Pipeline stress detection method and stress simulation calculation method

Abstract

The invention discloses a pipeline stress detection method and a stress simulation calculation method. The method comprises the following steps: S1, selecting a plurality of measuring points on the circumference of a cross section of the outer wall of a pipeline; s2, grinding the measuring points on the outer wall of the pipeline until a pipeline body appears; s3, a prefabricated X65 pipeline steel test piece is placed on the pipeline near the measuring point, an ultrasonic transducer probe is placed on the zero-stress test piece, and sound time and temperature during zero stress are obtained; s4, an ultrasonic transducer probe is coupled to the measuring point of the pipeline body along the axis, and the stress of the four positions of the outer wall of the pipeline is obtained; s5, according to the ultimate mechanical parameters of the pipe and the design standard of the pipe, the tension and pressure state, the bending degree and the safety coefficient in the working period of the measured position of the pipe are given; according to the method, a stress detection mode and a simulation calculation method are combined, detection, simulation model establishment and stress calculation are carried out on the pipeline in a simple and convenient mode, the pipeline safety analysis result can be accurately obtained under the condition that the pipeline safety is not affected, and the method has important significance in the field of geological exploration.

Description

Technical Field

[0001] The present invention relates to the field of geological exploration technology, and more specifically to a pipeline stress detection method and a stress simulation calculation method. Background Art

[0002] Landslide refers to the natural phenomenon that the soil or rock on the slope slides down the slope as a whole or in a dispersed manner along a certain weak surface or weak zone under the action of gravity due to factors such as river scouring, groundwater activity, rainwater soaking, earthquakes and artificial slope cutting. The moving rock (soil) is called a displacement body or sliding body, and the underlying rock (soil) that has not moved is called a sliding bed. The landslide phenomenon has a huge impact on the natural gas pipeline buried inside the soil.

[0003] Existing theories show that pipelines laid along the terrain from high to low or from low to high on a hillside will cause a large amount of earth to collapse rapidly when the equilibrium state of the hillside is destroyed, especially when the hillside is soaked by groundwater or rainwater. This phenomenon may occur during construction or operation. The pipeline in the landslide will be affected by the collapse force of the soil and will slide down along with the soil. The upper half of the pipeline on the longitudinal slope is under tension and the lower half is under compression. The maximum tensile stress is located at the top and the maximum compressive stress is located at the bottom. When the landslide is severe, the pipeline on the upper part of the hillside is in danger of being pulled apart, and the pipeline on the lower part of the hillside is prone to corrugated deformation and the pipeline is at risk of being crushed. After a landslide occurs, it is necessary to check the dangerous welds of the landslide pipe section to eliminate the risk in advance. However, in the prior art, there is no convenient and limited detection method or stress calculation method. Summary of the invention

[0004] One advantage of the present invention is that it provides a pipeline stress detection method and a stress simulation calculation method. By combining the stress detection method and the simulation calculation method, the pipeline is detected, a simulation model is established, and stress calculation is performed in a simple manner. The pipeline safety analysis results can be accurately obtained without affecting the safety of the pipeline, which is of great significance in the field of geological survey.

[0005] To achieve at least one of the above advantages of the present invention, the present invention provides a pipeline stress detection method, comprising:

[0006] S1: Select several measuring points on a cross-section circle of the outer wall of the pipe;

[0007] S2: Grind the measuring points on the outer wall of the pipeline until the pipeline body appears;

[0008] S3: Place the prefabricated X65 pipe steel specimen on the pipeline near the measuring point. After several minutes of placement, according to the temperature difference between the pipeline and the environment, place the ultrasonic transducer probe on the zero stress specimen and the temperature probe at the same time to start the zero stress acoustic time calibration of the steel and obtain the acoustic time and temperature at zero stress.

[0009] S4: The ultrasonic transducer probe is coupled to the measuring point of the pipeline body along the axis. The ultrasonic tester can read the acoustic time and temperature of the pipeline body. The X65 stress coefficient database obtained by calibration is used to interpolate and calculate the stress coefficient of the X65 steel at the corresponding temperature. The current pipeline stress is quickly calculated by the temperature influence coefficient based on the difference between the calibration temperature and the pipeline body temperature. By analogy, the stress at four locations on the outer wall of the pipeline can be obtained.

[0010] S5: According to the ultimate mechanical parameters of the pipe and the pipeline design standards, the tensile and compressive state, bending degree and safety factor during operation of the pipeline are given;

[0011] The pipeline stress detection method is applied to a detection device, including a low-power processor, and a liquid crystal display and interaction module, a temperature measurement module, a power management module, an ultrasonic transmitting module, an ultrasonic receiving module, a time measurement circuit module and an LCR wave transducer electrically connected to the processor, wherein the LCR wave transducer is electrically connected to the ultrasonic transmitting module and the ultrasonic receiving module.

[0012] According to an embodiment of the present invention, in step S1 , the circumference of the measuring point is 10 to 30 centimeters away from the weld.

[0013] According to an embodiment of the present invention, in step S3, the placement time is 1 to 5 minutes.

