Trenchless weak magnetic detection method for corrosion of oil and gas gathering and transportation pipeline

Abstract

The invention discloses a non-excavation weak magnetic detection method for corrosion of an oil and gas gathering and transportation pipeline. The non-excavation weak magnetic detection method comprises the following steps: S1, collecting and analyzing basic information of a target pipeline; s2, the pipeline trend and the pipeline burial depth are determined through a pipeline detector; s3, magnetic signals of the pipeline are scanned and collected, wherein the magnetic signals comprise space magnetic induction intensity in the horizontal x direction and the vertical y direction of the pipeline; s4, background geomagnetic field elimination and filtering processing are carried out on the acquired magnetic signal data; s5, identifying magnetic induction intensity gradient waveform characteristics of the corrosion position of the pipeline by using the corrosion model; and S6, positioning a corrosion position by using the waveform features identified in the S5. By analyzing the weak magnetic data, the corrosion state of the pipeline is accurately judged according to the waveform characteristics, and the detection accuracy is high.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas gathering and transportation pipeline detection, and in particular to a trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion. Background Art

[0002] Oil and gas gathering and transportation pipelines usually transport crude oil or associated gas, which generally contain corrosive media such as hydrogen sulfide and hydrogen chloride. At the same time, during the long-term operation of oil and gas gathering and transportation pipelines, they are affected by various factors, such as pipeline material and external environment, which can easily lead to corrosion defects in the pipelines. The existence of corrosion defects will not only affect the normal operation of the pipeline, but may also cause serious safety accidents. Therefore, regular inspection of oil and gas gathering and transportation pipelines is an important measure to ensure the safe operation of the pipelines.

[0003] At present, small-diameter (DN200 or less) pipelines are often used in oil and gas gathering and transportation pipelines, which are difficult to carry out magnetic flux leakage internal inspection. For pipelines within DN100, magnetic flux leakage internal inspection cannot be used; and conventional external inspection can only detect whether the anti-corrosion layer on the outside of the pipeline is damaged, and cannot fundamentally detect whether the pipeline body is corroded. The traditional corrosion detection method for oil and gas gathering and transportation pipelines mainly adopts the excavation detection method, that is, directly observing the surface condition of the pipeline by excavating the exposed part of the pipeline. Although this method is intuitive, it has great limitations, such as low detection efficiency, great damage to the pipeline, and only applicable to fixed-point detection. Therefore, the development of trenchless detection technology has become an urgent need in the industry.

[0004] The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion can detect the corrosion (including internal corrosion and external corrosion) of the gathering and transportation pipeline in service. The detection rate of the points with more serious corrosion is relatively high, which can effectively reduce the safety risk. The trenchless detection of gathering and transportation pipeline corrosion fills the gap in the detection of gathering and transportation pipeline corrosion. Summary of the invention

[0005] The purpose of the present invention is to provide a trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion. By using a weak magnetic field detection method, the axial position of the pipeline corrosion and its evaluation are determined by measuring the distribution of the weak magnetic field directly above the pipeline.

[0006] To achieve the above object, the present invention provides the following technical solution: a trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion, comprising the following steps: S1. Collect and analyze basic information of the target pipeline; S2. Use pipeline detector to determine the direction and buried depth of target pipeline; S3, scanning and collecting the magnetic signals of the pipeline, wherein the magnetic signals include the horizontal x and vertically along the pipeline y Spatial magnetic induction intensity in direction; S4, eliminating the background geomagnetic field and filtering the collected magnetic signal data; S5. Use the corrosion model to identify the magnetic induction intensity gradient waveform characteristics of the pipeline corrosion location: 1) Horizontal direction x Serving size: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② Two extreme points appear on the edges of the corrosion defect; ③ When the corrosion defect is pitting corrosion, the slope is the largest at the center of the corrosion defect; ④ When the corrosion defect is area corrosion, a peak value appears at the center of the corrosion defect and the prescription deviation is the largest at the center of the corrosion defect; 2) Vertical direction y Serving size: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② A peak appears at the center of the corrosion defect; ③The prescription difference is the largest at the center of the corrosion defect; S6. Use the waveform features identified in S5 to locate the corrosion position at the location where the pipeline appears, and make a preliminary assessment of the corrosion degree based on the basic information of the pipeline.

