A method for detecting a pipe axial stress type

Abstract

The application provides a pipeline axial stress type detection method and relates to the technical field of pipeline online internal detection. Firstly, a three-dimensional simulation model is established by using a finite element multi-physical field simulation software; a three-point bending test device is adjusted according to a load setting range; a load is loaded on a load loading area of a steel plate; a detection signal of an electromagnetic detection sensor containing a magnetic field receiving element is observed; an amplitude of an output voltage and a load value are recorded; a system offset of the electromagnetic detection sensor containing the magnetic field receiving element is calculated; then, pipeline axial stress detection signal characteristics are extracted and distinguished; N electromagnetic detection sensors containing the magnetic field receiving element are carried on a pipeline internal detector; the electromagnetic detection sensors are arranged at equal intervals along an inner wall of a pipeline to be detected; signals output by each electromagnetic detection sensor constitute a detection channel; an axial stress type is judged according to characteristics and phase characteristics of output voltages of the detection channel; and a pipeline axial stress value is calculated. U est ​

Description

Technical Field

[0001] This invention relates to the field of pipeline in-line inspection technology, and in particular to a method for detecting pipeline axial stress. Background Technology

[0002] When long-distance oil and gas pipelines traverse areas with complex geological environments, they are easily affected by various factors such as service environment, topography, and severe weather, leading to pipeline deformation. Different types of stress result in different outcomes. During operation, pipelines are subjected to axial stress, circumferential stress, and bending stress. Anomalies in these stresses can cause uneven local stress distribution, accelerated deformation, and even pipeline rupture. Among these, axial stress has become the primary threat inducing catastrophic failures such as buckling and fracture in buried pipelines. Once the axial stress exceeds a critical value, it will lead to pipeline structural failure, causing catastrophic accidents such as fractures or even explosions, resulting in enormous losses to the energy economy and the ecological environment. Therefore, regularly conducting axial stress testing of pipelines can help control risks and is of great significance for ensuring the inherent safety of national energy infrastructure.

[0003] In-line pipeline inspection technology is currently recognized as the most effective means of online pipeline defect detection. Under stress, the internal magnetic domain structure of ferromagnetic materials deflects or the domain walls shift, causing changes in macroscopic magnetic permeability. Therefore, compared to methods such as X-ray diffraction (which calculates residual stress by observing the shift of diffraction peaks in the diffraction angle) and ultrasonic testing (which quantitatively calculates pipeline stress by observing the propagation time of the critical refraction longitudinal wave), magnetoelasticity-based detection technology is the preferred solution for stress detection. In practical engineering, stress direction is a crucial factor in assessing pipeline risk. Tensile stress easily leads to the tensile expansion of internal pipeline defects, inducing pipe rupture. Compressive stress, on the other hand, is more likely to cause bulging, wrinkling, or even collapse of the pipe wall, serving as an indicator for assessing buckling criticality. Different treatment strategies are required for stress in different directions. Therefore, based on the effective detection of axial stress, accurately distinguishing the stress direction can provide a more reliable scientific basis for the assessment of buried pipeline environments, pipeline repair, reinforcement, and risk management.

[0004] Existing research on pipeline stress type identification mainly focuses on stress magnitude calculation and stress range assessment. For example, using strain gauges attached to the pipeline can accurately distinguish between axial and circumferential stresses and directly obtain local true stress values. However, this is a contact-point measurement, and the strain gauges and leads are easily affected by the medium, pressure, and temperature inside the pipeline, causing them to fail. This method cannot achieve full-circumferential and long-distance pipeline detection. While magnetoelastic stress detection technology has achieved good results in non-destructive real-time online stress detection of oil and gas pipelines, existing analytical methods mostly focus on distinguishing stress types by the magnitude of magnetic induction intensity, but cannot distinguish between tensile and compressive stress components, making it difficult to effectively determine the stress direction. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for detecting the type of axial stress in pipelines. Starting from the differences in the characteristics of tensile and compressive stress components of axial stress, a circumferential array sensor is used. Through a combination of qualitative analysis using finite element simulation and equivalent comparison correction, the characteristics of magnetic flux density, output voltage amplitude, and phase under tensile and compressive stress components are extracted and analyzed, thereby achieving the identification and quantification of tensile and compressive stress at the same axial position.

