Method for calculating reliability of buried PE (Poly Ethylene) pipeline

Abstract

The invention discloses a buried PE pipeline reliability calculation method, belongs to the field of pipeline safety calculation, and aims at solving the problem that an existing pipeline reliability calculation method is single in evaluation condition and improving the reliability calculation accuracy. Calculating the circumferential stress reliability P1 according to the vertical additional stress and the circumferential additional stress; the axial stress reliability P2 is calculated by considering the factors of the burial depth and the pipe diameter; and obtaining the reliability P0 of the pipeline according to the reliability P1 of the circumferential stress and the reliability P2 of the axial stress. According to the method, the stress response of the buried pipeline is obtained under the condition that the large load F is applied above the soil and the burial depth and the pipe diameter of the pipeline are comprehensively considered, the consideration is more comprehensive, the operation safety and reliability calculation of the buried pipeline is more accurate, and safety evaluation guidance suggestions can be more accurately and effectively proposed. Moreover, the adopted calculation index large load F, the measurement and acquisition of the burial depth and the pipe diameter of the pipeline are relatively easy, the acquisition time is short, and the reliable calculation can be quickly carried out.

Description

Technical Field

[0001] The invention relates to the field of pipeline safety calculation, and in particular to a method for calculating the reliability of a buried PE pipeline. Background Art

[0002] As an effective means of oil and gas transportation, pipelines play an important role in modern production and people's lives, and have become the primary mode of land transportation. Buried pipelines account for a large proportion of pipeline transportation due to their advantages such as stability and efficiency. However, buried pipelines are widely distributed, and the natural conditions and geological environment along the route are complex and diverse, and they are inevitably subject to various threats and infringements.

[0003] For example, the continuous increase of tall buildings, coupled with the impact of transportation facilities such as railways and bridges and transportation loads, has increased the large surface loads, which have become an important factor affecting the safety of oil and gas pipelines. Therefore, it is necessary to determine a fast and effective technology to analyze the probability of pipeline structure failure, that is, to conduct reliability analysis of buried pipelines under the condition of fully considering the interaction between pipes and soil and the combined effect of external loads.

[0004] At present, most of the buried pipeline reliability calculation methods focus on estimating the circumferential damage of pipeline defects, such as the invention patent application with application number CN2017107077898, entitled A method for safety detection of buried pipeline structures and a method for safety evaluation of buried pipeline structures. It discloses that the vertical displacement and horizontal displacement of the detection point of the buried pipeline are used as forced displacement boundary conditions, and the internal force of the buried pipeline is calculated by finite element analysis. Multiple measurements are made to determine the coefficient of variation of the internal force, thereby calculating the safety reliability of the buried pipeline. The evaluation index is the soil stiffness on the pipe side, which is directly reflected in the deformation of the buried pipeline. Therefore, the prior art mainly considers the circumferential deformation of the buried pipeline, and does not consider the axial damage of the pipeline. Although it is reasonable to use only circumferential damage in some cases, the collapse assessment of actual defects is affected by three-dimensional growth. Therefore, the prior art cannot accurately explain the geometric changes of defects.

[0005] Another example is the invention patent application with application number CN2019111175233, entitled Method for Safety Assessment of Buried Pipelines and Related Equipment, which discloses the establishment of a three-dimensional nonlinear finite element model of a buried pipeline including an erosion pit, the finite element analysis is performed, the pipeline stress of the buried pipeline is obtained, and the structural reliability of the buried pipeline is obtained. The three-dimensional nonlinear finite element model of the pipe-soil includes erosion pits; a training set is established according to the corresponding relationship between pipeline stress influencing parameters and pipeline stress pairs under different working conditions, wherein a finite element simulation analysis is performed according to the pipeline stress influencing parameters and the three-dimensional nonlinear finite element model of the pipe-soil to obtain the pipeline stress of the buried pipeline, and the pipeline stress influencing parameters include erosion pit parameters; the training set is used to perform network training to obtain a pipeline stress prediction model; the structural reliability of the buried pipeline is obtained according to the pipeline stress prediction model core and the pipeline structure reliability technical algorithm. When the pipeline structure reliability calculation algorithm is the Monte Carlo method, it is necessary to first establish the pipeline limit state equation, that is, the calculation equation for the bearing stress of the buried pipeline. After determining the ultimate strength of the buried pipeline, for pipelines subjected to various loads under the influence of erosion pits, the safety factor is an important indicator for judging whether the pipeline is reliable or not. When the pipeline stress exceeds the ultimate strength of the pipeline, the pipeline is judged to be failed. In the embodiment of the present invention, the longitudinal stress of the pipeline is taken as an example. When the longitudinal stress of the pipeline exceeds the ultimate strength of the pipeline, the pipeline is judged to be failed. Let X1, X2, ..., Xn be n random variables affecting the reliability of the pipeline structure (i.e., pipeline stress influencing parameters), for example, random variables X1, X2, ..., Xn are the geometric dimensions of the pipeline, soil characteristic parameters, external environmental factors, etc.

