Passive positioning technology for pipe cleaner based on acoustic-magnetic fusion

Abstract

The invention relates to a passive positioning technology and device for a pipe cleaner based on acoustic-magnetic fusion, and aims at solving the problems that in the prior art, the positioning of the pipe cleaner is limited by the burial depth and the wall thickness of a pipeline, and the instantaneous speed cannot be obtained, and the passive positioning is realized by fusing a magnetic signal and an acoustic vibration signal. The pipe cleaner generates a broadband acoustic vibration signal due to mechanical shock through a pipeline circumferential weld, and meanwhile a metal part of the pipe cleaner is overlapped with a geomagnetic field to form a magnetic anomaly gradient field; signals are synchronously collected through a magnetic sensor array arranged on the ground and an acoustic vibration sensor, the credibility of acoustic magnetic signals is weighted in combination with the D-S evidence theory, and the instantaneous speed of the pipe cleaner is calculated through the time difference of the double magnetic sensors after effective events are recognized. The device comprises a fluxgate sensor, an acoustic vibration sensor, a Beidou module and a data acquisition and processing module, accurate positioning in a large burial depth scene can be realized without modifying a pipe cleaner, the problems that a single signal is easily interfered and the speed is unknown are solved, and the safety and efficiency of pipe cleaning operation are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of pig or in-line inspection gauge positioning for buried long-distance oil and gas pipelines, and specifically to a passive pig positioning technology and device based on acoustic-magnetic fusion, which is used to real-time locate the position of the pig or in-line inspection gauge in the pipeline and evaluate the instantaneous speed, so as to ensure the safety of pipeline pigging operations. Background of the Invention

[0003] When conducting in-line pigging - in-line inspection operations on long-distance oil and gas pipelines, there is a problem that pigs or in-line inspection gauges are prone to jamming. Once jamming occurs, it will affect the oil and gas transportation efficiency and cause significant economic losses. At the same time, the in-pipeline flow velocity along the line is unknown, and it is impossible to real-time judge the running safety status of the pig or in-line inspection gauge. There is a need for "intelligent speed recognition" to provide technical support for mastering the entire process of in-line inspection of pipelines and ensure the safety of in-line inspection.

[0004] The existing technologies mainly include pressure fluctuation technology, noise and vibration technology, electromagnetic pulse technology, and distributed optical fiber sensing technology. For pressure fluctuation technology, pressure transmitters need to be installed on the pipeline, with low accuracy and poor mobility; for the noise and vibration method, a vibration generating device needs to be installed on the pig, and its versatility for different pipelines is not good. The low-frequency electromagnetic pulse method is currently the most commonly used pig positioning method. By installing a transmitter on the pig and using a ground positioning box to detect low-frequency electromagnetic waves, active positioning is achieved. However, this method is significantly affected by the shielding effect of the pipeline wall thickness and burial depth, and is only applicable to scenarios with shallow burial depth and thin wall thickness. Moreover, it is impossible to obtain the instantaneous running speed of the pig, making it difficult to meet the engineering requirements under complex working conditions. Distributed optical fiber sensing technology is a hot technology in recent years, but there are still many deficiencies in its engineering applicability:

[0005] (1) Some long-distance pipelines are laid parallel to national roads, highways, and railways. The optical fiber vibration signal is easily affected by the vibration generated by the passing of cars and trains;

[0006] (2) This technology requires that the accompanying optical cable of the long-distance pipeline has at least one spare core for connecting multiple optical modulator devices along the way. Some accompanying optical cables have no redundant inner cores, resulting in large limitations in practical applications.

[0007] Therefore, there is an urgent need for a positioning device that can be passively monitored, adapt to pipelines with large burial depth and large wall thickness, and can real-time analyze the speed, so as to ensure the safety, controllability, and high efficiency of pipeline pigging operations. Summary of the Invention

