Detection method for long-distance buried and near-spacing parallel metal pipeline

Abstract

The invention discloses a method for detecting long-distance buried and near-spacing parallel metal pipelines, which comprises the following steps of: scanning an area to be detected by using a metal pipeline detector, and determining the initial position and the initial direction of a target pipeline; according to the initial position and the initial direction, setting the metal pipeline detector as a preset detection parameter, and detecting an initial depth; and when the initial depth is greater than a preset threshold depth, determining the actual position of the target pipeline by adopting an inversion algorithm according to the magnetic field data detected by the metal pipeline detector by using different parameters. According to the scheme, accurate detection of long-distance buried and near-distance parallel metal pipelines can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline positioning, and in particular to a method for detecting long-distance buried and closely spaced parallel metal pipelines. Background Art

[0002] Urban underground pipelines are crucial infrastructure and the lifeblood of urban survival and development. In recent years, urban populations have surged, and demand for the underground pipelines upon which people rely for survival has rapidly increased. Limited by the shortage of available above- and underground space, a large number of new pipelines have been constructed around existing pipelines with minimal maintenance wells. This has led to the increasing prevalence of pipelines with long, hidden, closely spaced, and parallel distribution characteristics. Existing technologies use metal pipeline detectors based on the principles of frequency-domain electromagnetic methods to detect underground metal pipelines. For isolated, shallowly buried metal pipelines, the secondary induced magnetic field generated by the target pipeline is consistent with theory, enabling relatively accurate metal pipeline detection. However, when the target pipeline is long and hidden, and surrounded by closely spaced, parallel lateral pipelines, accurate detection of the target pipeline's direction, location, and burial depth becomes quite difficult due to interference from these lateral pipelines. Consequently, existing solutions suffer from poor detection accuracy. Summary of the Invention

[0003] In order to solve the above problems, the present invention proposes a method for detecting long-distance buried and closely spaced parallel metal pipelines, which can achieve accurate detection of long-distance buried and closely spaced parallel metal pipelines.

[0004] The present invention provides a method for detecting long-distance, buried, and closely spaced parallel metal pipelines, the method comprising:

[0005] Use a metal pipeline detector to scan the area to be detected to determine the preliminary position and direction of the target pipeline;

[0006] According to the preliminary position and the preliminary direction, the metal pipeline detector is set to preset detection parameters to detect a preliminary depth;

[0007] When the preliminary depth is greater than a preset threshold depth, an inversion algorithm is used to determine the actual position of the target pipeline based on magnetic field data detected by the metal pipeline detector using different parameters.

[0008] As a preferred solution, a metal pipeline detector is used to scan the area to be detected to determine the preliminary position and direction of the target pipeline, including:

[0009] Respectively setting the receiving parameters of the receiver and the transmitting parameters of the transmitter of the metal pipeline detector;

[0010] Keeping the transmitter horizontal and its long axis aligned with the long axis of the receiver, the transmitter is moved along the long axis of the receiver. When the initial value of the signal amplitude of the receiver decreases to a preset ratio, the plane distance between the receiver and the transmitter is determined as the scanning distance;

[0011] Based on the scanning distance, the transmitter and the receiver are rotated to scan the area to be detected to determine the preliminary position and preliminary direction of the target pipeline.

[0012] Furthermore, the receiving parameters include receiving direction, receiving gain, receiving frequency and receiving mode;

[0013] The transmission parameters include transmission direction, transmission power and transmission frequency.

[0014] Preferably, based on the scanning distance, the transmitter and the receiver are subjected to a rotation scanning method to scan the area to be detected, and a preliminary position and a preliminary direction of the target pipeline are determined, including:

[0015] Keeping the transmitter vertical with its minor axis aligned with the receiver, the transmitter performs circular motion with the receiver as the center and the scanning distance as the radius at a preset speed; while performing the circular motion, the receiving direction of the receiver is periodically changed at a preset swing speed within a preset receiving angle range, and the signal amplitude of the receiver is monitored;

[0016] When the rate of change of the signal amplitude of the receiver exceeds a preset change threshold, the position of the transmitter is fixed as the transmitting point, and the receiving direction of the receiver is continuously changed to determine the receiving point with the maximum signal amplitude;

[0017] The preliminary position and preliminary direction of the target pipeline are determined according to the line connecting the transmitting point and the receiving point.

[0018] Preferably, according to the preliminary position and the preliminary direction, the metal pipeline detector is set to preset detection parameters to detect the preliminary depth, including:

[0019] Measure the distance between the target pipeline and the nearest surrounding pipeline at the marked transmitting point and receiving point, and select the point with the larger distance as the signal transmitting point of the transmitter of the metal pipeline detector;

[0020] placing the receiver at the signal transmission point so that the long axis direction of the transmitter is consistent with the preliminary direction;

[0021] Place the transmitter at the corresponding receiving point, and set the optimal transmission parameters of the transmitter and the optimal receiving parameters of the receiver of the metal pipeline detector;

[0022] The preliminary depth of the target pipeline is detected using the direct reading method, the 70% method, or the 50% method.

[0023] Furthermore, the optimal transmission parameters include optimal power and optimal frequency;

[0024] The optimal power and the optimal frequency determination process includes:

[0025] Calculating a detection error between a first detection position obtained by the metal pipeline detector at different powers and frequencies and a second detection position obtained by detecting at a preset distance from the ground;

[0026] The frequency and power when the detection error is minimum are respectively used as the optimal power and the optimal frequency.

[0027] Furthermore, the optimal transmission parameters include an optimal polarization direction;

[0028] The optimal polarization direction determination process includes:

[0029] Setting the transmitter to transmit signals at an optimal transmission power and an optimal transmission frequency, and adjusting the polarization direction of the transmitter at a preset adjustment interval, and calculating the detection error between a third detection position obtained by the metal pipeline detector when detecting close to the ground and a fourth detection position obtained by detecting at a preset distance from the ground under different polarization directions;

[0030] The polarization direction with the smallest detection error is taken as the optimal polarization direction.