[0014] According to one embodiment of the present invention, the LCR transducer includes a shell, in which a plexiglass wedge, an excitation transducer and a receiving transducer are arranged. The excitation electrical signal is converted into an ultrasonic signal by the excitation transducer, and the ultrasonic signal is refracted when transmitted to the measured medium, wherein the LCR wave propagates along the surface of the measured medium and is received by the receiving transducer and converted into an electrical signal.

[0015] Stress simulation calculation method, applied to pipeline stress detection method, including

[0016] S01: Establish a geometric model based on the actual situation on site and the pipeline construction drawings, where the geometric model includes a soil model and a pipeline model;

[0017] S02: Use free meshing and swept meshing methods to divide the soil model and pipeline model;

[0018] S03: Apply gravity load to the geometric model and apply soil slip parameters to the measuring points according to the test results of the pipeline stress detection method;

[0019] S04: Draw pipeline stress cloud map and pipeline displacement cloud map according to the simulated structure of S03;

[0020] S05: Use polar coordinates to calculate the influence of internal pressure on pipeline stress, simplify pipeline stress into plane strain, obtain pipeline axial stress analysis formula, and use this stress analysis formula to calculate stress and establish an analysis model;

[0021] S06: For the analysis model, different uniformly distributed pressures are applied to the inner wall of the pipeline in the model to obtain a pipeline stress cloud map;

[0022] S07: The relationship between pipeline surface stress and pipeline internal pressure is obtained through finite element simulation analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the equipment module structure of the present invention;

[0024] Figure 2 It is a schematic diagram of the working principle of the transducer of the present invention;

[0025] Figure 3 This is a schematic diagram of the position of the pipeline measuring points of the present invention;

[0026] Figure 4 It is a schematic diagram of selecting equal wall thickness measuring points of the present invention;

[0027] Figure 5 This is a schematic diagram of stress measurement points of a variable wall thickness weld pipeline body according to the present invention;

[0028] Figure 6 It is a schematic diagram of stress measurement results at various points of the present invention;

[0029] Figure 7 It is a schematic diagram of the soil model of the present invention;

[0030] Figure 8 It is a schematic diagram of the pipeline model of the present invention;

[0031] Fig. 9 It is the pipeline stress cloud diagram of the present invention;

[0032] Fig.10 It is the pipeline displacement cloud map of the present invention;

[0033] Fig.11 It is a schematic diagram of polar coordinate solution of the present invention;

[0034] Fig.12 This is a diagram of internal pressure change and pipeline stress safety level according to the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention more clear, the following will be combined with the appended claims of the present invention. Figure 1 ~Attached Fig.12 , the present invention is described in more detail.

[0036] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0037] Those skilled in the art should understand that, in the disclosure of the specification, the orientation or position relationship indicated by the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the orientation or position relationship shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

[0038] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the element may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0039] The present invention provides a pipeline stress detection method, comprising:

[0040] S1: Select several measuring points on a cross-section circle of the outer wall of the pipe;

[0041] S2: Grind the measuring points on the outer wall of the pipeline until the pipeline body appears;

[0042] S3: Place the prefabricated X65 pipe steel specimen on the pipeline near the measuring point. After several minutes of placement, according to the temperature difference between the pipeline and the environment, place the ultrasonic transducer probe on the zero stress specimen and the temperature probe at the same time to start the zero stress acoustic time calibration of the steel and obtain the acoustic time and temperature at zero stress.

[0043] S4: The ultrasonic transducer probe is coupled to the measuring point of the pipeline body along the axis. The ultrasonic tester can read the acoustic time and temperature of the pipeline body. The X65 stress coefficient database obtained by calibration is used to interpolate and calculate the stress coefficient of the X65 steel at the corresponding temperature. The current pipeline stress is quickly calculated by the temperature influence coefficient based on the difference between the calibration temperature and the pipeline body temperature. By analogy, the stress at four locations on the outer wall of the pipeline can be obtained.

[0044] S5: According to the ultimate mechanical parameters of the pipe and the pipeline design standards, the tensile and compressive state, bending degree and safety factor during operation of the pipeline are given;

[0045] The pipeline stress detection method is applied to the above-mentioned pipeline stress detection method, comprising a detection device, including a low-power processor, and a liquid crystal display and interaction module electrically connected thereto, a temperature measurement module, a power management module, an ultrasonic transmitting module, an ultrasonic receiving module, a time measurement circuit module and an LCR wave transducer, wherein the LCR wave transducer is electrically connected to the ultrasonic transmitting module and the ultrasonic receiving module; in step S1, a distance of 10 to 30 centimeters is left between the circumference of the measuring point and the weld; in step S3, the placement time is 1 to 5 minutes; the LCR transducer comprises a shell, and an organic glass wedge, an excitation transducer and a receiving transducer are arranged inside the shell, the excitation electrical signal is converted into an ultrasonic signal by the excitation transducer, the ultrasonic signal is transmitted to the measured medium and refracted, wherein the LCR wave propagates along the surface of the measured medium and is received by the receiving transducer and converted into an electrical signal.