[0008] In view of the above problems, the present invention proposes a passive positioning technology for pigging devices based on acoustic-magnetic fusion, and provides a passive positioning device for pigging devices based on acoustic-magnetic fusion. By accurately capturing the acoustic vibration signal characteristics caused by the unevenness of the pipeline girth weld structure and the fluctuation characteristics of the static magnetic field superposition signal during the operation of the pigging device, it is possible to achieve passive positioning without modifying the pigging device and adding a transmitter. When the pigging device or the in-line inspection device passes through the girth weld, geometric unevenness such as the reinforcement height and misalignment in the weld area will cause periodic mechanical impacts between it and the pipe wall, exciting a broadband acoustic vibration signal containing rich information. This signal is coupled and propagated through multiple media such as the pipeline body and soil to the ground, forming an acoustic vibration abnormal signal that can be detected on the ground. At the same time, according to the principle of static magnetic field superposition, when a pigging device containing metal components (such as the metal skeleton of the pigging device and the magnetic ring of the in-line inspection device) operates, its own magnetic field is superposed with the geomagnetic field to form a magnetic anomaly gradient field, and a detectable magnetic anomaly fluctuation signal is formed on the ground. The acoustic-magnetic fusion technology uses high-precision acoustic vibration sensors and magnetic sensors to capture the abnormal signals when the pigging device passes on the ground. By deeply decoupling the acoustic vibration characteristics and the static magnetic field superposition effect, a multi-physical field mapping relationship of "mechanical vibration - electromagnetic signal - spatial position" is constructed, and the instantaneous speed of the pigging device is accurately evaluated through the time difference of passage of the two sensors.

[0009] The technical solution provided by the present invention to solve the above technical problems is a passive positioning technology for pigging devices based on acoustic-magnetic fusion, including a passive positioning method and device for pigging devices based on acoustic-magnetic fusion, which is characterized by including the following steps:

[0010] S1. Collect the basic design parameters of the pipeline to be pigged and operation information such as the length of the pigging device, the interference fit, and the starting pressure difference of the pigging device, and complete the preliminary work of passive positioning of the pigging device based on acoustic-magnetic fusion.

[0011] S2. Set monitoring points along the pipeline according to the pipeline laying situation. Use a pipe locator to determine the pipeline direction and burial depth at the monitoring points, and arrange 2 magnetic sensors, 1 acoustic vibration sensor, and a Beidou module at the monitoring points. The measurement result of the magnetic sensor is the magnetic induction intensity in the direction directly below this point, and the measurement result of the acoustic vibration sensor is the acoustic vibration displacement of the soil in this area. The Beidou module is used for timing and positioning.

[0012] S3. The magnetic sensor array and the acoustic vibration sensor are connected to a portable data acquisition box through a shielded cable to synchronously collect data, and continuously record the magnetic induction intensity (unit: nT) and the acoustic vibration displacement (unit: μm).

[0013] S4. Use the D-S evidence theory method to weight the credibility of the acoustic vibration signal and the magnetic signal. Identify the pigging device through the fluctuation characteristics of the magnetic sensor signal and the sudden change of the vibration amplitude of the acoustic vibration sensor, calculate the instantaneous speed of the pigging device according to the signal fluctuation time difference of the two magnetic sensors, and record the position coordinates of this point at the same time.

[0014] Preferably, in step S2, the described monitoring point setting method and sensor arrangement method include the following steps:

[0015] S21. Place two non-contact magnetic sensors horizontally in a straight line directly above the pipeline.

[0016] S22. Orient the sensitive directions of the two sensors downward, with the spacing equal to the length of the pig.

[0017] S23. Connect the acoustic vibration sensor to the listening steel probe and place it at the midpoint between the two magnetic sensors, and insert the probe 10 cm into the ground.

[0018] S24. Set a monitoring point every 2 km along the pipeline to be pigged in the same way.

[0019] Preferably, in step S4, the described signal processing method includes the following steps:

[0020] S41. Extract the extreme points of the time-domain signals of the two magnetic sensors. The calculation formula is:

[0021]

[0022] In the formula, B i is the magnetic signal, i is the serial number of the signal time series, and B ext is the extreme point.

[0023] S42. Calculate the difference between adjacent extreme points. If it satisfies formula (2), it is judged as a magnetic anomaly point:

[0024]

[0025] In the formula, k is the magnetic anomaly determination threshold, which is 3 times the baseline variance. Synchronously record the acquisition time of this data point.

[0026] S43. Calculate the fluctuation amplitude ΔB of the anomaly point. The calculation formula is:

[0027] ΔB = |2B exti - (B exti+1 + B exti-1 )| (3)

[0028] S44. Define the amplitude threshold of the acoustic vibration displacement. The threshold is 3 times the baseline variance. Since the displacement caused by vibration is usually continuous, the acoustic vibration displacement amplitude is calculated once every 1 second. When the acoustic vibration displacement amplitude exceeds the threshold, it is judged as an acoustic vibration anomaly point. The calculation formula for the acoustic vibration displacement amplitude is:

[0029] ΔS = S max - S min (4)

[0030] Where ΔS is the amplitude of the acoustic vibration displacement, S max is the maximum positive displacement within 1 second, and S min is the maximum negative displacement within 1 second.

