tightness of the cladding; the X-ray imaging method provides intuitive results and can assess weld quality, but the equipment is bulky, there is a radiation risk, and there are many restrictions on on-site implementation; the electromagnetic induction method is a non-contact detection method with a fast scanning speed, but the detection accuracy is low, it is sensitive to factors such as pipeline material and cladding thickness, and its reliability is unstable.

[0004] Among the methods described above, ultrasonic guided wave detection and electromagnetic induction are commonly used. However, ultrasonic guided wave detection requires breaking the cladding layer, and its detection range is affected by the actual structure, resulting in significant limitations in its application. Therefore, developing highly sensitive electromagnetic detection technology to achieve non-contact, precise positioning of weld seams in cladding pipes has significant engineering value.

[0005] Despite the advantages of pulsed eddy current (PEC) detection technology, such as non-contact operation and penetration of cladding layers, it still has significant limitations in practical applications for locating weld seams in clad pipelines. Existing PEC methods mostly employ single sensors or conventional probe structures to measure magnetic field decay rates, making them susceptible to interference in complex industrial environments and resulting in insufficient sensitivity for weld seam identification. Specifically: First, the eddy current field distribution excited by conventional radially or laterally placed probes is not concentrated enough, especially with energy dispersion in the circumferential direction of the pipeline, making it difficult to effectively cover the complete contour of the circumferential weld. Second, single-point measurement methods have weak resistance to local interference and are prone to misjudgment due to uneven cladding thickness, material differences, or on-site electromagnetic noise. Furthermore, existing methods do not adequately utilize the characteristic of the eddy current flowing around the entire circumference of the pipeline, failing to fully leverage the potential of multi-sensor collaborative measurement in enhancing the signal-to-noise ratio.

[0006] Therefore, there is an urgent need for a novel pulsed eddy current detection method that can fully utilize the eddy current field distribution characteristics of the longitudinal probe and combine multi-sensor signal fusion processing to solve the problems of low response sensitivity and weak anti-interference ability of existing technologies for welds, and to achieve accurate and efficient positioning of welds in pipes with cladding layers. Summary of the Invention

[0007] This application proposes a method and system for detecting the location of weld seams in coated pipelines based on the characteristics of magnetic field attenuation, in order to overcome the deficiencies of the prior art.

[0008] According to a first aspect of the embodiments of this application, a method for detecting the location of a weld seam in a coated pipeline based on magnetic field attenuation characteristics is provided, comprising:

[0009] A pulsed eddy current excitation is applied to the clad pipe, wherein the pulsed eddy current excitation uses a square wave or step wave signal;

[0010] Multiple magnetic field sensors are arranged along the circumference of the pipe and receive voltage signals containing secondary magnetic field decay signals induced by pulsed eddy currents in the pipe. The multiple magnetic field sensors are coils or magnetic sensors.

[0011] The magnetic field decay rate of the voltage signal received by each of the magnetic field sensors is measured, and the magnetic field decay rate is characterized by the attenuation slope of the secondary magnetic field decay signal.

[0012] The decay rate slope values ​​of multiple magnetic field sensors in the later stage of magnetic field decay are superimposed to obtain the superimposed decay rate slope value.

[0013] Based on the comparison between the superimposed decay rate slope value and the preset threshold, the existence and location of the weld are determined, wherein the preset threshold is set based on the decay rate slope value of the weldless region.

[0014] In some embodiments, applying pulsed eddy current excitation to the coated pipe includes:

[0015] A pulsed eddy current excitation is applied to the coated pipe using a longitudinally placed excitation probe;

[0016] The excitation probe is either a cylindrical longitudinally placed probe or a semi-circular longitudinally placed probe. The longitudinally placed excitation probe adopts a U-shaped magnetic core structure, with enameled copper wire wound on the magnetic core to form an excitation coil, which is used to enhance the circumferential characteristics of the eddy current in the pipe.