[0046] Stress simulation calculation method, applied to pipeline stress detection method, including

[0047] S01: Establish a geometric model based on the actual situation on site and the pipeline construction drawings, where the geometric model includes a soil model and a pipeline model;

[0048] S02: Use free meshing and swept meshing methods to divide the soil model and pipeline model;

[0049] S03: Apply gravity load to the geometric model and apply soil slip parameters to the measuring points according to the test results of the pipeline stress detection method;

[0050] S04: Draw pipeline stress cloud map and pipeline displacement cloud map according to the simulated structure of S03;

[0051] S05: Use polar coordinates to calculate the influence of internal pressure on pipeline stress, simplify pipeline stress into plane strain, obtain pipeline axial stress analysis formula, and use this stress analysis formula to calculate stress and establish an analysis model;

[0052] S06: For the analysis model, different uniformly distributed pressures are applied to the inner wall of the pipeline in the model to obtain a pipeline stress cloud map;

[0053] S07: The relationship between pipeline surface stress and pipeline internal pressure is obtained through finite element simulation analysis.

[0054] Embodiment 1 of the present invention is as follows:

[0055] Based on ultrasonic critical refraction longitudinal wave stress measurement technology, the axial stress level on the pipeline surface can be obtained quickly and non-destructively. The test results are accurate and can assist managers in quickly judging the current tension and compression state of the pipeline. The safety factor is calculated by accurately measuring the stress value, helping to decide whether the pipeline can continue to operate safely.

[0056] Within the elastic range of the material, there is a good linear relationship between stress and ultrasonic wave velocity. The relationship between the propagation velocity of the plane wave parallel to the stress loading direction and stress is shown in formula (1-1).

[0057]

[0058] Where: V 11 is the longitudinal wave velocity propagating parallel to the stress loading direction (referred to as parallel stress wave velocity), m / s; ρ 0 is the density of the material at zero stress; λ and μ are the second-order elastic modulus of the material; l, m, and n are the third-order elastic modulus of the material.

[0059] Further deriving and simplifying formula (1-1) yields formula (2-2):

[0060] Δσ=K(tt 0 )=KΔt (1-2)

[0061] Where:

[0062] Δσ is the change in pipeline stress; K is the material stress coefficient, which is a specific constant for each material; t and t 0 They represent the flight time of ultrasound under stress and zero stress respectively; t is the change in the flight time of sound waves in the material relative to zero stress.

[0063] It can be seen from formula (1-2) that the current stress value of the material can be calculated by calibrating the stress coefficient K of a specific material and measuring its ultrasonic flight time under stress and zero stress.

[0064] Based on the acoustic elasticity principle and the linear relationship between stress and LCR wave flight time, we independently developed a device specifically for measuring the stress of oil and gas pipelines under working conditions, which integrates a low-power processor, an ultrasonic transmitter module, an ultrasonic receiver module, a time measurement circuit module, a temperature measurement module, a liquid crystal display and interaction module, and a power management module. The device can be applied to various operating conditions and perform non-destructive measurement of pipeline surface stress. The time measurement accuracy is improved to 0.1ns, and the stress measurement error is ±10MPa, which directly obtains the pipeline stress size that engineers are most concerned about.

[0065] When using a stress ultrasonic measuring device to measure pipeline stress, it is necessary to couple the ultrasonic transducer to the pipeline surface. By studying the generation of LCR waves, the transducer was independently designed. It consists of an exciting transducer, a receiving transducer, and a plexiglass wedge. The sound path L is fixed at 35 mm, and L 1 =6mm, critical refraction angle θ 0The angle is 28°, the frequency of the transducer is 5MHz, and the measurement depth in the specimen is about 1.66mm, which can be equivalently measured by the drilling method. The excitation electrical signal is converted into an ultrasonic signal through the excitation transducer, and the ultrasonic signal is refracted when it is transmitted to the measured medium. The LCR wave propagates along the surface of the measured medium, is received by the receiving transducer, converted into an electrical signal, and transmitted to the collector.

[0066] The detection steps include:

[0067] Ensure that a working space of no less than 0.8m is excavated at the bottom of the pipeline to facilitate grinding and measurement. The specific steps are as follows:

[0068] (1) Selection of measuring points. To ensure the effectiveness of the measurement, the measuring points are located on a cross-sectional circumference of the outer wall of the pipe, generally at 0, 3, 6 and 9 of the pipe mouth (6 points can be selected if the working space is limited). In addition, the circumference of these four measuring points is a certain distance from the circumferential weld, which is about 10 to 30 cm.

[0069] (2) On-site grinding of measuring points. In ultrasonic measurement, the coupling quality directly affects the reliability of the measurement data. For this reason, the team conducted a large number of indoor tests and selected a sanding machine as the final grinding device for the measuring points. Through grinding experiments with sanding belts of different particle sizes, the team proposed an on-site grinding process for the pipeline measuring points, which ensured the flatness and surface finish. The insulation layer in the measuring point area was removed, and the sanding machine was used to grind along the axis of the pipeline for about 4 minutes until the silver-white pipeline body appeared.

