Pipeline stress detection method and stress simulation calculation method

Abstract

Pipeline stress detection method and stress simulation calculation method, including S1: selecting several measuring points on the circumference of a cross section of the pipeline outer wall; S2: polishing the pipeline outer wall measuring point until the pipeline body appears; S3: placing the prefabricated X65 pipeline steel specimen near the pipeline, placing the ultrasonic transducer probe on the zero stress specimen, and obtaining the sound time and temperature under zero stress; S4: coupling the ultrasonic transducer probe to the pipeline body measuring point along the axis, obtaining the stress of the pipeline outer wall at four positions; S5: according to the ultimate mechanical parameters of the pipe and the pipeline design standard, the tension and compression force state, the bending degree and the safety factor during work of the pipeline measuring point are given; combining the stress detection method and the simulation calculation method, the pipeline is detected, the simulation model is established and the stress is calculated through a simple method, the safety analysis result of the pipeline can be accurately obtained without affecting the safety of the pipeline, which has important significance in the field of geological exploration.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, and more specifically to pipeline stress detection methods and stress simulation calculation methods. Background Technology

[0002] A landslide is a natural phenomenon in which soil or rock masses on a slope slide downhill, either as a whole or in parts, under the influence of gravity, due to factors such as river erosion, groundwater activity, rainwater soaking, earthquakes, and artificial slope cutting. The moving rock (soil) mass is called a displaced body or sliding body, while the underlying rock (soil) mass that has not moved is called a sliding bed. Landslides have a significant impact on natural gas pipelines buried in the soil.

[0003] Existing theories indicate that pipelines laid along hillsides, either from high to low or low to high, can experience rapid collapses when the hillside's equilibrium is disrupted, particularly when the slope is infiltrated by groundwater or rainwater. This phenomenon can occur during construction or operation. Pipelines in the collapse are subjected to the force of the collapsing soil and slide down along with it. The upper half of the pipeline on the longitudinal slope is under tension, while the lower half is under compression, with maximum tensile stress at the top and maximum compressive stress at the bottom. In severe landslides, pipelines on the upper slope are at risk of breakage, while those on the lower slope are prone to corrugated deformation and crushing. After a landslide, it is necessary to inspect the dangerous weld joints of the collapsed pipeline section to mitigate risks in advance; however, current technology lacks a convenient and limited detection method or stress calculation method. Summary of the Invention

[0004] One advantage of this invention is that it provides a pipeline stress detection method and a stress simulation calculation method. By combining stress detection and simulation calculation methods, the pipeline can be detected, a simulation model can be established, and stress calculation can be performed in a simple way. This allows for accurate pipeline safety analysis results without affecting pipeline safety, which is of great significance in the field of geological exploration.

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

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

[0007] S2: Grind the measuring points on the outer wall of the pipe until the pipe body is exposed;

[0008] S3: Place the prefabricated X65 pipe steel specimen on the pipe near the measuring point. Based on the temperature difference between the pipe and the environment, after a few minutes, place the ultrasonic transducer probe on the zero-stress specimen and place 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: Couple the ultrasonic transducer probe along the axis to the measuring point on the pipe body. The ultrasonic tester can read the acoustic time and temperature of the pipe body. Using the X65 stress coefficient database obtained from the calibration, interpolate to calculate and select the stress coefficient of X65 steel at the corresponding temperature. Based on the temperature difference between the calibration temperature and the pipe body temperature, the current pipe stress can be quickly calculated using the temperature influence coefficient. By analogy, the stress at four locations on the outer wall of the pipe can be obtained.

[0010] S5: Based on the ultimate mechanical parameters of the pipe and the pipe design standards, provide the tensile and compressive state, degree of bending, and safety factor during operation at the pipe measurement point;

[0011] The method for detecting pipeline stress described above includes a detection device comprising a low-power processor, and electrically connected thereto 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, wherein the LCR wave transducer is electrically connected to the ultrasonic transmitting module and the ultrasonic receiving module.