[0007] In some embodiments, in S1, the basic information of the target pipeline includes the pipeline name, pipeline operating unit, pipeline operation time; pipeline length, pipeline wall thickness, pipeline outer diameter; operating pressure, design pressure; pipeline material; pipeline burial depth range; conveying medium; type and thickness of anti-corrosion layer; inspection status and pipeline maintenance status, etc.

[0008] In some embodiments, in S2, after the pipeline direction and buried depth are determined, the pipeline to be tested is divided into several sections using carrier phase differential RTK, and the starting point and end point of each section are marked and located, and the actual mileage of the starting point and end point of each section relative to the reference object is recorded. When dividing and locating the pipeline to be tested, if marker piles, elbows, embankments, cables, and magnetic field interference sources are encountered, their position coordinates and relative mileage are recorded.

[0009] In some embodiments, in S4, the minimum mean square error LMS is used to eliminate the background geomagnetic field processing of the weak magnetic signal data, and the Butterworth filter is used to filter the weak magnetic signal, which can effectively filter out the noise in a specific frequency range, such as interference from the negative protection test pile, the potential test pile, etc.

[0010] In some embodiments, in S5, the corrosion model includes the following steps: S51, discretizing the pipeline with corrosion defects into grids to obtain the coordinates of each grid; S52, using ANSYS software to analyze the stress state of the pipeline with corrosion defects, and derive the stress two-component values ​​of the nodes required in S51; S53, calculating the magnetization intensity of each grid to obtain the magnetic moment of each grid unit; S54, calculating the magnetic signal of each grid unit, obtaining the two components of the magnetic signal of each grid unit, and obtaining the magnetic signal of the pipeline containing corrosion defects by vector superposition.

[0011] In some embodiments, in S51, the pipeline is divided into m grid, remember i =1,2,3,…, m ; Divided along the pipeline radial direction n grid, remember j =1,2,3,…, n ; All grids form the identity matrix E ; (1); The volume of all grids constitutes the volume matrix V ; (2); Finally, the grid volume is obtained; (3); In the formula, For grid cells The corresponding central angle; For grid cells The corresponding axial length; For grid cells The corresponding wall thickness.

[0012] In some embodiments, in S52, the axial stress on the pipeline is: (4); In the formula, is the internal pressure of the pipeline; D is the inner diameter of the pipeline; δ is the wall thickness of the pipeline.

[0013] In some embodiments, in S53, the magnetization intensity of each grid is: (5); The magnetic moment of each grid cell is: (6); The magnetic moment matrix of the grid unit of the pipeline containing corrosion defects can be obtained through the magnetic moment F ; (7); In the formula, For grid cells The magnetization intensity; For grid cells The magnetic moment of i =1, 2, 3, …, m , m The number of grids divided along the axial direction of the pipeline; j =1, 2, 3, …, n , is the number of grids divided along the radial direction of the pipeline.

