A magnetic detection device and method for defects in coating-containing pipelines at oil and gas stations

Abstract

The present invention relates to a magnetic detection device and method for defects in cladding-containing pipelines at oil and gas stations. The device mainly comprises a permanent magnet magnetization device, a magnetic signal acquisition device, a gyroscope, a data acquisition terminal, and a portable computer. The permanent magnet magnetization device extends the armature to improve the magnetization effect. Eight permanent magnet magnetization devices are connected by a retractable hinge and can adapt to various pipe diameters. Aluminum tracks and aluminum counterweights are installed to ensure that the magnetic detection device only moves in the axial direction. The magnetic signal acquisition device is installed in a double-layer steel protective shell in the middle and lower part of the permanent magnet magnetization device to collect pipeline leakage magnetic fields. The gyroscope and displacement sensor collect motion data of the entire device. A magnetic detection method for pipeline defects is formed by clarifying pipeline information, clarifying the detection sequence, calibrating the detection instrument, installing the detection instrument, pipeline defect detection, magnetic field data inversion, and pipeline defect repair. The present invention can achieve rapid and accurate detection of cladding-containing pipelines at oil and gas stations.

Description

Technical Field

[0001] The patent of this invention relates to the field of pipeline detection, and specifically to a magnetic detection device and method for defects in coating-containing pipelines at oil and gas stations. Background Art

[0002] Oil and gas stations are crucial locations for oil and gas transportation, processing, processing, and storage. Pipelines within these stations are characterized by diverse types, diameters, and internal fluid media. To retain the cooling or heat of these fluids, some station pipelines are often coated with anti-corrosion, thermal insulation, and protective layers, collectively referred to as cladding. The presence of these cladding layers complicates pipeline inspection at these stations. Completely stripping the cladding from the pipeline surface would be prohibitively expensive and cumbersome. Conventional methods that don't strip the cladding are susceptible to various factors, making their accuracy insufficient to meet the inspection requirements of oil and gas station pipelines. Stress concentrations around pipeline defects cause changes in the pipeline's magnetic permeability, resulting in a leakage magnetic field on the outer surface of the defect. The magnetic induction intensity of this leakage magnetic field is much greater than that of the pipeline itself. Because magnetic fields have excellent penetration into the pipe cladding, the leakage magnetic field can penetrate the cladding and be detected directly by magnetic sensors. Common techniques for detecting pipeline defects using external magnetic leakage detection involve directly magnetizing the pipeline using permanent magnets or coils on its outer surface and collecting leakage magnetic field information near the defect to identify the defect. However, both the magnetization and detection processes for cladding-containing pipelines are affected by the cladding lift-off effect, resulting in limited magnetization and detection effectiveness. This invention proposes a magnetic detection device and method for cladding-containing pipeline defects at oil and gas stations, which improves magnetization and detection effectiveness, thereby enabling efficient and accurate detection of cladding-containing pipeline defects. Summary of the Invention

[0003] The purpose of this patented invention is to address the cumbersome process of stripping defects detection for coated pipelines at oil and gas stations, the difficulty of magnetizing the pipelines during non-stripping testing, and the low accuracy of non-stripping testing. This patented invention achieves efficient and accurate magnetization and detection of coated pipelines, thereby providing support for the safe protection of pipelines at oil and gas stations.

[0004] The technical solution adopted by the present invention is:

[0005] This patented invention provides a magnetic detection device and method for detecting defects in clad pipelines at oil and gas stations. To achieve the aforementioned objectives, the proposed magnetic detection device comprises a permanent magnet magnetization device, a magnetic signal acquisition device, a gyroscope, a data acquisition terminal, and a portable computer. The permanent magnet magnetization device consists of a permanent magnet, an armature, an aluminum protective housing, an aluminum track, a retractable hinge, an aluminum counterweight, and a displacement sensor. The magnetic signal acquisition device consists of a three-axis magnetic sensor, a double-layer steel protective housing, and a conductor. The portable computer runs real-time data display software. The magnetic detection device includes eight identical permanent magnet magnetization devices, evenly distributed in the eight clockwise directions of the pipeline and perpendicular to the pipeline surface. The eight permanent magnet magnetization devices are fixedly connected by a retractable hinge. The extension of the retractable hinge can be adjusted to ensure that the magnetic detection device is suitable for pipelines of different diameters and evenly distributed. A latch is provided in the retractable hinge at 6 o'clock to enable rapid installation and removal of inspections on different clad pipelines at the oil and gas station. The entire permanent magnet magnetization device is enclosed in an aluminum protective casing, and its associated equipment is fixedly mounted on the aluminum casing. Each permanent magnet magnetization device consists of two permanent magnets and an armature. The armature is 0.5 meters long. Extending the armature length increases the magnetic resistance between the two permanent magnets, allowing more of the magnetic field generated by the permanent magnets to penetrate the low-magnetic-resistance pipe. The two permanent magnets are mounted at opposite ends of the armature, forming a complete magnetic circuit between the pipe, the permanent magnets, and the armature. Two aluminum tracks are mounted on the outside of each aluminum protective casing to ensure that the entire magnetic detection device moves only axially and does not rotate circumferentially. During testing, technicians push the entire magnetic detection device forward axially. The aluminum track at the 12 o'clock position is connected to a displacement sensor to measure the displacement and speed of the entire magnetic detection device. When testing small-diameter pipes, an aluminum counterweight is installed on the aluminum protective casing at the 6 o'clock position to prevent circumferential rotation of the magnetic detection device during testing. When inspecting large-diameter pipes and those with a high number of defects, after the initial inspection, the entire magnetic inspection system is rotated 22.5° around the pipe's central axis and retested on pipes with coating defects to improve detection accuracy. Aluminum counterweights are placed on the two permanent magnet magnetization units near the 6 o'clock position to prevent circumferential rotation. A magnetic signal acquisition unit is mounted outside the aluminum protective housing in the center of each permanent magnet magnetization unit. The entire unit is encased in a cubic double-layer steel protective housing to shield against interference from the surrounding magnetic field. The side closest to the pipe is unprotected. A three-axis magnetic sensor is fixed within the double-layer steel protective housing and positioned 5mm from the outer surface of the pipe coating. Wires transmit the magnetic signals and the required electrical energy to the eight three-axis magnetic sensors, which are then transmitted to a data acquisition terminal for conversion into digital signals. The data acquisition terminal and gyroscope are fixed to the outer side of the permanent magnet magnetization unit at 12 o'clock.The data acquisition terminal collects magnetic field data from the triaxial magnetic sensor, axial displacement data from the displacement sensor, and motion data from the gyroscope. This data is then transmitted to a portable computer via an internal Wi-Fi transmitter for real-time display and storage. During inspection, technicians determine the location of potential pipeline defects based on the amplitude and gradient of the real-time magnetic field data and mark the outer surface of the cladding. After inspection, the outer cladding magnetic field data is converted into magnetic field data 2 mm from the pipeline surface, based on the relationship between the pipeline magnetic field and the lift-off height. Furthermore, based on the magnetic field distribution characteristics corresponding to different defect sizes, the basic shape and depth of the pipeline defect are determined through inversion.

[0006] Based on a magnetic detection device for detecting defects in cladding-coated pipelines at oil and gas stations, this invention provides a magnetic detection method for defects in cladding-coated pipelines at oil and gas stations. The permanent magnet magnetization device locally magnetizes the pipeline, and a magnetic signal acquisition device detects the leakage magnetic field generated by the defect. Combined with data from gyroscopes and displacement sensors, the method determines the specific location and size of the defect and provides appropriate treatment measures for the defective pipeline.

[0007] S1: Clearly define the pipeline information, including the information of the pipeline with coating layer to be tested, including pipeline material, pipeline wall thickness, pipeline diameter, fluid medium type, pressure level, pipeline route, coating thickness, and outer anti-corrosion layer material;

[0008] S2: Define the inspection sequence. According to the pipeline information, determine the inspection starting point and inspection end point of each pipeline, number each inspected pipeline, and determine the inspection sequence of each pipeline;

[0009] S3: Calibrate the testing instrument. Before testing, remove the eight three-axis magnetic sensors of the magnetic signal acquisition device, verify and adjust the orthogonality of the eight three-axis magnetic sensors in the x, y, and z directions, and adjust the magnetic induction intensity detection accuracy in each direction.