[0031] Preferably, the actual position of the target pipeline is determined using an inversion algorithm based on the magnetic field data detected by the metal pipeline detector using different parameters, including:

[0032] Setting the plane position and burial depth of the target pipeline and the interfering pipeline;

[0033] Determine the range of the survey line layout according to the set plane positions and buried depths of the target pipeline and the interfering pipeline, and layout measuring points at a preset point spacing within the survey line layout range to determine the coordinates of each measuring point;

[0034] Controlling the transmitter of the metal pipeline detector to transmit a signal with optimal transmission parameters to stimulate the target pipeline, and using the broad peak method function of the receiver of the metal pipeline detector to record the magnetic field value of each measuring point as the magnetic field profile data under the first set of current parameters;

[0035] Keeping the optimal power and the optimal frequency in the optimal transmission parameters unchanged, the polarization angle of the transmitter is rotated counterclockwise and clockwise by preset angles, respectively, and the magnetic field value of each measuring point is recorded, thereby obtaining magnetic field profile data under the second set of current parameters and magnetic field profile data under the third set of current parameters;

[0036] Based on the three sets of magnetic field profile data obtained, the set planar position, burial depth and current value of the target pipeline and the interfering pipeline, an objective function is constructed, and based on the genetic algorithm, the planar position and burial depth of the target pipeline and the interfering pipeline are solved when the objective function is minimized to obtain the actual position.

[0037] Preferably, the objective function

[0038] Where F is the target value, j = 1, 2, 3, representing three sets of magnetic field profile data from three measurements, i = 1, 2, 3…N, N represents the number of measurement points, and represent the current value of the target pipeline and the current value of the interfering pipeline in the jth group of magnetic field profile data, h1 and h2 are the burial depths of the target pipeline and the interfering pipeline, x1 and x2 are the burial depths of the target pipeline and the interfering pipeline, xi represents the coordinates of each measuring point, Represents the magnetic field value received by the receiver on the ground at the coordinate position of each measuring point xi in the jth group of magnetic field profile data.

[0039] Preferably, the method further comprises:

[0040] When the preliminary depth is not greater than the threshold depth, calculating a detection error between a fifth detection position obtained by the metal pipeline detector under different detection parameters through close-to-ground detection and a sixth detection position obtained through detection at a preset distance from the ground;

[0041] The average of the fifth detection position and the sixth detection position corresponding to the minimum detection error is used as the actual position of the target pipeline. The present invention provides a method for detecting long-distance buried and closely spaced parallel metal pipelines, which uses a metal pipeline detector to scan the area to be detected to determine the preliminary position and preliminary direction of the target pipeline; according to the preliminary position and the preliminary direction, the metal pipeline detector is set to a preset detection parameter to detect the preliminary depth; when the preliminary depth is greater than the preset threshold depth, the actual position of the target pipeline is determined by an inversion algorithm based on the magnetic field data detected by the metal pipeline detector using different parameters. The present application solution can achieve accurate detection of long-distance buried and closely spaced parallel metal pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1The present invention provides a flow chart of a method for detecting long-distance buried and closely spaced parallel metal pipelines. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0044] Long, hidden underground lines and closely spaced parallel pipelines (subdivided into shallow and deep buried lines) pose a challenge to the underground pipeline detection industry. This is primarily due to three key issues: 1. Due to the long, hidden underground lines, it is difficult to efficiently, quickly, and safely determine the number and location of hidden pipelines within the detection area; 2. Existing technologies are only moderately effective in suppressing interference from adjacent pipelines, resulting in significant errors; and 3. Deeply buried pipeline detection is inefficient, with significant human influence on detection results, resulting in poor accuracy and stability.

[0045] Therefore, the present application provides a method for detecting long-distance buried and closely spaced parallel metal pipelines. Figure 1 , is a flow chart of a method for detecting long-distance buried and closely spaced parallel metal pipelines provided by an embodiment of the present invention, the method comprising steps S1 to S3;

[0046] Step S1, using a metal pipeline detector to scan the area to be detected to determine the preliminary position and preliminary direction of the target pipeline;

[0047] Step S2, according to the preliminary position and the preliminary direction, setting the metal pipeline detector to preset detection parameters to detect a preliminary depth;

[0048] Step S3: When the preliminary depth is greater than a preset threshold depth, an inversion algorithm is used to determine the actual position of the target pipeline based on the magnetic field data detected by the metal pipeline detector using different parameters.

[0049] During the specific implementation of this embodiment, when detecting long-distance buried, closely spaced, and parallel pipelines, it is first necessary to preliminarily determine the approximate position and direction of the pipeline. Specifically, a metal pipeline detector based on the principle of frequency domain electromagnetic method can be used. The device consists of a transmitter and a receiver. The transmitter can excite the target pipeline through a direct connection method, a clamp method, or an induction method (one of the three methods), causing the target pipeline to generate an induced current and a secondary induced magnetic field; the receiver receives the secondary induced magnetic field and uses its spatial distribution characteristics to achieve pipeline positioning and depth determination.

[0050] When using existing metal pipeline detection instruments for detection of isolated, shallowly buried metal pipelines, the secondary induced magnetic field generated by the target pipeline is consistent with theory, allowing the pipeline to be located and determined at its depth using only a few characteristic points. However, when the target pipeline is buried over a long distance and surrounded by closely spaced parallel pipelines, accurate detection of the target pipeline's direction, location, and depth becomes quite difficult due to interference from these adjacent pipelines. Detection becomes even more challenging if the target pipeline is deeply buried (depth h > 3m).