[0012] According to one 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 one 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 housing, and an plexiglass wedge, an excitation transducer and a receiving transducer are disposed inside the housing. The excitation electrical signal is converted into an ultrasonic signal by the excitation transducer. The ultrasonic signal is transmitted to the measured medium and is refracted. 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 methods are applied to pipeline stress detection methods, including

[0016] S01: Establish a geometric model based on the actual site conditions and pipeline construction drawings. The geometric model includes a soil model and a pipeline model.

[0017] S02: The soil model and pipe model are divided using free mesh generation and swept mesh generation methods;

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

[0019] S04: Based on the simulated structure in S03, draw the pipe stress cloud diagram and the pipe displacement cloud diagram;

[0020] S05: The influence of internal pressure on pipeline stress is calculated using polar coordinates. The pipeline stress is simplified to plane strain, and the pipeline axial stress analysis formula is obtained. The stress analysis formula is used to calculate stress and establish an analysis model.

[0021] S06: For the analysis model, apply different uniformly distributed pressures to the inner wall of the pipe in the model to obtain the pipe stress cloud diagram;

[0022] S07: The simulation results of the relationship between the surface stress and internal pressure of the pipeline are obtained through finite element simulation analysis. Attached Figure Description

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

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

[0025] Figure 3 This is a schematic diagram showing the location of the pipeline measuring points in this invention;

[0026] Figure 4 This is a schematic diagram illustrating the selection of equal wall thickness measuring points in this invention;

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

[0028] Figure 6 This is a schematic diagram of the stress measurement results at various points in this invention;

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

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

[0031] Figure 9 This is a pipeline stress cloud diagram for the present invention;

[0032] Figure 10 This is a pipeline displacement cloud diagram for the present invention;

[0033] Figure 11 This is a schematic diagram of the polar coordinate solution of the present invention;

[0034] Figure 12 This is a diagram showing the internal pressure changes and pipeline stress safety levels of this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the following description will be provided in conjunction with the appendix of this invention. Figure 1 ~Attached Figure 12 The present invention will be described in more detail below.

[0036] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0037] Those skilled in the art should understand that, in the disclosure of this specification, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They 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, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting the present invention.

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

[0039] The present invention provides a method for detecting pipeline stress, including...

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

[0041] S2: Grind the measuring points on the outer wall of the pipe until the pipe body is exposed;

[0042] S3: Place the prefabricated X65 pipe steel specimen on the pipe near the measuring point. Based on the temperature difference between the pipe and the environment, after a few minutes, place the ultrasonic transducer probe on the zero-stress specimen and place 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: Couple the ultrasonic transducer probe along the axis to the measuring point on the pipe body. The ultrasonic tester can read the acoustic time and temperature of the pipe body. Using the X65 stress coefficient database obtained from the calibration, interpolate to calculate and select the stress coefficient of X65 steel at the corresponding temperature. Based on the temperature difference between the calibration temperature and the pipe body temperature, the current pipe stress can be quickly calculated using the temperature influence coefficient. By analogy, the stress at four locations on the outer wall of the pipe can be obtained.

[0044] S5: Based on the ultimate mechanical parameters of the pipe and the pipe design standards, provide the tensile and compressive state, degree of bending, and safety factor during operation at the pipe measurement point;

[0045] The method for detecting pipeline stress described above includes a detection device comprising a low-power processor and electrically connected to it an LCD 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. The LCR wave transducer is electrically connected to the ultrasonic transmitting module and the ultrasonic receiving module. In step S1, the circumference of the measuring point is 10-30 cm away from the weld. In step S3, the placement time is 1-5 minutes. The LCR transducer includes a housing, inside which are arranged an organic glass wedge, an excitation transducer, and a receiving transducer. The excitation electrical signal is converted into an ultrasonic signal by the excitation transducer. The ultrasonic signal is refracted at the medium being measured, and the LCR wave propagates along the surface of the medium being measured and is received by the receiving transducer and converted into an electrical signal.

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

[0047] S01: Establish a geometric model based on the actual site conditions and pipeline construction drawings. The geometric model includes a soil model and a pipeline model.

[0048] S02: The soil model and pipe model are divided using free mesh generation and swept mesh generation methods;

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

[0050] S04: Based on the simulated structure in S03, draw the pipe stress cloud diagram and the pipe displacement cloud diagram;

[0051] S05: The influence of internal pressure on pipeline stress is calculated using polar coordinates. The pipeline stress is simplified to plane strain, and the pipeline axial stress analysis formula is obtained. The stress analysis formula is used to calculate stress and establish an analysis model.