[0017] In some embodiments, arranging the plurality of magnetic field sensors along the circumference of the pipe includes:

[0018] Multiple magnetic field sensors are arranged at intervals along the circumference of the pipe with an angle range of 30° to 90°, so that the sensing range of the multiple magnetic field sensors covers the entire circumference of the pipe.

[0019] In some embodiments, measuring the magnetic field decay rate of the voltage signal received by each of the magnetic field sensors includes:

[0020] In the later stage after the pulsed eddy current excitation is turned off, the magnetic field decay rate of the voltage signal received by each of the magnetic field sensors is measured.

[0021] The later stage is determined based on the target stable action of the vortex flowing around the pipe in a circular motion. The decay rate slope value of the later stage tends to the target fluctuation range. The time range of the later stage is 0.01 seconds to 0.1 seconds.

[0022] In some implementations, the superposition process is an arithmetic average or weighted summation, used to correct for local interference experienced by individual sensors.

[0023] In some implementations, determining the presence and location of the weld seam based on a comparison of the superimposed decay rate slope value with a preset threshold includes:

[0024] When the slope value of the superimposed decay rate shows a peak or valley value at the target position relative to the preset threshold, it is determined that the weld exists and the target position is the location of the weld.

[0025] Otherwise, it is determined that the weld does not exist or the target location is not the location of the weld.

[0026] According to a second aspect of this application, a system for detecting the location of a coated pipe weld based on magnetic field attenuation characteristics is provided for implementing the above-mentioned method, comprising:

[0027] A pulse signal generator is used to generate square wave or step wave excitation signals.

[0028] A longitudinally placed excitation probe is connected to the pulse signal generator. The excitation probe is a cylindrical longitudinally placed probe or a semi-circular longitudinally placed probe, used to apply pulsed eddy current excitation to a pipe with a coating layer.

[0029] Multiple magnetic field sensors are arranged along the circumference of the pipe to receive magnetic field decay signals caused by eddy currents;

[0030] A data acquisition unit, connected to the plurality of magnetic field sensors, is used to acquire the signal voltage of each sensor;

[0031] The signal processing unit, connected to the data acquisition unit, is configured to measure the magnetic field decay rate slope of each sensor and superimpose the decay rate slope values ​​of multiple sensors to output the weld detection result.

[0032] In some embodiments, the plurality of magnetic field sensors are coil sensors or magnetoresistive sensors, installed at equal intervals along the circumference of the pipe with an interval angle of 30°; the excitation probe includes a magnetic core and enameled copper wire wound thereon, the magnetic core being cylindrical or U-shaped.

[0033] In some embodiments, the signal processing unit further includes a display module for visualizing the magnetic field decay curve and weld position indication.

[0034] In some implementations, the system further includes a positioning module that automatically calculates the axial position of the weld based on the difference in the slope of the superimposed decay rate and outputs the detection result through an alarm device.

[0035] The beneficial effects of the method and system for detecting the location of coated pipe welds based on magnetic field attenuation characteristics in this application include at least the following:

[0036] This application embodiment can excite an electromagnetic field containing rich frequency components by applying square wave or step wave pulse eddy current excitation to the coated pipe. The low frequency component has strong penetrating ability and can effectively penetrate the coating and excite the internal metal pipe, laying the foundation for non-contact detection. Compared to single-frequency excitation, this excitation method can acquire deeper detection information. By arranging multiple magnetic field sensors along the circumference of the pipeline and receiving secondary magnetic field decay signals, comprehensive coverage detection of the circumferential area of ​​the pipeline is achieved, avoiding missed detections that may be caused by single-point measurement. Moreover, the collaborative work of multiple sensors can simultaneously acquire magnetic field information from different spaces, providing a data foundation for subsequent signal fusion processing. By measuring the magnetic field decay rate of the signal received by each sensor and characterizing it as the decay slope, the dynamic characteristics of the eddy current field decay process can be focused on. This parameter is more sensitive to small changes in electromagnetic characteristics caused by the weld than static parameters such as amplitude. Furthermore, the extraction of the decay slope helps to reduce common-mode interference and improve the signal-to-noise ratio. By superimposing the decay rate slope values ​​of multiple sensors in the later stage of decay, detection information from different spatial locations can be effectively fused. The correlation of signals is used to enhance the effective signal components caused by the weld, while suppressing random noise and local interference. This spatial domain signal fusion strategy significantly improves the system's anti-interference capability and reliability. By comparing the slope value of the superimposed decay rate with a preset threshold to determine the weld position, the judgment process has a clear objective standard, reducing the influence of subjective factors and improving the consistency and repeatability of the detection results. The threshold is set based on the benchmark value of the weldless area, ensuring the rationality of the judgment basis and facilitating the accurate identification and positioning of the weld. Attached Figure Description