[0006] This invention provides a method for detecting the type of axial stress in a pipeline, comprising the following steps: Step 1: Establish preliminary feature relationships using finite element simulation analysis software; Step 1.1: Establish a three-dimensional simulation model using finite element multiphysics simulation software; The three-dimensional simulation model includes a steel plate P1 and an electromagnetic detection sensor. The simulation parameters to be set for the steel plate P1 include the length of the steel plate. L ,width W ,thickness T The length, width, and thickness directions correspond to the following in the spatial coordinate system: x axis, y axis, z axis; The steel plate along x The two end faces in the axial direction are M1 and M2, respectively, and M1 and M2 are used as fixed constraint surfaces; the range along the negative z-axis is [0, ... F max The load is measured in steps. F The maximum load Based on the yield strength of steel plate materials The geometric dimensions and boundary conditions of the steel plate determine the geometric center of the upper surface of the steel plate. * A load-bearing zone is defined, and its dimensions are determined based on the steel plate's geometry and the load's range. The load-bearing zone is defined along the positive z-axis, at a distance from the top surface of the steel plate. h The area with the same location and area as the load-bearing area is designated as the compressive stress change observation area. h According to the sensitivity settings of the electromagnetic detection sensor; the distance of the steel plate along the negative z-axis and the lower surface of the steel plate are set accordingly. h The area with the same location and area as the load-bearing area is designated as the tensile stress variation observation area; The electromagnetic detection sensor consists of a U-shaped magnetic core and an excitation coil, with the excitation coil wound around the U-shaped magnetic core. The electromagnetic detection sensor is positioned differently for both tensile stress change simulation and compressive stress change simulation: when performing tensile stress change simulation, the two end faces of the U-shaped magnetic core are placed on the lower surface of the steel plate, and the geometric center of the plane containing the two ends of the U-shaped magnetic core is collinear with the geometric center of the tensile stress change observation area; when performing compressive stress change simulation, the two end faces of the U-shaped magnetic core are placed on the upper surface of the steel plate, and the geometric center of the plane containing the two ends of the U-shaped magnetic core is collinear with the geometric center of the compressive stress change observation area. Step 1.2: In the three-dimensional simulation model, set up the solid mechanical field and the frequency domain magnetic field; the elastic modulus, Poisson's ratio, density, etc. in the solid mechanical field are determined according to the mechanical properties of the steel plate; the permeability, conductivity, and magnetic core permeability of the steel plate in the frequency domain magnetic field are determined according to the mechanomagnetic properties of the steel plate material; apply a frequency of... to the excitation coil. Amplitude The initial phase is A sinusoidal signal, where the frequency is... The amplitude is determined based on the magnetic permeability and electrical conductivity of the steel plate material, the thickness of the steel plate, and the required detection depth. The excitation field is determined based on the number of turns of the excitation coil, the coil impedance, the magnetization characteristics of the magnetic core, and the output capability of the excitation coil, ensuring that the generated excitation field does not cause the steel plate to reach a saturated magnetization state.

[0007] Step 1.3: In the three-dimensional simulation model, starting from the geometric center of the compressive stress change observation area, extend the lines along the positive and negative x-axis to form the upper surface analysis section. ltop In the tensile stress variation observation area, starting from the geometric center, extension lines are set along the positive and negative directions of the x-axis to form the lower surface analysis section. lback ,in, ltop and lback The length of each is L1. Specifically, it includes: (1) Place the electromagnetic sensor in the three-dimensional simulation model according to the content of the tensile stress change simulation settings, load it in the load loading area, and solve and extract the analysis cross-section of the lower surface under different loads in the finite element simulation analysis software. lback along x Magnetic flux density amplitude at the midpoint of the axial direction Bx With phase, obtained in the solution results Bx With axial tensile stress The changing dataset is used to obtain the first [value] through regression fitting. i Axial tensile stress under load With magnetic flux density amplitude Bxi The relationship, among which : (1); in, , , , These are the fitting coefficients for axial tensile stress simulation, and all of them are non-zero.

[0008] (2) Place the electromagnetic sensor in the three-dimensional simulation model according to the content of the compressive stress change simulation settings, load it in the load loading area, and solve and extract the upper surface analysis cross-section under different loads in the finite element simulation analysis software. ltop along x Magnetic flux density amplitude at the midpoint of the axial direction Bx 2 and phase, obtained in the solution results Bx 2 and axial compressive stress The changing dataset is used to obtain the first [value] through regression fitting. i Axial compressive stress under load With magnetic flux density amplitude Bx2i The relationship, among which : (2); in, , , , These are the fitting coefficients for the axial compressive stress simulation, and all are non-zero, and are related to... , , , Not exactly the same.

[0009] Step 2: Determine the correspondence between axial stress and the output of the electromagnetic detection sensor containing a magnetic field receiving element; Step 2.1: Take a steel plate P2 with the same material and geometric dimensions as the three-dimensional simulation model, and conduct a calibration test using a three-point bending test device. The load loading area and fixed constraint surface in the three-point bending test device are set up in the same way as in the three-dimensional simulation model. The spatial coordinate system, compressive stress change observation area and tensile stress change observation area are also set up in the same way as in the three-dimensional simulation model. At the geometric center of the compressive stress change observation area and the tensile stress change observation area of ​​the steel plate P2, respectively, a resistance strain gauge is attached along the x-axis. The resistance strain gauge is connected to the static resistance strain gauge using a three-wire quarter-bridge connection.

[0010] Step 2.2: Adjust the three-point bending test device according to the load setting range, apply load to the load area of ​​steel plate P2, observe the detection signal of the electromagnetic detection sensor containing the magnetic field receiving element, and record the amplitude of the output voltage and the load value; specifically including: (1) Compressive stress group test: Before loading begins, place the electromagnetic detection sensor containing the magnetic field receiving element on the upper surface of the steel plate, in the same position as the compressive stress change simulation. Start loading and observe the reading of the static resistance strain gauge. Record the strain value output by the strain gauge after each load level stabilizes when the load is changed. The output voltage amplitude and phase of an electromagnetic detection sensor containing a magnetic field receiving element are measured three times for each load level, and the arithmetic mean is taken to obtain the compressive stress experimental dataset X; any one of the compressive stress experimental data X... i Contains the first i Output voltage of an electromagnetic detection sensor containing a magnetic field receiving element under a loaded load U ci and the corresponding load value , .

[0011] (2) Tensile stress group test: After completing the compressive stress group test, the load was completely unloaded. After the strain gauge reading returned to zero and the steel plate P2 returned to the initial stress-free state, the electromagnetic detection sensor containing the magnetic field receiving element was placed on the lower surface of the steel plate, in the same position as the tensile stress change simulation. The load was then applied again and the strain value output by the strain gauge was recorded. ε p The output voltage amplitude and phase of an electromagnetic detection sensor containing a magnetic field receiving element are measured three times for each load level, and the arithmetic mean is taken to obtain a tensile stress experimental dataset. Q Any one of the tensile stress experimental data Including the i Output voltage of an electromagnetic detection sensor containing a magnetic field receiving element under a loaded load and the corresponding load value , .

