Pipeline corrosion detection method and detection system based on external normal magnetic field

Abstract

The present application relates to the field of pipeline nondestructive testing, and particularly relates to a pipeline corrosion detection method based on an external normal magnetic field and a corresponding pipeline corrosion detection system based on a pig. The scheme places a permanent magnet at a to-be-detected area of a ferromagnetic pipeline, magnetizes the pipeline using the permanent magnet, and causes a permeability distortion in the local pipe wall of the pipeline. The degree of the permeability distortion is related to the pipe wall thickness. On this basis, an eddy current sensor carried on the pig is used to scan the pipeline together with the pig. Then, the pipe wall thickness is obtained according to the obtained permeability distortion information of the pipe wall at each position of the pipeline, and corrosion detection of the inner pipe wall of the pipeline is realized. The present application also develops a corresponding pipeline corrosion detection system based on a pig on the basis of the related detection idea. The scheme can effectively overcome the problems of high cost and low efficiency of the existing pipeline internal detector.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of pipeline non-destructive testing, and in particular to a pipeline corrosion detection method based on an external normal magnetic field and a corresponding pipeline corrosion detection system based on a pig. BACKGROUND

[0002] Industrial pipelines and long-distance pipelines are usually subject to varying working conditions and have strong corrosive media, and are prone to surface local corrosion problems. Once corroded to leakage, it is easy to cause serious safety accidents, and non-destructive testing must be performed during maintenance. The current pipeline corrosion detection is usually manually detected periodically, and an ultrasonic thickness gauge is used for manual detection at specific positions, which is complex to operate, high in cost, and greatly interfered by human factors.

[0003] In view of the above problems existing in manual detection, technicians have developed various internal detection devices carried on a pipeline robot. However, the internal detector carrying a magnetic flux leakage or ultrasonic sensor has high detection cost and long cycle; and the internal detector carrying a magnetic flux leakage sensor is mainly used for volume defect detection and is difficult to identify the slowly changing corrosion. The ultrasonic internal detector cannot be applied to high-speed continuous measurement, and the measurement efficiency is low.

[0004] During the maintenance of long-distance pipelines, a pig is needed for dredging and cleaning; among them, the detection cycle of the traditional internal detector is 1-2 years, and the scanning cycle of the pig is 1-2 months. Therefore, using the pig to carry the internal detection device for pipeline measurement is becoming a popular direction in the field. By taking advantage of the high-frequency scanning of the pig, the pipeline corrosion trend can be efficiently, accurately and low-costly obtained, providing data support for intelligent operation and maintenance of the pipeline. However, the existing technology lacks a solution that can be carried on the pig and can realize low-cost and rapid measurement of pipeline corrosion. SUMMARY

[0005] In order to solve the problems of high cost and low efficiency of the existing pipeline internal detector, the present application provides a pipeline corrosion detection method based on an external normal magnetic field and a corresponding pipeline corrosion detection system based on a pig.

[0006] The technical scheme provided by the present application is as follows:

[0007] A pipeline corrosion detection method based on an external normal magnetic field, comprising:

[0008] A detachable annular permanent magnet is arranged at a specified segment of the outer wall of the ferromagnetic pipeline to form an external normal magnetic field; and a pig with an eddy current sensor is used to collect a dynamic impedance signal Δ Z ( t ).

[0009] The impedance signal Δ Z (t ) Filtering and signal extraction are performed to obtain the various segments. i The effective signal at each segment is used, and the peak-to-peak value of the effective signal is taken as the sensor impedance at each segment. Z i .

[0010] Based on sensor impedance Z i Query a preset permeability-impedance mapping Z = f ( μ ), and thus obtain the permeability distortion Δ at the corresponding segment position. μ i Based on the current diameter of the pipe to be tested D Select a pre-calibrated wall thickness-permeability mapping μ = f D ( L ), will distort the permeability Δ μ i Convert to corresponding wall thickness measurement value L i .

[0011] When the wall thickness measurement value at any segment L i With standard wall thickness The difference Δ L Exceeding the preset security threshold L At time 0, it is determined that pipeline corrosion has occurred at the corresponding section.

[0012] The present invention also includes a pipeline corrosion detection system based on a pipeline pig, which includes: multiple annular permanent magnets, a multifunctional pipeline pig, and a data processing device.

[0013] A ring-shaped permanent magnet is used to be detachably installed at a designated section on the outer wall of the ferromagnetic pipe to be tested, so as to form the required normal magnetic field at the corresponding section.

[0014] The multi-functional pigging device includes a pig body, two magnetic brushes, an eddy current sensor array, and a data storage unit. The pig body is dumbbell-shaped, comprising two coaxially connected elastic friction elements and a connecting shaft. The eddy current sensor array includes multiple eddy current sensors arranged in a ring along the middle section of the connecting shaft. The two magnetic brushes are mounted on the connecting shaft near the friction elements, and are used to attract ferromagnetic impurities and provide a uniform magnetic field environment at the eddy current sensors. The eddy current sensors are used to synchronously acquire impedance signals during the pigging process, and the data storage unit stores the impedance signals detected by each eddy current sensor.

[0015] The data processing device is used for acquiring impedance signals collected by each eddy current sensor in the multifunctional pig, and the impedance signals collected by each eddy current sensor are processed by using the pipeline corrosion detection method based on the external normal magnetic field as described above, so that the wall thickness information at different circumferential positions in each segment of the pipeline is obtained, and the corrosion states of the pipeline at different positions are analyzed.

[0016] As a further improvement of the present application, the eddy current sensor array comprises a plurality of detection probes and an expandable elastic support; the elastic support comprises a plurality of support rods hinged to the connecting shaft and extending radially outward; each support rod is fixedly connected to the connecting shaft through a respective fixing seat or a same fixing ring; the support rod and the fixing seat or the connecting shaft are rotatably connected. The detection probes are installed at the ends of the support rods; the support rods are inclined backward along the traveling direction of the pig, and the included angle between the support rods and the connecting shaft is adjusted to adapt to different pipe diameters. Elastic members for applying outward prestress to the support rods are also arranged on the support rods, so that each detection probe closely abuts against the inner wall of the pipeline.

[0017] The present application has the following beneficial effects:

[0018] The present application provides a new scheme for detecting the corrosion condition of the inner wall of a long-distance pipeline, which preinstalls permanent magnets at a to-be-detected position to generate an excitation field in a local pipeline, then loads eddy current sensors for detecting the local magnetic permeability distortion of the pipeline on a pig, and performs pipeline inspection during the cleaning process of the pig to obtain the corrosion states of the pipeline in different regions. Compared with the traditional scheme, the technical scheme provided by the present application can realize automatic detection, greatly improve the detection efficiency, save manpower and ensure the reliability of the detection results.