[0037] Figure 1 This is a schematic flowchart of the method for detecting the location of a covered pipe weld based on the magnetic field attenuation characteristics according to an embodiment of this application.

[0038] Figure 2 This is a schematic diagram illustrating the principle of pulsed eddy current detection for coated pipelines according to an embodiment of this application.

[0039] Figure 3 This is a schematic diagram illustrating the working principle of pulsed eddy current detection excitation and signal reception for pipes with cladding layers according to an embodiment of this application.

[0040] Figure 4 This is a schematic diagram of a simulation model of different sensor types for pulsed eddy current detection of coated pipelines according to an embodiment of this application;

[0041] Figure 5 This is a schematic diagram of the axial tangential eddy current density distribution according to an embodiment of this application;

[0042] Figure 6This is a schematic diagram of the radial cross-sectional eddy current density distribution according to an embodiment of this application;

[0043] Figure 7-8 This is a schematic diagram of the dynamic distribution of the eddy current field in the longitudinal probe pipe according to an embodiment of this application;

[0044] Figure 9 This is a schematic diagram illustrating the dynamic proportion of circulation in pipes of different outer diameters according to an embodiment of this application;

[0045] Figure 10 This is a schematic diagram of the U-shaped excitation coil and series detection coils according to an embodiment of this application;

[0046] Figure 11 This is a schematic diagram of the sensor arrangement according to an embodiment of this application;

[0047] Figure 12 This is a schematic diagram of the voltage signals received by the detection sensor at different locations according to an embodiment of this application. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the method and system for detecting the location of welded pipes based on magnetic field attenuation characteristics will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of this application. Obviously, the described embodiments are only some embodiments of the embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0049] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed embodiments of the present application, but merely to illustrate selected embodiments of the present application. Other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort are all within the scope of protection of the embodiments of the present application.

[0050] It can be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it will not be further defined and explained in subsequent figures according to the embodiments of this application.

[0051] See attached document Figure 1As shown in the figure, this application discloses a method for detecting the location of weld seams in coated pipelines based on magnetic field attenuation characteristics. This method is implemented using a system for detecting the location of weld seams in coated pipelines based on magnetic field attenuation characteristics. The purpose of this method is to provide a novel pulsed eddy current detection method that can fully utilize the eddy current field distribution characteristics of the longitudinal probe and combine multi-sensor signal fusion processing to solve the problems of low weld seam response sensitivity and weak anti-interference ability in existing technologies, thereby achieving accurate and efficient positioning of weld seams in coated pipelines. The method includes steps 110-150.

[0052] Step 110: Apply pulsed eddy current excitation to the cladding pipe. The pulsed eddy current excitation uses a square wave or step wave signal.

[0053] Pulsed eddy current testing is an electromagnetic non-destructive testing technique, a type of eddy current testing, based on the principle of electromagnetic induction. As a novel testing method, it possesses advantages not found in traditional eddy current testing. Unlike the sinusoidal excitation method of traditional eddy current testing, pulsed eddy current testing typically uses square wave excitation with a specific duty cycle or bipolar square wave excitation as the signal source. Since the square wave excitation signal contains a spectrum from the fundamental frequency to higher harmonics, lower frequency signals can penetrate deeper into the test specimen, while higher frequency signals are more sensitive to surface defects. Therefore, in principle, pulsed eddy current testing can detect specimens of different thicknesses and defects of different depths with a single excitation, and the received signal contains more useful information.