[0070] (3) Zero stress specimen calibration. The prefabricated X65 pipe steel specimen is placed on the pipeline near the measuring point. After 1 to 5 minutes, depending on the temperature difference between the pipeline and the environment, the ultrasonic transducer (probe) is placed on the zero stress specimen, and the temperature probe is placed at the same time to start the zero stress acoustic time calibration of the steel to obtain the acoustic time and temperature at zero stress.

[0071] (4) Pipeline stress measurement. The ultrasonic transducer (probe) is coupled to the measuring point of the pipeline body along the axis. The ultrasonic tester can read the acoustic time and temperature of the pipeline body. The X65 stress coefficient database obtained through calibration is used to interpolate and select the X65 steel stress coefficient at the corresponding temperature. Based on the difference between the calibration temperature and the pipeline body temperature, the current pipeline stress is quickly calculated using the temperature influence coefficient. By analogy, the stress at four locations on the outer wall of the pipeline can be obtained.

[0072] (5) Data analysis and report writing. According to the ultimate mechanical parameters of the pipe and the pipeline design standards, the tensile and compressive state of the pipeline measurement point, the degree of bending and the safety factor during operation are directly given to quickly give a safety evaluation. When the equilibrium state of the slope is destroyed, especially when the slope is soaked by groundwater or rainwater, the pipeline laid from high to low or from low to high will cause a large amount of earth to collapse rapidly. This phenomenon occurs both during construction and during operation. The pipeline in the landslide will be affected by the collapse force of the soil and will slide down along with the soil.

[0073] The method for selecting the measuring point position is as follows:

[0074] There is no axial deformation in the middle of the pipeline, that is, the stress here is zero. The upper half of the pipeline on the longitudinal slope is under tension, and the lower half is under compression. The maximum tensile stress is located at the top x = l, and the maximum compressive stress is located at the bottom x = 0. When the landslide is serious, the pipeline on the upper part of the slope is in danger of being pulled apart, and the pipeline on the lower part of the slope is prone to corrugated deformation, and the pipeline is at risk of collapse.

[0075] According to the above analysis, if Figure 3 As shown in the figure, a total of 6 measuring points were selected, including 4 welds and 2 straight pipes. The measured welds are the 4 welds of the pipeline that are most affected by the landslide: the weld at the top of the slope; the first and second welds from the top of the slope; the first weld at the bottom of the slope. The straight pipes are: the upper side of the retaining wall at the bottom of the slope; the other side of the dirt road at the bottom of the slope. By testing the six locations and combining simulation calculations to analyze the location of the most dangerous point of the pipeline and the degree of danger, a reliable reference is provided for future protection and management.

[0076] The allowable stress of oil and gas pipelines can be calculated according to the following formula (1-3):

[0077] [σ]=Fσ s (1-3)

[0078] Where: [σ] is the allowable stress of oil and gas pipeline steel, MPa; F is the strength design factor.

[0079] When evaluating the stress measurement results of the pipeline in the excavation pit, the pipeline strength coefficient under the current operating state should be calculated according to the following formula 1-4:

[0080]

[0081] Where max is the maximum stress measurement value of each measuring point in the excavation pit, MPa; f is the strength coefficient of the pipeline in the current operating state. By comparing the strength coefficient of the current pipeline in real-time operation with the strength design coefficient allowed by the safety level of the corresponding area in the area, the current safety status of the pipeline can be quickly evaluated. According to the design drawings, this area is a secondary area, so when the measured stress is less than 350MPa, it can pass the evaluation.

[0082] Measurement results of each measuring point:

[0083] Measuring point ①:

[0084] According to the above scheme, the surface anti-corrosion paint of the measuring point needs to be removed, the surface oxide layer needs to be cleaned, and then the surface needs to be polished into a flat surface using a polishing machine. The measurement is carried out after calibration at ambient temperature, and the online stress measurement result statistical table is filled in:

[0085]

[0086] Measuring point ②:

[0087] According to the above scheme, the surface anti-corrosion paint of the measuring point needs to be removed, the surface oxide layer needs to be cleaned, and then the surface needs to be polished into a flat surface using a polishing machine. The measurement is carried out after calibration at ambient temperature, and the online stress measurement result statistical table is filled in:

[0088]

[0089] Measuring point ③:

[0090] According to the above scheme, the surface anti-corrosion paint of the measuring point needs to be removed, the surface oxide layer needs to be cleaned, and then the surface needs to be polished into a flat surface using a polishing machine. The measurement is carried out after calibration at ambient temperature, and the online stress measurement result statistical table is filled in:

[0091]

[0092] Measuring point ④:

[0093] According to the above scheme, the surface anti-corrosion paint of the measuring point needs to be removed, the surface oxide layer needs to be cleaned, and then the surface needs to be polished into a flat surface using a polishing machine. The measurement is carried out after calibration at ambient temperature, and the online stress measurement result statistical table is filled in:

[0094]