[0012] Step 2.3: Calculate the system offset of the electromagnetic detection sensor containing the magnetic field receiving element. .

[0013] When the load value is 0, based on the tensile stress experimental data... U l1 and B x1 Calculate the system offset according to formula (3) : (3); Where k is the sensitivity coefficient of the electromagnetic detection sensor containing a magnetic field receiving element, and b is the zero-point offset of the electromagnetic detection sensor containing a magnetic field receiving element. Step 3: Extraction and differentiation of features of pipeline axial stress detection signals; Step 3.1: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require N An electromagnetic detection sensor containing a magnetic field receiving element is mounted on a pipe detector and arranged at equal intervals along the circumference of the inner wall of the pipe to be detected. The signal output from each electromagnetic detection sensor with a magnetic field receiving element constitutes a detection channel, and they are numbered sequentially in a clockwise direction along the circumference of the pipe. Cv , v =1,2,... N ; Based on the characteristics of circumferential welds in electromagnetic detection signals, all circumferential welds of the pipeline to be inspected are identified; let the total number of detected circumferential welds be... M and M≥ 2 ， The inspection channel data of the pipeline under inspection is divided according to the axial position of the characteristic peak of the circumferential weld. M -1 independent pipe section; Step 3.2: Based on the output voltage of the detection channel U est Determining the type of axial stress based on its characteristics and phase features: (1) If the output voltage of the detection channel has no gradual peak or trough in any pipe section, it is considered that the current detection channel has not detected axial stress. (2) If the output voltage of the detection channel is a single peak bulging upward inverted U-shape within any pipe section, and the phase exhibits a continuous and symmetrical single valley U-shaped characteristic, then it is determined that there is axial compressive stress in the detection channel.

[0014] (3) If the output voltage of the detection channel is a positive U-shape with a single valley concave downwards and the phase exhibits a continuous and symmetrical single-peak inverted U-shape, then it is determined that there is axial tensile stress in the detection channel.

[0015] (4) If within the same pipe section, circumferentially adjacent N s If all detection channels satisfy the judgment in (2) or (3), then... N s The axial stress types of each channel are output sequentially, where 2≤ N s ≤ N .

[0016] Step 3.3: Verification of the axial stress detection channel; After completing the axial stress type determination in step 3.2, the results are verified based on the radial symmetry characteristics of the pipeline: for a total of N detection channels, channels with axial compressive stress are identified. C m Satisfies formula (4), where C j To and C mChannels containing axial tensile stress within the same pipe section, m and j Indicates the corresponding channel number: (4); in, round () represents the rounding function; If the detection channel number in the same pipe section that was determined according to step 3.2 meets the formula (4), the determination result is valid; if it does not meet the formula, the detection channel needs to be selected again according to step 3.2, and the adjacent channel of the previous determination should be selected first.

[0017] Step 4: Calculate the axial stress value of the pipe; (1) Single-channel stress calculation: For any axial stress detection channel determined in step 3, the peak value of the output voltage of the detection channel will be calculated. Uest Substituting into formula (5), the measured magnetic induction intensity of the detection channel is obtained. Breal Then Breal The corresponding axial stress value is obtained based on the type of axial stress it is determined to be. If it is determined to be axial tensile stress, it is entered into formula (1) for calculation. If it is determined to be axial compressive stress, it is entered into formula (2) for calculation.

[0018] (5); (2) Multi-channel stress detection: If multiple detection channels detect axial stress after step 3, the output voltage of each detection channel is calculated according to the single-channel stress calculation method. The maximum value among all calculation results of the detection channels under the axial stress type is taken as the final detection value of this type of axial stress in the pipeline.

[0019] The beneficial effects of adopting the above technical solution are as follows: Traditional stress detection methods based on the magnetoelastic effect can only reflect the magnitude of stress, making it difficult to distinguish the nature of the stress. This invention proposes a method for detecting the type of axial stress in pipelines. By deeply analyzing the mapping relationship between the output signal characteristics of electromagnetic detection sensors and axial tensile and compressive stress, a quantitative calculation model of signal characteristics and axial stress is constructed through a combination of simulation and experiment. By dividing the pipe section, it can identify and distinguish between axial tensile and compressive stress for specific working conditions in different sections, and calculate the specific value of axial stress. Simultaneously, a symmetry verification of axial stress channels at the same cross-sectional location is set up. On the one hand, it provides more accurate qualitative analysis results for pipeline stress state analysis; on the other hand, it provides technical support for pipeline integrity management and remaining life assessment through quantitative analysis. Combined with conventional pipeline internal inspection techniques, it has the advantages of non-contact, online detection, and wide coverage, effectively reducing detection costs and improving operational efficiency. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for detecting the type of axial stress in a pipeline according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a three-dimensional simulation model of an embodiment of the present invention; Wherein, 2-1 is steel plate P1, 2-2 is electromagnetic detection sensor, 2-3 is load loading area, and 2-4 is upper surface analysis section. l top 2-5 are the lower surface analysis cutoff lines. l back ; Figure 3 This illustrates the relationship between magnetic flux density amplitude and axial stress in an embodiment of the present invention. Among them, (a) is Bx The relationship between the axial tensile stress and the stress is shown in diagram (b). Bx2 Relationship diagram with axial compressive stress; Figure 4 This refers to the axial stress detection data of the electromagnetic detection sensor mounted on the pipe detector in this embodiment of the invention. Among them, (a) shows the detection voltage offset value of the detection channel, and (b) shows the detection channel. C 4. C Phase feature map of 5, (c) is the detection channel. C 9. C Phase characteristic map of 1. Detailed Implementation

