Natural gas pipeline corrosion earthquake probability analysis method considering soil parameter random spatial correlation

Abstract

The invention discloses a corrosion natural gas pipeline seismic probability analysis method considering soil parameter random spatial correlation. The method comprises the steps that a soil random field model in the axial direction of a pipeline is established; based on the soil random field model, establishing an earthquake response model of the corroded natural gas pipeline; performing probability analysis on the seismic response model of the corroded natural gas pipeline to obtain a probability density function and a cumulative density function; and calculating the failure probability of the corroded natural gas pipeline. The invention provides a corroded natural gas pipeline seismic probability analysis method considering soil parameter random spatial correlation, and aims to solve the problem of insufficient seismic probability analysis accuracy of buried corroded natural gas pipelines in the prior art. The earthquake damage probability of the corroded pipeline is analyzed on the premise of considering the uncertainty of the soil property, and the earthquake probability analysis accuracy is improved.

Description

Technical Field

[0001] The invention relates to the field of natural gas pipelines, and in particular to a seismic probability analysis method for corroded natural gas pipelines taking into account random spatial correlation of soil parameters. Background Art

[0002] Under the combined effects of corrosion and earthquakes, natural gas pipelines have complex disaster characteristics, such as cross-scale disasters, evolutionary correlations, and frequent damage. Accurate assessment and prediction of evolutionary patterns are essential for effective control of earthquake risks. Buried natural gas pipelines are subject to transient ground deformations caused by seismic waves, as well as permanent ground deformations caused by various types of ground displacements (such as lateral movement and faults). Transient ground deformations can lead to different types of failure modes in pipelines. However, the performance deterioration of corroded pipelines is uncertain, and earthquake disasters are difficult to predict. Uniform corrosion has no significant effect on the average stress-strain, while the dynamic non-uniform distribution of corrosion defects can lead to severe degradation of mechanical properties and random updates of stress-stress distribution. Under the combined effects of corrosion and earthquakes, the damage behavior and catastrophic failure modes of pipelines have random characteristics.

[0003] Soil variables in geotechnical engineering have uncertainties, such as inherent variability and insufficient data, which will affect the mechanical response of buried pipelines. The complex evolution of soil deposition and physical or chemical changes will lead to distribution uncertainty of soil parameters. For buried natural gas pipeline structures, soil properties change significantly along the pipeline axis; in the prior art, the simulation of soil media is limited to uniform soil or soil structures with planar changes, which is not suitable for the linear structure of buried natural gas pipelines. In addition, the soil medium model in the prior art has multiple uncertainties, which will lead to deviations in probabilistic results and have a negative impact on the calculation accuracy, which is not conducive to providing an effective seismic reference for natural gas pipeline structures with corrosion defects. Summary of the invention

[0004] The present invention provides a seismic probability analysis method for corroded natural gas pipelines taking into account the random spatial correlation of soil parameters, so as to solve the problem of insufficient accuracy of seismic probability analysis of buried corroded natural gas pipelines in the prior art, and achieve the purpose of analyzing the seismic damage probability of corroded pipelines under the premise of taking into account the uncertainty of soil properties and improving the accuracy of seismic probability analysis.

[0005] The present invention is achieved through the following technical solutions:

[0006] The seismic probability analysis method for corroded natural gas pipelines considering the random spatial correlation of soil parameters includes:

[0007] S1. Establish a soil random field model along the pipeline axis;

[0008] S2. Based on the soil random field model, a seismic response model of the corroded natural gas pipeline is established to obtain a seismic response result;

[0009] S3, performing probability analysis on the earthquake response results to obtain a probability density function and a cumulative density function;

[0010] S4. Calculate the failure probability of corroded natural gas pipelines under earthquake action.

[0011] In the prior art, almost all previous studies are based on an ideal deterministic analysis of 3D geotechnical structures with uncertain soil parameters. Specifically, the simulation of soil media related to buried corroded natural gas pipelines in the prior art is limited to uniform soil or soil structures with planar changes, which is not suitable for seismic probability analysis of buried natural gas pipelines. For buried natural gas pipeline structures, the soil properties change significantly along the axis of the pipeline. Therefore, this application first establishes a random field model of the soil along the axis of the pipeline, and then establishes a seismic response model of the corroded natural gas pipeline to obtain the seismic response results; then, a probability analysis is performed on the seismic response results of the corroded natural gas pipeline to obtain a probability density function and a cumulative density function. Finally, based on the probability density function and / or the cumulative density function, the failure probability of the corroded natural gas pipeline under earthquake action is calculated.

[0012] The present application solves the problem of insufficient accuracy of earthquake probability analysis of buried corroded natural gas pipelines in the prior art, and realizes the analysis of the earthquake damage probability of corroded pipelines under the premise of considering the uncertainty of soil properties, thereby reducing the deviation of probability results and improving the accuracy of earthquake probability analysis.

[0013] Furthermore, step S1 specifically includes:

[0014] S101, establishing a random field model of any two soil parameters with potential correlation, and obtaining a correlation coefficient expression;

[0015] S102. Randomly generate sample pairs of soil parameters with potential correlation.