[0014] In some embodiments, in S54, the magnetic signal of each grid unit is: (8); (9); (10); The two components of the magnetic signal calculated for each grid are vector-superimposed to obtain the two components of the magnetic signal of the pipeline with corrosion defects: (11); (12); In the formula, is the magnetic induction intensity of the grid unit of the pipeline with corrosion defects at point P x Axial component; is the y-axis component of the magnetic induction intensity of the grid unit of the pipeline with corrosion defects at point P; is the straight-line distance between the grid unit of the pipeline with corrosion defects and point P; is the vacuum permeability; For grid cells along x Direction of the magnetic moment component; For point P xy Edge on the plane x Axis projection length; For point P yz Edge on the plane x Axis projection length; For grid cells The angle with the x-axis; For grid cells along y Direction of the magnetic moment component; For grid cells along z Direction of the magnetic moment component; For point P zx Edge on the plane z Axis projection length; is the magnetic moment component of any microelement on the pipeline along the y direction; is the magnetic moment component of any microelement on the pipeline along the z direction; For grid cells The corresponding axial length; For grid cells The corresponding central angle; is the magnetic induction intensity of the corrosion defect pipeline at point P x Axial component; is the y-axis component of the magnetic induction intensity of the corrosion-defective pipeline at point P.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts trenchless detection, which does not require the surface of the component to be tested to be cleaned in advance, does not damage the pipeline, does not affect the normal operation of the pipeline, and improves the safety of detection; (2) The present invention does not require a professional magnetizing device and can be detected under the natural geomagnetic field, with high detection efficiency; (3) Applicable to ferromagnetic pipes of any diameter, especially small-diameter pipes such as DN100 and DN80 that cannot be internally inspected; (4) The present invention analyzes weak magnetic data and accurately determines the pipeline corrosion state according to waveform characteristics, with high detection accuracy; (5) The present invention can classify and evaluate the pipeline safety level, providing a basis for subsequent maintenance and repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the forward modeling of magnetic signals of a pipeline with corrosion defects according to an embodiment of the present invention; Figure 2 This is a schematic diagram of discrete tiling of a pipeline grid containing corrosion defects according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the derivation of the forward model of a pipeline with corrosion defects according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the waveform of corrosion defects detected by weak magnetic field during pitting corrosion according to an embodiment of the present invention; Figure 5 It is a pitting diagram of an embodiment of the present invention; Figure 6 This is a waveform diagram of large-area weak magnetic detection of corrosion defects according to an embodiment of the present invention; Figure 7 This is a large-area etching pattern of an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] See also Figure 1 - Figure 7 , a trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion, comprising the following steps: S1. Collect and analyze basic information of the target pipeline; According to the "Weak Magnetic Detection Method for Nondestructive Testing of Pipelines" GB / T 35090-2018, collect the data of the pipeline to be tested. Check and analyze the pipeline design, pipeline operation and operation documents of the target pipeline, and make a preliminary judgment on the parts of the pipeline that may be corroded.

[0019] The information that needs to be collected mainly includes: pipeline name; operating unit; time when the pipeline was put into operation; pipeline length, pipeline wall thickness, pipeline outer diameter; pipeline operating pressure, pipeline design pressure; pipeline material; pipeline burial depth range; main components and corrosiveness of pipeline transportation media; type and thickness of pipeline anti-corrosion layer; recent pipeline inspection status (inspection time, inspection standard, inspection method and results, etc.); pipeline maintenance status (maintenance time, maintenance method and location, etc.); other information (parallel pipelines, crossing pipelines, etc.).

[0020] S2. Use pipeline detector to determine the pipeline direction and buried depth; The pipeline detector is mainly composed of a signal transmitter and a receiver. The transmitter is connected to the pipeline and the earth to form an equivalent circuit and applies an electrical signal to the pipeline. The induction coil in the receiver detects the signal and determines the buried depth and direction of the pipeline by identifying the size and direction of the signal current.

[0021] At the same time, the carrier phase difference technology (RTK) is used to divide the pipeline. The pipeline to be tested is divided into several small sections, and the starting and ending points of each section are marked and located. At the same time, the actual mileage of the starting and ending points of each section relative to the reference object (usually mileage pile) is recorded. When dividing and locating the pipeline to be tested, if marker piles, elbows, embankments, cables and magnetic field interference sources are encountered, their position coordinates and relative mileage are recorded.

[0022] S3, scanning and collecting the magnetic signals of the pipeline, wherein the magnetic signals include the horizontal x and vertically along the pipeline y Spatial magnetic induction intensity in direction; The inspector holds a weak magnetic detection device (Grad-13 gradient magnetometer) and walks directly above the pipeline axis along the route calibrated by the pipeline detector to scan and collect the magnetic signal of the pipeline. The collected magnetic signal is the horizontal magnetic field along the pipeline. x Direction and vertical along the pipeline y The spatial magnetic induction intensity in the direction.