[0010] S4: Install the testing instrument. Before the test, fix the eight permanent magnet magnetization devices on the pipeline. Adjust the extension distance of the retractable hinge to evenly distribute the eight permanent magnet magnetization devices on the outer surface of the pipeline containing the coating layer. Install the eight magnetic signal acquisition devices in the middle of the eight permanent magnet magnetization devices respectively. Install the gyroscope and data acquisition terminal on the outside of the permanent magnet magnetization device at the 12 o'clock position.

[0011] S5: Pipeline defect detection. Two technicians work together during the inspection. One technician pushes the permanent magnet magnetization device along the pipeline at a constant speed to measure the three-axis magnetic field data, axial displacement data, and motion data of eight channels along the pipeline. The other technician uses a portable computer to view the collected real-time magnetic field data and mark the suspected pipeline defect locations.

[0012] S6: Magnetic field data inversion: Based on the relationship between magnetic induction intensity and lift-off height, the magnetic field data at 2 mm from the pipeline surface is determined. The magnetic field detection results in eight clock directions on the pipeline are plotted separately to form a grid distribution map of the pipeline magnetic field. The specific location of the defect on the pipeline is determined by combining the magnetic induction intensity amplitude and gradient values ​​in the pipeline magnetic field distribution map with the axial displacement data measured by the displacement sensor and the steering data measured by the gyroscope. The defect size is then determined based on the magnetic field distribution characteristics corresponding to different defect sizes.

[0013] S7: Repair of pipeline defects, determine the size of the defects and evaluate their severity, determine the corresponding repair measures, including regular inspections, pipeline welding and pipeline replacement; determine the cause of the defects based on the basic conditions of the pipeline, and eliminate the factors that cause the defects in a targeted manner, including replacing the protective layer with better sealing, controlling the corrosiveness of the medium, improving the cathodic protection system and repairing the anti-corrosion layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a diagram of the composition of the patented magnetic detection device for defects in a coating-containing pipeline.

[0015] Figure 2 This is a distribution diagram of the eight permanent magnet magnetization devices of the patented invention.

[0016] In the figure: 1. Permanent magnet magnetization device, 11. Permanent magnet, 12. Armature, 13. Aluminum protective shell, 14. Aluminum track, 15. Retractable hinge, 16. Aluminum counterweight, 17. Displacement sensor, 2. Magnetic signal acquisition device, 21. Three-axis magnetic sensor, 22. Double-layer steel protective shell, 23. Wire, 3. Gyroscope, 4. Data acquisition terminal, 5. Portable computer. DETAILED DESCRIPTION