[0051] It should be noted that due to their buried nature, detection of long-distance, closely spaced, and parallel pipelines often makes it difficult to locate manholes or underground outlets within a radius of 100 meters or even greater around the detection area. Therefore, induction excitation is the only method available. Unlike direct connection and clamp excitation methods, induction excitation does not require manholes or exposed sections. It offers fewer restrictions and flexible excitation methods. In many cases, it is the only excitation method, requiring only ground contact around the target pipeline. The principle of induction excitation is relatively simple: a transmitter houses a coil, with the coil plane parallel to the transmitter's bottom surface. When an alternating current is applied to the coil, it emits an alternating electromagnetic field in the form of a cone (polarized vertically downward) along the normal direction of the coil plane. The energy is strongest in the center of the cone and decreases toward the outer edges, with energy decaying according to a specific pattern.

[0052] Therefore, in this case, a metal pipeline detector is first used to scan the area to be detected to determine the preliminary position and preliminary direction of the target pipeline. It should be noted that when performing preliminary position and preliminary direction detection in this application, existing detection schemes such as the scanning method can be used. The operation method of the scanning method is that one person holds a handheld transmitter at one end of the detection area, and another person holds a handheld receiver at the other end. The two operators move slowly in a certain direction at the same time. When the transmitter and receiver are both located near the top of the pipeline, the amplitude of the magnetic field signal displayed on the receiver screen will suddenly increase, and the peak position of the amplitude is directly above the pipeline. At this time, the position of the amplitude peak point is marked with spray paint. Next, the positions of the transmitter and receiver are exchanged, and the transmitter is placed at the peak point position and remains stationary, with the long axis of the transmitter roughly consistent with the direction of the pipeline; the receiver searches for the peak point of the magnetic field amplitude and marks it with spray paint. At this time, the line connecting the two points marked with spray paint on the ground is the position and direction of the underground buried pipeline. By implementing a single scan, it is possible to determine whether there are pipelines running at a certain angle in the detection area. Usually, multiple scans are required to ensure full angle coverage and avoid missed detections. After completing the scan at all angles, the preliminary position information of all buried pipelines in the detection area is obtained, thereby determining the preliminary position and preliminary direction of the target pipeline.

[0053] It's important to note that when implementing the plan, it's recommended to gather underground pipeline data and a 1:500 topographic map of the survey area in advance. This map can then be overlaid with the pipeline map and printed. The pipeline map should be brought to the site for verification, and the locations of existing pipelines should be marked on the ground. Because existing pipeline data is often compiled from completion acceptance documents, design drawings, survey data, construction drawings, and manual drawings, its integrity is difficult to guarantee. In addition to the existing pipeline data on the drawings, there's a high probability that other long-distance, hidden pipelines may exist in the survey area.

[0054] After determining the preliminary position and direction of the target pipeline, each underground buried pipeline is located and measured in depth.

[0055] According to the preliminary position and the preliminary direction, adjusting the detection parameters of the metal pipeline detector to detect the preliminary depth;

[0056] Therefore, this case aims to suppress the interference of the adjacent pipelines and improve the accuracy of positioning and depth determination by adjusting the detection parameters of the metal pipeline detector, namely adjusting the transmitter position, transmitter signal transmission power and transmission frequency, etc.

[0057] To address interference from other pipelines, adjusting the transmitter's position and utilizing the selective excitation method can effectively reduce the secondary induced field strength of non-target pipelines. The key to this selective excitation method is to locate isolated segments of the target pipeline where non-target pipelines are absent or far away. This allows the transmitter to weakly excite the non-target pipeline, or even only excite the target pipeline, thereby reducing interference. Due to differences in materials and characteristics between the target and non-target pipelines, when the frequency and power of the primary alternating electromagnetic field emitted by the transmitter vary, the secondary induced magnetic field strength generated by the target and non-target pipelines will also vary. The transmitter's frequency and power are adjusted to minimize the magnitude of the secondary induced magnetic field of the non-target pipeline to zero.

[0058] By adjusting the detection parameters such as transmission power and transmission frequency, the interference of the side pipelines can be suppressed to the greatest extent, and the detection accuracy of the initial depth can be maximized.

[0059] It should be noted that when conducting preliminary depth detection, existing detection schemes such as the direct reading method, the 70% method and the 50% method can be used.

[0060] Assuming the target pipeline is isolated, it will be excited by an alternating electromagnetic field, generating an induced current and, in turn, a secondary induced magnetic field. The receiver utilizes the spatial distribution of this secondary induced magnetic field to locate and determine the target pipeline's depth. The direct reading method, the 70% method, and the 50% method all utilize the fact that the magnetic field is strongest directly above the target pipeline to determine the target pipeline's horizontal position. While the principles of the direct reading, 70% and 50% methods differ, their essence is the same. The direct reading method uses a numerical relationship between the upper and lower horizontal component antennas built into the receiver directly above the pipeline, allowing the pipeline depth to be estimated. Since the magnetic field intensity is highest directly above the pipeline and gradually decreases on either side, the horizontal distance between two points on either side of the pipeline where the intensity is 70% of the maximum is equal to the pipeline's depth. This is the 70% method. Similar to the 70% principle, the 50% method states that the pipeline's depth is determined by the horizontal distance between any two points where the intensity is 50% of the maximum to the point where the intensity is the highest.

[0061] It should be noted that the above detection parameters are only a preferred implementation mode, and in other embodiments, they can be adjusted according to actual conditions.

[0062] When the target pipeline is deeply buried (burial depth h>3m), the secondary induced magnetic field of the pipeline is attenuated by spherical diffusion and earth absorption, and the signal received by the receiver on the ground is very weak. The magnetic field values of each point, including the characteristic points, are easily interfered with. The direct reading method, 70% method and 50% method fail in this case. In this case, the existing method uses the fitting inversion method to solve the pipeline plane position and depth.

[0063] The fitting inversion method requires collecting a magnetic field profile at the detection site, returning it to the laboratory for data processing to determine the pipeline location and depth, and then returning it to the field for accuracy verification. If the results after field verification are inaccurate, the above steps are repeated until a satisfactory result is obtained, thus accurately determining the target pipeline location.