[0031] S44. Construct the basic probability amplitude function of the D-S evidence theory; define the frame of discernment, where H1 is the pigging tool and H2 is the interference event; determine the reliability m1 of the magnetic signal and the reliability m2 of the acoustic vibration signal. The calculation formula is:

[0032]

[0033] Where α is the correction coefficient.

[0034] S45. Use the Dempster combination rule to calculate the combined reliability. The calculation formula is:

[0035]

[0036] Where K is the conflict factor.

[0037] S46. When m1(H1) ≥ 0.7 and |m1(H1) - m2(H1)| < 0.3|, it is determined as a valid event.

[0038] S47. Extract the magnetic anomaly points of the two sensors determined as valid events and their corresponding acquisition times for calculating the instantaneous velocity. The calculation formula is:

[0039]

[0040] Where v is the instantaneous velocity, L is the length of the pigging tool, and t1 and t2 are the corresponding acquisition times of the magnetic anomaly points of the two magnetic sensors respectively.

[0041] The characteristics of the passive positioning device for the pigging tool based on acoustic-magnetic fusion include:

[0042] Data acquisition and processing module, fluxgate sensor, acoustic vibration sensor, Beidou positioning module, listening steel probe;

[0043] The data acquisition and processing module is used to collect the data of the fluxgate sensor, acoustic vibration sensor, and Beidou positioning module.

[0044] The data acquisition module includes:

[0045] Data acquisition unit, used to acquire the original signals of the fluxgate sensor, acoustic vibration sensor, and Beidou positioning module;

[0046] Pretreatment unit, used to extract abnormal data from the measured magnetic signal and acoustic vibration signal respectively; and record the current time and position information;

[0047] A data fusion decision-making unit, which is configured to input the extracted magnetic anomaly data and acoustic vibration data into the basic probability amplitude function model of the D-S evidence theory to analyze and predict whether this set of data is a pig signal;

[0048] A data output unit, which is configured to output time, position coordinates, and instantaneous speed information through a 4G network.

[0049] The pig passive positioning device based on acoustic-magnetic fusion as described above, wherein the magnetic sensor is encapsulated by a carbon fiber outer shell, the acoustic vibration sensor and the listening steel probe are connected in a screwed form, and the Beidou positioning module and the acoustic vibration sensor are fixed by plastic outer shell encapsulation.

[0050] The pig passive positioning device based on acoustic-magnetic fusion as described above, wherein the data acquisition and processing module is encapsulated by a plastic outer shell and is equipped with a detachable handle.

[0051] The pig passive positioning device based on acoustic-magnetic fusion as described above, wherein the magnetic sensor, the acoustic vibration sensor, the Beidou positioning module and the data acquisition and processing module are connected by shielded cables.

[0052] The beneficial effects of the present invention are:

[0053] 1. The acoustic-magnetic fusion method proposed by the present invention does not require an active emission device to be installed on the pig or internal detector, and locates through the weak magnetism of its own metal components and the acoustic vibration behavior during the traveling process, reducing the operation cost and complexity.

[0054] 2. The present invention overcomes the limitations of pipeline wall thickness and burial depth through acoustic-magnetic signal fusion, and at the same time solves the problems of single signal interference and indistinguishable effective positioning, and is applicable to the full coverage identification of pigs and internal detectors, improving the positioning accuracy.

[0055] 3. The present invention realizes the ground analysis of the instantaneous speed of the pig, solves the problem of unknown instantaneous speed of the pig, and provides key data support for judging the operation safety state. Description of the Drawings

[0056] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present invention and do not limit the present invention.