[0017] The present invention will be described in detail below in conjunction with the embodiments and drawings. This specific implementation is carried out based on the technical solution of the present invention, and a detailed implementation method and specific operation process are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0018] The present invention discloses a magnetic detection device and method for defects in clad pipelines at oil and gas stations. The device comprises a permanent magnet magnetization device 1, a magnetic signal acquisition device 2, a gyroscope 3, a data acquisition terminal 4, and a portable computer 5. The permanent magnet magnetization device 1 includes a permanent magnet 11, an armature 12, an aluminum protective shell 13, an aluminum track 14, a retractable hinge 15, an aluminum counterweight 16, and a displacement sensor 17. The magnetic signal acquisition device 2 includes a three-axis magnetic sensor 21, a double-layer steel protective shell 22, and a conductor 23. The portable computer 5 is equipped with real-time data display software for displaying and storing magnetic field data collected by the eight magnetic signal acquisition devices 2. There are eight permanent magnet magnetization devices 1 in total, and each has identical dimensions and magnetization capacity. Permanent magnets 1 are distributed along the pipeline's eight clockwise directions, with the spacing between adjacent permanent magnets 1 being uniform, forming a 45° angle with respect to a circle centered on the pipeline axis. The eight permanent magnets 1 are securely connected by retractable hinges 15, ensuring that each permanent magnet 1 is perpendicular to the pipeline surface. The spacing between adjacent permanent magnets 1 is adjusted by adjusting the extension of the retractable hinges 15, ensuring an even distribution of the eight permanent magnets 1 along the pipeline and adapting to pipes of varying diameters. When inspecting small-diameter pipes, the retractable hinges 15 extend at a smaller distance; when inspecting larger-diameter pipes, the retractable hinges 15 extend at a larger distance, adjusting the extension of the hinges 15 to match the corresponding pipe circumference. A retractable hinge 15 near the 6 o'clock permanent magnet 1 allows for quick installation and removal by plugging and unplugging a latch. The magnetic detection device for defects in coated pipelines at oil and gas stations is stored in an explosion-proof box, with its eight permanent magnet magnetization devices 1 placed side by side. When it is necessary to inspect the coated pipeline, the magnetic detection device is removed and placed on the pipeline. The pin of a retractable hinge 15 near the 6 o'clock position of the permanent magnet magnetization device 1 is inserted to secure the magnetic detection device to the coated pipeline. Each permanent magnet magnetization device 1 consists of two identical cubic permanent magnets 11 and a cubic armature 12. The permanent magnets are made of neodymium iron boron material with a high magnetic energy product. The armature 12 is 0.5 meters long, and the two permanent magnets 11 are mounted at both ends of the armature 12, with the north pole and south pole facing the pipeline, respectively. The magnetic lines of force can be thought of as emanating from the north pole of one permanent magnet 11, partially passing through the air into the pipe beneath the sheath, and then re-exiting the pipe near the south pole, re-entering the air and reaching the south pole of the other permanent magnet 11. They then return to their starting point via the armature 12. At this point, the pipe, two permanent magnets 11, and armature 12 form a complete closed magnetic circuit. The armature 12 in common contact-type magnetization and detection devices for pipe outer surfaces is relatively short, typically no longer than 0.2 m, because a long armature 12 increases the magnetic resistance of the overall magnetic circuit.When performing magnetic testing on a pipe containing a coating, the coatings, such as the anti-corrosion layer, thermal insulation layer, and protective layer, cause the entire permanent magnet magnetization device 1 and magnetic signal acquisition device 2 to be lifted off the pipe surface to a certain height. To ensure that the pipe is magnetized to the required degree for testing, the present invention extends the armature 12 to increase the air reluctance between the two permanent magnets 11, allowing the magnetic field generated by the permanent magnets 11 to enter more of the low-reluctance pipe, rather than directly forming a magnetic circuit through the air. The permanent magnets 11 and armature 12 are both fixedly mounted within an aluminum protective shell 13. Two aluminum tracks 14 are installed on the exterior of the aluminum protective shell 13 of each permanent magnet magnetization device 1. During testing, technicians push the entire magnetic detection device forward at a uniform speed along the axial direction of the pipe. The aluminum tracks 14 ensure smooth forward movement of the entire magnetic detection device. Due to the characteristics of the aluminum tracks 14, the entire magnetic detection device can move only in the axial direction without circumferential rotation, allowing the eight three-axis magnetic sensors 21 to detect magnetic field data corresponding to the same clockwise direction on the pipe. The aluminum track 14 at 12 o'clock is connected to a displacement sensor 17, which is used to detect the displacement distance and real-time speed of the entire three-axis magnetic sensor 21. An aluminum counterweight 16 is installed on the permanent magnet magnetization device 1 at 6 o'clock to further ensure that the magnetic signal acquisition device 2 of each permanent magnet magnetization device 1 is oriented in the corresponding clock direction throughout the entire testing process. For some large-diameter pipes and those containing cladding that require special inspection, after the above-mentioned inspection, the magnetic detection device is removed and reinstalled on the pipe, rotating the entire magnetic detection device 22.5° around the central axis of the pipe. At this time, the pipe containing cladding defects is inspected again. For pipes suspected of having a large number of defects or an outer diameter greater than 300mm, the above method should be repeated to improve the detection capability of defects in all positions of the pipe. Aluminum counterweights 16 are installed on the two permanent magnet magnetization devices 1 near 6 o'clock to ensure that the second inspection path is also straight. The aluminum counterweights 16 are made of pure aluminum to prevent the influence of iron on the magnetic inspection results. A magnetic signal acquisition device 2 is installed in the middle of each permanent magnet magnetization device 1 to collect magnetic field signals emitted by defects in the pipe containing the coating. The magnetic signal acquisition device 2 is enclosed by a cubic double-layer steel protective shell 22. The double-layer steel protective shell 22 is made of a complete steel plate and is annealed to remove the inherent abnormal magnetic field. The double-layer steel protective shell 22 is open on the side closest to the pipeline. The double-layer steel protective shell 22 can shield the adjacent pipelines and other equipment at the oil and gas station from interfering with the detection results of the three-axis magnetic sensor 21 and only collect the magnetic field generated by defects in the pipe containing the coating. A three-axis magnetic sensor 21 is fixedly installed in the double-layer steel protective shell 22. The vertical distance between the three-axis magnetic sensor 21 and the pipe coating is fixed at 5mm. The x-axis of each three-axis magnetic sensor 21 is parallel to the pipeline axis, the z-axis is perpendicular to the pipeline surface, and the y-axis is parallel to the pipeline surface.Each triaxial magnetic sensor 21 transmits the collected magnetic signal and required electrical energy via a wire 23. The wire 23 uploads the collected data from the eight triaxial magnetic sensors 21 to the data acquisition terminal 4, which converts the electrical signal into a digital signal. The data acquisition terminal 4 is also fixedly mounted outside the permanent magnet magnetization device 1 at 12 o'clock. A gyroscope 3 is also mounted outside the permanent magnet magnetization device 1 at 12 o'clock to collect motion data from the entire device during the detection process. The data acquisition terminal 4 collects the magnetic field data from the eight triaxial magnetic sensors 21, the axial displacement data from the displacement sensor 17, and the motion data from the gyroscope 3, and converts these signals into digital signals. A Wi-Fi transmitter is installed within the data acquisition terminal 4, which transmits the three digital signals to a portable computer 5. The portable computer 5 runs real-time data display software that directly displays the real-time magnetic field data from the eight triaxial magnetic sensors 21. During inspection, technicians determine the location of potential pipeline defects based on the amplitude and gradient of real-time magnetic field data and mark them on the outer surface of the coating. Suspected pipeline defects are typically detected where there are sudden changes in the three-dimensional magnetic field amplitude or gradient. Once the entire pipeline, including the coating, has been inspected, the three-dimensional magnetic field data is converted into magnetic field data at a distance of 2 mm from the pipeline surface, based on the correlation between the pipeline's magnetic field and lift-off height. Further, based on the magnetic field distribution characteristics corresponding to different defect sizes, the basic shape and depth of the pipeline defect are determined through inversion.