[0023] S4, eliminating the background geomagnetic field and filtering the collected magnetic signal data; The minimum mean square error (LMS) is used to eliminate the background geomagnetic field processing of the collected weak magnetic data. The minimum mean square error (LMS) is an adaptive filtering method that uses the stochastic gradient descent method to minimize the mean square error function, that is, the weight vector is updated by the inverse gradient vector of the objective function. The update rule of the LMS algorithm is to iterate along the steep descent direction of the mean square error surface, so that the output of the filter approaches the expected signal. Therefore, the error between the expected signal and the actual output of the filter is minimized by continuously adjusting the coefficient of the filter. In the application of eliminating background magnetic field signals, the LMS algorithm can effectively identify and reduce unnecessary magnetic field interference, thereby improving the quality of the signal. The Butterworth filter is used to effectively filter out noise in a specific frequency range, such as interference sources such as negative protection test piles and potential test piles, and eliminate interference to improve the accuracy and reliability of data.

[0024] S5. Use the corrosion model to identify the magnetic induction intensity gradient waveform characteristics at the pipeline corrosion location.

[0025] like Figure 1 As shown in the figure, the difference between corrosion defects and pipeline bodies mainly lies in the stress state, the volume of ferromagnetic materials and the distribution of ferromagnetic materials. In order to calculate the magnetic signal of pipelines with corrosion defects, the grid discretization method is used to divide the pipelines with corrosion defects into several small units, and the magnetic signal of each unit is calculated. Then, the magnetic signal of the pipeline with corrosion defects is obtained by vector superposition.

[0026] The following steps are involved: In the first step, the pipeline with corrosion defects is discretized into grids and the coordinates of each grid are obtained.

[0027] This embodiment uses a method of gradually encrypting local grids to reduce errors. The grid is most densely divided at the corrosion defect, and the grid is moderately reduced around the corrosion defect, and the grid is reduced again away from the corrosion defect. Figure 2 As shown, the pipeline is divided into m grid, remember i =1,2,3,..., m ; Divided radially into n grid, remember j =1,2,3,..., n. The coordinates of the upper left corner node of each grid Denote the coordinates of each grid, Represents the volume of each grid. All grids constitute a cell matrix E : (1); The volume of all grids constitutes the volume matrix V ; (2); The volume of the grid is: (3); In the formula, For grid cells The corresponding central angle; For grid cells The corresponding axial length; For grid cells The corresponding wall thickness.

[0028] In the second step, based on the finite element concept, ANSYS software is used to analyze the stress state of the pipeline with corrosion defects, and the two-component stress values ​​of the nodes required in the first step (all grids for mesh discretization of the pipeline with corrosion defects) are derived.

[0029] The meshed model is loaded, where symmetric constraints are imposed on the two axial sections of the pipeline model to simulate the situation in the entire pipe section. A uniform pressure load is applied along the inner surface of the pipeline model. The axial displacement of the left end face of the pipeline model is constrained to be 0, and the axial tensile stress load caused by the internal pressure on the right end face is: (4); In the formula, is the internal pressure of the pipeline; D is the inner diameter of the pipeline; δ is the wall thickness of the pipeline.

[0030] The third step is to calculate the magnetization intensity of each grid and obtain the magnetic moment of each grid cell.

[0031] Due to the influence of the defects, the stress distribution of the pipeline with corrosion defects cannot be expressed by a continuous function, resulting in the discontinuity of its magnetization intensity distribution. Therefore, it is necessary to calculate the magnetization intensity of each grid unit of the corrosion defect and its affected area, so as to obtain the magnetization intensity corresponding to each grid unit. , and then the magnetic intensity matrix of the pipeline with corrosion defects can be obtained M : (5); The magnetic moment vector of each grid cell is: (6); The magnetic moment matrix of the grid cell of the pipeline containing corrosion defects can be obtained through the magnetic moment vector. F ; (7); In the formula, For grid cells The magnetization intensity; For grid cells The magnetic moment of i =1, 2, 3, …, m , m The number of grids divided along the axial direction of the pipeline; j =1, 2, 3, …, n , is the number of grids divided along the radial direction of the pipeline.