[0016] The inventors of this case found in the research process that the mechanical behavior of pipe-soil interaction mainly depends on the shear characteristics of soil parameters; different soil parameters are correlated. Therefore, in this scheme, a probability-based sampling method is used to simulate the uncertain soil random field. In this scheme, all generated samples are discrete data points along the longitudinal pipeline. Therefore, by randomly generating sample pairs of soil parameters with potential correlation, the uncertain parameters are sampled to obtain spatially distributed random variables.

[0017] In this solution, the soil parameters may include any of the following parameters: internal friction angle, cohesion coefficient, unit soil weight. The random field model described in this solution may be obtained using existing technology.

[0018] Preferably, the correlation coefficient expression is:

[0019]

[0020] Where: a, b are two soil parameters with potential correlation; ρ a,b is the correlation coefficient of soil parameters a and b; l a,b is the correlation length of the random field model composed of soil parameters a and b.

[0021] Preferably, sample pairs of soil parameters with potential correlation are randomly generated by the following formula:

[0022] a ran =exp(u a +σ a N a,b

[0023] b ran =exp(u b +σ b N a,b

[0024] Where: a ran is a randomly generated sample of soil parameters a; b ran is a randomly generated sample of soil parameter b; u a and u b is the average value of the random field; σ a and σ b is the standard deviation of the random field; N a,b The product of the inverse function representing the probability function and the Cholesky decomposition is calculated by the following formula:

[0025] N a,b =f -1 (a,b)U

[0026] Where: f --1 (a, b) is the inverse of the bivariate normal probability density function f(a, b); U represents Cholesky decomposition; the bivariate normal probability density function f(a, b) is:

[0027]

[0028]

[0029] Where: a,b is the correlation coefficient between soil parameters a and b.

[0030] Those skilled in the art should understand that the Cholesky decomposition in this solution is calculated based on the correlation coefficient of soil parameters.

[0031] Furthermore, step S2 specifically includes:

[0032] S201. Based on soil parameters, a maximum spring force model per unit length along the pipeline axis and a maximum soil lateral elastic force model per unit pipeline length are established;

[0033] S202. Establish a seismic response model of corroded natural gas pipelines.

[0034] Preferably, the maximum spring force model per unit length along the pipeline axial direction is:

[0035]

[0036] Where: T u,i is the maximum spring force per unit length of the pipeline axial direction; D is the outer diameter of the pipeline; c i is the i-th cohesion coefficient of the soil; H is the soil depth above the center of the pipeline; is the i-th effective unit weight of the soil; α is the soil adhesion coefficient; f is the friction coefficient between the pipeline and the soil; is the i-th internal friction angle of the soil; K0 is the soil pressure coefficient; where i = 1, 2, 3…, n; n is the total number of samples;

[0037] The maximum soil lateral elastic force model per unit pipeline length is:

[0038]

[0039] Where: P u,i is the maximum soil lateral elastic force per unit pipe length; N ch is the horizontal bearing capacity coefficient of clay; N ch is the horizontal bearing capacity coefficient of sand.

[0040] Preferably, the seismic response model of the corroded natural gas pipeline is established as follows:

[0041]

[0042]

[0043]

[0044] Where: ε ta,ij is the maximum axial strain of the corroded pipeline under instantaneous earthquake action; ε pa,ij is the maximum axial strain of the corroded pipeline under permanent ground deformation caused by earthquake; pb,ijis the maximum bending strain of the corroded pipeline under permanent ground deformation caused by earthquake; λ is the apparent wavelength of the seismic wave; is the jth equivalent outer radius of the corroded pipeline; is the jth equivalent inner radius of the corroded pipeline; is the i-th effective unit weight of soil; L is the area of ​​permanent ground deformation; is the jth equivalent corrosion growth of the corroded pipeline; wt is the wall thickness; E is the elastic modulus of the pipeline material; σ y is the yield stress of the pipeline material; W is the width of the displacement zone caused by the earthquake; δ d t Design for lateral displacement of the ground.

[0045] Furthermore, in step S3, the probability density function obtained is:

[0046]

[0047] Where: f(x) represents the probability density function; N is the total number of earthquake response samples; n represents the nth earthquake response sample; σ is the standard deviation of the earthquake response sample; d is the number of sample dimensions; x is the target earthquake response sample value; x n is the nth earthquake response sample value;

[0048] The cumulative density function is: Where: D(X) represents the cumulative density function.