[0095]

[0096] Measuring point ⑤:

[0097] According to the above scheme, the surface anti-corrosion paint of the measuring point needs to be removed, the surface oxide layer needs to be cleaned, and then the surface needs to be polished into a flat surface using a polishing machine. The measurement is carried out after calibration at ambient temperature, and the online stress measurement result statistical table is filled in:

[0098]

[0099] Measuring point ⑥:

[0100] According to the above scheme, the surface anti-corrosion paint of the measuring point needs to be removed, the surface oxide layer needs to be cleaned, and then the surface needs to be polished into a flat surface using a polishing machine. The measurement is carried out after calibration at ambient temperature, and the online stress measurement result statistical table is filled in:

[0101]

[0102]

[0103] For the analysis of the above measurement results, a total of 6 tests were conducted, including stress near 4 girth welds and stress at 2 straight pipes. The statistical results are as follows:

[0104]

[0105]

[0106] Draw the stress measurement results of each measuring point in the table into a curve graph, such as Figure 6 shown.

[0107] (1) The maximum stress value measured was 300 MPa, located at the 3-point direction of measuring point ①, reaching 0.60 times the minimum yield strength of X65. It is known that the regional grade of the pipeline design was a secondary area, and the measured results meet the pipeline design requirements.

[0108] (2) The measuring point ⑤ at the bottom of the slope of the pipeline is under compressive stress, while the measuring points ①②③⑥ are mainly under tensile stress, indicating that the soil near measuring points ③ to ⑤ collapses longitudinally along the direction of the pipeline, causing the pipeline here and the pipeline on the slope to be tensile, and the pipeline at measuring point ⑤ at the bottom of the slope to be compressed. The terrain where the pipeline is located is steep and the soil thickness is uneven. The soil layer is thicker closer to the bottom of the slope and thinner closer to the top of the slope. Under the gravity of the pipeline and other effects, the soil gradually becomes dense from loose, and slowly settles, causing the surrounding soil to slowly slide, eventually causing the pipeline at the bottom of the slope to be compressed and the pipeline at the landslide to be tensile. At the same time, the collapse of the soil in the area near point ③ is also the main reason for the cracks in the retaining wall at the bottom of the slope.

[0109] (3) The stress on both sides of the pipeline at the top of the slope (point 3 and point 9) is uneven, with significant differences. At measuring point ②, the stress on the side of point 3 is positive, while the stress on the side of point 9 is negative, indicating that the pipeline has bent toward the side of point 3 due to a lateral landslide of the soil perpendicular to the direction of the pipeline.

[0110] Through the on-site investigation and stress measurement of this section of pipeline, we know that:

[0111] (1) After the transformation, the pipeline in this area still bears the additional soil load caused by the surface displacement. The pipeline at the top of the slope is under tension, and the pipeline at the bottom of the slope is under compression. The maximum stress is 300 MPa at the top of the slope, which currently meets the pipeline safety level requirements.

[0112] (2) The soil at measuring points ③ to ⑤ experienced a slow longitudinal landslide, which caused the pipeline near measuring point ③ to be pulled, the pipeline at the bottom of the slope to be compressed, and longitudinal cracks to appear in the retaining wall. The retaining wall has been dismantled and reconstructed.

[0113] (3) At measuring point ② on the top of the slope, the soil slides horizontally in the vertical direction of the pipeline, causing the pipeline to bend and deform. Anchor piers can be installed to constrain the lateral displacement of the pipeline and soil.

[0114] (4) The area where this section of the pipeline is located has heavy rainfall, moist and loose soil, and poor geological conditions. There is a possibility of continued geological disasters such as landslides. A surface displacement monitoring system or a pipeline deformation detection system should be installed. Once an early warning is issued, timely measures should be taken to avoid the occurrence of disasters.

[0115] The relevant data are obtained through the above detection method, and the stress numerical simulation calculation is performed on the relevant data. The process is as follows:

[0116] First, a geometric model should be established. The establishment of a geometric model is the basis for numerical analysis, but the actual geometric model needs to be adjusted or simplified. This simulation fully examined the actual situation on site and the pipeline construction drawings. The pipeline and soil were simplified while fully respecting the actual situation on site. In order to be able to display the stress and displacement distribution of the pipeline intuitively and clearly, the pipeline wall thickness is now unified to 11.9mm, and clay is used to establish a pipe-soil contact model. The material parameters are shown in the following table, and the materials are all homogeneous and isotropic.

[0117] Parameter name Parameter Value Parameter name Parameter Value Buried depth(m) 1-3 Soil expansion angle (°) 0 Pipe elastic modulus E(GPa) 210 Pipe Poisson's ratio 0.3 Internal friction angle of soil (°) 25 Friction coefficient of soil-pipe 0.3 Pipe elastic modulus E(GPa) 0.11 Poisson's ratio of soil 0.25

[0118] The geometric model includes soil model and pipeline model, where the soil model is as follows:

[0119] According to the actual size of the engineering drawing, the 7.46° elbow at the bottom of the landslide body is ignored. The rest of the pipeline length, direction, and elbows are established according to the actual engineering drawings. The soil model is simplified to a hillside with a total length of 150m, a maximum of 50m, and a width of 20m. The 20m wide soil is divided into three parts, and the middle 10m is the landslide body. No protective measures are set for the soil in this model.