[0019] The detection system used in the scheme of the present application can be based on the existing pig design, has a simple structure and low cost, and does not need to develop a related pipeline scanning robot, thereby reducing the development cost and use cost, and being beneficial to energy saving and environmental protection. In the scheme, permanent magnets are used as excitation devices to generate the required external normal magnetic field. Compared with the traditional detection equipment which performs magnetic flux leakage detection by using built-in electromagnets or performs ultrasonic detection by using ultrasonic equipment, the scheme does not need additional energy consumption, reduces energy consumption, and is beneficial to energy saving and environmental protection.

[0020] In addition, the scheme provided by the present application can complete quality detection simultaneously with the pipeline cleaning process, and has a higher detection frequency. The detection process does not affect the normal medium transportation of the long-distance pipeline; the practicability is excellent, and the market prospect is broad. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The step flow chart of the pipeline corrosion detection method based on the external normal magnetic field provided in Embodiment 1 of the present application.

[0022] Figure 2 A schematic diagram of the principle of local magnetization of the permanent magnet to the pipeline to be measured.

[0023] Figure 3 A flow chart of the calibration method of the wall thickness-permeability mapping in embodiment 1 of the present application.

[0024] Figure 4 A comparison diagram of the magnetic field simulation of the permanent magnet to the pipeline to be measured under different wall thickness conditions.

[0025] Figure 5 A functional image of a typical wall thickness-permeability mapping obtained by simulation.

[0026] Figure 6 A system architecture diagram of the pipeline corrosion detection system based on the pig provided in embodiment 3 of the present application.

[0027] Figure 7 An assembly schematic diagram of the permanent magnet and the clamp used in embodiment 3 of the present application.

[0028] Figure 8 A structural schematic diagram of the multifunctional pig provided in embodiment 3 of the present application.

[0029] Figure 9 An eddy current sensor array image used by the multifunctional pig in embodiment 3 of the present application.

[0030] The figure is marked as:

[0031] 1, annular permanent magnet; 2, multifunctional pig; 11, clamp; 21, friction body; 22, connecting shaft; 23, magnetic brush, 24, eddy current sensor array; 241, support rod; 242, detection probe; 243, elastic member. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0034] Embodiment 1

[0035] In view of the difficulty in maintenance during operation of the existing long-distance pipeline, the embodiment provides a pipeline corrosion detection method based on an external normal magnetic field. The method only needs to install a detachable permanent magnet outside the original pipeline, and uses a pig carrying an eddy current sensor to complete the corrosion detection task of the inner wall of the pipeline while the pipeline is being cleaned. The technical concept of the technical solution provided by the embodiment is as follows:

[0036] A magnet is placed on the outer wall of the pipeline in the specified detection area. The magnet magnetizes the pipeline, causing a magnetic permeability distortion in the local pipe wall, and the degree of the magnetic permeability distortion is related to the pipe wall thickness. On this basis, a magnetic permeability detection sensor (such as an eddy current sensor) carried on the pig is used to scan the pipeline together with the pig. Then, the pipe wall thickness is obtained according to the obtained pipe wall magnetic permeability distortion information, and the corrosion detection of the inner side of the pipeline is realized.

[0037] Specifically, as shown in Figure 1 The pipeline corrosion detection method based on an external normal magnetic field provided by the embodiment includes the following steps:

[0038] S1: A detachable annular permanent magnet is arranged at a specified segment of the outer wall of the ferromagnetic pipeline to be measured, and a dynamic changing impedance signal Δ Z t is collected by a pig with an eddy current sensor during the pigging process.

[0039] In the embodiment, a permanent magnet needs to be installed on the outer wall of the ferromagnetic pipeline to be measured before the inner wall corrosion detection of the long-distance pipeline is performed. The permanent magnet is used to magnetize the pipeline to facilitate subsequent measurement. In actual application, the permanent magnet is installed at each specified detection area on the pipeline, and each detection area is distributed at intervals in the extension direction of the pipeline. In any detection area, in order to realize measurement in any direction around the pipeline, an annular permanent magnet is installed at the corresponding segment.

[0040] In addition, it should be emphasized that in the installation state of the permanent magnet in the embodiment, the direction of the pole line inside the permanent magnet should be perpendicular to the pipe wall. For example, the side of the permanent magnet close to the pipe wall can be N-pole, and the side far from the pipe wall can be S-pole, or the side close to the pipe wall can be S-pole, and the side far from the pipe wall can be N-pole. Then, the required external normal magnetic field is formed outside the pipe wall by using the permanent magnet.

[0041] As shown in Figure 2 , after installing the permanent magnet at any position on the pipeline, it is assumed that the magnetic motive force generated by the permanent magnet is F ​, the permanent magnet and the pipe wall and the air near the permanent magnet constitute a complete magnetic circuit. Taking the side of the annular permanent magnet near the pipe exterior as the N pole and the side far from the pipe wall as the S pole as an example, in the magnetic circuit, the magnetic flux from the N pole of the permanent magnet, downward from directly below into the pipe wall, the magnetic resistance of the corresponding section of the pipe wall in this embodiment is denoted as R After passing through the pipe wall, the magnetic flux again leaves the pipe wall near the permanent magnet and finally returns to the S pole of the permanent magnet along the air near the permanent magnet. The magnetic resistance of the air in this embodiment is denoted as r , then according to the Ohm's law of magnetic field, we can obtain:

[0042] ;

[0043] wherein the magnetic flux in the magnetic circuit and the magnetic resistance of the pipe to be measured R respectively satisfy the following formulae:

[0044] ;

[0045] ;

[0046] In the above formulae, B denotes the magnetic field strength of the magnetic circuit, μ denotes the magnetic permeability of the pipe to be measured, S is the cross-sectional area of the magnetic circuit; L is the wall thickness of the pipe; H denotes the magnetization strength of the local region of the pipe to be measured.

[0047] Based on the above formulae, the magnetization strength of the local region of the pipe to be measured H satisfies the following formula:

[0048] ;

[0049] In the above formulae, the magnetic motive force generated by the permanent magnet F and S are usually related to the parameters such as the material, shape and specifications of the permanent magnet and can be considered as a constant value, μ is related to the material of the pipe to be measured and can be considered as a constant value; r is also usually a constant; therefore, H is actually only related to the value of L , and the value of L decreases as the wall thickness H of the pipe to be measured increases.

[0050] Further according to the BH curve of the material, the magnetic permeability H of the material gradually decreases as the magnetization strength μ of the material increases. Therefore, when the wall thickness LAs it increases, its corresponding permeability will μ The magnetic permeability of the pipe wall in a localized area will decrease after applying an external normal magnetic field. Therefore, this characteristic is subsequently utilized in this embodiment to perform corrosion detection on the pipe wall.

[0051] After the permanent magnet is installed, this embodiment utilizes a pig equipped with an eddy current sensor to acquire signals. Once the pig is inserted into the long-distance pipeline, it rapidly travels along the pipeline under the pressure of the transport medium. During this process, based on the basic working principle of the pig, the eddy current sensor comes into contact with the pipe wall as the pig moves through the pipeline. Therefore, as the pig travels along the pipeline, it simultaneously detects the magnetic permeability of the pipe wall along the pipeline's extension direction and obtains the corresponding impedance signal Δ. Z ( t ).