[0064] In another embodiment provided by the present invention, the step S1 specifically includes:

[0065] Respectively setting the receiving parameters of the receiver and the transmitting parameters of the transmitter of the metal pipeline detector;

[0066] Keeping the transmitter horizontal and its long axis aligned with the long axis of the receiver, the transmitter is moved along the long axis of the receiver. When the initial value of the signal amplitude of the receiver decreases to a preset ratio, the plane distance between the receiver and the transmitter is determined as the scanning distance;

[0067] Based on the scanning distance, the transmitter and the receiver are rotated to scan the area to be detected to determine the preliminary position and preliminary direction of the target pipeline.

[0068] During the specific implementation of this embodiment, one operator holds a receiver in the detection area, and another operator holds a transmitter to set the working parameters of the receiver and transmitter of the metal pipeline detector to facilitate detection.

[0069] Place the transmitter horizontally with the long axis facing the transmitter and the short axis facing upwards, and adjust the receiver signal gain to a maximum of 140dB. At this time, the distance between the transmitter and the receiver is relatively close, so the signal strength will be displayed as 100%;

[0070] The transmitter is of a "7" shape, comprising a long axis and a short axis that are perpendicular to each other.

[0071] Keep the long axis of the transmitter consistent with the long axis of the receiver, and move slowly along the long axis of the receiver, and observe the amplitude of the receiver synchronously. As the transmitter gradually moves away from the receiver, the signal strength will weaken until it reaches 10%. At this time, it means that the external background interference is very small, that is, the various interference clutters from the air are very small. At such a distance, it can be determined that the signal received by the receiver must come from underground rather than from the air. By presetting the distance, the interference of electromagnetic wave signals in the air can be eliminated, and the plane distance between the transmitter and the receiver at this time is measured as the scanning distance D.

[0072] It should be noted that the preset ratio in this embodiment is 10%. In other embodiments, the preset ratio may be set to other values.

[0073] Rapidly locating hidden underground pipelines is the most crucial step in achieving precise positioning and depth determination. Because the direction of buried pipelines crossing the detection area is unknown, using a scanning method to locate them presents significant workload and traffic risks. This invention proposes the use of rotational scanning technology to quickly and accurately locate hidden pipelines. This technology requires two operators, a transmitter, and a receiver. Based on the scanning distance, the transmitter and receiver use a rotational scanning method to scan the target area to determine the initial position and orientation of the target pipeline.

[0074] In another embodiment of the present invention, the receiving parameters include receiving direction, receiving gain, receiving frequency and receiving mode;

[0075] The transmission parameters include transmission direction, transmission power and transmission frequency.

[0076] In the specific implementation of this embodiment, when the rotation scanning method is used for detection, it is necessary to set the parameters of the transmitter and receiver respectively, specifically:

[0077] Adjust the receiver gain to maximum, the receiving frequency to 32.8Khz, the receiving mode to the broad peak method, and keep the receiver perpendicular to the ground;

[0078] Adjust the transmit power to maximum and the transmit frequency to 32.8Khz.

[0079] At maximum power, use the same receiving frequency and transmitting frequency for rotation scanning to ensure the maximum scanning range and improve work efficiency.

[0080] In another embodiment of the present invention, the process of determining the preliminary position and preliminary direction of the target pipeline using the rotation scanning method specifically includes:

[0081] The receiver is kept perpendicular to the ground with its minor axis aligned with the transmitter, and is subjected to circular motion at a preset speed with the receiver as the center and the scanning distance as the radius; while performing the circular motion, the receiving direction of the receiver is periodically changed at a preset swing speed within a preset receiving angle range, and the signal amplitude of the receiver is monitored;

[0082] When the rate of change of the signal amplitude of the receiver exceeds a preset change threshold, the position of the transmitter is fixed as the transmitting point, and the receiving direction of the receiver is continuously changed to determine the receiving point with the maximum signal amplitude;

[0083] The preliminary position and preliminary direction of the target pipeline are determined according to the line connecting the transmitting point and the receiving point.

[0084] During the implementation of this embodiment, one operator holds the receiver vertically downward, motionless. Another operator holds the transmitter, maintaining a constant transmission frequency and power, and maintains a distance D from the receiver. The transmitter's long axis is always aligned with the receiver, and the transmitter makes a circular motion around the receiver. The transmitter's circular motion speed is approximately 1 m / s. Simultaneously, the operator holding the receiver, facing the transmitter, holds the receiver upright downward, adjusts the gain to maximum, the frequency to 32.8 kHz, and the mode to broad peak, and swings the receiver back and forth around the center of the body, forming a semicircle at a frequency of 2 swings / s.

[0085] During the transmitter's circular motion and the receiver's swinging motion, if the receiver displays a sudden increase in the received signal amplitude, immediately stop the transmitter and place it vertically on the ground. Continue swinging the receiver back and forth to determine the point of maximum signal amplitude. Use the direct reading method, the 70% method, or the 50% method to determine the approximate buried depth of the pipeline. Mark the ground at the point of maximum amplitude and the transmitter's location. The direction and location of the potential underground pipeline will be the line connecting the two marked points.

[0086] The transmitter and receiver continue to work according to the above steps to find the location of the next potential underground pipeline until the transmitter completes a circle of scanning and stops working, and the scanning work is completed.