[0120] The pipeline model is as follows:

[0121] The diameter of the pipeline model is 610 mm. In order to facilitate the analysis of the stress distribution law in the landslide area, the wall thickness is unified to 11.9 mm, and the total length of the pipeline is 190 m.

[0122] Free meshing and sweeping meshing are used for meshing. Since the soil model is too complex, a mixed unit method of hexahedron 8 nodes and unihedron 6 nodes is used. Hexahedron elements are used where there are no pipes on both sides of the soil, and tetrahedron elements are used in the center of the soil where there are pipes.

[0123] There are 1 meshing method for solid elements, which are free meshing, mapped meshing, hybrid meshing and swept meshing. In this model, the hexahedron is meshed by swept meshing, the unihedron is meshed by free meshing, and there are 273060 soil meshes in total.

[0124] The pipeline model is relatively regular and all uses hexahedral mesh sweeping to divide the mesh. There are 5818 pipeline meshes in total.

[0125] Boundary conditions were set, gravity load was applied to the whole model, the internal pressure of the pipeline was 4.0 MPa, no constraints were imposed on both ends of the pipeline, and no constraints were imposed on the other surfaces except the bottom surface. A soil slip of a maximum of 0.6 m and a minimum of 0.2 m was imposed on slip surface ①, a soil slip of a maximum of 0.4 m and a minimum of 0.2 m and a lateral slip of 0.2 m were imposed on slip surface ②, and a soil slip of 0.4 m was imposed on slip surface ③.

[0126] The soil and the pipeline adopt a surface-to-surface contact mode, a finite slip calculation formula is set, and the contact action attribute is set to a friction coefficient of 0.3. The remaining parameters are all set in the system.

[0127] According to the numerical simulation results, there are three obvious stress concentration points in the pipeline, which are located at three elbows. The maximum stress reaches 350 (MPa) and the strength coefficient is 0.73. The results show that under the boundary conditions of this model, the pipeline reaches 0.73 times the minimum yield strength, and the reserve strength is insufficient. If a landslide displacement greater than 0.6m is found in the future, the stress concentration points of the pipeline should be checked in time.

[0128] According to the numerical simulation results, the landslide section pipeline was intercepted to analyze the axial displacement change of the pipeline. The pipeline displacement distribution is as follows: Fig.10 As shown, the maximum displacement of the upper part of the pipeline can reach 0.1m, and the minimum displacement of the bottom of the pipeline is 0.05m. The maximum and minimum difference is 0.05m. The overall rule is consistent with the cognition of this research group.

[0129] Through the establishment of the above geometric model, it can be seen that under the condition that the maximum landslide of the landslide body is equal to 0.6m, the pipeline stress is concentrated in the following areas: Fig. 9 Among the three elbows shown, the stress at the bottom elbow is the largest. Under the boundary conditions of this model, the maximum stress of the pipeline appears at stress concentration point 2, which is 350MPa. The pipeline reaches 0.73 times the minimum yield strength, and the reserve strength is insufficient. If the maximum landslide of the landslide body is less than 0.6m, it can be basically considered that the pipeline has sufficient reserve strength.

[0130] The maximum displacement of the pipeline occurs when Fig. 9The maximum stress concentration in the two locations is 0.1m. The maximum pipeline displacement and maximum stress appear at the same location, indicating that the pipeline here is the most dangerous. In the future, more attention should be paid to this location.

[0131] The relevant deductions of the circular tube structure are carried out based on the knowledge of elastic mechanics, and the polar coordinates are used to solve the problem considering the structural characteristics of the circular tube itself.

[0132] According to the relationship between the plane rectangular coordinate system and the polar coordinate system, we can get:

[0133]

[0134] According to the force balance condition, we have:

[0135]

[0136] The equilibrium differential equation of the plane rectangular coordinate system is:

[0137]

[0138] The relationship between the body force components in the plane rectangular coordinate system and the polar coordinate system is:

[0139]

[0140] Substituting the stress component and the body force component into the equilibrium differential equation in the plane rectangular coordinate system, we can obtain the equilibrium differential equation in polar coordinates:

[0141]

[0142] For axisymmetric problems such as circular tubes and cylinders, the geometric shape and external load of the component do not change with the polar angle, the stress distribution is independent of the polar angle, and the shear stress is equal to zero. The stress function is only a function of the radius vector, and the stress biharmonic function degenerates into:

[0143]

[0144] The general solution is:

[0145] Φ=A lnρ+Bρ 2 lnρ+Cρ 2 +D (3-7)

[0146] The stress components obtained by solving the stress function are:

[0147]

[0148] The strain components are solved as:

[0149]

[0150] The displacement components are solved as:

[0151]

[0152] For thin-walled pipes subjected to uniform internal pressure, stress and displacement deformation analysis is performed.