[0052] In this embodiment, the eddy current sensor mounted on the pig includes an excitation coil and a receiving coil. The excitation coil is energized with alternating current, and there is mutual inductance between the excitation coil and the pipe wall, which equates the magnetic permeability distortion in the pipe wall to a ring-shaped magnetic permeability distortion block. Based on the working principle of the eddy current sensor, it outputs an impedance value related to the magnetic permeability of the object being measured. Therefore, in this embodiment, the impedance signal Δ collected by the eddy current sensor during the movement of the pig is... Z ( t The signal is a continuous time-domain signal, where the amplitude at each point in the signal reflects the magnetic permeability of the pipe wall at the corresponding time position of the eddy current sensor.

[0053] S2: For the impedance signal Δ Z ( t ) Filtering and signal extraction are performed to obtain the various sections of the pipeline under test. i The effective signal at each segment is used, and the peak-to-peak value of the effective signal is taken as the sensor impedance at each segment. Z i .

[0054] For the continuous impedance signal collected by the eddy current sensor during the pipeline cleaning process, this embodiment first filters it to remove environmental interference and background magnetic field, etc.; then the filtered impedance signal is extracted to obtain the segmented signal at each section of the pipeline where a permanent magnet is installed, which is the required effective signal.

[0055] Specifically, this embodiment uses a threshold method to extract the effective signal from the original impedance signal. As discussed earlier, the strength of the impedance signal is negatively correlated with the pipe wall thickness. The more severe the corrosion of the pipe wall, the thinner the wall, and the stronger the impedance signal acquired by the eddy current sensor. Conversely, the thicker the pipe wall, the weaker the impedance signal acquired by the eddy current sensor. Therefore, this embodiment uses the sensor impedance determined during the pipe diameter-permeability mapping calibration stage when the wall thickness of the pipe under test is at the standard value. Z 0 As a threshold reference; the threshold reference is scaled by a preset scaling factor less than 1. product As a signal threshold. In practical applications, the scaling factor. The value can be set to 0.8~0.95 as needed. Finally, extract the impedance signal Δ. Z ( t The portion of the signal above the signal threshold is taken as the effective signal Δ for each segment. Z i .

[0056] In this embodiment, for any section of the pipeline to be tested, even if the pipe wall thickness is the same, the permeability distortion block is more pronounced closer to the projection range of the permanent magnet under the influence of the external normal magnetic field, resulting in a stronger impedance signal. Conversely, the impedance signal detected further away from the edge of the magnetic field is relatively weaker. To address this characteristic, this embodiment uses the peak-to-peak value of the effective signal corresponding to each section as the sensor impedance at each section. Z i Among them, peak-to-peak value Z pp The calculation formula is as follows:

[0057] Z pp = Z max - Z min ;

[0058] In the above formula, Z max and Z min These represent the maximum and minimum values ​​of the signal amplitude within the corresponding interval of the valid signal, respectively.

[0059] S3: Based on sensor impedance Z i Query a preset permeability-impedance mapping Z = f ( μ ), and thus obtain the permeability distortion Δ at the corresponding segment position.μ i .

[0060] In the embodiment, the mapping relationship between the impedance value detected by the eddy current sensor and the magnetic permeability distortion at the measured object can be calibrated in advance by finite element magnetic simulation or experiment. Further, the required magnetic permeability-impedance mapping Z = f ( μ ). The magnetic permeability-impedance mapping actually reflects the relationship between the different strength of magnetic permeability distortion generated by the measured pipeline under the influence of the external normal magnetic field and the output of the measured eddy current sensor.

[0061] In the embodiment, the expression of the magnetic permeability-impedance mapping obtained by simulation is as follows:

[0062] ;

[0063] In the above formula, r denotes the axial distance of the distortion region; z denotes the radial distance of the distortion region; r 0denotes the radius of the annular coil; z 0denotes the axial coordinate of the disturbance center; denotes the first type of magnetic vector potential of the excitation coil position when there is distortion; denotes the magnetic vector potential without distortion; I denotes the amplitude of the excitation current; ω denotes the frequency of the time-harmonic field; μ 0denotes the background magnetic permeability; denotes the first type of Green function used to associate the magnetic vector potential of the distortion region with the magnetic vector potential of the coil position; denotes the third type of magnetic vector potential without disturbance; denotes the step function used to define the distortion region; j denotes the imaginary unit; denotes the magnetic permeability of the distortion region, ; denotes the radial variation rate of the reciprocal of the magnetic permeability; denotes the radial gradient of the magnetic vector potential; denotes the axial variation rate of the reciprocal of the magnetic permeability; denotes the axial gradient of the magnetic vector potential. In addition, denotes the integral symbol; denotes the partial derivative symbol; and are the first derivatives of r and z respectively; and the symbol d in is the differential symbol.

[0064] In the above expression for the permeability-impedance mapping, the physical meanings of each term are as follows:

[0065] Through the first equation This reflects that impedance change is essentially a manifestation of magnetic vector potential change, and the change in magnetic vector potential at the coil position directly reflects the influence of disturbance on the electromagnetic field. Wherein, Δ Z This is the impedance change, specifically the difference between the impedance Z with permeability perturbation and the impedance Z0 without perturbation, ΔZ = Z - Z0. Essentially, it represents the change in coil voltage Δ. V The ratio of Δ to the excitation current I. Z =Δ V / I ;Δ Z This reflects the impact of local distortion of the pipeline on electromagnetic field energy loss (real part) and energy storage (imaginary part). It is a constant factor derived from the geometric properties (circumference) of the toroidal coil. ) and the frequency characteristics of the time harmonic field ( jω (Indicates phase lag). The second equation is the expansion of the first equation, containing two terms, the former corresponding to the loss change (a real term, without...). j ) and reactance change (imaginary term, with j ).

[0066] In the real terms (reflecting changes in losses), the power loss is related to... ω 2 Proportional, therefore Contains ω 2 Permeability distortion Δ μ Caused by defects, impurities, etc. in the pipeline; Green's function of the first kind Used to correlate the magnetic vector potential of the distorted region with the magnetic vector potential of the coil position; the physical meaning of the Green's function is the field distribution generated in space by the "point source"; in cylindrical coordinates, it satisfies the Dirichlet boundary conditions: r =0 A limited, r →∞ A →0. Third kind magnetic vector potential without distortion. Then the Neumann boundary conditions are satisfied, that is: ,in, n For example, the boundary normal vector, such as the magnetic potential gradient at the material surface, is 0. Step function. Then it satisfies: when hour =1; otherwise 0. r 1 represents the radial dimension of the distorted region. This formula utilizes a step function. Limiting the integration range ensures that the integration process occurs only within the distorted region. Integration operators. Indicates the axial direction within the distortion region ( z ) and radial ( r Integrate the results.