[0006] Z=σ s -σ(X1,X2,…Xn),

[0007] Where: s is the ultimate strength of the pipeline, and σ(X1,X2,…Xn) is the longitudinal stress of the pipeline under the action of random variables.

[0008] When Z>0, the structure of the buried pipeline has the specified function, that is, it is in a reliable state;

[0009] When Z < 0, the structure of the buried pipeline loses its specified function, that is, it is in a failure state;

[0010] When Z=0, the structure of the buried pipeline is in a critical state or a limit state.

[0011] It predicts the longitudinal stress of the pipeline and does not consider the annular damage of the pipeline.

[0012] In summary, the existing reliability assessment methods and conditions for buried oil and gas pipelines are single. As an important underground project in oil and gas storage and transportation, the buried pipeline structure needs to reduce the possibility of failure and damage, and the accuracy of reliability calculation is particularly important. Summary of the invention

[0013] The purpose of the present invention is to provide a buried PE pipeline reliability calculation method, which fully considers the interaction between pipe and soil and the combined effect of external loads to perform reliability calculation on PE pipelines, solves the problem of single evaluation conditions in existing pipeline reliability calculation methods, and improves the accuracy of reliability calculation.

[0014] The technical solution adopted by the present invention is: a method for calculating the reliability of buried PE pipelines, calculating the hoop stress reliability P1 according to the vertical additional stress and the hoop additional stress; calculating the axial stress reliability P2 by considering the burial depth and the pipe diameter factors; and obtaining the pipeline reliability P0 according to the hoop stress reliability P1 and the axial stress reliability P2.

[0015] Furthermore, the pipeline reliability P0 is taken as:

[0016] When P1>0, P2>0, and P1>P2, P0=P2;

[0017] When P1>0, P2>0, and P1<P2, P0=P1;

[0018] When P1≤0, P0=0;

[0019] When P2≤0, P0=0.

[0020] Furthermore, the calculation process of the hoop stress reliability P1 is:

[0021] First, the vertical additional stress and the hoop additional stress are calculated; then, the hoop stress reliability is calculated;

[0022] The calculation process of axial stress reliability P1 is:

[0023] First, calculate the vertical load on the pipeline;

[0024] Next, calculate the pipe bending moment;

[0025] Then, calculate the maximum bending moment of the pipeline;

[0026] Next, calculate the maximum axial stress in the pipe;

[0027] Finally, the axial stress reliability is calculated.

[0028] Furthermore, the specific process of calculating the vertical additional stress and the hoop additional stress is as follows:

[0029] First, a spatial rectangular coordinate system is established with the load action point as the origin, the axial direction of the pipeline as the x-axis, and the positive direction of the z-axis perpendicular to the pipeline and vertically downward as the positive direction;

[0030] Next, the ground load acting on the surface is taken as F, and the additional load of the pipeline is taken as the additional stress in the soil at the corresponding position; the foundation is defined as a semi-infinite elastic body, and the vertical additional stress σ of the buried pipeline is calculated h and the additional hoop stress σ c ;

[0031] Vertical additional stressσ h for:

[0032]

[0033] Where R is the distance from any point to the load application point.

[0034] Additional hoop stressσ c for:

[0035]

[0036] Where n is the number of soil layers; r i is the bulk density of the soil in the i-th layer. i is the thickness of the i-th soil layer.