[0019] Based on a magnetic detection device for detecting defects in cladding-coated pipelines at oil and gas stations, this invention provides a magnetic detection method for defects in cladding-coated pipelines at oil and gas stations. The permanent magnet magnetization device 1 locally magnetizes the pipeline being inspected and uses a magnetic signal acquisition device 2 to collect the leakage magnetic field generated by the defect. Combined with a gyroscope 3 and a displacement sensor 17, the method determines the specific location and size of the defect and provides appropriate treatment measures.

[0020] S1: Clarify pipeline information, including the information of the coated pipelines at the target oil and gas station, including pipeline material, pipeline wall thickness, pipeline diameter, fluid medium type, pressure level, pipeline route, coating thickness, and outer anti-corrosion layer material. Analyze the matters needing attention and basic parameters during the inspection process of the coated pipelines, and fill in the pipeline parameter data in the inspection record book;

[0021] S2: Define the inspection sequence. Based on the information of the coated pipeline and the installation of elbows, valves, tees, and flow meters, avoid the aforementioned pipeline accessories during inspection. If any pipeline accessories are present, skip them. Determine the inspection starting and end points for each pipeline. Number each coated pipeline within the oil and gas station and determine the inspection sequence for each pipeline. For the same pipeline, complete the inspection from front to back according to the flow direction of the fluid before proceeding to the next pipeline.