[0067] In the formula, the real terms represent the volume integral of the permeability distortion, which reflects the change in magnetic energy loss in the distortion region. When Δ μ The larger the value, the greater the change in loss. For example, defects in the material (such as cracks and inclusions) can lead to a significant increase in Δ. μ ≠0, thus increasing the energy loss of the electromagnetic field and increasing the real part of the impedance (resistance).

[0068] In the imaginary term (reflecting changes in reactance), the imaginary unit... j This item is identified as a change in reactance; it includes... This indicates the frequency dependence of the reactance characteristic; reactance and ω Proportional, therefore the imaginary term contains ω . The permeability of the distorted region, in this embodiment, satisfies the formula... The expression within the square brackets is the combination of gradient terms of the magnetic vector potential in cylindrical coordinates, derived from the expansion of Maxwell's equations.

[0069] Specifically, the radial rate of change of the reciprocal of permeability Capable of reflecting the change of magnetic permeability with radial position; effective radial derivative in cylindrical coordinates. The radial gradient corresponding to the magnetic vector potential. The axial rate of change of the reciprocal of the permeability. This reflects the change in permeability with axial position; This represents the axial gradient of the magnetic vector potential.

[0070] The imaginary term in the formula comes from the curl change of the magnetic vector potential, reflecting the change in the electromagnetic field energy stored in the distortion region, where Δ μ A change in the distribution of the electromagnetic field causes a change in the inductance (reactance) of the coil. For example, non-uniformity in a material (such as variations in grain size) can lead to a change in Δ. μ The spatial changes alter the stored energy of the electromagnetic field, causing a change in the imaginary part of the impedance (reactance).

[0071] It should be noted that the derivation of the above formula is based on the small perturbation approximation (i.e., Δ). μ << μ 0), ignore Δ μ The higher-order terms are retained, with only first-order minterms. The core logic is: permeability distortion (Δ... μ This alters the magnetic vector potential distribution of the electromagnetic field (Δ). A = A - A0 ); Magnetic vector potential change (Δ A ) through Green's function ( G 1) Transferred to the coil position ( r = r 0); Change in magnetic vector potential at coil position (Δ) A 1) Converted into impedance change (Δ Z ), where: the real number term corresponds to the change in loss, and Δ μ It is proportional to the first power; the imaginary term corresponds to the change in reactance, and is proportional to Δ. μ It is proportional to the rate of spatial change.

[0072] Based on the established permeability-impedance mapping, this embodiment will measure each pipe segment obtained during the measurement process. i Sensor impedance at the location Z i By inputting the value, the intensity value Δ of the permeability distortion block in the corresponding region can be calculated. μ i .

[0073] S4: Based on the current pipe diameter of the pipe to be tested D Select a pre-calibrated wall thickness-permeability mapping μ = f D ( L ), will distort the permeability Δ μ i Convert to corresponding wall thickness measurement value L i .

[0074] As previously described, under the measurement conditions of this embodiment, there is a correlation between the state of the permeability distortion block generated by the pipe being affected by the same external normal magnetic field and the pipe wall. In practical applications, this embodiment pre-calibrates this correlation and constructs a wall thickness-permeability mapping, and then uses the actually measured permeability distortion Δ μ i Input the values ​​into the mapping to obtain the required pipe wall thickness measurements.

[0075] In practical applications, considering the permeability distortion Δ corresponding to the measurement results... μ i Not only is the wall thickness parameter in the shape features of the object being measured affected, but it is also affected by the pipe diameter parameter in the shape features of the pipe. Therefore, the wall thickness-permeability mapping constructed in this embodiment is a pipe diameter-related mapping, and a dedicated wall thickness-permeability mapping is set for each pipe diameter in the actual application scenario.

[0076] Specifically, in practical applications, such asFigure 3 As shown, the calibration method for the wall thickness-permeability mapping of any type of pipe is as follows:

[0077] S01: Obtain pipe samples with different wall thicknesses corresponding to each pipe diameter. The wall thickness range for each pipe is as follows: ; L max-D This indicates the maximum allowable corrosion rate for a pipe with a diameter of D.

[0078] In this embodiment, considering that the pipeline will thin due to corrosion in actual applications, and that the standard pipe diameter is usually the thickest state of the pipeline under the current measurement conditions, this embodiment sets the range of calibrated pipe wall thickness as between the standard pipe diameter (corresponding to the thickest state) and the wall thickness corresponding to the maximum allowable corrosion amount of the pipeline in engineering applications (corresponding to the thinnest allowable state). Furthermore, it should be noted that in actual measurements, localized thickening of the pipeline inner wall due to contamination may occur. However, since the measurement process of this invention is based on a pipeline cleaning tool, which cleans away such contaminants as it passes through the corresponding pipeline section, this situation does not need to be considered in actual measurements in this embodiment.

[0079] S02: Select a pipe sample, install a detachable annular permanent magnet on its outer wall, and install an eddy current sensor on the inner wall opposite the position of the annular permanent magnet.

[0080] During calibration, to avoid measurement errors, the specifications and parameters of the annular permanent magnet and eddy current sensor should be identical to those used in the actual measurement process. Unlike practical applications where eddy current sensors employ continuous long-range dynamic measurements, this embodiment uses a static short-range measurement strategy. If necessary, multiple eddy current sensors can be spaced out along the extension direction of the corresponding pipe sample, or an auxiliary testing device can be installed to drive the sensor to move between the beginning and end of the pipe sample. Under this static testing method provided in this embodiment, the obtained calibration parameters are more accurate, improving the precision of the corrosion detection scheme provided in this embodiment.

[0081] S03: Connect the pipe sample to the delivery pipeline under standard operating conditions via a flange, and measure the current pipe diameter D and wall thickness. t i Sensor impedance under certain conditions Z i .

[0082] In this embodiment, the calibration process is completed in a simulation environment. This embodiment can utilize equipment such as pipes, pumps, and storage tanks to build a test environment similar to the actual pipeline transportation environment. The fluid material, flow rate, pressure, and other parameters in the test environment (referred to as standard operating conditions in this embodiment) need to be consistent with the actual application process. Based on this, this embodiment installs pipe samples along with flanges and other components into the pipeline of the measurement environment to collect relevant parameters.

[0083] In the testing system used to acquire calibration data, this embodiment can configure the pipeline as a parallel two-branch structure in the section where the pipe sample is installed. One branch is a fixed initial section, and the other is a test section. In practical applications, this embodiment can switch the pipeline to the initial section via a valve each time a pipe sample with a different wall thickness is replaced, and then replace the pipe sample in the test section. After the replacement is completed, the pipeline can be switched back to the replaced test section via a valve. Repeating the above process allows for faster testing while different testing systems are running continuously.

[0084] S04: Sensor impedance Z i According to the preset permeability-impedance mapping, it is converted into permeability distortion Δ μ i And obtain a set of sample data ( t i Δ μ i ).

[0085] The data acquisition and processing process is consistent with the application stage method described above, and will not be repeated here in this embodiment.