[0032] The fourth step is to calculate the magnetic signal of each grid unit, obtain the two components of the magnetic signal of each grid unit, and obtain the magnetic signal of the pipeline with corrosion defects through vector superposition.

[0033] like Figure 3 As shown in the figure, after obtaining the magnetization intensity of the grid unit, the forward model of the magnetic signal of the pipeline with corrosion defects can be obtained based on the magnetic dipole model. Taking the center point of the corrosion defect as the coordinate origin, x The axis direction is perpendicular to the pipeline axis direction. y The direction is the pipeline axis direction. z The direction is perpendicular to the plane where the pipeline is located, so as to establish a Cartesian coordinate system. Finally, the calculation expression of the magnetic signal of each grid unit can be obtained: (8); (9); (10); The two components of the magnetic signal calculated for each grid are vector-superimposed to obtain the two components of the magnetic signal of the pipeline with corrosion defects: (11); (12); In the formula, is the magnetic induction intensity of the grid unit of the pipeline with corrosion defects at point P x Axial component; is the y-axis component of the magnetic induction intensity of the grid unit of the pipeline with corrosion defects at point P; is the straight-line distance between the grid unit of the pipeline with corrosion defects and point P; is the vacuum permeability; For grid cells along x Direction of the magnetic moment component; For point P xy Edge on the plane x Axis projection length; For point P yz Edge on the plane x Axis projection length; For grid cells The angle with the x-axis; For grid cells along y Direction of the magnetic moment component; For grid cells along z Direction of the magnetic moment component; For point P zx Edge on the plane z Axis projection length; is the magnetic moment component of any microelement on the pipeline along the y direction; is the magnetic moment component of any microelement on the pipeline along the z direction; For grid cells The corresponding axial length; For grid cells The corresponding central angle; is the magnetic induction intensity of the corrosion defect pipeline at point P x Axial component; is the y-axis component of the magnetic induction intensity of the corrosion-defective pipeline at point P.

[0034] S6. Use the waveform features identified in S5 to locate the corrosion position. Combined with the irregular characteristics of pipeline corrosion, the magnetic induction intensity gradient waveform features at the corrosion position are as follows: 1) Horizontal direction x Serving size: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② Two extreme points appear on the edges of the corrosion defect; ③ When the corrosion defect is pitting corrosion, the slope is the largest at the center of the corrosion defect; ④ When the corrosion defect is area corrosion, a peak value appears at the center of the corrosion defect and the prescription deviation is the largest at the center of the corrosion defect, that is, the signal fluctuation is the largest; 2) Vertical direction y Serving size: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② A peak appears at the center of the corrosion defect; ③ The prescription deviation of the corrosion defect center is the largest, that is, the signal fluctuation is the largest.

[0035] The location of the pipeline corrosion defect point can be found by finding the location of the pipeline corresponding to the magnetic induction intensity gradient waveform characteristics where the above corrosion defects appear.

[0036] In a specific embodiment, 1. Collect basic information of the target pipeline. The basic information of the target pipeline is shown in Table 1. Table 1 Pipeline basic information table

[0037] 2. Pipeline routing and burial depth mapping; The 6.8km long pipeline was divided into 40 sections for testing according to the on-site testing environment, as shown in Table 2; Table 2 Pipeline route depth mapping and segmentation table

[0038] 3. Pipeline weak magnetic signal collection The inspectors hold the pipeline weak magnetic detection equipment and walk along the route calibrated by the pipeline detector directly above the pipeline axis to scan and collect the magnetic signals directly above the pipeline.

[0039] It should be noted that during the magnetic signal acquisition process, the detection equipment must be located directly above the pipeline axis, remain stable and at the same height as the body, and move forward at a constant speed. Since the detection equipment uses a very sensitive sensor, during the scanning process directly above the pipeline axis, it is necessary to ensure that the detection personnel have no ferromagnetic accessories or other electronic products on their body to avoid interference with the detection caused by the external magnetic field.