[0153] Suppose there is a ring or cylinder with inner radius a and outer radius b, and it is subjected to internal pressure p. Obviously, the stress distribution should be axisymmetric. Therefore, the stress component expression is

[0154]

[0155] According to the boundary conditions, we can know that:

[0156]

[0157] From the stress component expressions, it can be found that the first two boundary conditions are satisfied, while the last two boundary conditions need to be satisfied:

[0158]

[0159] Considering the single value condition of displacement, from the displacement components under the axisymmetric stress state,

[0160] In the circumferential displacement u φ In the expression of A term is multi-valued: for the same ρ value, such as ρ = ρ 1 , when φ=φ 1 When φ=φ 1 When +2π, the circumferential displacement difference is, This is inconsistent with the actual deformation of the tube, because (ρ 1 ,φ 1 ) and (ρ 1 ,φ 1 +2π) is the same point and it is impossible for them to have different displacements. According to the single-valued displacement condition, B=0.

[0161] So we can get

[0162]

[0163] Substituting A, B, and C into the response force component expression, we finally get the following solution

[0164]

[0165] For long-distance oil and gas pipelines, solving and analyzing pipeline stress can be simplified to a plane strain problem. According to the polar coordinate representation of the physical equation of the spatial axisymmetric problem, see formula (3-17):

[0166]

[0167] Then there is

[0168]

[0169] Substituting equation (3-16) into equation (3-18), the axial stress of the pipeline is obtained after simplification:

[0170]

[0171] It can be seen from formulas (3-16) and (13-9) that when the pipeline size is fixed, the pipeline stress is proportional to the internal pressure of the pipeline.

[0172] Taking a Φ610mm, 11.9mm thick pipe as an example, stress calculation can be performed to obtain the relationship between the pipe surface annular stress and the pipe internal pressure:

[0173] Pipeline internal pressure (MPa) Hoop stress(MPa) Axial stress (MPa) 1 24.1 7.2 2 48.2 14.4 3 72.4 21.7 4 95.6 28.9 5 120.7 36.2 6 144.8 43.4 7 168.9 50.6 8 193.1 57.9 9 217.2 65.1 10 241.4 72.4

[0174] For the pipeline numerical analysis model established above, different uniformly distributed pressures are applied to the inner wall of the pipeline, and the pipeline stress cloud diagram is calculated.

[0175] By sorting out the finite element simulation results, we can obtain the changes in pipeline stress under different internal pressures, such as the statistical table of the relationship between pipeline surface stress and sub-simulation inside the pipeline:

[0176]

[0177]

[0178] It can be found that the error between the theoretical calculation results and the finite element simulation results is about 0.5%. For every 1MPa increase in the pressure inside the pipe, the annular stress on the outer wall of the pipe increases by 24MPa, and the axial stress on the outer wall of the pipe increases by about 7MPa. The error between the theoretical calculation results and the finite element simulation results is about 0.5%. For every 1MPa increase in the pressure inside the pipe, the annular stress on the outer wall of the pipe increases by 24MPa, and the axial stress on the outer wall of the pipe increases by about 7MPa.

[0179] The results of theoretical and numerical analysis show that for every 1MPa increase in the gas pressure in the pipe, the axial stress of the pipe increases by 7MPa. It is known that the current pipeline transportation pressure is 4.5MPa during the test, and the maximum axial stress is 300MPa, indicating that the soil around the pipe has shifted, bringing additional load to the pipeline.

[0180] It can be seen that when the pipeline operates under reduced pressure or maintains the current transportation pressure, the pipeline strength coefficient is less than 0.6, meeting the requirements of Class II areas; when the pipeline pressure increases by 0.01 - 3.8 MPa, that is, when the actual operating pressure is less than 8.3 MPa, the pipeline strength coefficient is 0.6 < f < 0.72, belonging to Class I areas. The pipeline still has a certain safety margin and will not be damaged without other external load conditions, but it no longer meets the requirements of the area classification; when the pipeline pressure increases by more than 3.8 MPa, that is, when the actual operating pressure is greater than 8.3 MPa, the pipeline strength coefficient is greater than 0.8, and the pipeline safety margin is small, and there is a possibility of damage at any time.

[0181] From the above analysis, it can be seen that the current axial stress of the pipeline has approached the maximum stress allowed by the area classification, and it is not recommended to increase the pressure for operation before treatment.

[0182] According to the stress detection results, the pipeline at this location and the pipeline on the slope are in tension, and the pipeline at the bottom of the slope is in compression. The terrain where the pipeline is located is relatively steep, and the soil thickness is uneven. The soil layer is thicker closer to the bottom of the slope and thinner closer to the top of the slope. Under the action of the pipeline gravity and other factors, the soil gradually becomes dense from loose, undergoes slow settlement, and drives the surrounding soil to undergo slow landslides, ultimately resulting in the pipeline at the bottom of the slope being in compression and the pipeline at the landslide being in tension. The maximum stress is 260 Mpa at the No. ② measuring point at the top of the slope, which currently meets the requirements of the pipeline safety level.