[0087] It should be noted that the existing technology is implemented through a pair-sweeping method. The pair-sweeping method is implemented as follows: one person at one end of the detection area holds a handheld transmitter, and another person at the other end in the opposite direction holds a handheld receiver. At the same time, they move slowly and synchronously in a direction perpendicular to the direction of the line connecting the two people. This can determine whether there are buried metal pipelines running in the direction of the line connecting the two people passing through the target area. Implementing the pair-sweeping technique once can only determine buried metal pipelines in one direction. In order to cover all possible directions, multiple pair-sweeping methods must be implemented. During the pair-sweeping method, the two operators need to move at the same time, which poses a huge safety risk on roads with heavy traffic. It will also increase the obstruction to traffic flow and make it difficult to ensure the safety of the instrument. The present invention proposes a rotational scanning technology, which requires one person to hold a handheld receiver and remain motionless in the detection area, while the other person holds a handheld transmitter and maintains a certain distance from the detection area. The long axis of the transmitter always points to the receiver and moves slowly around the receiver to complete a circle of scanning. During this period, the receiver swings rapidly left and right to scan simultaneously. Rotating scanning technology requires only the operator walking with the transmitter in hand, and a single sweep covers all directions, effectively reducing safety risks for operators and equipment, and minimizing traffic obstruction. Compared to the parallel scanning method, it is simpler, more efficient, faster, and safer. Because it performs continuous scanning, unlike the parallel scanning method, there are no missed scans.

[0088] This embodiment utilizes a rotation scanning method to efficiently, quickly, and safely determine the number and location of buried pipelines in the detection area.

[0089] In another embodiment provided by the present invention, step S2 specifically includes the following steps:

[0090] Measure the distance between the target pipeline and the nearest surrounding pipeline at the marked transmitting point and receiving point, and select the point with the larger distance as the signal transmitting point of the transmitter of the metal pipeline detector;

[0091] placing the transmitter at the signal transmission point so that the long axis direction of the transmitter is consistent with the preliminary direction;

[0092] Placing the receiver at the corresponding receiving point, setting the optimal transmission parameters of the transmitter and the optimal receiving parameters of the receiver of the metal pipeline detector;

[0093] The preliminary depth of the target pipeline is detected using the direct reading method, the 70% method, or the 50% method.

[0094] During the specific implementation of this embodiment, each underground buried pipeline has two marking points on the ground. The distances between the two marking points and the nearest surrounding pipelines are measured respectively, and the point with the larger distance is selected as the transmitter signal transmission point.

[0095] Place the transmitter on the ground at a marked transmitting point, with the long axis aligned with the direction of the pipeline. Adjust the transmitting power to 50%, the frequency to 32.8Khz, and the receiver's receiving signal frequency to 32.8Khz. Use the receiver to track the target pipeline, set detection points according to specifications, and use direct reading or 70% or 50% to locate and determine the depth of each detection point.

[0096] It should be noted that the optimal transmission parameters and the corresponding optimal reception parameters given in this embodiment are only a preferred embodiment. In other embodiments, they can be set or adjusted according to the actual equipment and working scenarios.

[0097] By setting the optimal transmission parameters, the interference from the side pipelines is effectively suppressed, so that the signal received by the receiver on the ground basically comes from the target pipeline, thereby improving the detection accuracy.

[0098] In another embodiment of the present invention, the optimal transmission parameters include optimal power and optimal frequency;

[0099] The optimal power and the optimal frequency determination process includes:

[0100] Calculating a detection error between a first detection position obtained by the metal pipeline detector at different powers and frequencies and a second detection position obtained by detecting at a preset distance from the ground;

[0101] The frequency and power when the detection error is minimum are respectively used as the optimal power and the optimal frequency.

[0102] In the specific implementation of this embodiment, the optimal transmission parameters include optimal power and optimal frequency.

[0103] When determining the optimal power and optimal frequency, the following steps are performed:

[0104] Count the number of pipelines and their specific locations preliminarily determined by the rotating scanning method, and make preliminary preparations for the detection of each pipeline, including safety measures, personnel division of labor, and instrument and tool preparation.

[0105] For the two marks on the ground of a pipeline, measure the distance between them and the adjacent pipelines respectively, and place the transmitter directly above the pipeline with the larger distance, keeping the long axis direction of the transmitter consistent with the direction of the pipeline.

[0106] The degree of interference from side pipelines under different transmission powers and transmission frequencies is tested and evaluated. The evaluation method is to place the bottom of the transmitter close to the ground, and use the direct reading method or 70% or 50% to determine the pipeline position and burial depth respectively. Then, the antenna is raised 30 cm above the ground to repeat the detection and compare the two detection results. The detection error of the metal pipeline detector obtained by close detection and detection at a preset distance from the ground under different powers and frequencies is calculated, and the transmission power and transmission frequency of the detection result with the smallest error value are taken as the optimal power and optimal frequency.

[0107] By pre-testing different frequencies and parameters, the optimal power and frequency can be determined, thereby improving the accuracy of subsequent testing.

[0108] In another embodiment provided by the present invention, the optimal transmission parameter includes an optimal polarization direction;

[0109] The optimal polarization direction determination process includes:

[0110] Setting the transmitter to transmit signals at an optimal transmission power and an optimal transmission frequency, and adjusting the polarization direction of the transmitter at a preset adjustment interval, and calculating the detection error between a third detection position obtained by the metal pipeline detector when detecting close to the ground and a fourth detection position obtained by detecting at a preset distance from the ground under different polarization directions;

[0111] The polarization direction with the smallest detection error is taken as the optimal polarization direction.

[0112] During the specific implementation of this embodiment, in step S1 of the embodiment provided by the present invention, a long-distance buried pipeline is quickly located and its depth is initially determined by a rotating scanning method. If there are no other interfering pipelines around the target pipeline, the pipeline burial depth determined by the direct reading method or the 70% or 50% method is basically consistent, and the detection accuracy can meet the specification requirements; if there are interfering pipelines around the target pipeline and the interference is large, the direct reading method or the 70% or 50% detection results will be quite different, and it is necessary to suppress the interference for more accurate detection. This embodiment proposes to suppress the interference by changing the polarization direction of the transmitter. When the transmitter is placed flat on the ground, the coil with alternating current inside the body will emit an electromagnetic waveform vertically downward in a cone (polarization direction vertically downward) to form an alternating electromagnetic field. The energy in the middle of the cone is the strongest, and the closer to the outside, the weaker the energy. Compared with the vertical electromagnetic field energy, the energy at the side position decays exponentially, and the greater the angle from the center line, the smaller the energy. The present invention utilizes this energy attenuation characteristic when confirming the optimal transmission parameters, and changes the polarization direction of the antenna through an auxiliary device to enhance the coupling degree of the target pipeline and weaken the non-target pipeline, thereby achieving the effect of suppressing interference.