[0086] S05: Replace with the next sample and obtain the corresponding sample data through steps S2~S4 until the calibration task of all pipe samples under the current pipe diameter is completed.

[0087] The measurement procedure after replacing the test pipe sample in this step is the same as described above, and will not be repeated in this embodiment.

[0088] S06: Fit all measured sample data to obtain the wall thickness-permeability mapping of the ferromagnetic pipe under the current pipe diameter D. μ = f D ( L ).

[0089] To verify the relevant solutions, this embodiment simulates relevant scenarios. Among them, Figure 4Simulation images of pipes with different wall thicknesses are provided. In this simulation scenario, the pipe is 500mm long, and the wall thickness increases from 7.5mm to 25mm. The permanent magnet is placed in the middle of the outer wall of the pipe, close to the outer wall, with a width of 5mm and a height of 10mm. The magnetic pole direction is perpendicular to the pipe, and the residual magnetic flux is 1T. To improve simulation accuracy, the air mesh inside the pipe directly below the permanent magnet and near the inner wall of the pipe is refined. The permeability of the refined region inside the pipe in the simulation model with different wall thicknesses is plotted as a contour map. Figure 4 In the end, based on the simulation results, the function graph of one typical wall thickness-permeability mapping is fitted as follows: Figure 5 As shown in the figure, there is a negative correlation between magnetic permeability and wall thickness; the greater the pipe wall thickness, the lower the magnetic permeability.

[0090] In practical applications, to ensure the accuracy of the fitted wall thickness-permeability mapping, this embodiment can, on the one hand, employ any function fitting method (such as least squares method or B-spline curve fitting) to process the data, or select the most suitable function model (such as polynomial model or logarithmic model) based on the actual mapping relationship between parameters to complete the above function fitting process. On the other hand, this embodiment can also increase the density of the obtained test sample data, such as reducing the gradient of wall thickness variation of different pipe samples within a specified pipe wall thickness range, setting more pipe samples, and obtaining more sample data.

[0091] S07: Repeat steps S02~S06, using the same strategy to construct wall thickness-permeability mappings for different pipe diameters.

[0092] In this embodiment, by changing the pipe diameter of the pipe sample used in the test process and repeating the aforementioned experimental process, the wall thickness-permeability mapping under different pipe diameters can be obtained. μ = f D ( L The various wall thickness-permeability mappings obtained together constitute the data in the calibration database required for pipeline corrosion detection in this embodiment.

[0093] Considering that the material type of the pipe under test may affect the measurement process, in this further optimized embodiment, the wall thickness-permeability mapping can be more finely divided based on the pipe material. The wall thickness-permeability mapping applicable to each material type M (such as the steel grade used in the pipe) and pipe diameter D is denoted in this embodiment as follows: μ = f D-M ( L ).exist μ = f D-M ( LDuring the calibration process, pipe samples with different wall thicknesses for various specified pipe diameters and materials are obtained, and the wall thickness-permeability mapping corresponding to various specified materials and pipe diameters is constructed according to the same strategy using the methods in steps S02 to S06.

[0094] Accordingly, in practical applications, a pre-calibrated wall thickness-permeability mapping is selected based on the pipe diameter D and material M of the pipe to be tested. μ = f D-M ( L ), and use this wall thickness-permeability mapping to measure the permeability distortion Δ μ i Convert to corresponding pipe wall thickness measurement values L i .

[0095] S5: Wall thickness measurement value at any segment position L i With standard wall thickness The difference Δ L Exceeding the preset security threshold L At time 0, it is determined that pipeline corrosion has occurred at the corresponding section.

[0096] In practical applications of this embodiment, the difference between the measured wall thickness and the standard wall thickness (i.e., the original value of the pipe wall thickness) can be used to determine if corrosion has occurred in the pipe. To balance errors and reduce misjudgments, this embodiment sets a safety threshold for the amount of pipe wall thinning. L 0; when the measured thinning amount (i.e., Δ) L When the corrosion rate exceeds this safety threshold, it can be determined that significant corrosion has occurred in the pipeline at this location.

[0097] In practical applications, this embodiment can further analyze the severity of corrosion at various points in the pipeline based on the measured thickness reduction; analyze the spatial distribution of pipeline corrosion by combining the differences in thickness reduction at different pipeline sections; and even assess the changing trend of corrosion status based on the changes in historical data of the same section within different testing cycles.

[0098] The preceding text of this embodiment only used a single eddy current sensor as an example to introduce how to measure the corrosion status at different sections of a pipeline. In a further optimized solution of this embodiment, additional sensors distributed along the circumference of the pipeline can be installed on the pig. n There are eddy current sensors, n≥2. By scientifically arranging the installation positions of the eddy current sensors, mutual interference can be avoided among them. Based on this, this embodiment synchronously collects the detection signals of each eddy current sensor and extracts the peak-to-peak value of the effective signal collected by each eddy current sensor, thereby obtaining the sensor impedance at each section of the pipeline.Z i1 ~ Z in In practical applications, this embodiment can further analyze the corrosion situation at different circumferential locations along the same section of the pipeline under test based on the detection results of each sensor.

[0099] Considering that the pipeline pig does not always move in a fixed posture during its advancement along the pipeline, and may even spin and roll, this can cause the measurement orientation of the same eddy current sensor to shift at different segments. To address this issue, this embodiment can further incorporate a sensor (such as a gyroscope) within the pipeline pig to collect its attitude information. This allows for the simultaneous acquisition of the pig's attitude information during the pigging process, while simultaneously acquiring impedance signals. Then, based on the attitude information, the spatial orientation offset of the impedance signal received by each eddy current sensor at each segment relative to the initial segment is determined, and correction is performed accordingly. This process then allows for the inversion of any... j Sensor impedance collected by an eddy current sensor Z ij In the i The actual location of each pipeline segment; j =1… n Finally, this is combined with the impedance of each detected sensor. Z ij Based on its corresponding spatial orientation, this embodiment can generate the pipe wall thickness at different circumferential orientations of the same segment of the pipe, thereby enabling a more precise measurement of the corrosion state of the pipe's inner wall.

[0100] Example 2

[0101] This embodiment provides a pipeline corrosion detection method based on an external normal magnetic field. Building upon the scheme in Embodiment 1, this embodiment offers a further optimized solution. Specifically, compared to the scheme in Embodiment 1, in step S1, this embodiment utilizes an eddy current sensor mounted on a pipeline pig to acquire an impedance signal Δ for analyzing pipeline corrosion. Z ( t Simultaneously, the mileage data of the pig during its journey is collected and used as an impedance signal Δ. Z Location information of each point in the middle.

[0102] In step S1, when installing the annular permanent magnets on the outer wall of the pipeline, the positions of each annular permanent magnet (i.e., each measurement segment on the pipeline) can be encoded according to their distance from the inlet of the pipeline pig. Next, by using any distance-measuring sensor or component mounted on the pipeline pig, the travel distance of the pipeline pig within the pipeline can be measured in real time, and the corresponding position signal can be obtained. In this embodiment, this is denoted as... X (t ).