[0054] In some embodiments, applying pulsed eddy current excitation to the coated pipe includes applying pulsed eddy current excitation to the coated pipe through a longitudinally placed excitation probe.

[0055] The excitation probe is either a cylindrical longitudinally placed probe or a semi-circular longitudinally placed probe. The longitudinally placed excitation probe adopts a U-shaped magnetic core structure, with enameled copper wire wound on the magnetic core to form an excitation coil, which is used to enhance the circumferential characteristics of the eddy current in the pipe.

[0056] Step 120: Arrange multiple magnetic field sensors along the circumference of the pipe and receive voltage signals containing secondary magnetic field decay signals induced by pulsed eddy currents in the pipe. The multiple magnetic field sensors are coils or magnetic sensors.

[0057] In some embodiments, arranging multiple magnetic field sensors along the circumference of the pipe includes: arranging the multiple magnetic field sensors at intervals of 30° to 90° along the circumference of the pipe, so that the sensing range of the multiple magnetic field sensors covers the entire circumference of the pipe. (See attached figure) Figure 11The diagram shows the relative angular arrangement of the excitation coil and multiple detection sensors (i.e., magnetic field sensors, such as coils or magnetic sensors). Preferably, one detection sensor is arranged every 30°, so that the detection range covers the entire circumference.

[0058] For example, see Appendix Figure 1 The diagram illustrates the basic principle of pulsed eddy current testing of coated pipe specimens, including a signal generator capable of generating square wave signals, a data acquisition unit capable of acquiring and receiving coil voltages, and a computer capable of processing data, as well as referenced in the appendix. Figure 2 As shown, attached Figure 2 The diagram illustrates the working principle of the excitation and reception signals. Pulse eddy current detection first excites the excitation coil with a square wave signal of a certain voltage. For the detection of pipes with cladding, due to the low frequency (generally below 100Hz) and the relatively short fall time and period of the rectangular wave, the excitation magnetic field and eddy current magnetic field can be simplified into roughly separate primary and secondary magnetic fields. When the square wave voltage is not zero, the DC component in the coil excites the primary magnetic field, which is a constant magnetic field; the receiving coil is not working at this time. When the DC component in the excitation square wave is turned off, the current in the excitation coil rapidly decays to zero. At this time, the magnetic field in the workpiece also begins to decay, and eddy currents are generated in the workpiece due to the decay of the magnetic field. The magnetic field generated by the eddy currents is called the secondary magnetic field. The receiving coil then begins to collect the induced signal from the secondary magnetic field. If there are defects or other discontinuities in the specimen, the secondary magnetic field will differ from that without discontinuities, resulting in a different induced voltage in the receiving coil, thus achieving the purpose of detecting defects or measuring the thickness of the specimen.

[0059] Step 130: Measure the magnetic field decay rate of the voltage signal received by each magnetic field sensor. The magnetic field decay rate is characterized by the attenuation slope of the secondary magnetic field decay signal.

[0060] In some embodiments, measuring the magnetic field decay rate of the voltage signal received by each magnetic field sensor includes measuring the magnetic field decay rate of the voltage signal received by each magnetic field sensor in the later stage after the pulsed eddy current excitation is turned off.

[0061] The later stage is determined based on the target stable motion of the vortex flowing around the pipe. The decay rate slope value of the later stage tends to the target fluctuation range. The corresponding time range of the later stage is 0.01 seconds to 0.1 seconds.