[0057] Figure 1 Schematic diagram of the effective signal distribution of the pig positioning magnetic sensor of the present invention

[0058] Figure 2 Schematic diagram of the effective signal distribution of the pig positioning acoustic vibration sensor of the present invention

[0059] Figure 3 Schematic diagram of the passive positioning method of the pig based on acoustic-magnetic fusion according to the present invention

[0060] Figure 4 Schematic diagram of the passive positioning device of the pig based on acoustic-magnetic fusion according to the present invention

[0061] As shown in the figure

[0062] 1 - Pig, 2 - Pipeline, 3 - Magnetic sensor, 4 - Acoustic vibration sensor, 5 - Listening steel probe, 6 - Beidou positioning module, 7 - Magnetic sensor, 8 - Acoustic vibration sensor, 9 - Listening steel probe, 10 - Beidou positioning module, 11 - Data acquisition and processing module, 12 - Shielded cable Specific embodiment

[0063] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention

[0064] In a specific embodiment, the above steps are sequentially executed

[0065] Integrated detection and safety evaluation method for the load-bearing state of the pipeline in the crossing section, including the following steps

[0066] S1. Collect on-site data: In a specific embodiment, the pipeline to be pigged is a buried long-distance natural gas pipeline, the pipeline material is X70 steel, the pipeline diameter is 1016 mm, the pipeline wall thickness is 17.5 mm, the outer coating is 3PE, the operating pressure is 6.5 MPa, the total length of the pipeline is 107.2 km, and the average burial depth is 3 m; the pig is a combined pig of leather cup / straight plate, with a length of 1.62 m, an interference amount of 3%, and a starting pressure of 0.3 MPa

[0067] S2. Monitor the pig for the buried long-distance pipeline. Starting from the pigging station yard, a monitoring point is set every 2 km. Use a pipe detector to determine the pipeline direction and burial depth at the monitoring point, and arrange 2 magnetic sensors, 1 acoustic vibration sensor and Beidou module at the monitoring point. The measurement result of the magnetic sensor is the magnetic induction intensity in the direction directly below the point, and the measurement result of the acoustic vibration sensor is the acoustic vibration displacement of the soil in this area. The Beidou module is used for timing and positioning

[0068] S3. The magnetic sensor array and the acoustic vibration sensor are connected to a portable data acquisition box through a shielded cable to synchronously collect data, and continuously record the magnetic induction intensity (unit: nT) and the acoustic vibration displacement (unit: μm). At a certain monitoring point, the pig positioning magnetic signal is asFigure 1 As shown, the acoustic-vibration displacement signal is as Figure 2 shown.

[0069] S4. Use the D-S evidence theory method to weight the credibility of the acoustic-vibration signal and the magnetic signal. Identify the pig by the fluctuation characteristics of the magnetic sensor signal and the sudden change in the vibration amplitude of the acoustic-vibration sensor, calculate the instantaneous speed of the pig according to the signal fluctuation time difference of the double magnetic sensors, and record the position coordinates of this point at the same time.

[0070] Preferably, in step S2, the monitoring point setting method and the sensor arrangement method described are as Figure 3 shown, including the following steps:

[0071] S21. Place two non-contact magnetic sensors in a straight line along the pipeline directly above the pipeline and keep them horizontal.

[0072] S22. Place the sensitive directions of the two sensors facing directly downward, and the distance is the same as the length of the pig.

[0073] S23. Connect the acoustic-vibration sensor to the listening steel probe and place it at the midpoint of the two magnetic sensors, and insert the probe 10 cm into the ground.

[0074] Preferably, in step S4, the signal processing method described includes the following steps:

[0075] S41. Extract the extreme points of the time-domain signals of the two magnetic sensors. In the pig signal of the embodiment, the extreme points of magnetic sensor 1 are (2359, 28160), (2939, 28522), (3128, 28136); the extreme points of magnetic sensor 1 are (2392, 28624), (3003, 29033), (3127, 28620).

[0076] S42. The magnetic anomaly determination threshold of magnetic sensor 1 is 28276, so (2939, 28522) is an abnormal point. The magnetic anomaly determination threshold of magnetic sensor 2 is 28639, so (3003, 29033) is an abnormal point.

[0077] S43. Calculate the fluctuation amplitude ΔB of the abnormal point. ΔB1 is 374 nT and ΔB2 is 411 nT.

[0078] S44. Define the amplitude threshold of the acoustic-vibration displacement. The threshold is 3 times the baseline variance. In the embodiment, the acoustic-vibration displacement amplitude threshold is 0.00071 m. In the acoustic-vibration signal of the pig, the maximum positive displacement S max is 0.00134 m, the maximum negative displacement S min is -0.0021 m, and the amplitude of the acoustic-vibration displacement ΔS is 0.00155 m. Since it is greater than the threshold, it is judged as an abnormal point.