[0052] S06: For the analysis model, apply different uniformly distributed pressures to the inner wall of the pipe in the model to obtain the pipe stress cloud diagram;

[0053] S07: The simulation results of the relationship between the surface stress and internal pressure of the pipeline are 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 help managers quickly determine the current tensile and compressive state of the pipeline. By calculating the safety factor through the accurate measured stress value, it can help 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 a plane wave parallel to the stress loading direction and the stress is shown in equation (1-1).

[0057]

[0058] In the formula: V 11 Let ρ be the longitudinal wave velocity (referred to as parallel stress wave velocity) propagating parallel to the stress loading direction, in m / s; ρ0 is the density of the material at zero stress; λ and μ are the second-order elastic moduli of the material; l, m, and n are the third-order elastic moduli of the material, respectively.

[0059] Further differentiating and simplifying equation (1-1), we obtain equation (2-2):

[0060] Δσ=K(t-t0)=KΔt (1-2)

[0061] In the formula:

[0062] Δσ is the change in pipe stress; K is the stress coefficient of the material, which is a specific constant for each material; t and t0 represent the flight time of the ultrasonic wave under stress and zero stress conditions, respectively; t is the change in the flight time of the sound wave in the material relative to the zero stress condition.

[0063] As can be seen from equation (1-2), the current stress value of a 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 principles of acoustoelasticity and the linear relationship between stress and LCR wave flight time, a device specifically designed for measuring stress in oil and gas pipelines under operating conditions has been independently developed. This device integrates a low-power processor, an ultrasonic transmitting module, an ultrasonic receiving module, a time measurement circuit module, a temperature measurement module, an LCD display and interaction module, and a power management module. Applicable to various operating conditions, this device performs non-destructive measurement of pipeline surface stress, achieving a time measurement accuracy of 0.1 ns and a stress measurement error of ±10 MPa, directly providing engineers with the pipeline stress magnitude they are most concerned with.

[0065] Measuring pipeline stress using an ultrasonic stress measurement device requires coupling an ultrasonic transducer to the pipeline surface. Based on the study of LCR wave generation, a transducer was independently designed, consisting of an excitation transducer, a receiving transducer, and an acrylic wedge. The acoustic path L is fixed at 35 mm, L1 = 6 mm, and the critical refraction angle θ... 0The angle is 28°, the transducer frequency is 5MHz, and its measurement depth in the specimen is approximately 1.66mm, which can be equivalently measured by drilling. The excitation electrical signal is converted into an ultrasonic signal by the excitation transducer. The ultrasonic signal is refracted at the measured medium, and 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 acquisition unit.

[0066] The testing steps include:

[0067] A working space of at least 0.8m should be excavated at the bottom of the pipe to facilitate grinding and measurement. The specific steps are as follows:

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

[0069] (2) On-site grinding of measuring points. In ultrasonic measurement, coupling quality directly affects the reliability of measurement data. Therefore, the team conducted extensive indoor experiments and selected a belt sander as the final grinding device for measuring points. Through grinding experiments with sanders of different grit sizes, an on-site grinding process for pipe measuring points was proposed, which effectively ensured flatness and surface smoothness. The insulation layer in the measuring point area was removed, and the belt sander was used to grind along the pipe axis for about 4 minutes until the silvery-white pipe body appeared.

[0070] (3) Zero-stress specimen calibration. Place the prefabricated X65 pipe steel specimen on the pipe near the measuring point. After 1 to 5 minutes, based on the temperature difference between the pipe and the environment, place the ultrasonic transducer (probe) on the zero-stress specimen and place 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.