[0062] Furthermore, the dynamic distribution of magnetic fields and eddy currents differs depending on the type of sensor. Analysis of experimental data in this application's embodiments reveals that specific sensor types are beneficial for improving the accuracy of weld seam detection and positioning. For example, refer to the attached... Figure 4As shown, in this embodiment of the application, finite element simulation software can be used to establish quarter-scale models of the cylindrical coil in three orientations: radial, lateral, and longitudinal. The receiving coil and excitation coil of the probe are placed coaxially. (See attached diagram.) Figure 5 The diagram shows axial cross-sectional views of the pipe induced eddy current density distribution using radial, lateral, and longitudinal probes. Data in the diagram is taken at a lift height of 50 mm and a time interval of 0.02 s. (See attached diagram.) Figure 5 As shown, the eddy current at the center directly below the radial probe is very weak, with a blind zone in the middle; the focusing characteristics of the transverse and longitudinal probes are significantly improved in the axial section, with more concentrated energy; in the axial direction, the longitudinal probe has the most concentrated energy. (See attached diagram.) Figure 6 As shown, the vortex distribution diagrams of the three probes in the radial section of the pipe are illustrated. The data is from the time 0.02s, with a lift-off height of 50mm. According to... Figure 6 As shown, the eddy currents of radial and longitudinal probes diffuse more extensively in the circumferential direction. However, the situation is more unique for the transverse probe. A significant characteristic of the eddy current field in the transverse probe is the concentration of current in the circumferential direction. This is because the magnetic field is radial, while the eddy current direction is axial, resulting in no eddy current loops in the circumferential direction. The current energy primarily flows axially, thus concentrating the energy in the circumferential direction. However, the eddy current field of the longitudinal probe possesses a special property, which is one of the application scenarios adopted in the embodiments of this application. (Refer to the appendix...) Figure 7-8 The figure shows the dynamic distribution of the eddy current field of the longitudinal probe. In the early stage after the pulse signal is turned off, the eddy current field is divided into two parts, forming two different loops. The figure shows a quarter-loop model. Figure 7 The diagram shows the circulation at the top of the pipe, the end closest to the probe. Figure 8 The circulation around the entire circumference of the pipe is shown. In order to... Figure 7-8 The two circulating currents are separated. In this embodiment, a method of decoupling the two circulating currents by using simultaneous integral equations in simulation is proposed. The total current around the top is the average of the absolute value integral of the current density at the top cross-section and the current density integral, as shown in equation (1); the circulating current around the pipe is the absolute value integral of the current density at the bottom cross-section, as shown in equation (2). Equations (1) and (2) can be used to separate the local circulating current at the top and the circulating current in the pipe.

[0063] Equation (1);

[0064] Equation (2);

[0065] in, This indicates the total current value around the top; The surface integral representing the absolute value of the current density at the top cross section; This represents the surface integral of the current density at the top cross section; This indicates the value of the circulating current in the pipeline; This represents the surface integral of the absolute value of the current density at the bottom cross section.

[0066] See attached document Figure 9 As shown, the output displays the dynamic proportion of the pipe circulation over time, from the attached... Figure 9 As can be seen, the initial current is mainly localized circulation at the top, while the later current is mainly circulation around the pipe. Based on this, the longitudinal probe used in this embodiment allows the current to be initially focused at the top and then flow around the entire circumference, thus enabling detection of the entire circumference.

[0067] Step 140: The decay rate slope values ​​of multiple magnetic field sensors in the later stage of magnetic field decay are superimposed to obtain the superimposed decay rate slope value.

[0068] In some implementations, the superposition process is an arithmetic average or weighted summation, used to correct for localized interference experienced by individual sensors.

[0069] Based on the simulation results above, it can be seen that when detecting circumferential welds in pipes with cladding layers, if a longitudinal probe is used for detection, the eddy currents will flow around the entire circumference in the later stages. If the weld is present, it will cause greater eddy current disturbances compared to areas without welds, and the magnetic field decay rate will also change significantly. Using a receiving coil or other sensors to detect the magnetic field decay rate is beneficial for detecting the presence of the weld and for accurate positioning.