[0021] The specific implementation methods of this application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] A method for detecting the type of axial stress in a pipeline, such as Figure 1 As shown, it includes the following steps: Step 1: Establish preliminary feature relationships using finite element simulation analysis software; Step 1.1: Establish a three-dimensional simulation model using finite element multiphysics simulation software, such as... Figure 2 As shown; The three-dimensional simulation model includes steel plate P12-1 and electromagnetic detection sensor 2-2. The simulation parameters to be set for steel plate P1 include the length of the steel plate. L ,width W ,thickness T The length, width, and thickness directions correspond to the following in the spatial coordinate system: x axis, y axis, z axis; The steel plate along xThe two end faces in the axial direction are M1 and M2, respectively, and M1 and M2 are used as fixed constraint surfaces; the range along the negative z-axis is [0, ... F max The load is measured in steps. F The maximum load Based on the yield strength of steel plate materials The geometric dimensions and boundary conditions of the steel plate determine its shape. The setting places the steel plate in a non-yielding elastic deformation stage. At the geometric center of the upper surface of the steel plate... * Loading zones 2-3 are defined, with their dimensions determined based on the steel plate's geometry and the load's range. These zones are located along the positive z-axis, at a distance from the top surface of the steel plate. h The area with the same location and area as the load-bearing area is designated as the compressive stress change observation area. h According to the sensitivity settings of the electromagnetic detection sensor; the distance of the steel plate along the negative z-axis and the lower surface of the steel plate are set accordingly. h The area with the same location and area as the load-bearing area is designated as the tensile stress variation observation area; In this embodiment, a three-dimensional simulation model is established using the finite element multiphysics simulation software COMSOL Multiphysics. The three-dimensional simulation model includes a steel plate P1 and an electromagnetic detection sensor. In this embodiment, the parameters to be set for the steel plate P1 are: steel plate length... L= 200 mm ,width W= 70 mm ,thickness T= 8 mm The length, width, and thickness directions correspond to the following in the spatial coordinate system: x axis, y axis, z The z-axis is defined as the direction from the lower surface of the steel plate to the upper surface of the steel plate.

[0023] Fixed steel plate x The two end faces M1 and M in the axial direction 2 M1, M 2 They are steel plate edges x The left and right end faces in the axial direction serve as fixed constraint surfaces; a load ranging from [0, 140 kN] is applied along the negative z-axis, with increments of 14 kN, where the maximum load is 140 kN. The load is applied at the geometric center of the upper surface of the steel plate. * A load-bearing zone is set up, and in this embodiment, the load-bearing zone has a specific size of 10*70mm. A region along the positive z-axis, 1mm from the upper surface of the steel plate, with the same area as the load-bearing zone, is set as the compressive stress change observation zone; a region along the negative z-axis, 1mm from the lower surface of the steel plate, with the same area as the load-bearing zone, is set as the tensile stress change observation zone.

[0024] The electromagnetic detection sensor consists of a U-shaped magnetic core and an excitation coil, with the excitation coil wound around the U-shaped magnetic core. The electromagnetic detection sensor is positioned differently for both tensile stress change simulation and compressive stress change simulation: when performing tensile stress change simulation, the two end faces of the U-shaped magnetic core are placed on the lower surface of the steel plate, and the geometric center of the plane containing the two ends of the U-shaped magnetic core is collinear with the geometric center of the tensile stress change observation area; when performing compressive stress change simulation, the two end faces of the U-shaped magnetic core are placed on the upper surface of the steel plate, and the geometric center of the plane containing the two ends of the U-shaped magnetic core is collinear with the geometric center of the compressive stress change observation area. Step 1.2: In the three-dimensional simulation model, set up the solid mechanical field and the frequency domain magnetic field; the elastic modulus, Poisson's ratio, density, etc. in the solid mechanical field are determined according to the mechanical properties of the steel plate; the permeability, conductivity, and magnetic core permeability of the steel plate in the frequency domain magnetic field are determined according to the mechanomagnetic properties of the steel plate material; apply a frequency of... to the excitation coil. Amplitude The initial phase is A sinusoidal signal, where the frequency is... The amplitude is determined based on the magnetic permeability and electrical conductivity of the steel plate material, the thickness of the steel plate, and the required detection depth. The excitation field is determined based on the number of turns of the excitation coil, the coil impedance, the magnetization characteristics of the magnetic core, and the output capability of the excitation coil, ensuring that the generated excitation field does not cause the steel plate to reach a saturated magnetization state.

[0025] In this embodiment, a sinusoidal signal with a frequency of 1000Hz, an amplitude of ±5V, and an initial phase of 0 is applied to the excitation coil. Under this condition, it can be ensured that the generated excitation field does not cause the steel plate to reach a saturated magnetization state.

[0026] Step 1.3: In the three-dimensional simulation model, starting from the geometric center of the compressive stress change observation area, extend the lines along the positive and negative x-axis to form the upper surface analysis section. ltop 2-4. In the tensile stress variation observation area, starting from the geometric center, extend the lines along the positive and negative x-axis to form the lower surface analysis section. lback 2-5, of which, ltop and lback The length of each component is L1. In this embodiment, L1 = 20 mm. Specifically, it includes: (1) Place the electromagnetic sensor in the three-dimensional simulation model according to the content of the tensile stress change simulation settings, load it in the load loading area, and solve and extract the analysis cross-section of the lower surface under different loads in the finite element simulation analysis software. lback along x Magnetic flux density amplitude at the midpoint of the axial direction Bx With phase, obtained in the solution results Bx With axial tensile stress Changes in datasets, such as Figure 3 In (a), the first is obtained through regression fitting. i Axial tensile stress under load With magnetic flux density amplitude Bxi The relationship, among which : (1); in, , , , These are the fitting coefficients for axial tensile stress simulation, and all of them are non-zero.