[0103] Due to the impedance signal Δ collected by the two sensors on the same pig, Z ( t ) and position signal X ( t The position signal is time-domain synchronized. Therefore, when the movement mileage of the pig displayed by the position signal matches the position code of a certain ring permanent magnet, it means that the eddy current sensor on the pig has also reached the corresponding measurement segment.

[0104] Based on this, in practical applications, the scheme of this embodiment can use the synchronously acquired location information to reflect the real-time location of the pig, and this location information can be used as the impedance signal Δ Z Reference information for extracting valid signals can be obtained. For example, in this embodiment, the collected location data can be compared with the valid information extracted using the threshold method described above on a time axis to ensure the measurement accuracy of the scheme. Alternatively, in other embodiments, valid signals can be extracted solely based on location information.

[0105] In this embodiment, the technicians discovered that the process of extracting valid signals from the impedance signals output by the eddy current sensor, as described above, is essentially a process of time-domain signal segmentation. The basis for this signal segmentation is essentially retaining the signal when the eddy current sensor and the permanent magnet are aligned, and discarding the signal when their positions do not align. Therefore, in a further optimized solution of this embodiment, a signal sampling module can be set at the signal output terminal of the eddy current sensor. This module is used to discretely sample the continuous impedance signals acquired by the eddy current sensor, thereby shielding invalid signals during the detection process. Specifically, in practical applications, this embodiment can determine the phase position between the eddy current sensor and the permanent magnet based on the location information of the pig. When a match is detected between the real-time position of the pig and the preset installation position of the permanent magnet, the corresponding port of the signal sampling module is activated to acquire the corresponding impedance signal and use it as a valid signal. Conversely, when the real-time position of the pig does not match the preset installation position of the permanent magnet, the corresponding port of the signal sampling module is closed, and the invalid signal output by the eddy current sensor at this time is discarded.

[0106] From the perspective of effective signal extraction methods, the optimized scheme provided in this embodiment is essentially based on the computer program-based signal "soft sampling" strategy provided in Embodiment 1, and provides another signal "hard sampling" strategy.

[0107] Example 3

[0108] Based on the solutions in Examples 1 and 2, this embodiment further provides a pipeline corrosion detection system based on a pipeline pig. This system is a typical device for implementing the pipeline corrosion detection method based on an external normal magnetic field provided in Examples 1 and 2. Specifically, as... Figure 6 As shown, the system includes multiple ring-shaped permanent magnets 1, at least one multi-functional pig 2, and a data processing device.

[0109] In this embodiment, the annular permanent magnet 1 is detachably installed at a designated segment on the outer wall of the ferromagnetic pipe to be tested, forming the required normal magnetic field at the corresponding segment. In practical applications, the annular permanent magnet 1 can adopt a split structure and be detachably installed on the pipe to be tested using a clamp similar to clamp 11. The detachable design adopted in this embodiment facilitates the removal of the permanent magnet after each round of measurement to avoid affecting the pipe; and it can be reinstalled before the start of the next round of measurement, with the segment of the area to be measured on the pipe being changed. This structural design allows for the recycling of the annular permanent magnet 1, thereby reducing the application cost of the detection system.

[0110] In order to generate the required external normal magnetic field, the direction of the magnetic pole connection line of the ring-shaped permanent magnet should be perpendicular to the pipe wall at all points. Therefore, the magnetization method of the permanent magnet used in this embodiment is to magnetize the inner and outer sides of the assembled magnetic ring as the N pole and S pole of the magnet, respectively. Of course, the split permanent magnet used in this embodiment is not only more conducive to equipment installation in the application stage, but also more conducive to reducing costs in the product manufacturing stage.

[0111] Specifically, such as Figure 7 As shown, in practical applications, this embodiment can provide a concave groove on the inner side of the clamp 11. Then, the various arc-shaped ceramic plates used to assemble the magnetic ring are fixedly installed inside the clamp 11 by adhesive or snap-fit ​​methods. When the clamp 11 is fitted onto the pipe to be tested, the magnetic ring is fixed to the outer circumference of the pipe. Furthermore, the clamp 11 provides protection for the internal magnetic ring, preventing damage from external forces during daily use. In practical applications, the clamp 11 is preferably made of a non-ferromagnetic material to avoid interfering with the aforementioned testing process.

[0112] like Figure 8As shown, the multifunctional pig 2 provided in this embodiment includes a pig body, two magnetic brushes 23, an eddy current sensor array 24, and a data storage unit. The pig body is dumbbell-shaped and includes two coaxially connected elastic friction bodies 21 and a connecting shaft 22. Both the friction bodies 21 and the connecting shaft 22 are made of non-ferromagnetic materials. In practical applications, the friction bodies 21 in this embodiment can be rubber cups, foam, etc., found in various traditional pigs. To improve the pig's passability in curved or variable-diameter conditions, the connecting shaft 22 in this embodiment can be a variable-direction connecting shaft 22 containing multiple universal connectors as joints. When the friction bodies 21 are made of foam material in a columnar structure, the front end of the friction body 21 along the travel direction can be set as a cone to reduce the resistance caused by the transmission medium during travel.

[0113] like Figure 9 As shown, the eddy current sensor array 24 used in this embodiment includes multiple eddy current sensors arranged in a ring around the middle section of the connecting shaft 22; each eddy current sensor is used to synchronously acquire impedance signals during the pigging process. In practical applications, the eddy current sensor array 24 of this embodiment consists of multiple detection probes 242 and an expandable elastic support. The elastic support is made of a non-ferromagnetic material and includes multiple support rods 241 extending radially outward along the circumference of the connecting shaft 22. Each support rod 241 can be hinged to a base fixed on the connecting shaft 22 or fitted onto a fixing ring on the connecting shaft 22. Each detection probe 242 is installed at the end of each support rod 241 and arranged at intervals along the circumference of the connecting shaft 22. In the elastic support, each support rod 241 is tilted backward along the direction of travel of the pig, thereby changing the diameter of the annular detection surface formed by each detection probe 242 by adjusting its angle with the connecting shaft 22 to adapt to different pipe diameters in practical applications. In practical applications, this embodiment also includes an elastic element 243 on each support rod 241 to apply outward prestress to the support rod 241. This allows each detection probe 242 to adaptively adjust its structure according to changes in the pipeline during operation, ensuring that each detection probe 242 is tightly fitted to the inner wall of the pipeline and preventing any lift-off zone between the probe and the pipe wall, thus guaranteeing the detection accuracy of the eddy current sensor. In practical applications, the elastic element 243 providing the prestress can be a spring or a gas spring. Furthermore, a ceramic wear-resistant layer is provided at the contact surface between the detection probe 242 and the inner wall of the pipeline. This embodiment improves the surface hardness of the detection probe 242 through the ceramic wear-resistant layer, preventing excessive friction with the inner wall of the pipeline during application.