[0022] S3: Calibrate the detection instrument. Before the test, remove the eight three-axis magnetic sensors 21 on the magnetic signal acquisition device 2, verify and adjust the orthogonality of the eight three-axis magnetic sensors 21 in the x, y, and z directions, and adjust the magnetic induction intensity detection accuracy in each direction. A uniform magnetic field can be applied to the three-axis magnetic sensors 21. The magnetic field detection accuracy of the three-axis magnetic sensors 21 can be adjusted by adjusting the data acquisition terminal 4. At the same time, the magnetic sensors are left to stand for 1 hour under a constant magnetic field and their data is checked for fluctuations to ensure that the detection results of the three-axis magnetic sensors 21 do not fluctuate significantly over time.

[0023] S4: Install the detection instrument. The entire magnetic detection device is stored in an explosion-proof box when not in use. Before the detection is carried out, eight permanent magnet magnetization devices 1 are fixedly installed on the pipeline; the eight permanent magnet magnetization devices 1 are evenly arranged on the outer surface of the pipeline containing the coating layer by adjusting the extension of the retractable hinge 15, and eight magnetic signal acquisition devices 2 are respectively installed in the middle position of the corresponding eight permanent magnet magnetization devices 1; the double-layer steel protective shell 22 in the magnetic signal acquisition device 2 is fixedly connected to the aluminum protective shell 13 of the permanent magnet magnetization device 1 to shield the surrounding interfering magnetic field. A three-axis magnetic sensor 21 is installed inside the double-layer steel protective shell 22 to only collect magnetic anomalies around defects in the pipeline containing the coating layer; the gyroscope 3 and the data acquisition terminal 4 are installed on the outside of the permanent magnet magnetization device 1 at the 12 o'clock position;

[0024] S5: Pipeline defect detection. Two technicians work together during the inspection. One technician pushes the permanent magnet magnetization device 1 along the pipeline at a constant speed to measure the three-axis magnetic field data, axial displacement data, and motion data of eight channels along the pipeline. The other technician uses a handheld portable computer 5 to view the obtained real-time magnetic field data. Based on the characteristics of sudden changes in magnetic induction intensity amplitude and magnetic induction intensity gradient at the suspected pipeline defect location, the possible pipeline defect location is marked.

[0025] S6: Magnetic field data inversion. Based on the relationship between the three-axis magnetic field induction intensity and lift-off height at defect-free and defective locations on the pipeline, the three-component magnetic field data at a distance of 2 mm from the pipeline surface are determined. The three components of the magnetic field detection results in eight clock directions on the pipeline are plotted separately to form three gridded pipeline magnetic field distribution maps. The specific location of the defect on the pipeline is determined based on the magnetic induction intensity amplitude and gradient values ​​in the pipeline magnetic field distribution maps. The specific location of the defect on the pipeline is determined by combining the axial displacement data measured by the displacement sensor 17 and the steering data measured by the gyroscope 3. The size of the defect is then determined based on the specific location of the defect on the pipeline and the magnetic field distribution characteristics corresponding to different defect sizes.

[0026] S7: Pipeline defect repair. After determining the size of the defect, determine the pipeline defect repair measures based on the severity of the defect. Carry out regular inspections and defect repair welding operations for minor defects, while for serious defects, immediately implement maintenance and emergency repair measures, including adding sleeves and replacing pipes. To prevent similar defects from continuing to develop and appear, determine the cause of the defect in combination with the basic conditions of the pipeline, and eliminate the factors that cause the defect in a targeted manner, including replacing a protective layer with better sealing, controlling the corrosiveness of the medium, improving the cathodic protection system, and repairing the anti-corrosion layer.