[0037] Furthermore, the hoop stress reliability P1 is:

[0038]

[0039] Among them, σ a Take the annular pressure when the minimum failure time of the pipeline hydrostatic compaction is 1000h.

[0040] Furthermore, the specific calculation process of the pipeline vertical load is:

[0041] First, ignoring the influence of soil changes on pipeline stress, considering the factors of burial depth and pipe diameter, the vertical load on the pipeline under the action of ground load F acting on the surface is calculated as:

[0042]

[0043] Among them, h is the burial depth, F is the ground load acting on the surface, and D is the pipe diameter;

[0044] Then, by analyzing formula (4), the x-coordinate of the maximum vertical load on the pipeline is obtained as:

[0045]

[0046] Among them, W y The maximum vertical load on the pipeline.

[0047] Furthermore, the axial failure of the pipeline is considered when the pipeline is subjected to stress, and the bending moment of the pipeline is obtained as:

[0048]

[0049] Among them, β is the foundation characteristic coefficient, E P is the elastic coefficient of the pipe, and I is the moment of inertia. s is the elastic coefficient of foundation soil; F p The radial force acting on the pipe.

[0050] Furthermore, the process of obtaining the maximum bending moment of the pipeline is as follows:

[0051] First, calculate the load distribution range L on the pipeline as:

[0052]

[0053] Where θ is the stress diffusion angle;

[0054] Next, the pipe is regarded as a beam. Assuming that the length of the beam tends to be infinite, and the load distribution range on the beam is small, the distributed load on the pipe surface can be integrated and regarded as a concentrated load for calculation, that is:

[0055]

[0056] Finally, substitute the x coordinate of the maximum vertical load on the pipeline obtained from formula (5) into (8) to obtain P, and let F p =P, the maximum bending moment is:

[0057]

[0058] Furthermore, the maximum axial stress of the pipeline is:

[0059]

[0060] Furthermore, the axial stress reliability is:

[0061]

[0062] Among them, σ b Take the tensile yield strength of the material.

[0063] The invention has the following beneficial effects: the buried PE pipeline reliability calculation method disclosed in the invention comprehensively considers the reliability calculation of the buried pipeline under the external load effect and the pipe-soil interaction, obtains the buried pipeline stress response under the large load F applied above the soil and the pipeline burial depth and pipe diameter, and considers more comprehensively, so that the buried pipeline operation safety reliability calculation is more accurate, and is more conducive to accurately and effectively proposing safety evaluation guidance suggestions. Moreover, the measurement and acquisition of the calculation indicators large load F, pipeline burial depth and pipe diameter adopted by the invention are relatively easy, and the acquisition time is short, which is more conducive to quickly making reliability calculations. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a flow chart of the first implementation method of the buried PE pipeline reliability calculation method disclosed in the present invention. DETAILED DESCRIPTION

[0065] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0066] The invention discloses a method for calculating the reliability of a buried PE pipeline. The method calculates the hoop stress reliability P1 according to the vertical additional stress and the hoop stress; calculates the axial stress reliability P2 by considering the buried depth and the pipe diameter; and obtains the pipeline reliability P0 according to the hoop stress reliability P1 and the axial stress reliability P2.

[0067] In specific implementation, the hoop stress reliability P1 can be calculated before the axial stress reliability, and the reliability P0 can be determined last. Of course, the hoop stress reliability P1 can also be calculated after the axial stress reliability, and the reliability P0 can be determined last.

[0068] That is, you can proceed according to the first step below:

[0069] Step 1: Calculation of vertical additional stress and hoop additional stress

[0070] Step 2: Calculation of hoop stress reliability;

[0071] Step 3: Calculate the vertical load of the pipeline;

[0072] Step 4: Calculate the pipe bending moment;

[0073] Step 5: Calculate the maximum bending moment of the pipeline;

[0074] Step 6: Calculate the maximum axial stress of the pipeline;

[0075] Step 7: Calculation of axial stress reliability;

[0076] Step 8: Reliability determination.

[0077] You can also follow the second step below:

[0078] Step 1: Calculate the vertical load of the pipeline;

[0079] Step 2: Calculate the pipe bending moment;

[0080] Step 3: Calculate the maximum bending moment of the pipeline;

[0081] Step 4: Calculate the maximum axial stress of the pipeline;

[0082] Step 5: Calculation of axial stress reliability;

[0083] Step 6: Calculation of vertical additional stress and annular additional stress

[0084] Step 7: Calculation of hoop stress reliability;

[0085] Step 8: Reliability determination.