[0040] 4. Data processing; The minimum mean square error (LMS) algorithm is used to eliminate the background magnetic field of the collected weak magnetic data, and the Butterworth filter is used to filter and eliminate interference to improve the accuracy and reliability of the data.

[0041] 5. Identification of corrosion point defects; Identify abnormal points in the data, identify and locate the locations where corrosion exists, and make a preliminary assessment of the degree of corrosion based on the basic information of the pipeline.

[0042] According to the "Weak Magnetic Detection Method for Nondestructive Testing of Pipelines" GB / T 35090-2018, determine the pipeline damage and take corresponding measures according to the situation. The pipeline damage level is shown in Table 3 below.

[0043] Table 3 GB / T 35090-2018 Pipeline Damage Grade Table

[0044] 5.1. Pitting corrosion; like Figure 4As shown in the figure, after data preprocessing and abnormal point identification, the magnetic induction intensity gradient feature appears at the 80m-83m position in the 16th section, so it is determined that this is a corrosion defect, and there are mileage pile (metal) interference at 5m and 106m. The magnetic induction intensity gradient feature at the corrosion defect is: 1) Horizontal (x) component: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② Two extreme points appear on the edges of the corrosion defect; ③The slope is the largest and the signal fluctuation is the largest at the center of the corrosion defect.

[0045] 2) Vertical (y) component: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② A peak appears at the center of the corrosion defect; ③ The center of the corrosion defect has the largest prescription deviation and the largest signal fluctuation; like Figure 5 As shown, after non-destructive testing after excavation, the maximum wall thickness in this area was measured to be 6.76mm, the minimum wall thickness was 5.48mm, and the maximum wall thickness thinning rate was 18.93%.

[0046] 5.2. Large area corrosion; like Figure 6 As shown in the figure, after data preprocessing and abnormal point identification, the characteristics of magnetic induction intensity gradient appear at the position of 95m-97m, which is determined to be a corrosion defect, and there is mileage pile (metal) interference at 77m-78m. The characteristics of magnetic induction intensity gradient at the corrosion defect are: 1) Horizontal (x) component: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② Two extreme points appear on the edges of the corrosion defect; ③ A peak appears at the center of the corrosion defect; ④ The prescription deviation of the corrosion defect center is the largest and the signal fluctuation is the largest.

[0047] 2) Vertical (y) component: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② A peak appears at the center of the corrosion defect; ③The prescription deviation of the corrosion defect center is the largest and the signal fluctuation is the largest.

[0048] like Figure 7 As shown in the figure, after nondestructive testing after excavation, the maximum wall thickness in this area was measured to be 7.22mm, the minimum wall thickness was 3.88mm, and the maximum wall thickness reduction rate was 46.26%. In addition, there were corrosion pits of different corrosion degrees in the 95m-97m area.

Claims

1. A trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion, characterized in that: The following steps are involved: S1. Collect and analyze basic information of the target pipeline; S2. Use pipeline detector to determine the direction and buried depth of target pipeline; S3, scanning and collecting the magnetic signals of the pipeline, wherein the magnetic signals include the horizontal x and vertically along the pipeline y Spatial magnetic induction intensity in direction; S4, eliminating the background geomagnetic field and filtering the collected magnetic signal data; S5. Use the corrosion model to identify the magnetic induction intensity gradient waveform characteristics of the pipeline corrosion location: 1) Horizontal direction x Serving size: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② Two extreme points appear on the edges of the corrosion defect; ③ When the corrosion defect is pitting corrosion, the slope is the largest at the center of the corrosion defect; ④ When the corrosion defect is area corrosion, a peak value appears at the center of the corrosion defect and the prescription deviation is the largest at the center of the corrosion defect; 2) Vertical direction y Serving size: ① Sawtooth-shaped fluctuations appear in the corrosion defect area; ② A peak appears at the center of the corrosion defect; ③The prescription difference is the largest at the center of the corrosion defect; S6. Locate the corrosion position using the waveform features identified in S5.