Claims

1. A magnetic detection device for defects in coating-containing pipelines at oil and gas stations, characterized by: The invention comprises a permanent magnet magnetization device (1), a magnetic signal acquisition device (2), a gyroscope (3), a data acquisition terminal (4) and a portable computer (5); the permanent magnet magnetization device (1) comprises a permanent magnet (11), an armature (12), an aluminum protective shell (13), an aluminum crawler (14), a retractable hinge (15), an aluminum counterweight (16) and a displacement sensor (17); the magnetic signal acquisition device (2) comprises a three-axis magnetic sensor (21), a double-layer steel protective shell (22) and a wire (23); the portable computer (5) runs real-time data display software; the magnetic detection device comprises eight completely identical permanent magnet magnetization devices (1), which are evenly distributed in the eight clock directions of the pipeline and perpendicular to the pipeline surface; the entire permanent magnet magnetization device (1) is wrapped by the aluminum protective shell (13), and its auxiliary facilities are fixedly installed The invention relates to a method for detecting a magnetic field of a pipe comprising: mounting a magnetic field on an aluminum protective shell (13); each permanent magnet magnetizing device (1) is internally composed of two permanent magnets (11) and an armature (12), and the two permanent magnets (11) are respectively mounted at the two ends of the armature (12) and have opposite magnetic poles, so that the pipe, the permanent magnet (11) and the armature (12) form a complete magnetic circuit; two aluminum tracks (14) are mounted on the outside of each aluminum protective shell (13); an aluminum counterweight (16) is mounted on the aluminum protective shell (13) at the bottom of the magnetic detection device to ensure that the magnetic detection device does not rotate in a circular direction during the entire detection process; a three-axis magnetic sensor (21) of a magnetic signal acquisition device (2) is mounted at the middle lower part of the permanent magnet magnetizing device (1) and is wrapped in a double-layer steel protective shell (22); a data acquisition terminal (4) and a gyroscope (3) are fixedly mounted on the outside of the permanent magnet magnetizing device (1) at 12 o'clock.

2. The magnetic detection device for defects in coating-containing pipelines at oil and gas stations according to claim 1, characterized in that: Eight permanent magnet magnetization devices (1) are connected through a retractable hinge (15). The extension of the retractable hinge (15) is adjusted to ensure that the magnetic detection device is suitable for pipelines with different diameters and is evenly distributed. A latch is provided in the retractable hinge (15) at 6 o'clock to realize rapid assembly and disassembly detection on pipelines with different coating layers in oil and gas stations.

3. The magnetic detection device for defects in coating-containing pipelines at oil and gas stations according to claim 1, characterized in that: The length of the armature (12) is 0.5 m. Extending the length of the armature (12) increases the magnetic resistance between the two permanent magnets (11), so that more magnetic fields generated by the permanent magnets (11) enter the pipeline with low magnetic resistance.

4. The magnetic detection device for defects in coating-containing pipelines at oil and gas stations according to claim 1, characterized in that: The aluminum crawler (14) ensures that the entire magnetic detection device only moves axially without circumferential rotation. During detection, the technician pushes the entire magnetic detection device forward along the axial direction; the aluminum crawler (14) at 12 o'clock is connected to the displacement sensor (17) to detect the displacement and speed of the entire magnetic detection device.

5. The magnetic detection device for defects in coating-containing pipelines at oil and gas stations according to claim 1, characterized in that: When inspecting small-diameter pipes, an aluminum counterweight (16) is installed on the aluminum protective shell (13) at 6 o'clock to ensure that the magnetic detection device does not rotate in the circumferential direction during the entire inspection process; when inspecting large-diameter pipes and pipes with a large number of defects, after the first inspection is completed, the entire magnetic detection device is rotated 22.5° around the central axis of the pipe, and the pipe with coating defects is inspected again to improve the detection effect. At this time, aluminum counterweights (16) are set on the two permanent magnet magnetization devices (1) near 6 o'clock to avoid circumferential rotation.