[0071] (4) Pipeline stress measurement. The ultrasonic transducer (probe) is coupled to the measuring point on the pipeline body along the axis. The ultrasonic tester can read the acoustic time and temperature of the pipeline body. Using the X65 stress coefficient database obtained by calibration, the stress coefficient of X65 steel at the corresponding temperature is interpolated and selected. Based on the temperature difference between the calibration temperature and the pipeline body temperature, the current pipeline stress is quickly calculated by 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. Based on the ultimate mechanical parameters of the pipe material and the pipeline design standards, the tensile and compressive states, bending degree, and safety factor during operation at the pipe measurement points are directly provided, and a safety assessment is quickly given. Pipelines laid along hillsides from high to low or low to high can cause rapid collapse of large amounts of soil when the balance of the hillside is disrupted, especially when the hillside is soaked by groundwater or rainwater. This phenomenon occurs both during construction and operation. Pipelines in the collapse are subjected to the downward force of the soil and slide down with the soil.

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

[0074] No axial deformation occurs in the middle of the pipeline, meaning the stress at this point is zero. On the longitudinal slope, the upper half of the pipeline is under tension, and the lower half 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). In severe landslides, the pipeline at the top of the slope is at risk of breakage, while the pipeline at the bottom is prone to corrugated deformation and collapse.

[0075] Based on the above analysis, such as Figure 3 A total of six measuring points were selected, including four weld seams and two straight pipe sections. The weld seams measured were the four weld seams most affected by the landslide: the weld seam at the top of the slope; the first and second weld seams descending from the top of the slope; and the first weld seam at the bottom of the slope. The straight pipe sections were located on the upper side of the retaining wall at the bottom of the slope and on the other side of the dirt road at the bottom of the slope. By measuring these six locations and combining the results with simulation calculations, the location and severity of the most dangerous points on the pipeline were determined, providing a reliable reference 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] In the formula: [σ] is the allowable stress of the steel for oil and gas pipelines, MPa; F is the strength design coefficient.

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

[0080]

[0081] In the formula, max represents the maximum stress measured at each measuring point within the excavation pit, in MPa; f is the pipeline strength coefficient under the current operating condition. By comparing the current pipeline strength coefficient under real-time operating conditions with the allowable strength design coefficient for the corresponding safety level of the region, the current safety status of the pipeline can be quickly evaluated. According to the design drawings, this region is a level II region; therefore, when the measured stress is less than 350 MPa, the evaluation is passed.

[0082] Measurement results at each measuring point:

[0083] Measurement point ①:

[0084] The measurement should be performed according to the above plan. The surface anti-corrosion paint at the measuring points must be removed, the surface oxide layer cleaned, and the surface polished to a flat surface using a polishing machine. After calibration at ambient temperature, the measurement should be performed, and the online stress measurement results should be recorded in the statistical table.

[0085]

[0086] Measurement point ②:

[0087] The measurement should be performed according to the above plan. The surface anti-corrosion paint at the measuring points must be removed, the surface oxide layer cleaned, and the surface polished to a flat surface using a polishing machine. After calibration at ambient temperature, the measurement should be performed, and the online stress measurement results should be recorded in the statistical table.

[0088]

[0089] Measurement point ③:

[0090] The measurement should be performed according to the above plan. The surface anti-corrosion paint at the measuring points must be removed, the surface oxide layer cleaned, and the surface polished to a flat surface using a polishing machine. After calibration at ambient temperature, the measurement should be performed, and the online stress measurement results should be recorded in the statistical table.

[0091]

[0092] Measurement point ④:

[0093] The measurement should be performed according to the above plan. The surface anti-corrosion paint at the measuring points must be removed, the surface oxide layer cleaned, and the surface polished to a flat surface using a polishing machine. After calibration at ambient temperature, the measurement should be performed, and the online stress measurement results should be recorded in the statistical table.

[0094]

[0095]

[0096] Measurement point ⑤:

[0097] The measurement should be performed according to the above plan. The surface anti-corrosion paint at the measuring points must be removed, the surface oxide layer cleaned, and the surface polished to a flat surface using a polishing machine. After calibration at ambient temperature, the measurement should be performed, and the online stress measurement results should be recorded in the statistical table.

[0098]

[0099] Measurement point ⑥:

[0100] The measurement should be performed according to the above plan. The surface anti-corrosion paint at the measuring points must be removed, the surface oxide layer cleaned, and the surface polished to a flat surface using a polishing machine. After calibration at ambient temperature, the measurement should be performed, and the online stress measurement results should be recorded in the statistical table.