[0027] In this embodiment, i =1, 2, ..., 11, then: (6); in, , , , The values ​​are 0.0517, 0.0896, 0.0475, and 64.8336, respectively.

[0028] (2) Place the electromagnetic sensor in the three-dimensional simulation model according to the content of the compressive stress change simulation settings, load it in the load loading area, and solve and extract the upper surface analysis cross-section under different loads in the finite element simulation analysis software. ltop along x Magnetic flux density amplitude at the midpoint of the axial direction Bx 2 and phase, obtained in the solution results Bx 2 and axial compressive stress Changes in datasets, such as Figure 3 In (b), the first value is obtained through regression fitting. i Axial compressive stress under load With magnetic flux density amplitude Bx2i The relationship, among which : (2); in, , , , These are the fitting coefficients for the axial compressive stress simulation, and all are non-zero, and are related to... , , , Not exactly the same.

[0029] In this embodiment i =1, 2, ..., 11, then: (7); in, , , , The values ​​were 0.02063, 4.8392, 0.0299, and 73.0027, respectively. , , , Not exactly the same.

[0030] Step 2: Determine the correspondence between axial stress and the output of the electromagnetic detection sensor containing a magnetic field receiving element; Step 2.1: Take a steel plate P2 with the same material and geometric dimensions as the three-dimensional simulation model, and conduct a calibration test using a three-point bending test device. In this embodiment, a three-point bending test machine is specifically used. The load loading area and fixed constraint surface in the three-point bending test device are set in the same way as in the three-dimensional simulation model. The spatial coordinate system, compressive stress change observation area, and tensile stress change observation area are also set in the same way as in the three-dimensional simulation model. At the geometric center of the compressive stress change observation area and the tensile stress change observation area of ​​the steel plate P2, respectively, a resistance strain gauge is attached along the x-axis. The resistance strain gauge is connected to the static resistance strain gauge using a three-wire quarter-bridge connection.

[0031] Step 2.2: Adjust the three-point bending test device according to the load setting range, apply load to the load area of ​​steel plate P2, observe the detection signal of the electromagnetic detection sensor containing the magnetic field receiving element, and record the amplitude of the output voltage and the load value; in this embodiment, the electromagnetic detection sensor is connected to a lock-in amplifier and an oscilloscope to observe the detection signal; specifically including: (1) Compressive stress group test: Before loading begins, place the electromagnetic detection sensor containing the magnetic field receiving element on the upper surface of the steel plate, in the same position as the compressive stress change simulation. Start loading and observe the reading of the static resistance strain gauge. Record the strain value output by the strain gauge after each load level stabilizes when the load is changed. The output voltage amplitude and phase of an electromagnetic detection sensor containing a magnetic field receiving element are measured three times for each load level, and the arithmetic mean is taken to obtain the compressive stress experimental dataset X; any one of the compressive stress experimental data X... iContains the first i Output voltage of an electromagnetic detection sensor containing a magnetic field receiving element under a loaded load U ci and the corresponding load value , .

[0032] (2) Tensile stress group test: After completing the compressive stress group test, the load was completely unloaded. After the strain gauge reading returned to zero and the steel plate P2 returned to the initial stress-free state, the electromagnetic detection sensor containing the magnetic field receiving element was placed on the lower surface of the steel plate, in the same position as the tensile stress change simulation. The load was then applied again and the strain value output by the strain gauge was recorded. ε p The output voltage amplitude and phase of an electromagnetic detection sensor containing a magnetic field receiving element are measured three times for each load level, and the arithmetic mean is taken to obtain the tensile stress experimental dataset Q. Any tensile stress experimental data point... Including the i Output voltage of an electromagnetic detection sensor containing a magnetic field receiving element under a loaded load and the corresponding load value , .

[0033] Step 2.3: Calculate the system offset of the electromagnetic detection sensor containing the magnetic field receiving element. .

[0034] When the load value is 0, based on the tensile stress experimental data... U l1 and B x1 Calculate the system offset according to formula (3) : (3); Where k is the sensitivity coefficient of the electromagnetic detection sensor containing a magnetic field receiving element, and b is the zero-point offset of the electromagnetic detection sensor containing a magnetic field receiving element. Both are set according to the parameters of the selected electromagnetic detection sensor device. In this embodiment U l1 =3V, Bx 1 = 0.05, k and b are 1.2 and 0 respectively, after calculation It is 2.45.

[0035] (8); Step 3: Extraction and differentiation of features of pipeline axial stress detection signals; Step 3.1: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require NAn electromagnetic detection sensor containing a magnetic field receiving element is mounted on a pipe detector and arranged at equal intervals along the circumference of the inner wall of the pipe to be detected. The signal output from each electromagnetic detection sensor with a magnetic field receiving element constitutes a detection channel, and they are numbered sequentially in a clockwise direction along the circumference of the pipe. Cv , v =1,2,... N In this embodiment N =9, v =1,2,...9; Based on the characteristics of circumferential welds in electromagnetic detection signals, all circumferential welds of the pipeline to be inspected are identified (Fan X, Yang L. Exploring weak magnetic signal characteristics of pipeline welds:insights into stress non-uniformity effects.[J].Sensors, 2024, 24(15): 5074-5074.); let the total number of detected circumferential welds be... M and M≥2， The inspection channel data of the pipeline under inspection is divided according to the axial position of the characteristic peak of the circumferential weld. M -1 independent pipe section; the total number of circumferential welds detected in this embodiment is 2. ， The inspection channel data of the pipeline under inspection is divided into an independent pipe segment interval based on the axial position of the characteristic peak of the circumferential weld. Specific inspection signals are shown in the appendix. Figure 4 .in Figure 4 (a) shows the detection voltage offset values ​​of the detection channel. The offset values ​​are not included in the calculation of step 3; step 3 only uses the unoffset values ​​for calculation. Figure 4 (b) is the detection channel. C 4. C Phase feature map of 5, Figure 4 (c) is the detection channel. C 9. C Phase characteristic map of 1; Step 3.2: Based on the output voltage of the detection channel U est Determining the type of axial stress based on its characteristics and phase features: (1) If the output voltage of the detection channel has no gradual peak or trough in any pipe section, it is considered that the current detection channel has not detected axial stress. (2) If the output voltage of the detection channel is a single peak bulging upward inverted U-shape within any pipe section, and the phase exhibits a continuous and symmetrical single valley U-shaped characteristic, then it is determined that there is axial compressive stress in the detection channel.