2. The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion according to claim 1 is characterized in that: In S1, the basic information of the target pipeline includes the pipeline name, pipeline operating unit, pipeline operation time; pipeline length, pipeline wall thickness, pipeline outer diameter; operating pressure, design pressure; pipeline material; pipeline burial depth range; conveying medium; type and thickness of anti-corrosion layer; inspection status and pipeline maintenance status.

3. The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion according to claim 1 is characterized in that: In S2, after the pipeline direction and buried depth are determined, the pipeline to be measured is divided into several sections using carrier phase differential RTK, and the starting point and end point of each section are marked and located, and the actual mileage of the starting point and end point of each section relative to the reference object is recorded.

4. The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion according to claim 1 is characterized in that: In S4, the minimum mean square error LMS is used to eliminate the background geomagnetic field from the weak magnetic signal data, and the Butterworth filter is used to filter the weak magnetic signal.

5. The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion according to claim 1 is characterized in that: In S5, the corrosion model includes the following steps: S51, discretizing the pipeline with corrosion defects into grids to obtain the coordinates of each grid; S52, using ANSYS software to analyze the stress state of the pipeline with corrosion defects, and derive the stress two-component values ​​of the nodes required in S51; S53, calculating the magnetization intensity of each grid to obtain the magnetic moment of each grid unit; S54, calculating the magnetic signal of each grid unit, obtaining the two components of the magnetic signal of each grid unit, and obtaining the magnetic signal of the pipeline containing corrosion defects by vector superposition.

6. The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion according to claim 5 is characterized in that: In S51, the pipeline is divided into m grid, remember i =1,2,3,…, m ; The pipeline is divided into n grid, remember j =1,2,3,…, n ; All grids form the identity matrix E ; （1）； The volume of all grids constitutes the volume matrix V ; （2）； Finally, the grid volume is obtained; （3）； In the formula, For grid cells The corresponding central angle; For grid cells The corresponding axial length; For grid cells The corresponding wall thickness.

7. The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion according to claim 5 is characterized in that: In S52, the axial stress on the pipe is: （4）； In the formula, is the internal pressure of the pipeline; D is the inner diameter of the pipeline; δ is the wall thickness of the pipeline.

8. The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion according to claim 5 is characterized in that: In S53, the magnetization intensity of each grid is: （5）； The magnetic moment of each grid cell is: （6）； The magnetic moment matrix of the grid unit of the pipeline containing corrosion defects can be obtained through the magnetic moment F ; （7）； In the formula, For grid cells The magnetization intensity; For grid cells The magnetic moment of i =1, 2, 3, ..., m , m The number of grids divided along the axial direction of the pipeline; j =1, 2, 3, ..., n , is the number of grids divided along the radial direction of the pipeline.

9. The trenchless weak magnetic detection method for oil and gas gathering and transportation pipeline corrosion according to claim 5 is characterized in that: In S54, the magnetic signal of each grid cell is: （8）； （9）； （10）； The two components of the magnetic signal calculated for each grid are vector-superimposed to obtain the two components of the magnetic signal of the pipeline with corrosion defects: （11）； （12）； In the formula, The grid unit of the pipeline with corrosion defects The magnetic induction intensity at point P x Axial component; The grid unit of the pipeline with corrosion defects The y-axis component of the magnetic induction intensity at point P; The grid unit of the pipeline with corrosion defects The straight-line distance to point P; is the vacuum permeability; For grid cells along x Direction of the magnetic moment component; For point P xy Edge on the plane x Axis projection length; For point P yz Edge on the plane x Axis projection length; For grid cells The angle with the x-axis; For grid cells along y Direction of the magnetic moment component; For grid cells along z Direction of the magnetic moment component; For point P zx Edge on the plane z Axis projection length; is the magnetic moment component of any microelement on the pipeline along the y direction; is the magnetic moment component of any microelement on the pipeline along the z direction; For grid cells The corresponding axial length; For grid cells The corresponding central angle; is the magnetic induction intensity of the corrosion defect pipeline at point P x Axial component; is the y-axis component of the magnetic induction intensity of the corrosion-defective pipeline at point P.

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