[0113] Therefore, the optimal transmission parameters include the optimal polarization direction. When determining the optimal polarization direction, it is specifically achieved by the following steps:

[0114] Set the transmitter parameters to the optimal transmit power and frequency, and set the receiver's receiving frequency to match the transmit frequency. Place the transmitter on the polarization direction adjustment auxiliary device and place it on the ground at the original transmitter location. Use the latch and angle positioning hole to adjust the initial polarization direction to vertically downward. Facing away from the interfering pipeline, use the angle positioning hole to test each polarization direction one by one at 15° intervals to find the optimal polarization direction. The test method is to compare the error between the two detections, close to the ground and 30cm above the ground. The polarization direction corresponding to the minimum error is the optimal polarization direction, and the corresponding positioning and depth determination result is the detection result of this detection point.

[0115] By changing the polarization direction of the transmitting antenna and making full use of the laws of antenna polarization and pipeline coupling, electromagnetic wave field attenuation, etc., the interference of nearby pipelines can be effectively suppressed, and then the interference can be further suppressed by using the optimal transmitting point, optimal transmitting power and optimal transmitting frequency. According to practical tests, the interference can be suppressed into a weak signal, and the magnetic field shape is close to the theoretical magnetic field of a single pipeline, and the detection accuracy and efficiency can be effectively improved.

[0116] In another embodiment provided by the present invention, the step S3 specifically includes:

[0117] Setting the plane position and burial depth of the target pipeline and the interfering pipeline;

[0118] Determine the range of the survey line layout according to the set plane positions and buried depths of the target pipeline and the interfering pipeline, and layout measuring points at a preset point spacing within the survey line layout range to determine the coordinates of each measuring point;

[0119] Controlling the transmitter of the metal pipeline detector to transmit a signal with optimal transmission parameters to stimulate the target pipeline, and using the broad peak method function of the receiver of the metal pipeline detector to record the magnetic field value of each measuring point as the magnetic field profile data under the first set of current parameters;

[0120] Keeping the optimal power and the optimal frequency in the optimal transmission parameters unchanged, the polarization angle of the transmitter is rotated counterclockwise and clockwise by preset angles, respectively, and the magnetic field value of each measuring point is recorded to obtain magnetic field profile data under the second set of current parameters and the magnetic field profile data under the third set of current parameters;

[0121] Based on the magnetic field profile data obtained under the three sets of current parameters and the set planar positions and burial depths of the target pipeline and the interfering pipeline, an objective function is constructed, and based on a genetic algorithm, the planar positions and burial depths of the target pipeline and the interfering pipeline are solved when the objective function is minimized to obtain the actual position.

[0122] When this embodiment is implemented, the present application fully utilizes the advantages of the direct reading method or 70% or 50% simplicity and high efficiency, and greatly suppresses interference by mainly using the optimal polarization direction and supplemented by the optimal power and frequency, thereby achieving rapid and accurate positioning of long-distance buried, closely spaced and parallel shallowly buried pipelines. Long-distance buried, closely spaced and parallel deep-buried pipelines are a special case among long-distance buried, closely spaced and parallel pipelines. Compared with shallowly buried pipelines, their detection difficulty and detection methods are different. Due to the attenuation of spherical diffusion and the attenuation of earth absorption, the signal of the deeply buried pipeline is very weak when it reaches the ground. In addition, there are closely spaced and parallel interfering pipelines on the side, and the direct reading method or 70% or 50% has failed. The existing fitting inversion method technology also has the disadvantages of low operating efficiency, low detection accuracy, and large influence of human factors.

[0123] This invention proposes to develop a targeted algorithm built into the receiver, collect three magnetic field profile data for each detection point, and use the built-in professional algorithm to solve the problem on site, quickly obtaining accurate and stable detection results, and realizing accurate detection of deep buried pipelines. The specific implementation steps are as follows:

[0124] Use spray paint to mark the projected positions of the target pipeline and adjacent interfering pipelines above the detection point. Assume that the planar positions and buried depths of the target pipeline and interfering pipeline are x1, x2 and h1, h2, respectively (all in meters).

[0125] At the x1 position, mark the position x1-1.5h1 along the direction perpendicular to the target pipeline and away from the interference pipeline; similarly, at the x2 position, mark the position x2+1.5h2 along the direction perpendicular to the target pipeline and away from the target pipeline.

[0126] A survey line is laid out with x1-1.5h1 as the starting point and x2+1.5h2 as the end point, and measuring points are laid out on the survey line. The distance between the measuring points is 0.25m, so the number of measuring points is N (N=[(x2+1.5h2-x1+1.5h1) / 0.25], [] is the rounding symbol), and the coordinates of each measuring point are xi (i=1,2,3…N).

[0127] The transmitter transmits a signal in the optimal polarization direction, optimal power and optimal frequency state to stimulate the target pipeline, and the wide peak method module function of the receiver is used to record the magnetic field value of the measuring point xi As the magnetic field profile data under the first set of current parameters, the current values of the target pipeline and the interference pipeline under the current excitation conditions are set to and The magnetic field data is directly calculated by the receiver's internal chip and induction coil. The specific value will be displayed directly on the screen and can be read directly.

[0128] Keep the optimal transmission power and frequency unchanged, rotate the polarization direction counterclockwise and clockwise by 15° (minimum scale), and repeatedly record the x value at each measurement point. i The magnetic field value and The current values of the target pipeline and the interference pipeline under two excitation conditions are set to and and The magnetic field profile data under the second set of current parameters and the magnetic field profile data under the third set of current parameters can be obtained;

[0129] An objective function is constructed based on the obtained magnetic field profile data under the three sets of current parameters, the set plane positions, burial depths and current values of the target pipeline and the interfering pipeline.