[0036] (3) If the output voltage of the detection channel is a positive U-shape with a single valley concave downwards and the phase exhibits a continuous and symmetrical single-peak inverted U-shape, then it is determined that there is axial tensile stress in the detection channel.

[0037] (4) If within the same pipe section, circumferentially adjacent N s If all detection channels satisfy the judgment in (2) or (3), then... N s The axial stress types of each channel are output sequentially, where 2≤ N s ≤ N .

[0038] In this embodiment, there is one independent pipe section, and a detection channel is located within this pipe section. C 4. C The output voltage of detection channel 5 is approximately a single-peak upward-convex inverted U-shape, and the phase exhibits a continuous, symmetrical single-valley U-shaped characteristic, indicating that axial compressive stress exists in these two detection channels; detection channels C 1. C The output voltage of detection channel 9 is approximately a single-valley concave U-shape, and the phase exhibits a continuous, symmetrical single-peak inverted U-shaped characteristic, indicating that axial tensile stress exists in these two detection channels; detection channels C 2. C 3. C 6. C 7. C 8. Since there are no obvious gradual peaks or troughs, it is believed that no axial stress was detected in these three detection channels.

[0039] Step 3.3: Verification of the axial stress detection channel; After completing the axial stress type determination in step 3.2, the results are verified based on the radial symmetry characteristics of the pipeline: for a total of N detection channels, channels with axial compressive stress are identified. C m Satisfies formula (4), where C j To and C m Channels containing axial tensile stress within the same pipe section, m and j Indicates the corresponding channel number: (4); in, round () represents the rounding function; If the detection channel number in the same pipe section that was determined according to step 3.2 meets the formula (4), the determination result is valid; if it does not meet the formula, the detection channel needs to be selected again according to step 3.2, and the adjacent channel of the previous determination should be selected first.

[0040] In this embodiment, the axial stress detection channel is verified. After completing the axial stress type judgment in step 3.2, the result is verified based on the radial symmetry characteristics of the pipeline: for a total of 9 detection channels, according to formula (4), the channels with axial compressive stress are calculated. C 4. C 5. The channel containing axial tensile stress in the same pipe section is: C 9 and C 1. If the result is consistent with the judgment result in step 3.2, it means that the judgment result is valid.

[0041] Step 4: Calculate the axial stress value of the pipe; (1) Single-channel stress calculation: For any axial stress detection channel determined in step 3, the peak value of the output voltage of the detection channel will be calculated. Uest Substituting into formula (5), the measured magnetic induction intensity of the detection channel is obtained. Breal Then Breal The corresponding axial stress value is obtained based on the type of axial stress it is determined to be. If it is determined to be axial tensile stress, it is entered into formula (1) for calculation. If it is determined to be axial compressive stress, it is entered into formula (2) for calculation.

[0042] (5); (2) Multi-channel stress detection: If multiple detection channels detect axial stress after step 3, the output voltage of each detection channel is calculated according to the single-channel stress calculation method. The maximum value among all calculation results of the detection channels under the axial stress type is taken as the final detection value of this type of axial stress in the pipeline.

[0043] Based on the determination result of step 3 in this embodiment, axial stress has been detected in multiple channels. The detected channels will be processed sequentially. C 4. C 5 and C 1. C 9 peak output voltage Uest Substituting into formula (5), where Substituting the result obtained from formula (8) into the equation, the measured magnetic flux density of the corresponding channel can be calculated. Breal In this embodiment, the detection channel C 4. C 5 and C 1. C 9 peak output voltage Uest and the measured magnetic flux density of the corresponding channel Breal See Table 1.

[0044] Table 1. Peak output voltage of the detection channel and corresponding measured magnetic flux density of the channel in this embodiment.

[0045] Since this example demonstrates multi-channel stress detection, the following steps are performed sequentially: C 4. C Substituting the measured magnetic induction intensity of 5 into formula (7) and finding the inverse function, the axial compressive stress values ​​of the corresponding channels are 50.23 MPa and 53.09 MPa, respectively; C 1. C Substituting the measured magnetic induction intensity of 9 into formula (6) to obtain the inverse function, the axial tensile stress values ​​of the corresponding channel are 50.45MPa and 52.57MPa respectively; therefore, the axial compressive stress value of the pipeline at this point is 53.09MPa and the axial tensile stress value is 52.57MPa.

[0046] Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or part of the technical solution, can be embodied in the form of a computer program product.

[0047] The various embodiments in this application are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0048] The scope of protection of this application is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from the scope and spirit of this disclosure. If such modifications and variations fall within the scope of the methods disclosed herein and their equivalents, then the intent of this disclosure also includes such modifications and variations.

Claims

1. A method for detecting the type of axial stress in a pipeline, characterized in that, Includes the following steps: Step 1: Establish preliminary feature relationships using finite element simulation analysis software; Step 2: Determine the correspondence between axial stress and the output of the electromagnetic detection sensor containing a magnetic field receiving element; Step 3: Extraction and differentiation of features of pipeline axial stress detection signals; Step 4: Calculate the axial stress value of the pipeline.