[0070] In addition, in some embodiments, besides the excitation coil structure with a cylindrical coil placed longitudinally, the embodiments of this application also use a semi-circular (U-shaped similar) excitation coil structure. The distribution of the eddy current field when the semi-circular excitation coil is placed longitudinally is the same as the dynamic distribution of the eddy current field when the cylindrical coil is placed longitudinally, which is also beneficial for detecting the existence of the weld and for accurate positioning.

[0071] For example, see Appendix Figure 10 As shown, in this embodiment, a semi-circular (U-shaped or similar) excitation coil (with surrounding small coils serving as receiving coils) is used as the excitation source for pulsed eddy current detection. Simulation studies show that the distribution of the eddy current field is the same as that of an eddy current field using a cylindrical coil placed longitudinally. This embodiment utilizes multiple sensors, measuring at regular intervals at the same circumferential position, enabling detection by a single sensor moving around the circumference or simultaneous reception by multiple sensors at different angular positions on the circumference. Preferably, this embodiment employs a multi-sensor operating mode, which can achieve higher detection efficiency.

[0072] This application embodiment fully utilizes the characteristics of longitudinal cylindrical and U-shaped excitation probes, where the eddy current flows through the entire circumference and then through the entire weld. During weld inspection, longitudinal probes (cylindrical longitudinal; semi-circular longitudinal; U-shaped longitudinal) are used for excitation to amplify the interference of the weld on the eddy current field, thereby increasing the slope difference of the magnetic field attenuation curve.

[0073] See attached document Figure 12 As shown, the attenuation rate of the eddy current magnetic field is represented by the received signal voltage from the receiving sensor at different angular positions. The upper solid line curve represents the area with welds, and the lower dashed line curve represents the area of ​​the pipe body without welds. (See attached diagram.) Figure 12 It can be seen that regardless of the sensor's location on the circumference, the attenuation rate differs between areas with and without welds, while the subsequent slope values ​​remain essentially consistent for both. By superimposing the slope values ​​of the signals received by all sensors, if the slope value at a certain location differs significantly from other locations, it indicates the presence of a weld directly below that location. This embodiment of the application also enhances the anti-interference capability of weld detection by superimposing the subsequent slope values ​​of all sensors. This is achieved through the correction effect of other sensors on the same circumference when a single sensor is subject to localized interference. Furthermore, superposition also strengthens the signal when the weld signal is weak.

[0074] Step 150: Based on the comparison between the superimposed decay rate slope value and the preset threshold, determine the existence and location of the weld.

[0075] The preset threshold is the decay rate slope value of the weldless region. Additionally, in this embodiment, before formal testing, the decay rate slope values ​​of multiple sensors can be collected on a known weldless pipe section, and their average value can be used as the benchmark for the preset threshold.

[0076] In some implementations, determining the existence and location of the weld seam based on the comparison between the superimposed decay rate slope value and a preset threshold includes: when the superimposed decay rate slope value has a peak or valley value at the target location relative to the preset threshold, determining that the weld seam exists and that the target location is the location of the weld seam; otherwise, determining that the weld seam does not exist or that the target location is not the location of the weld seam.

[0077] The significant difference is determined by a relative deviation threshold. For example, when the slope value at a certain position deviates from the average value at other positions on the same circumference by more than 15% (which can be determined by a calibration test), it is identified as a peak or valley value.