6. The magnetic detection device for defects in coating-containing pipelines at oil and gas stations according to claim 1, characterized in that: A magnetic signal acquisition device (2) is installed in the middle lower part of the aluminum protective shell (13) in the middle of each permanent magnet magnetization device (1). The magnetic signal acquisition device (2) is wrapped by a cubic double-layer steel protective shell (22) to shield the surrounding magnetic field interference. There is no protective shell on the side close to the pipeline; the three-axis magnetic sensor (21) is fixed in the double-layer steel protective shell (22) and is fixed at a distance of 5mm from the coating layer on the outer surface of the pipeline; the magnetic signals and the required electric energy are transmitted to the eight three-axis magnetic sensors (21) through the wire (23), and the magnetic signals are transmitted to the data acquisition terminal (4) and converted into digital signals; the data acquisition terminal (4) collects the three-axis magnetic signals The magnetic field data of the magnetic sensor (21), the axial displacement data of the displacement sensor (17) and the motion data of the gyroscope (3) are transmitted to the portable computer (5) through the WIFI transmitter inside the data acquisition terminal (4) for real-time display and storage; during the inspection, the technicians determine the location of the potential pipeline defect based on the amplitude and gradient value of the real-time magnetic field data and make a mark outside the coating layer; after the inspection is completed, the magnetic field data outside the coating layer is converted into magnetic field data 2 mm away from the pipeline surface in combination with the relationship between the pipeline magnetic field and the lift-off height; further, based on the magnetic field distribution characteristics corresponding to different defect sizes, the basic shape and depth of the pipeline defect are determined by inversion.

7. A magnetic detection method for defects in coating-containing pipelines at oil and gas stations, characterized in that: The following steps are involved: S1: Clearly define the pipeline information, including the information of the pipeline with coating layer to be tested, including pipeline material, pipeline wall thickness, pipeline diameter, fluid medium type, pressure level, pipeline route, coating thickness, and outer anti-corrosion layer material; S2: Define the inspection sequence. According to the pipeline information, determine the inspection starting point and inspection end point of each pipeline, number each inspected pipeline, and determine the inspection sequence of each pipeline; S3: Calibrate the detection instrument. Before the detection is carried out, remove the eight three-axis magnetic sensors (21) of the magnetic signal acquisition device (2), verify and adjust the orthogonality of the eight three-axis magnetic sensors (21) in the x, y and z directions, and adjust the magnetic induction intensity detection accuracy in each direction; S4: Install the detection instrument. Before the detection is carried out, eight permanent magnet magnetization devices (1) are fixedly installed on the pipeline. The extension distance of the retractable hinge (15) is adjusted to evenly distribute the eight permanent magnet magnetization devices (1) on the outer surface of the pipeline containing the coating layer. Eight magnetic signal acquisition devices (2) are respectively installed in the middle position of the corresponding eight permanent magnet magnetization devices (1). The gyroscope (3) and the data acquisition terminal (4) are installed on the outside of the permanent magnet magnetization device (1) at the 12 o'clock direction. S5: Pipeline defect detection. During the detection, two technicians work together. One technician pushes the permanent magnet magnetization device (1) along the pipeline at a constant speed to measure the three-axis magnetic field data, axial displacement data and motion data of eight channels along the pipeline. The other technician uses a portable computer (5) to view the collected real-time magnetic field data and mark the suspected defect location of the pipeline. S6: Inversion of magnetic field data: Based on the relationship between magnetic induction intensity and lift-off height, the magnetic field data at 2 mm from the pipeline surface is determined, and the magnetic field detection results in eight clock directions on the pipeline are plotted separately to form a pipeline magnetic field grid distribution map; the specific location of the defect on the pipeline is determined by combining the magnetic induction intensity amplitude and gradient value in the pipeline magnetic field distribution map with the axial displacement data measured by the displacement sensor (17) and the steering data measured by the gyroscope (3); and the size of the defect is determined based on the magnetic field distribution characteristics corresponding to different defect sizes; S7: Repair of pipeline defects, determine the size of the defects and evaluate their severity, determine the corresponding repair measures, including regular inspections, pipeline welding and pipeline replacement; determine the cause of the defects based on the basic conditions of the pipeline, and eliminate the factors that cause the defects in a targeted manner, including replacing the protective layer with better sealing, controlling the corrosiveness of the medium, improving the cathodic protection system and repairing the anti-corrosion layer.

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