[0101]

[0102]

[0103] Analyzing the above measurement results, a total of 6 stress points were measured in this inspection, including 4 stress points near the circumferential weld and 2 stress points at the straight pipe. The statistical results are shown in the table below:

[0104]

[0105]

[0106] Plot the stress measurement results at each measuring point in the table into a curve, such as... Figure 6 As shown.

[0107] (1) The maximum stress value was measured to be 300 MPa, located at the 3-point direction of measuring point ①, which is 0.60 times the minimum yield strength of X65; it is known that the area where the pipeline was designed was a level II area, and the measured result meets the pipeline design requirements.

[0108] (2) At the pipeline slope bottom, measuring point ⑤ is subjected to compressive stress, while measuring points ①, ②, ③, and ⑥ are mainly subjected to tensile stress. This indicates that the soil near measuring points ③ to ⑤ collapses longitudinally along the pipeline direction, causing tension on the pipeline at this location and on the slope, while the pipeline at measuring point ⑤ at the slope bottom is subjected to compression. The terrain where the pipeline is located is relatively steep, and the soil thickness is uneven, with the soil layer being thicker closer to the slope bottom and thinner closer to the slope top. Under the influence of pipeline gravity and other forces, the soil gradually becomes denser, resulting in slow settlement and causing a slow landslide in the surrounding soil, ultimately leading to compression on the pipeline at the slope bottom and tension on the pipeline at the landslide site. At the same time, the soil collapse in the area near point ③ is also the main reason for the cracks appearing in the retaining wall at the slope bottom.

[0109] (3) The stress on both sides of the pipeline at the top of the slope (points 3 and 9) is uneven and there is a significant difference. At measuring point ②, the stress on the 3-point side is positive and the stress on the 9-point side is negative, indicating that the pipeline has bent and deformed towards the 3-point side due to a transverse landslide of the soil perpendicular to the pipeline direction.

[0110] Based on the on-site investigation and stress measurement of this section of pipeline, it can be concluded that:

[0111] (1) After the pipeline was modified, it 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 pressure. The maximum stress is 300 MPa at the top of the slope, which currently meets the pipeline safety level requirements.

[0112] (2) A slow longitudinal landslide occurred at the locations of measuring points ③ to ⑤, causing tension on the pipeline near measuring point ③ and compression on the pipeline at the bottom of the slope, resulting in longitudinal cracks in the retaining wall. The retaining wall at this location has been demolished and reconstructed.

[0113] (3) A transverse landslide occurred at the top of the slope at measuring point ②, which was perpendicular to the pipeline, causing the pipeline to bend and deform. Anchor blocks can be installed to restrain the transverse displacement of the pipeline and the soil.

[0114] (4) The area where this 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, measures should be taken in time to avoid the occurrence of disasters.

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

[0116] First, a geometric model needs to be established, which is the foundation for numerical analysis. However, the actual geometric model needs to be adjusted or simplified. This simulation fully considers the actual site conditions and pipeline construction drawings. While fully respecting the actual site conditions, the pipeline and soil have been simplified. In order to clearly show the stress and displacement distribution of the pipeline, the pipeline wall thickness is now uniformly set to 11.9mm. The soil is uniformly set to clay to establish the pipe-soil contact model. The material parameters are shown in the table below. All materials are homogeneous and isotropic.

[0117] Parameter name Parameter value Parameter name Parameter value Burial depth (m) 1-3 Soil expansion angle (°) 0 Pipe elastic modulus E (GPa) 210 Pipeline Poisson's ratio 0.3 Angle of friction within the soil (°) 25 soil-to-pipe friction coefficient 0.3 Pipe elastic modulus E (GPa) 0.11 Poisson's ratio of soil 0.25

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

[0119] Based on the actual dimensions in the engineering drawings, the 7.46° bend at the bottom of the landslide body is ignored. The length, direction, and bends of the remaining pipes are all established according to the actual engineering drawings. The soil model is simplified to a hillside with a total length of 150m, a maximum height of 50m, and a width of 20m. The 20m wide soil body is divided into three parts, with the middle 10m being the landslide body. No protective measures are set for the soil body in this model.