[0114] like Figure 8As shown, in this embodiment, the two magnetic brushes 23 of the multifunctional pig 2 are respectively mounted on the connecting shaft 22 near the friction body 21. In this embodiment, the magnetic brushes 23 can be made of porous annular ceramic plates and sleeved on the connecting shaft 22. Alternatively, a structure similar to the eddy current sensor array 24 can be adopted. For example, the magnetic brushes 23 are composed of a permanent magnet and an elastic support made of magnetically conductive material. The permanent magnet and the elastic support together form a magnetic "sieve". This sieve can block solid impurities leaking from the friction block and adsorb tiny ferromagnetic materials leaking from the front end. This provides a uniform magnetic field environment for the turbine sensor between the two magnetic brushes 23, thereby improving detection accuracy. In the product design stage of the multifunctional pig 2, finite element magnetic analysis can also be performed to optimize the relative position, spatial shape, and magnetic parameters of the permanent magnets of the magnetic brushes 23 and the eddy current sensor array 24. This ensures that the impurity filtration and adsorption effects are maintained while avoiding interference with the detection performance of the eddy current sensor.

[0115] In a further optimized embodiment, the multi-functional pig 2 also integrates a roller rangefinder and / or a gyroscope. The roller rangefinder is used to measure the travel distance of the pig within the pipeline and uses it as position information from the impedance signal detected by the eddy current sensor. The gyroscope is used to detect the spatial attitude of the pig during its travel and uses it as attitude information from the impedance signal detected by the eddy current sensor.

[0116] The data storage unit synchronously stores the impedance signals, position information, and attitude information detected by each eddy current sensor. The data processing unit combines the position information with the impedance signals Δ collected from each eddy current sensor. Z Extract the valid signal; and invert any first [signal] based on the attitude information. j Sensor impedance collected by an eddy current sensor Z ij In the i The orientation of each pipe segment is determined; then, based on the impedance of each detected sensor, the pipe wall thickness at different circumferential orientations of each pipe segment along the axial direction is generated.

[0117] Furthermore, based on the measured position signal, this embodiment can also upgrade the elastic support in the eddy current sensor array 24 to an electrically controlled support. For example, the gas spring controlling the opening angle of the support rod 241 can be replaced with a controllable electric telescopic cylinder. Based on this, in practical applications, the position information of the pig can be obtained in real time through the data processing module. When the pig approaches the next permanent magnet positioned ahead, the support rod 241 is controlled to expand outward, bringing the detection probe 242 into close contact with the inside of the pipeline for signal acquisition. After the pig passes the corresponding permanent magnet, the support rod 241 is controlled to retract inward, switching the detection probe 242 to a non-contact state with the inner wall of the pipeline; thus avoiding excessive wear on the turbine sensor probe during use.

[0118] In the multi-functional pipeline pig 2 of this embodiment, the data storage unit is used to store the impedance signals detected by each eddy current sensor. During the pipeline cleaning process, the multi-functional pipeline pig 2 stores all collected detection signals in the data storage unit. After the pig completes its cleaning task and exits the pipeline, the data stored in the data storage unit is read and processed using the relevant detection data from Embodiment 1 or 2 to obtain the detection results of the pipeline corrosion status. In other embodiments, a wireless communication module can also be installed on the multi-functional pipeline pig 2 to communicate with an external base station and transmit the collected detection data in real time.

[0119] In this embodiment, the data processing device acquires the impedance signals collected by each eddy current sensor in the multi-functional pig 2, and processes the impedance signals collected by each eddy current sensor using a pipeline corrosion detection method based on an external normal magnetic field, as described in Embodiment 1 or 2. This process yields the wall thickness information at different circumferential locations in each section of the pipeline and analyzes the corrosion state at each location. Essentially, this data processing device is a computer device. In practical applications, this computer device can be an embedded device integrated into the multi-functional pig 2 to directly process the signals detected by various sensors. Alternatively, a standalone computer device can be used, such as a laptop, tablet, desktop computer, or a rack-mount server, blade server, tower server, or cabinet server (including standalone servers or server clusters composed of multiple servers) capable of executing computer programs; thereby processing the sensor data output from the front end.

[0120] The computer device in this embodiment includes, but is not limited to, a memory and a processor that can be interconnected via a system bus. In this embodiment, the memory (i.e., the readable storage medium) includes flash memory, hard disk, multimedia card, card-type memory (e.g., SD or DX memory), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic memory, magnetic disk, optical disk, etc. In some embodiments, the memory can be an internal storage unit of the computer device, such as the hard disk or RAM of the computer device. In other embodiments, the memory can also be an external storage device of the computer device, such as a plug-in hard disk, smart media card (SMC), secure digital card (SD), flash card, etc. Of course, the memory can also include both internal storage units and external storage devices of the computer device. In this embodiment, the memory is typically used to store the operating system and various application software installed on the computer device. Furthermore, the memory can also be used to temporarily store various types of data that have been output or will be output. In some embodiments, the processor may be a central processing unit (CPU), a controller, a microcontroller, a microprocessor, or other data processing chip. The processor is typically used to control the overall operation of a computer device.

[0121] The above-described embodiments are merely one implementation of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for detecting pipeline corrosion based on an external normal magnetic field, characterized in that, It includes: A detachable ring-shaped permanent magnet is placed at a designated section on the outer wall of the ferromagnetic pipe to be tested to form an external normal magnetic field. During the pipe cleaning process, a pig equipped with an eddy current sensor collects the dynamically changing impedance signal Δ. Z ( t ); For impedance signal Δ Z ( t ) Filtering and signal extraction are performed to obtain the various segments. i The effective signal at each segment is used, and the peak-to-peak value of the effective signal is taken as the sensor impedance at each segment. Z i ; Based on the detected sensor impedance Z i Query a preset permeability-impedance mapping Δ Z = f (Δ) μ ), and thus obtain the permeability distortion Δ at the corresponding segment position. μ i Based on the current diameter of the pipe to be tested D Select a pre-calibrated wall thickness-permeability mapping μ = f D ( L ), will Δ μ i Convert to corresponding wall thickness measurement value L i ; The expression for the permeability-impedance mapping is: ； In the above formula, r Indicates the axial distance of the distorted region; z Indicates the radial distance of the distorted region; Indicates the integral symbol; Indicates the partial derivative sign; and They are respectively r and z The first derivative; and symbols in d The differential symbol; r 0 represents the radius of the loop coil; ω Indicates the frequency of the time-harmonic field; I Indicates the amplitude of the excitation current; μ 0 indicates background permeability; This represents the first kind of Green's function used to correlate the magnetic vector potential of the distorted region with the magnetic vector potential of the coil position; This represents the third kind of magnetic vector potential without distortion. This represents the step function used to define the region of distortion. j Represents the imaginary unit; Indicates the permeability of the distorted region. ; The radial rate of change of the reciprocal of the permeability; Represents the radial gradient of the magnetic vector potential; The axial rate of change of the reciprocal of the permeability; Represents the axial gradient of the magnetic vector potential; When the wall thickness measurement value at any segment L i With standard wall thickness The difference Δ L Exceeding the preset security threshold L At time 0, it is determined that pipeline corrosion has occurred at the corresponding section.