2. The method for detecting the type of axial stress in a pipeline according to claim 1, characterized in that, Step 1 includes the following steps: Step 1.1: Establish a three-dimensional simulation model using finite element multiphysics simulation software; The three-dimensional simulation model includes a steel plate P1 and an electromagnetic detection sensor. The simulation parameters to be set for the steel plate P1 include the length of the steel plate. L ,width W ,thickness T The length, width, and thickness directions correspond to the following in the spatial coordinate system: x axis, y axis, z axis; Step 1.2: In the three-dimensional simulation model, set up the solid mechanical field and the frequency domain magnetic field; the elastic modulus, Poisson's ratio, density, etc. in the solid mechanical field are determined according to the mechanical properties of the steel plate; the permeability, conductivity, and magnetic core permeability of the steel plate in the frequency domain magnetic field are determined according to the mechanomagnetic properties of the steel plate material; apply a frequency of... to the excitation coil. Amplitude The initial phase is A sinusoidal signal, where the frequency is... The amplitude is determined based on the magnetic permeability and electrical conductivity of the steel plate material, the thickness of the steel plate, and the required detection depth. The excitation field is determined based on the number of turns of the excitation coil, the coil impedance, the magnetization characteristics of the magnetic core, and the output capability of the excitation coil, ensuring that the generated excitation field does not cause the steel plate to reach a saturated magnetization state. Step 1.3: In the three-dimensional simulation model, starting from the geometric center of the compressive stress change observation area, extend the lines along the positive and negative x-axis to form the upper surface analysis section. ltop In the tensile stress variation observation area, starting from the geometric center, extension lines are set along the positive and negative directions of the x-axis to form the lower surface analysis section. lback ,in, ltop and lback The length of each is L1.

3. The method for detecting the type of axial stress in a pipeline according to claim 2, characterized in that, In step 1.1, the steel plate along x The two end faces in the axial direction are M1 and M2, respectively, and M1 and M2 are used as fixed constraint surfaces; the range along the negative z-axis is [0, ... F max The load is measured in steps. F The maximum load Based on the yield strength of steel plate materials The geometric dimensions and boundary conditions of the steel plate determine the geometric center of the upper surface of the steel plate. * The load-bearing zone is set up in the region, and its size is determined based on the geometry of the steel plate and the range of load application; the load-bearing zone is located along the positive z-axis, at a distance from the upper surface of the steel plate. h The area with the same location and area as the load-bearing area is designated as the compressive stress change observation area. h According to the sensitivity settings of the electromagnetic detection sensor; the distance of the steel plate along the negative z-axis and the lower surface of the steel plate are set accordingly. h The area with the same location and area as the load-bearing area is designated as the tensile stress variation observation area; The electromagnetic detection sensor consists of a U-shaped magnetic core and an excitation coil, with the excitation coil wound around the U-shaped magnetic core. The electromagnetic detection sensor is positioned differently for both tensile stress change simulation and compressive stress change simulation: when performing tensile stress change simulation, the two ends of the U-shaped magnetic core are placed on the lower surface of the steel plate, and the geometric center of the plane containing the two ends of the U-shaped magnetic core is collinear with the geometric center of the tensile stress change observation area; when performing compressive stress change simulation, the two ends of the U-shaped magnetic core are placed on the upper surface of the steel plate, and the geometric center of the plane containing the two ends of the U-shaped magnetic core is collinear with the geometric center of the compressive stress change observation area.

4. The method for detecting the type of axial stress in a pipeline according to claim 3, characterized in that, Step 1.3 specifically includes: (1) Place the electromagnetic sensor in the three-dimensional simulation model according to the content of the tensile stress change simulation settings, load it in the load loading area, and solve and extract the analysis cross-section of the lower surface under different loads in the finite element simulation analysis software. lback along x Magnetic flux density amplitude at the midpoint of the axial direction Bx With phase, obtained in the solution results Bx With axial tensile stress The changing dataset is used to obtain the first [value] through regression fitting. i Axial tensile stress under load With magnetic flux density amplitude Bxi The relationship, among which : （1）； in, , , , These are the fitting coefficients for the axial tensile stress simulation, and all of them are non-zero. (2) Place the electromagnetic sensor in the three-dimensional simulation model according to the content of the compressive stress change simulation settings, load it in the load loading area, and solve and extract the upper surface analysis cross-section under different loads in the finite element simulation analysis software. ltop along x Magnetic flux density amplitude at the midpoint of the axial direction Bx 2 and phase, obtained in the solution results Bx 2 and axial compressive stress The changing dataset is used to obtain the first [value] through regression fitting. i Axial compressive stress under load With magnetic flux density amplitude Bx2i The relationship, among which : （2）； in, , , , These are the fitting coefficients for the axial compressive stress simulation, and all are non-zero, and are related to... , , , Not exactly the same.