[0120] The pipeline model is as follows:

[0121] The pipe model has a diameter of 610mm. To facilitate the analysis of stress distribution in the landslide area, the wall thickness is uniformly set to 11.9mm. The total length of the pipe is 190m.

[0122] Meshing was performed using both free meshing and swept meshing methods. Due to the complexity of the soil model, a hybrid meshing method of 8-node hexahedral and 6-node tetrahedral elements was chosen. Hexahedral elements were used where there were no pipes on either side of the soil, while tetrahedral elements were used at the center of the soil where pipes were present.

[0123] There are one meshing method for solid elements: free meshing, mapped meshing, hybrid meshing, and swept meshing. In this model, the hexahedrons are meshed using swept meshing, and the monohedrons are meshed using free meshing, resulting in a total of 273,060 soil meshes.

[0124] The pipeline model is relatively regular and is entirely divided into six-sided swept meshes, with a total of 5818 pipeline meshes.

[0125] Set boundary conditions: apply gravity load to the model as a whole, the internal pressure of the pipe is 4.0 MPa, no constraints are applied at both ends of the pipe, and no constraints are applied to the soil except for the bottom surface which is fully constrained. Apply soil slip of a maximum of 0.6 m and a minimum of 0.2 m at slip surface ①, apply soil slip of a maximum of 0.4 m and a minimum of 0.2 m at slip surface ② and apply 0.2 m of lateral slip, and apply 0.4 m of soil slip at slip surface ③.

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

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

[0128] Based on the numerical simulation results, the axial displacement of the pipeline in the landslide section was analyzed. The pipeline displacement distribution is as follows: Figure 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 difference between the maximum and the minimum is 0.05m, and the overall pattern is the same as that observed by our research group.

[0129] Based on the geometric model established above, it can be seen that under the condition that the maximum landslide depth is 0.6m, the stress concentration in the pipeline is as follows: Figure 9 As shown in the figure, the lowest bend has the greatest stress. Under the boundary conditions of this model, the maximum stress in the pipeline occurs at stress concentration point 2, which is 350 MPa. The pipeline reaches 0.73 times the minimum yield strength, which is insufficient. If the maximum landslide depth is less than 0.6 m, the pipeline can be considered to have sufficient reserve strength.

[0130] The maximum displacement of the pipeline occurs when, for example Figure 9The stress concentration points shown are 0.1m in maximum. The fact that the maximum pipe displacement and the maximum stress occur at the same location indicates that this is the most dangerous part of the pipe, and more attention should be paid to this area in the future.

[0131] Based on the knowledge of elasticity, the relevant derivation of the circular tube structure is carried out. Considering the structural characteristics of the circular tube itself, polar coordinates are used for solution.

[0132] Based on the relationship between the Cartesian coordinate system and the polar coordinate system, we can obtain:

[0133]

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

[0135]

[0136] The equilibrium differential equations for the Cartesian coordinate system are:

[0137]

[0138] The relationship between the body force components in the Cartesian coordinate system and the polar coordinate system is as follows:

[0139]

[0140] Substituting the stress components and body force components into the equilibrium differential equations in the Cartesian coordinate system, we obtain the equilibrium differential equations in polar coordinates:

[0141]

[0142] For axisymmetric problems involving circular tubes and cylinders, the geometry and external loads of the components do not change with the polar angle, the stress distribution is independent of the polar angle, and the shear stress is zero. The stress function is only a function of the radius vector, and the biharmonic stress 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 are obtained from the stress function:

[0147]

[0148] The strain components are obtained as follows:

[0149]

[0150] The displacement components are obtained as follows:

[0151]

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

[0153] Consider a circular ring or cylinder with inner radius *a* and outer radius *b*, subjected to internal pressure *p*. Clearly, the stress distribution should be axisymmetric. Therefore, we take the stress component expression...

[0154]

[0155] Based on the boundary conditions, we can conclude that:

[0156]

[0157] From the stress component expression, it can be seen that the first two boundary conditions are satisfied, while the latter two boundary conditions need to be satisfied:

[0158]

[0159] Considering the single-valued condition of displacement, the displacement components under axisymmetric stress state,

[0160] In circumferential displacement u φ In the expression, One term has multiple values: for the same ρ value, such as ρ = ρ1, the circumferential displacement differs between φ = φ1 and φ = φ1 + 2π. This does not match the actual deformation of the circular tube, because (ρ1, φ1) and (ρ1, φ1+2π) are the same point and cannot have different displacements. Therefore, according to the single-valued displacement condition, B = 0.