[0183] According to the simulation results of this time, under the condition that the maximum landslide of the landslide body is 0.6 m, the pipeline stress is concentrated at the three elbows as shown in Fig. 9 the figure. Among them, the stress of the lowest elbow is the largest. Under the boundary conditions of this model, the maximum pipeline stress appears at the stress concentration point 2 and is 350 MPa, which is 0.73 times the minimum yield strength of the pipeline, and the reserve strength is insufficient. If the maximum landslide of the landslide body is less than 0.6 m, it can be basically considered that the pipeline has sufficient reserve strength. The maximum pipeline displacement appears at the stress concentration point 2 and is at most 0.1 m. The maximum pipeline displacement and the maximum stress appear at the same position, indicating that the pipeline at this location is the most dangerous, and the stress situation at this location should be closely monitored.

[0184] In some alternative embodiments, the functions / operations mentioned in the block diagrams may not occur in the order mentioned in the operation diagrams. For example, depending on the functions / operations involved, two consecutive blocks shown may actually be executed substantially simultaneously or the above-mentioned blocks can sometimes be executed in the reverse order. In addition, the embodiments presented and described in the system diagrams of the present invention are provided by way of example for the purpose of providing a more comprehensive understanding of the technology. The disclosed method is not limited to the operations and logical processes presented herein. Alternative embodiments are foreseeable, in which the order of various operations is changed and the sub-operations described as part of a larger operation are executed independently.

[0185] The logic and / or steps represented in the system diagram or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute the instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0186] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0187] In the above description of this specification, the description with reference to the terms "one embodiment / example", "another embodiment / example" or "certain embodiments / examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0188] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

[0189] The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the above embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A pipeline stress detection method, characterized in that: include S1: Select several measuring points on a cross-section circle of the outer wall of the pipe; S2: Grind the measuring points on the outer wall of the pipeline until the pipeline body appears; S3: Place the prefabricated X65 pipe steel specimen on the pipeline near the measuring point. After several minutes of placement, according to the temperature difference between the pipeline and the environment, place the ultrasonic transducer probe on the zero stress specimen and the temperature probe at the same time to start the zero stress acoustic time calibration of the steel and obtain the acoustic time and temperature at zero stress. S4: The ultrasonic transducer probe is coupled to the measuring point of the pipeline body along the axis. The ultrasonic tester can read the acoustic time and temperature of the pipeline body. The X65 stress coefficient database obtained by calibration is used to interpolate and calculate the stress coefficient of the X65 steel at the corresponding temperature. The current pipeline stress is quickly calculated by the temperature influence coefficient based on the difference between the calibration temperature and the pipeline body temperature. By analogy, the stress at four locations on the outer wall of the pipeline can be obtained. S5: According to the ultimate mechanical parameters of the pipe and the pipeline design standards, the tensile and compressive state, bending degree and safety factor during operation of the pipeline are given; The pipeline stress detection method is applied to a detection device, including a low-power processor, and a liquid crystal display and interaction module, a temperature measurement module, a power management module, an ultrasonic transmitting module, an ultrasonic receiving module, a time measurement circuit module and an LCR wave transducer electrically connected to the processor, wherein the LCR wave transducer is electrically connected to the ultrasonic transmitting module and the ultrasonic receiving module.

2. The pipeline stress detection method according to claim 1, characterized in that: In step S1, the circumference of the measuring point is 10 to 30 centimeters away from the weld.

3. The pipeline stress detection method according to claim 1, characterized in that: In step S3, the standing time is 1 to 5 minutes.

4. The pipeline stress detection method according to claim 1, characterized in that: The LCR transducer includes a shell, in which an organic glass wedge, an excitation transducer and a receiving transducer are arranged. The excitation electrical signal is converted into an ultrasonic signal by the excitation transducer, and the ultrasonic signal is refracted when transmitted to the measured medium, wherein the LCR wave propagates along the surface of the measured medium and is received by the receiving transducer and converted into an electrical signal.

5. A stress simulation calculation method, applied to the pipeline stress detection method according to any one of claims 1 to 4, characterized in that: include S01: Establish a geometric model based on the actual situation on site and the pipeline construction drawings, where the geometric model includes a soil model and a pipeline model; S02: Use free meshing and swept meshing methods to divide the soil model and pipeline model; S03: Apply gravity load to the geometric model and apply soil slip parameters to the measuring points according to the test results of the pipeline stress detection method; S04: Draw pipeline stress cloud map and pipeline displacement cloud map according to the simulated structure of S03; S05: Use polar coordinates to calculate the influence of internal pressure on pipeline stress, simplify pipeline stress into plane strain, obtain pipeline axial stress analysis formula, and use this stress analysis formula to calculate stress and establish an analysis model; S06: For the analysis model, different uniformly distributed pressures are applied to the inner wall of the pipeline in the model to obtain a pipeline stress cloud map; S07: The relationship between pipeline surface stress and pipeline internal pressure is obtained through finite element simulation analysis.

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