[0078] This application embodiment can excite an electromagnetic field containing rich frequency components by applying square wave or step wave pulse eddy current excitation to the coated pipe. The low frequency component has strong penetrating ability and can effectively penetrate the coating and excite the internal metal pipe, laying the foundation for non-contact detection. Compared to single-frequency excitation, this excitation method can acquire deeper detection information. By arranging multiple magnetic field sensors along the circumference of the pipeline and receiving secondary magnetic field decay signals, comprehensive coverage detection of the circumferential area of ​​the pipeline is achieved, avoiding missed detections that may be caused by single-point measurement. Moreover, the collaborative work of multiple sensors can simultaneously acquire magnetic field information from different spaces, providing a data foundation for subsequent signal fusion processing. By measuring the magnetic field decay rate of the signal received by each sensor and characterizing it as the decay slope, the dynamic characteristics of the eddy current field decay process can be focused on. This parameter is more sensitive to small changes in electromagnetic characteristics caused by the weld than static parameters such as amplitude. Furthermore, the extraction of the decay slope helps to reduce common-mode interference and improve the signal-to-noise ratio. By superimposing the decay rate slope values ​​of multiple sensors in the later stage of decay, detection information from different spatial locations can be effectively fused. The correlation of signals is used to enhance the effective signal components caused by the weld, while suppressing random noise and local interference. This spatial domain signal fusion strategy significantly improves the system's anti-interference capability and reliability. By comparing the slope value of the superimposed decay rate with a preset threshold to determine the weld position, the judgment process has a clear objective standard, reducing the influence of subjective factors and improving the consistency and repeatability of the detection results. The threshold is set based on the benchmark value of the weldless area, ensuring the rationality of the judgment basis and facilitating the accurate identification and positioning of the weld.

[0079] This application also discloses a system for detecting the location of a coated pipe weld based on the magnetic field attenuation characteristics, used to implement the above method, comprising: a pulse signal generator, a longitudinally placed excitation probe, multiple magnetic field sensors, a data acquisition unit, and a signal processing unit.

[0080] The system includes a pulse signal generator for generating square wave or step wave excitation signals; a longitudinally placed excitation probe connected to the pulse signal generator, which is either a cylindrical or semi-circular longitudinally placed probe, for applying pulsed eddy current excitation to the cladding pipe; multiple magnetic field sensors arranged along the circumference of the pipe for receiving magnetic field decay signals caused by eddy currents; a data acquisition unit connected to the multiple magnetic field sensors for acquiring the signal voltage of each sensor; and a signal processing unit connected to the data acquisition unit, configured to measure the magnetic field decay rate slope of each sensor and superimpose the decay rate slope values ​​of multiple sensors to output the weld inspection results.

[0081] In some embodiments, the plurality of magnetic field sensors are coil sensors or magnetoresistive sensors, installed at equal intervals along the circumference of the pipe with an interval angle of 30°; the excitation probe includes a magnetic core and enameled copper wire wound thereon, the magnetic core being cylindrical or U-shaped.

[0082] In some implementations, the signal processing unit also includes a display module for visualizing the magnetic field decay curve and weld position indication.

[0083] In some implementations, the system also includes a positioning module that automatically calculates the axial position of the weld based on the difference in the slope of the superimposed decay rate and outputs the detection results through an alarm device.

[0084] This application utilizes the characteristic of current flowing around the entire circumference in the later stages of cylindrical and semi-circular longitudinally placed probes. When detecting the presence and location of welds, cylindrical and semi-circular longitudinally placed probes are used for excitation. A single sensor is used to receive the changes in the magnetic field caused by the eddy current field by shifting along the circumference, or multiple sensors along the circumference are used to receive the changes in the magnetic field. By detecting the magnetic field decay rate and superimposing the magnetic field decay rates at different positions, the detection sensitivity and anti-interference ability are improved.

[0085] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this application, and this application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this application, and these modifications and improvements are also considered to be within the scope of protection of this application.