2. The pipeline corrosion detection method based on an external normal magnetic field according to claim 1, characterized in that, The method for extracting the effective signal is as follows: The sensor impedance when the wall thickness of the pipe under test, determined during the pipe diameter-permeability mapping calibration stage, is at the standard value. Z 0 As a threshold benchmark; Threshold baseline with a scaling factor less than 1 product As a signal threshold; extract the impedance signal Δ Z ( t The portion of the signal above the signal threshold is taken as the effective signal Δ for each segment. Z i .

3. The pipeline corrosion detection method based on an external normal magnetic field according to claim 1, characterized in that: The calibration method for the wall thickness-permeability mapping is as follows: S1: Obtain pipe samples with different wall thicknesses for each pipe diameter. The wall thickness range for each pipe is as follows: ; L max-D This indicates the maximum allowable corrosion rate for a pipe with a diameter of D. S2: Select a pipe sample, install a detachable annular permanent magnet on its outer wall, and install an eddy current sensor on the inner wall opposite the position of the annular permanent magnet. S3: Connect the pipe sample to the delivery pipeline under standard operating conditions via a flange, and measure the current pipe diameter D and wall thickness. t i Sensor impedance under certain conditions Z i ; S4: Adjust sensor impedance Z i According to the preset permeability-impedance mapping, it is converted into permeability distortion Δ μ i And obtain a set of sample data ( t i Δ μ i ); S5: Replace the next sample and obtain the corresponding sample data through steps S2~S4 until the calibration task of all pipe samples under the current pipe diameter is completed; S6: Fit all the measured sample data to obtain the wall thickness-permeability mapping of the ferromagnetic pipe under the current pipe diameter D. μ = f D ( L ); S7: Repeat steps S2 to S6, using the same strategy to construct wall thickness-permeability mappings for different pipe diameters.

4. The pipeline corrosion detection method based on an external normal magnetic field according to claim 1, characterized in that: Based on the pipe diameter D and material M of the pipe to be tested, select a pre-calibrated wall thickness-permeability mapping. μ = f D-M ( L ), will distort the permeability Δ μ i Convert to corresponding pipe wall thickness measurement values L i ; Among them, the wall thickness-permeability mapping μ = f D-M ( L During the calibration process, pipe samples with different wall thicknesses for various specified pipe diameters and materials are obtained, and the wall thickness-permeability mapping corresponding to various specified materials and pipe diameters is constructed using the same strategy in steps S2 to S6.

5. The pipeline corrosion detection method based on an external normal magnetic field according to claim 4, characterized in that: The mileage data of the pipeline pig during its journey is collected synchronously and used as an impedance signal Δ. Z Location information of each point in the middle; The location information is used as the impedance signal Δ Z Reference information for extracting valid signals; Alternatively, the impedance signal Δ can be adjusted directly based on the location information during the signal acquisition phase. Z ( t The signal sampling method is used to directly obtain the effective signal.

6. The pipeline corrosion detection method based on an external normal magnetic field according to claim 5, characterized in that: The pipeline pig has components distributed along the circumference of the pipeline. n One eddy current sensor, n ≥2; Extract the peak-to-peak value of the effective signal collected by each eddy current sensor to obtain the sensor impedance at each section of the pipeline. Z i1 ~ Z in ; The attitude information of the pig during the pigging process is collected synchronously, and then any second pig can be retrieved based on the attitude information. j Sensor impedance collected by an eddy current sensor Z ij In the i The location of each pipeline segment; Then, based on the impedance of each detected sensor, the pipe wall thickness at different circumferential orientations of the same segment of the pipe is generated.

7. A pipeline corrosion detection system based on a pipeline pig, characterized in that, It includes: Multiple ring-shaped permanent magnets are used for detachable installation at designated sections on the outer wall of the ferromagnetic pipe to be tested; To create the required normal magnetic field at the corresponding segment position; A multi-functional pipeline cleaning tool includes a cleaning tool body, two magnetic brushes, an eddy current sensor array, and a data storage unit. The cleaning tool body is dumbbell-shaped and includes two coaxially connected elastic friction bodies and a connecting shaft. The eddy current sensor array includes multiple eddy current sensors arranged in a ring around the middle section of the connecting shaft. The two magnetic brushes are respectively mounted on the connecting shaft near the friction bodies. The magnetic brushes are used to adsorb ferromagnetic impurities and provide a uniform magnetic field environment at the eddy current sensors. The eddy current sensors are used to synchronously acquire impedance signals during the cleaning process, and the data storage unit is used to store the impedance signals detected by each eddy current sensor. The data processing device is used to acquire the impedance signals collected by each eddy current sensor in the multi-functional pipeline pig, and to process the impedance signals collected by each eddy current sensor using the pipeline corrosion detection method based on an external normal magnetic field as described in any one of claims 1-6, thereby obtaining the wall thickness information at different circumferential positions in each section of the pipeline and analyzing the corrosion state at each location of the pipeline.

8. The pipeline corrosion detection system based on a pipeline pig as described in claim 7, characterized in that: The eddy current sensor array includes multiple detection probes and an expandable elastic support. The elastic support includes multiple support rods hinged to a connecting shaft and extending radially outward. Each support rod is fixedly connected to the connecting shaft via its own fixing seat or the same fixing ring. The support rods are rotatably connected to the fixing seats or connecting shaft. The detection probes are installed at the ends of each support rod. The support rods are tilted backward along the travel direction of the pig and can be adjusted to accommodate different pipe diameters by adjusting their angle with the connecting shaft. The support rods are also provided with elastic elements for applying outward prestress to the support rods so that each detection probe fits tightly against the inner wall of the pipe. And / or, In the detection probe, a ceramic wear-resistant layer is provided at the contact surface with the inner wall of the pipe.

9. The pipeline corrosion detection system based on a pipeline pig as described in claim 7, characterized in that: The multi-functional pipeline pig also integrates a roller rangefinder and a gyroscope; the roller rangefinder is used to measure the travel distance of the pipeline pig in the pipeline and use it as position information of the impedance signal detected by the eddy current sensor; the gyroscope is used to detect the spatial attitude of the pipeline pig during travel and use it as attitude information of the impedance signal detected by the eddy current sensor. And / or, the data storage unit is used to synchronously store the impedance signals detected by each eddy current sensor, as well as the position information and attitude information; The data processing device combines the position information with the impedance signals Δ collected from each eddy current sensor. Z Extract the valid signal; and invert any first [signal] based on the attitude information. j Sensor impedance collected by an eddy current sensor Z ij In the i Location of each pipeline section; Then, based on the impedance of each detected sensor, the pipe wall thickness at different circumferential positions of each segment along the pipe axis is generated.

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