[0161] Therefore, we can obtain

[0162]

[0163] Substituting A, B, and C into the expression for the stress components, we obtain the following solution.

[0164]

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

[0166]

[0167] Then there is

[0168]

[0169] Substituting equation (3-16) into equation (3-18) and simplifying, we obtain the axial stress of the pipe.

[0170]

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

[0172] Taking a pipe with a diameter of 610mm and a wall thickness of 11.9mm as an example, stress calculations can yield the following table showing the relationship between the circumferential stress on the pipe surface and the internal pressure:

[0173] Pipeline internal pressure (MPa) Circumferential 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 organizing the finite element simulation results, we can obtain the stress changes in the pipeline under different internal pressures, such as the statistical table of the relationship between pipeline surface stress and internal pressure simulation:

[0176]

[0177]

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

[0179] Theoretical and numerical analysis results show that for every 1 MPa increase in the gas pressure inside the pipe, the axial stress in the pipe increases by 7 MPa. Given that the current pipeline transport pressure was 4.5 MPa during the test, and the maximum measured axial stress was 300 MPa, this indicates that the soil around the pipe has shifted, imposing an additional load on 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 reserve 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 reserve 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 causes the surrounding soil to undergo slow landslides, ultimately resulting in the pipeline at the bottom of the slope being compressed and the pipeline at the landslide location 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 equal to 0.6 m, the pipeline stress is concentrated at the three elbows as shown in Figure 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 contemplated, where 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 a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-including system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can mean any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0186] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0187] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

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

[0189] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A method for detecting pipeline stress, characterized in that: include S1: Select several measuring points on a cross-sectional circumference of the outer wall of the pipe, leaving a distance of 10-30 cm between the measuring points and the weld. S2: Grind the measuring points on the outer wall of the pipe until the pipe body is exposed; S3: Place the prefabricated X65 pipe steel specimen on the pipe near the measuring point. Based on the temperature difference between the pipe and the environment, after a few minutes, place the ultrasonic transducer probe on the zero-stress specimen and place 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: Couple the ultrasonic transducer probe along the axis to the measuring point on the pipe body. The ultrasonic tester can read the acoustic time and temperature of the pipe body. Using the X65 stress coefficient database obtained from the calibration, interpolate to calculate and select the stress coefficient of X65 steel at the corresponding temperature. Based on the temperature difference between the calibration temperature and the pipe body temperature, the current pipe stress can be quickly calculated using the temperature influence coefficient. By analogy, the stress at four locations on the outer wall of the pipe can be obtained. S5: Based on the ultimate mechanical parameters of the pipe and the pipe design standards, provide the tensile and compressive state, degree of bending, and safety factor during operation at the pipe measurement point; The application of the above-mentioned pipeline stress detection method includes a detection device, comprising a low-power processor, and electrically connected thereto 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, 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 S3, the placement time is 1 to 5 minutes.

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

4. A stress simulation calculation method, applied to the pipeline stress detection method according to any one of claims 1 to 3, characterized in that: include S01: Establish a geometric model based on the actual site conditions and pipeline construction drawings. The geometric model includes a soil model and a pipeline model. S02: The soil model and pipe model are divided using free mesh generation and swept mesh generation methods; S03: Apply gravity load to the geometric model, and apply soil slip parameters to the measuring points based on the test results of the pipeline stress detection method; S04: Based on the simulated structure in S03, draw the pipe stress cloud diagram and the pipe displacement cloud diagram; S05: The influence of internal pressure on pipeline stress is calculated using polar coordinates. The pipeline stress is simplified to plane strain, and the pipeline axial stress analysis formula is obtained. The stress analysis formula is used to calculate stress and establish an analysis model. S06: For the analysis model, apply different uniformly distributed pressures to the inner wall of the pipe in the model to obtain the pipe stress cloud diagram; S07: The simulation results of the relationship between the surface stress and internal pressure of the pipeline are obtained through finite element simulation analysis.

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