Claims

1. A method for detecting the position of a weld of a pipe with a cladding based on the magnetic field decay characteristics, characterized by, include: A pulsed eddy current excitation is applied to the clad pipe, wherein the pulsed eddy current excitation uses a square wave or step wave signal; Multiple magnetic field sensors are arranged along the circumference of the pipe and receive voltage signals containing secondary magnetic field decay signals induced by pulsed eddy currents in the pipe. The multiple magnetic field sensors are coils or magnetic sensors. The magnetic field decay rate of the voltage signal received by each of the magnetic field sensors is measured, and the magnetic field decay rate is characterized by the attenuation slope of the secondary magnetic field decay signal. The decay rate slope values ​​of multiple magnetic field sensors in the later stage of magnetic field decay are superimposed to obtain the superimposed decay rate slope value. Based on the comparison between the superimposed decay rate slope value and the preset threshold, the existence and location of the weld are determined, wherein the preset threshold is set based on the decay rate slope value of the weldless region.

2. The method according to claim 1, characterized in that, The application of pulsed eddy current excitation to the coated pipe includes: A pulsed eddy current excitation is applied to the coated pipe using a longitudinally placed excitation probe; The excitation probe is either a cylindrical longitudinally placed probe or a semi-circular longitudinally placed probe. The longitudinally placed excitation probe adopts a U-shaped magnetic core structure, with enameled copper wire wound on the magnetic core to form an excitation coil, which is used to enhance the circumferential characteristics of the eddy current in the pipe.

3. The method according to claim 1, characterized in that, The arrangement of multiple magnetic field sensors along the circumference of the pipe includes: Multiple magnetic field sensors are arranged at intervals along the circumference of the pipe with an angle range of 30° to 90°, so that the sensing range of the multiple magnetic field sensors covers the entire circumference of the pipe.

4. The method according to claim 1, characterized in that, The measurement of the magnetic field decay rate of the voltage signal received by each of the magnetic field sensors includes: In the later stage after the pulsed eddy current excitation is turned off, the magnetic field decay rate of the voltage signal received by each of the magnetic field sensors is measured. The later stage is determined based on the target stable action of the vortex flowing around the pipe in a circular motion. The decay rate slope value of the later stage tends to the target fluctuation range. The time range corresponding to the later stage is 0.01 seconds to 0.1 seconds.

5. The method according to claim 1, characterized in that, The superposition process is an arithmetic average or weighted summation, used to correct local interference experienced by a single sensor.

6. The method according to claim 1, characterized in that, The step of determining the existence and location of the weld seam based on the comparison between the superimposed decay rate slope value and a preset threshold includes: When the slope value of the superimposed decay rate shows a peak or valley value at the target position relative to the preset threshold, it is determined that the weld exists and the target position is the location of the weld. Otherwise, it is determined that the weld does not exist or the target location is not the location of the weld.

7. A system for detecting the location of a coated pipe weld based on the attenuation characteristics of a magnetic field, used to implement the method described in any one of claims 1 to 6, characterized in that, include: A pulse signal generator is used to generate square wave or step wave excitation signals. A longitudinally placed excitation probe is connected to the pulse signal generator. The excitation probe is a cylindrical longitudinally placed probe or a semi-circular longitudinally placed probe, used to apply pulsed eddy current excitation to a pipe with a coating layer. Multiple magnetic field sensors are arranged along the circumference of the pipe to receive magnetic field decay signals caused by eddy currents; A data acquisition unit, connected to the plurality of magnetic field sensors, is used to acquire the signal voltage of each sensor; The signal processing unit, connected to the data acquisition unit, is configured to measure the magnetic field decay rate slope of each sensor and superimpose the decay rate slope values ​​of multiple sensors to output the weld detection result.

8. The system according to claim 7, characterized in that, The plurality of magnetic field sensors are coil sensors or magnetoresistive sensors, installed at equal intervals along the circumference of the pipe, with an interval angle of 30°; the excitation probe includes a magnetic core and enameled copper wire wound on it, the magnetic core being cylindrical or U-shaped.

9. The system according to claim 7, characterized in that, The signal processing unit also includes a display module for visualizing the magnetic field decay curve and weld position indication.

10. The system according to claim 7, characterized in that, The system also includes a positioning module, which automatically calculates the axial position of the weld based on the difference in the slope of the superimposed decay rate, and outputs the detection results through an alarm device.

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