[0130] When the genetic algorithm is used to solve the minimum value of the objective function, the plane position and burial depth of the target pipeline and the interfering pipeline, ie, x1, x2 and h1, h2, can be solved to obtain the actual position of the target pipeline.

[0131] The three magnetic field profile data collected are all high-quality data with the target pipeline signal component as the main component. The present invention specifically constructs the objective function, comprehensively considers the solution speed, accuracy and quality of the solution, and proposes to use a genetic algorithm to solve the objective function. The solution obtained is more accurate and stable. When using the genetic algorithm to solve the minimum value of the objective function, there is no need to give an initial value or human participation in the calculation. The solution is both high-quality and stable. Since the solution process utilizes three magnetic field profile data, the multi-solution nature of the geophysical inversion is greatly reduced, no erroneous solutions are generated, and the solution accuracy is higher.

[0132] To solve the problem of accurate detection of long-distance, closely spaced, and parallel deep-buried pipelines, the existing technology collects magnetic field profile data on-site, returns it to the indoor environment, and uses the fitting inversion method to solve the pipeline's plane position and burial depth, and then verifies it on-site. This workflow is not only inefficient, but the inversion results rely on personal experience and lack systematicity and scientificity. The existing technology's indoor and outdoor work separation method is cumbersome and inefficient, and does not conform to the practice of on-site detection. The fitting inversion method is used to solve the pipeline's plane position and burial depth. This algorithm is not strictly used to solve the minimum value of the objective function, but is a human-computer interactive method to solve the optimal value of the objective function rather than the minimum value. It is highly dependent on personal experience, and the results processed by different technicians may vary greatly. The method lacks systematicity and scientificity. The present application scheme uses multiple magnetic field profile data, a targeted joint inversion algorithm, and an algorithm package integrated into the receiver to achieve fast, accurate, efficient, precise, and stable detection of long-distance, closely spaced, parallel deep-buried pipelines underground. It can realize on-site data collection, on-site processing, on-site verification results, and on-site measurement, truly realizing the integration of indoor and outdoor operations.

[0133] In another embodiment provided by the present invention, the objective function

[0134] Where F is the target value, j = 1, 2, 3, representing three sets of magnetic field profile data from three measurements, i = 1, 2, 3…N, N represents the number of measurement points, and represent the current value of the target pipeline and the current value of the interfering pipeline in the jth group of magnetic field profile data, h1 and h2 are the burial depths of the target pipeline and the interfering pipeline, x1 and x2 are the burial depths of the target pipeline and the interfering pipeline, xi represents the coordinates of each measuring point, Indicates the magnetic field profile data of the jth group at each measuring point x i The magnetic field value received by the receiver on the ground at the coordinate location.

[0135] In another embodiment of the present invention, the method further includes:

[0136] When the preliminary depth is not greater than the threshold depth, the detection error between the fifth detection position obtained by the metal pipeline detector through close-to-the-ground detection and the sixth detection position obtained through detection at a preset distance from the ground under different detection parameters is calculated; and the average of the fifth detection position and the sixth detection position corresponding to the minimum detection error is taken as the actual position of the target pipeline.

[0137] When this embodiment is implemented, the direct reading method, the 70% method and the 50% method are simple, convenient and efficient, and particularly meet the needs of field detection work. They are currently the most frequently used, most important, most efficient and most suitable methods for positioning and determining the depth of shallow buried pipelines (burial depth h≤3m).

[0138] Therefore, when the detected preliminary depth is within the preset threshold depth, the precise position can be detected directly.

[0139] Closely spaced and parallel pipelines refer to the presence of side pipelines within 1.5m to the left and right of the target pipeline. The side pipelines will also be excited by the transmitter's induction coil to generate induced current and thus form a secondary induced magnetic field. The secondary induced magnetic field will affect the secondary induced magnetic field shape and characteristic point values of the target pipeline in the form of vector superposition, making the magnetic field above the ground no longer meet the magnetic field shape of a single pipeline, affecting the positioning and depth accuracy of the direct reading method, 70% method and 50% method to a certain extent.

[0140] In order to ensure the detection accuracy of the direct reading method, 70% method and 50% method in the presence of interfering pipelines, the excitation position, excitation parameters and excitation state of the transmitter can be changed to excite the target pipeline as much as possible while the side pipelines are not excited or weakly excited.

[0141] Calculate the detection error between the fifth detection position obtained by ground detection and the sixth detection position obtained by detection at a preset distance above the ground under different detection parameters; that is, if the fixed depth is less than 3m, compare the error values of ground detection and detection 30cm above the ground under different transmission powers and different transmission frequencies.

[0142] It should be noted that the specific detection method used for the detection position can still use the direct reading method, the 70% method, or the 50% method to achieve the positioning and depth determination of shallow buried pipelines.

[0143] The detection result with the smallest error value is taken as the final detection result, and the average of the fifth detection position and the sixth detection position corresponding to the minimum detection error is taken as the actual position of the target pipeline. At the same time, the optimal power and the optimal frequency are also obtained. The present application solution places the emitter at the optimal emission point, sets it to the optimal polarization direction, the optimal emission power and the optimal frequency, and suppresses the interference of the prominent target pipe signal to the greatest extent, which can overcome the following defects of the existing technology: a) low efficiency of indoor and outdoor separation operations; b) low quality of collected magnetic field profile data; c) simple fitting inversion method with poor effect; d) large interference from human factors in the detection results; e) easy to produce inversion errors. The present application solution can achieve accurate detection of long-distance buried and closely spaced parallel metal pipelines.

[0144] It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for detecting long-distance buried and closely spaced parallel metal pipelines, characterized in that: The method comprises: Use a metal pipeline detector to scan the area to be detected to determine the preliminary position and direction of the target pipeline; According to the preliminary position and the preliminary direction, the metal pipeline detector is set to preset detection parameters to detect a preliminary depth; When the preliminary depth is greater than a preset threshold depth, an inversion algorithm is used to determine the actual position of the target pipeline based on magnetic field data detected by the metal pipeline detector using different parameters.

2. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 1 is characterized in that: Use a metal pipeline detector to scan the area to be detected to determine the preliminary location and direction of the target pipeline, including: respectively setting the transmission parameters of the transmitter and the receiving parameters of the receiver of the metal pipeline detector; Keeping the transmitter horizontal and its long axis aligned with the long axis of the receiver, the transmitter is moved along the long axis of the receiver. When the initial value of the signal amplitude of the receiver decreases to a preset ratio, the plane distance between the receiver and the transmitter is determined as the scanning distance; Based on the scanning distance, the transmitter and the receiver are rotated to scan the area to be detected to determine the preliminary position and preliminary direction of the target pipeline.

3. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 2, characterized in that: The receiving parameters include receiving direction, receiving gain, receiving frequency and receiving mode; The transmission parameters include transmission direction, transmission power and transmission frequency.

4. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 3 is characterized in that: Based on the scanning distance, the transmitter and the receiver are rotated to scan the detection area to determine the preliminary position and preliminary direction of the target pipeline, including: Keeping the transmitter vertical with its minor axis aligned with the receiver, the transmitter performs circular motion with the receiver as the center and the scanning distance as the radius at a preset speed; while performing the circular motion, the receiving direction of the receiver is periodically changed at a preset swing speed within a preset receiving angle range, and the signal amplitude of the receiver is monitored; When the rate of change of the signal amplitude of the receiver exceeds a preset change threshold, the position of the transmitter is fixed as the transmitting point, and the receiving direction of the receiver is continuously changed to determine the receiving point with the maximum signal amplitude; The preliminary position and preliminary direction of the target pipeline are determined according to the line connecting the transmitting point and the receiving point.

5. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 1 is characterized in that: According to the preliminary position and the preliminary direction, the metal pipeline detector is set to a preset detection parameter to detect a preliminary depth, including: Measure the distance between the target pipeline and the nearest surrounding pipeline at the marked transmitting point and receiving point, and select the point with the larger distance as the signal transmitting point of the transmitter of the metal pipeline detector; placing the transmitter at the signal transmission point so that the long axis direction of the transmitter is consistent with the preliminary direction; Placing the receiver at the corresponding receiving point, setting the optimal transmission parameters of the transmitter and the optimal receiving parameters of the receiver of the metal pipeline detector; The preliminary depth of the target pipeline is detected using the direct reading method, the 70% method, or the 50% method.

6. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 5, characterized in that: The optimal transmission parameters include optimal power and optimal frequency; The optimal power and the optimal frequency determination process includes: Calculating a detection error between a first detection position obtained by the metal pipeline detector at different powers and frequencies and a second detection position obtained by detecting at a preset distance from the ground; The frequency and power when the detection error is minimum are respectively used as the optimal power and the optimal frequency.

7. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 6, characterized in that: The optimal transmission parameters include an optimal polarization direction; The optimal polarization direction determination process includes: Setting the transmitter to transmit signals at an optimal transmission power and an optimal transmission frequency, and adjusting the polarization direction of the transmitter at a preset adjustment interval, and calculating the detection error between a third detection position obtained by the metal pipeline detector when detecting close to the ground and a fourth detection position obtained by detecting at a preset distance from the ground under different polarization directions; The polarization direction with the smallest detection error is taken as the optimal polarization direction.

8. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 1 is characterized in that: The actual position of the target pipeline is determined using an inversion algorithm based on magnetic field data detected by the metal pipeline detector using different parameters, including: Setting the plane position and burial depth of the target pipeline and the interfering pipeline; Determine the range of the survey line layout according to the set plane positions and buried depths of the target pipeline and the interfering pipeline, and layout measuring points at a preset point spacing within the survey line layout range to determine the coordinates of each measuring point; Controlling the transmitter of the metal pipeline detector to transmit a signal with optimal transmission parameters to stimulate the target pipeline, and using the broad peak method function of the receiver of the metal pipeline detector to record the magnetic field value of each measuring point as the magnetic field profile data under the first set of current parameters; Keeping the optimal power and optimal frequency in the optimal transmission parameters unchanged, the polarization angle of the transmitter is rotated counterclockwise and clockwise by preset angles respectively, and the magnetic field value of each measuring point is recorded, and the magnetic field profile data under the second set of current parameters and the magnetic field profile data under the third set of current parameters are correspondingly obtained; based on the obtained magnetic field profile data under the three sets of current parameters, the plane position, burial depth and current value of the target pipeline and the interfering pipeline are set, and an objective function is constructed. Based on the genetic algorithm, the plane position and burial depth of the target pipeline and the interfering pipeline are solved when the objective function is minimized to obtain the actual position.

9. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 8, characterized in that: The objective function Where F is the target value, j = 1, 2, 3, representing three sets of magnetic field profile data from three measurements, i = 1, 2, 3…N, N represents the number of measurement points, and represent the current value of the target pipeline and the current value of the interfering pipeline in the jth group of magnetic field profile data, h1 and h2 are the burial depths of the target pipeline and the interfering pipeline, x1 and x2 are the burial depths of the target pipeline and the interfering pipeline, xi represents the coordinates of each measuring point, Indicates the j-th group of magnetic field profile data at each measuring point x i The magnetic field value received by the receiver on the ground at the coordinate location.

10. The method for detecting long-distance buried and closely spaced parallel metal pipelines according to claim 1, characterized in that: The method further comprises: When the preliminary depth is not greater than the threshold depth, calculating a detection error between a fifth detection position obtained by the metal pipeline detector under different detection parameters through close-to-ground detection and a sixth detection position obtained through detection at a preset distance from the ground; The average of the fifth detection position and the sixth detection position corresponding to the minimum detection error is used as the actual position of the target pipeline.

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