[0086] Attached Figure 1 A flowchart showing the first step is shown.

[0087] Specifically, the specific process of calculating vertical additional stress and hoop additional stress is:

[0088] First, a spatial rectangular coordinate system is established with the load point as the origin, the axial direction of the pipeline as the x-axis, and the z-axis perpendicular to the pipeline and vertically downward as the positive direction;

[0089] Next, the ground load acting on the surface is taken as F, and the additional load of the pipeline is taken as the additional stress in the soil at the corresponding position; the foundation is defined as a semi-infinite elastic body, and the vertical additional stress σ of the buried pipeline is calculated h and the additional hoop stress σ c ;

[0090] Vertical additional stressσ h for:

[0091]

[0092] Where R is the distance from any point to the load application point.

[0093] Additional hoop stressσ c for:

[0094]

[0095] Where n is the number of soil layers; r i is the bulk density of the soil in the i-th layer. i is the thickness of the i-th soil layer.

[0096] The hoop stress reliability P1 is:

[0097]

[0098] Among them, σ a Take the annular pressure when the minimum failure time of the pipeline hydrostatic compaction is 1000h.

[0099] The specific calculation process of pipeline vertical load is as follows:

[0100] First, ignoring the influence of soil changes on pipeline stress, considering the factors of burial depth and pipe diameter, the vertical load on the pipeline under the action of ground load F acting on the surface is calculated as:

[0101]

[0102] Among them, h is the burial depth, F is the ground load acting on the surface, and D is the pipe diameter;

[0103] Then, by analyzing formula (4), the x-coordinate of the maximum vertical load on the pipeline is obtained as:

[0104]

[0105] Among them, W y The maximum vertical load on the pipeline.

[0106] Considering the axial failure of the pipeline under stress, the bending moment of the pipeline is obtained as:

[0107]

[0108] Among them, β is the foundation characteristic coefficient, E P is the elastic coefficient of the pipe, and I is the moment of inertia. s is the elastic coefficient of foundation soil; F p The radial force acting on the pipe.

[0109] The process of obtaining the maximum bending moment of the pipeline is as follows:

[0110] First, calculate the load distribution range L on the pipeline as:

[0111]

[0112] Where θ is the stress diffusion angle;

[0113] Next, the pipe is regarded as a beam. Assuming that the length of the beam tends to be infinite, and the load distribution range on the beam is small, the distributed load on the pipe surface can be integrated and regarded as a concentrated load for calculation, that is:

[0114]

[0115] Finally, substitute the x-coordinate of the maximum vertical load on the pipeline obtained from formula (5) into (8) to obtain P, let Fp = P, and the maximum bending moment is obtained as:

[0116]

[0117] The maximum axial stress of the pipeline is:

[0118]

[0119] The axial stress reliability is:

[0120]

[0121] Among them, σ b Take the tensile yield strength of the material.

[0122] Since the reliability values ​​calculated by P1 and P2 are different, they are selected in the following two ways:

[0123] (1) If P1>0, P2>0, and P1>P2, then P0=P2;

[0124] (2) If P1>0, P2>0, and P1<P2, then P0=P1;

[0125] (3) If P1≤0, then P0=0;

[0126] (4)If P2≤0, then P0=0.

[0127] The buried PE pipeline reliability calculation method disclosed in the present invention comprehensively considers the reliability calculation of the buried pipeline under the external load effect and the pipe-soil interaction, obtains the stress response of the buried pipeline under the large load F applied above the soil and the pipeline burial depth and pipe diameter, and considers more comprehensively, so that the calculation of the safety and reliability of the operation of the buried pipeline is more accurate, and is more conducive to accurately and effectively proposing safety evaluation guidance suggestions. Moreover, the measurement and acquisition of the calculation indicators large load F, pipeline burial depth and pipe diameter adopted by the method are relatively easy, and the acquisition time is short, which is more conducive to quickly making reliability calculations.