[0079] S44. Construct the basic probability amplitude function of D-S evidence theory; define the frame of discernment, where H1 is the pigging tool and H2 is the interference event; determine the reliability m1 of the magnetic signal and the reliability m2 of the acoustic vibration signal, and the calculation formula is as follows:

[0080]

[0081] In the formula, α is equal to 0.25, is 0.00041 m, and it can be calculated that m2(H1) is 0.9451

[0082] S45. Use the Dempster combination rule to calculate the combined reliability, and the calculation formula is as follows:

[0083]

[0084] In the formula, K is taken as 0.2, and it can be calculated that m(H1) is 1.0499.

[0085] When m1(H1) = 0.9998 > 0.7 and |m1(H1) - m2(H1)| = 0.0547 < 0.3, it is determined as an effective event.

[0086] S47. The data point position of the magnetic sensor 1 is 2939, the data point position of the magnetic sensor 2 is 3003, and the sampling frequency of the magnetic sensor is 200 Hz. Then t2 - t1 is equal to 0.32 s, L is the length of the pigging tool, which is 1.46 m. Then the instantaneous speed v of the pigging tool can be calculated as follows:

[0087]

[0088] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content within the scope of the technical solution of the present invention to obtain equivalent embodiments with equivalent changes. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

[0089] Based on the characteristics of the passive positioning device for pigging tools with acoustic-magnetic fusion, as Figure 4 shown, it includes:

[0090] A data acquisition and processing module, a fluxgate sensor, an acoustic vibration sensor, a Beidou positioning module, and a listening steel probe;

[0091] The data acquisition and processing module is used to collect the data of the fluxgate sensor, the acoustic vibration sensor, and the Beidou positioning module.

[0092] The data acquisition module includes:

[0093] A data acquisition unit for acquiring the original signals of a fluxgate sensor, an acoustic vibration sensor, and a Beidou positioning module;

[0094] A preprocessing unit for separately extracting abnormal data from the magnetic signal to be measured and the acoustic vibration signal; and recording the current time and position information;

[0095] A data fusion and decision-making unit for inputting the extracted magnetic anomaly data and acoustic vibration data into a D-S evidence theory basic probability amplitude function model to analyze and predict whether this set of data is a pig signal;

[0096] A data output unit for outputting time, position coordinates, and instantaneous speed information through a 4G network.

[0097] For the pig passive positioning device based on acoustic and magnetic fusion as described above, the magnetic sensor is encapsulated by a carbon fiber outer shell, the acoustic vibration sensor and the listening steel probe are connected in a screwed form, and the Beidou positioning module and the acoustic vibration sensor are fixed by plastic outer shell encapsulation.

[0098] For the pig passive positioning device based on acoustic and magnetic fusion as described above, the data acquisition and processing module is encapsulated by a plastic outer shell and is equipped with a detachable handle.

[0099] For the pig passive positioning device based on acoustic and magnetic fusion as described above, the magnetic sensor, the acoustic vibration sensor, the Beidou positioning module and the data acquisition and processing module are connected by shielded cables.

Claims

1. A passive positioning technology for a pigging device based on acoustic-magnetic fusion, including a passive positioning method and device for a pigging device based on acoustic-magnetic fusion, characterized in that, It includes the following steps: S1. Collect the basic design parameters of the pipeline to be pigged, as well as operation information such as the length of the pig, the interference fit, and the starting pressure difference of the pig, and complete the preliminary work for the passive positioning of the pig based on the fusion of sound and magnetism. S2. Set monitoring points along the pipeline according to the pipeline laying conditions. Use a pipe detector to determine the pipeline orientation and burial depth at the monitoring points, and arrange 2 magnetic sensors, 1 acoustic vibration sensor, and a Beidou module at the monitoring points. The measurement result of the magnetic sensor is the magnetic induction intensity in the direction directly below the point, and the measurement result of the acoustic vibration sensor is the acoustic vibration displacement of the soil in this area. The Beidou module is used for timing and positioning. S3. The magnetic sensor array and the acoustic vibration sensor are connected to a portable data acquisition box through a shielded cable to synchronously collect data, and continuously record the magnetic induction intensity (unit: nT) and the acoustic vibration displacement (unit: μm). S4. Use the D-S evidence theory method to weight the credibility of the acoustic vibration signal and the magnetic signal. Identify the pig through the fluctuation characteristics of the magnetic sensor signal and the sudden change in the vibration amplitude of the acoustic vibration sensor, calculate the instantaneous speed of the pig according to the time difference of the signal fluctuations of the two magnetic sensors, and record the position coordinates of this point at the same time.