5. The method for detecting the type of axial stress in a pipeline according to claim 4, characterized in that, Step 2 includes the following steps: Step 2.1: Take a steel plate P2 with the same material and geometric dimensions as the 3D simulation model, and conduct a calibration test using a three-point bending test device. The load loading area and fixed constraint surface in the three-point bending test device are set up in the same way as in the 3D simulation model. The spatial coordinate system, compressive stress change observation area, and tensile stress change observation area are also set up in the same way as in the 3D simulation model. At the geometric center of the compressive stress change observation area and the tensile stress change observation area of ​​the steel plate P2, respectively, a resistance strain gauge is attached along the x-axis. The resistance strain gauge is connected to the static resistance strain gauge using a three-wire quarter-bridge connection. Step 2.2: Adjust the three-point bending test device according to the load setting range, load the load area of ​​steel plate P2, observe the detection signal of the electromagnetic detection sensor containing the magnetic field receiving element, and record the amplitude of the output voltage and the load value. Step 2.3: Calculate the system offset of the electromagnetic detection sensor containing the magnetic field receiving element. ; When the load value is 0, based on the tensile stress experimental data... U l1 and B x1 Calculate the system offset according to formula (3) : （3）； Where k is the sensitivity coefficient of the electromagnetic detection sensor containing a magnetic field receiving element, and b is the zero-point offset of the electromagnetic detection sensor containing a magnetic field receiving element.

6. The method for detecting the type of axial stress in a pipeline according to claim 5, characterized in that, Step 2.2 specifically includes: (1) Compressive stress group test: Before loading begins, place the electromagnetic detection sensor containing the magnetic field receiving element on the upper surface of the steel plate, in the same position as the compressive stress change simulation. Start loading and observe the reading of the static resistance strain gauge. Record the strain value output by the strain gauge after each load level stabilizes when the load is changed. The output voltage amplitude and phase of an electromagnetic detection sensor containing a magnetic field receiving element are measured three times for each load level, and the arithmetic mean is taken to obtain the compressive stress experimental dataset X; any one of the compressive stress experimental data X... i Contains the first i Output voltage of an electromagnetic detection sensor containing a magnetic field receiving element under a loaded load U ci and the corresponding load value , ; (2) Tensile stress group test: After completing the compressive stress group test, the load was completely unloaded. After the strain gauge reading returned to zero and the steel plate P2 returned to the initial stress-free state, the electromagnetic detection sensor containing the magnetic field receiving element was placed on the lower surface of the steel plate, in the same position as the tensile stress change simulation. The load was then applied again and the strain value output by the strain gauge was recorded. ε p The output voltage amplitude and phase of an electromagnetic detection sensor containing a magnetic field receiving element are measured three times for each load level, and the arithmetic mean is taken to obtain a tensile stress experimental dataset. Q Any one of the tensile stress experimental data Including the i Output voltage of an electromagnetic detection sensor containing a magnetic field receiving element under a loaded load and the corresponding load value , .

7. The method for detecting the type of axial stress in a pipeline according to claim 6, characterized in that, Step 3 includes the following steps: Step 3.1: [The text appears to be incomplete and contains several grammatical errors. A more accurate translation would require the full context.] N An electromagnetic detection sensor containing a magnetic field receiving element is mounted on a pipe detector and arranged at equal intervals along the circumference of the inner wall of the pipe to be detected. The signal output from each electromagnetic detection sensor with a magnetic field receiving element constitutes a detection channel, and they are numbered sequentially in a clockwise direction along the circumference of the pipe. Cv , v =1,2,... N ; Based on the characteristics of circumferential welds in electromagnetic detection signals, all circumferential welds of the pipeline to be inspected are identified; let the total number of detected circumferential welds be... M and M≥ 2 ， The inspection channel data of the pipeline under inspection is divided into categories based on the axial position of the characteristic peak of the circumferential weld. M -1 independent pipe section; Step 3.2: Based on the output voltage of the detection channel U est Determining the type of axial stress based on its characteristics and phase features: Step 3.3: Verification of the axial stress detection channel; After completing the axial stress type determination in step 3.2, the results are verified based on the radial symmetry characteristics of the pipeline: for a total of N detection channels, channels with axial compressive stress are identified. C m Satisfies formula (4), where C j To and C m Channels containing axial tensile stress within the same pipe section, m and j Indicates the corresponding channel number: （4）； in, round () represents the rounding function; If the detection channel number in the same pipe section that was determined according to step 3.2 meets the formula (4), the determination result is valid; if it does not meet the formula, the detection channel needs to be selected again according to step 3.2, and the adjacent channel of the previous determination should be selected first.

8. The method for detecting the type of axial stress in a pipeline according to claim 7, characterized in that, Step 3.2 specifically includes: (1) If the output voltage of the detection channel has no gradual peak or trough in any pipe section, it is considered that the current detection channel has not detected axial stress. (2) If the output voltage of the detection channel is a single peak bulging upward inverted U-shape within any pipe section, and the phase exhibits a continuous and symmetrical single valley U-shaped characteristic, then it is determined that there is axial compressive stress in the detection channel. (3) If the output voltage of the detection channel is a positive U-shape with a single valley concave downwards and the phase exhibits a continuous and symmetrical single-peak inverted U-shape, then it is determined that there is axial tensile stress in the detection channel. (4) If within the same pipe section, circumferentially adjacent N s If all detection channels satisfy the judgment in (2) or (3), then... N s The axial stress types of each channel are output sequentially, where 2≤ N s ≤ N .

9. A method for detecting the type of axial stress in a pipeline according to claim 8, characterized in that, Step 4 specifically includes: (1) Single-channel stress calculation: For any axial stress detection channel determined in step 3, the peak value of the output voltage of the detection channel will be calculated. Uest Substituting into formula (5), the measured magnetic induction intensity of the detection channel is obtained. Breal Then Breal The corresponding axial stress value is obtained according to the type of axial stress it is determined to be. That is, if it is determined to be axial tensile stress, it is entered into formula (1) for calculation, and if it is determined to be axial compressive stress, it is entered into formula (2) for calculation. （5）； (2) Multi-channel stress detection: If multiple detection channels detect axial stress after step 3, the output voltage of each detection channel is calculated according to the single-channel stress calculation method. The maximum value among all calculation results of the detection channels under the axial stress type is taken as the final detection value of this type of axial stress in the pipeline.

Images