Claims

1. The reliability calculation method of buried PE pipeline is characterized by: The hoop stress reliability P1 is calculated based on the vertical additional stress and the hoop additional stress. The axial stress reliability P2 is calculated considering the burial depth and pipe diameter factors. The pipeline reliability P0 is obtained based on the hoop stress reliability P1 and the axial stress reliability P2.

2. The method for calculating the reliability of a buried PE pipeline according to claim 1, characterized in that: The pipeline reliability P0 value is: When P1>0, P2>0, and P1>P2, P0=P2; When P1>0, P2>0, and P1<P2, P0=P1; When P1≤0, P0=0; When P2≤0, P0=0.

3. The method for calculating the reliability of buried PE pipeline according to claim 1 or 2, characterized in that: The calculation process of hoop stress reliability P1 is: First, the vertical additional stress and the hoop additional stress are calculated; then, the hoop stress reliability is calculated; The calculation process of axial stress reliability P1 is: First, calculate the vertical load on the pipeline; Next, calculate the pipe bending moment; Then, calculate the maximum bending moment of the pipeline; Next, calculate the maximum axial stress in the pipe; Finally, the axial stress reliability is calculated.

4. The method for calculating the reliability of buried PE pipeline according to claim 3, characterized in that: The specific process of calculating vertical additional stress and hoop additional stress is: First, a spatial rectangular coordinate system is established with the load action point as the origin, the axial direction of the pipeline as the x-axis, and the positive direction of the z-axis perpendicular to the pipeline and vertically downward as the positive direction; Next, the ground load acting on the surface is taken as F, and the additional load of the pipeline is taken as the additional stress in the soil at the corresponding position; the foundation is defined as a semi-infinite elastic body, and the vertical additional stress σ of the buried pipeline is calculated h and the additional hoop stress σ c ; Vertical additional stressσ h for: Where R is the distance from any point to the load application point. Additional hoop stressσ c for: Where n is the number of soil layers; r i is the soil bulk density of the i-th layer. i is the thickness of the i-th soil layer.

5. The method for calculating the reliability of buried PE pipeline according to claim 4, characterized in that: The hoop stress reliability P1 is: Among them, σ a Take the annular pressure when the minimum failure time of the pipeline hydrostatic compaction is 1000h.

6. The method for calculating the reliability of buried PE pipeline according to any one of claims 3 to 5, characterized in that: The specific calculation process of pipeline vertical load is as follows: First, ignoring the influence of soil changes on pipeline stress, considering the factors of burial depth and pipe diameter, the vertical load on the pipeline under the action of ground load F acting on the surface is calculated as: Among them, h is the burial depth, F is the ground load acting on the surface, and D is the pipe diameter; Then, by analyzing formula (4), the x-coordinate of the maximum vertical load on the pipeline is obtained as: Where Wy is the maximum vertical load on the pipeline.

7. The method for calculating the reliability of buried PE pipeline according to claim 6, characterized in that: Considering the axial failure of the pipeline under stress, the bending moment of the pipeline is obtained as: Among them, β is the foundation characteristic coefficient, E P is the elastic coefficient of the pipe, and I is the moment of inertia. s is the elastic coefficient of foundation soil; F p The radial force acting on the pipe.

8. The method for calculating the reliability of buried PE pipeline according to claim 7, characterized in that: The process of obtaining the maximum bending moment of the pipeline is as follows: First, calculate the load distribution range L on the pipeline as: Where θ is the stress diffusion angle; Next, the pipe is regarded as a beam. Assuming that the length of the beam tends to be infinite, and the load distribution range on the beam is small, the distributed load on the pipe surface can be integrated and regarded as a concentrated load for calculation, that is: Finally, substitute the x-coordinate of the maximum vertical load on the pipeline obtained from formula (5) into (8) to obtain P, let Fp = P, and the maximum bending moment is obtained as: Among them, M max is the maximum bending moment.

9. The method for calculating the reliability of buried PE pipeline according to claim 8, characterized in that: The maximum axial stress of the pipeline is: Where D is the pipe diameter and I is the moment of inertia.

10. The method for calculating the reliability of buried PE pipeline according to claim 9, characterized in that: The axial stress reliability is: Among them, σ b Take the tensile yield strength of the material.

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