2. The passive positioning technology of a pigging device based on acoustic-magnetic fusion according to claim 1, wherein In step S2, the monitoring point setting method and the sensor arrangement method include the following steps: S21. Place two non-contact magnetic sensors horizontally in a straight line above the pipeline along the pipeline. S22. Place the sensitive directions of the two sensors facing directly downward, and the distance between them is the same as the length of the pig. S23. Connect the acoustic vibration sensor to a listening steel probe and place it at the midpoint of the two magnetic sensors, and insert the probe 10 cm into the ground. S24. Set a monitoring point every 2 km along the pipeline to be pigged in the same way.

3. A pig passive positioning technology based on acoustic-magnetic fusion according to claim 1, characterized in that In step S4, the signal processing method includes the following steps: S41. Extract the extreme points of the time-domain signals of the two magnetic sensors, and the calculation formula is: where B i is the magnetic signal, i is the serial number of the signal time series, and B ext is the extreme point. S42. Calculate the difference between adjacent extreme points. If it satisfies formula (2), it is judged as a magnetic anomaly point: In the formula, k is the magnetic anomaly determination threshold, which is 3 times the baseline variance. Synchronously record the acquisition time of this data point. S43. Calculate the fluctuation amplitude ΔB of the anomaly point, and the calculation formula is: ΔB = |2B exti -(B exti+1 +B exti-1 )| (3) S44. Define the amplitude threshold of the acoustic vibration displacement. The threshold is 3 times the baseline variance. Since the displacement caused by vibration is usually continuous, the acoustic vibration displacement amplitude is calculated once every 1 second. When the acoustic vibration displacement amplitude exceeds the threshold, it is judged as an acoustic vibration anomaly point. The calculation formula for the amplitude of the acoustic vibration displacement is: ΔS = S max -S min (4) where ΔS is the amplitude of acoustic vibration displacement, S max is the maximum positive displacement within 1 second, and S min is the maximum negative displacement within 1 second. S44. Construct the basic probability amplitude function of the D-S evidence theory; define the identification framework, H1 is the pig, and H2 is the interference event; determine the credibility m1 of the magnetic signal and the credibility m2 of the acoustic vibration signal, and the calculation formula is: In the formula, α is the correction coefficient. S45. Use the Dempster combination rule to calculate the combined credibility, and the calculation formula is: In the formula, K is the conflict factor. S46. When m1(H1)≥0.7 and |m1(H1)-m2(H1)|<0.3|, it is determined as an effective event. S47. Extract the magnetic anomaly points of the two sensors determined as effective events and their corresponding acquisition times for calculating the instantaneous speed, and the calculation formula is: Where v is the instantaneous velocity, L is the length of the pig, and t1 and t2 are the corresponding acquisition times of the magnetic anomaly points of the two magnetic sensors respectively.

4. The passive positioning device for the pig based on acoustic-magnetic fusion, comprising: A data acquisition and processing module, a fluxgate sensor, a sound vibration sensor, a Beidou positioning module, and a listening steel probe; The data acquisition and processing module is used to acquire the data of the fluxgate sensor, the sound vibration sensor, and the Beidou positioning module. The data acquisition module includes: A data acquisition unit, which is used to acquire the original signals of the fluxgate sensor, the sound vibration sensor, and the Beidou positioning module; A preprocessing unit, which is used to extract abnormal data from the measured magnetic signal and the sound vibration signal respectively; and record the current time and position information; A data fusion decision unit, which is used to input the extracted magnetic anomaly data and sound vibration data into the basic probability amplitude function model of the D-S evidence theory to analyze and predict whether this group of data is a pig signal; A data output unit, which is used to output the time, position coordinates, and instantaneous velocity information through the 4G network. For the passive positioning device for the pig based on acoustic-magnetic fusion as described above, the magnetic sensor is encapsulated by a carbon fiber outer shell, the sound vibration sensor and the listening steel probe are connected in a screwed form, and the Beidou positioning module and the sound vibration sensor are fixed by plastic outer shell encapsulation. For the passive positioning device for the pig based on acoustic-magnetic fusion as described above, the data acquisition and processing module is encapsulated by a plastic outer shell and is equipped with a detachable handle. For the passive positioning device for the pig based on acoustic-magnetic fusion as described above, the magnetic sensor, the sound vibration sensor, the Beidou positioning module and the data acquisition and processing module are connected by a shielded cable.

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