[0049] Furthermore, the calculation method of the failure probability of the corroded natural gas pipeline in step S4 includes:

[0050] S401. Establish the structural limit state equation to define the failure event of the corroded natural gas pipeline:

[0051] g(x)=xx a

[0052] Where: g(x) is the performance function in reliability analysis; x is the target earthquake response sample value, and x = ε ta,ij ,ε pb,ij ,ε pa,ij ;x a is the allowable strain corresponding to x, take x a =[ε ta,ij ],[ε pb,ij ],[ε pa,ij ];

[0053] S402. Calculate the failure probability of corroded natural gas pipelines using the following formula:

[0054]

[0055] Where: P f is the probability of failure of the corroded natural gas pipeline; P(F) is the probability of the final failure event; P(F1) is the probability of the first intermediate failure event; i represents the i-th intermediate failure event; m represents the number of intermediate failure events; P(F i+1 |F i ) represents the conditional failure probability; F i represents a series of intermediate failure events and is defined by the following formula:

[0056] F i ={g(x)≤g i}

[0057] Where: g i is the failure threshold value of the i-th failure intermediate event;

[0058] Assume that the independent and identically distributed sample points obtained using the cumulative density function D(X) are expressed as: P(F1) is calculated by the following formula:

[0059]

[0060] in: is the probability estimate of the first intermediate failure event; N1 is the number of independent and identically distributed sample points corresponding to the first intermediate failure event; is the first indicator function, The j here represents the jth independent and identically distributed sample point.

[0061] Preferably, the conditional failure probability P(F i+1 |F i ) is calculated by the following formula:

[0062]

[0063] Where: is the second indicator function; represents the jth independent and identically distributed sample point corresponding to the i+1th intermediate failure event; i represents the i-th intermediate failure event; N i+1 Represents the number of independent and identically distributed sample points corresponding to the i+1th intermediate failure event.

[0064] Those skilled in the art should understand that intermediate failure events refer to the introduction of reasonable intermediate failure events to divide the probability space into a series of subsets with sequential inclusion relationships, thereby expressing a small failure probability as the product of a series of larger conditional probabilities. Let F be the final failure event, and introduce a series of intermediate failure events F1, F2, ..., F m , and exists

[0065] In addition, the calculation formula of the second indicator function in this application is consistent with the first indicator function, that is:

[0066]

[0067] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0068] 1. The seismic probability analysis method for corroded natural gas pipelines taking into account the random spatial correlation of soil parameters in the present invention solves the problem of insufficient accuracy of seismic probability analysis of buried corroded natural gas pipelines in the prior art, and realizes the analysis of the seismic damage probability of corroded pipelines under the premise of considering the uncertainty of soil properties, thereby reducing the deviation of probability results and improving the accuracy of seismic probability analysis.

[0069] 2. The present invention provides a seismic probability analysis method for corroded natural gas pipelines that takes into account the random spatial correlation of soil parameters, and uses a probability-based sampling method to simulate uncertain soil random fields, thus filling the gap in the prior art.

[0070] 3. The seismic probability analysis method of corroded natural gas pipelines in the present invention taking into account the random spatial correlation of soil parameters can effectively analyze the failure probability of buried corroded natural gas pipelines under accidental earthquakes, which is conducive to evaluating the future seismic performance of buried corroded natural gas pipelines affected by earthquakes. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0072] Figure 1 It is a schematic diagram of a flow chart of a specific embodiment of the present invention. DETAILED DESCRIPTION

[0073] In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the examples and the accompanying drawings. The schematic embodiments of the present invention and the description thereof are only used to explain the present invention and are not intended to limit the present invention. In the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application.

[0074] Embodiment 1:

[0075] A seismic probability analysis method for corroded natural gas pipelines considering random spatial correlation of soil parameters includes:

[0076] Step 1: Establish a soil random field model along the pipeline axis. Specifically:

[0077] (1) Establish a random field model for any two soil parameters with potential correlation and obtain the correlation coefficient expression:

[0078]

[0079] Where: a, b are two soil parameters with potential correlation; ρ a,b is the correlation coefficient of soil parameters a and b; l a,b is the correlation length of the random field model composed of soil parameters a and b.

[0080] (2) Randomly generate sample pairs of soil parameters with potential correlation:

[0081] a ran =exp(u a +σ a N a,b )

[0082] b ran =exp(u b +σ b N a,b )

[0083] Where: a ran is a randomly generated sample of soil parameters a; b ran is a randomly generated sample of soil parameter b; u a and u b is the average value of the random field; σ a and σ b is the standard deviation of the random field; N a,b The product of the inverse function representing the probability function and the Cholesky decomposition is calculated by the following formula:

[0084] N a,b =f -1 (a,b)U

[0085] Where: f --1 (a, b) is the inverse of the bivariate normal probability density function f(a, b); U represents Cholesky decomposition; the bivariate normal probability density function f(a, b) is:

[0086]

[0087]

[0088] Where: a,b is the correlation coefficient between soil parameters a and b.

[0089] Step 2: Based on the soil random field model, establish a seismic response model of the corroded natural gas pipeline to obtain seismic response results. Specifically:

[0090] (1) Based on soil parameters, a model of the maximum spring force per unit length of the pipeline axis and a model of the maximum soil lateral elastic force per unit length of the pipeline are established.

[0091] The maximum spring force model per unit length along the pipeline axial direction is:

[0092]

[0093] Where: T u,i is the maximum spring force per unit length of the pipeline axial direction; D is the outer diameter of the pipeline; c i is the i-th cohesion coefficient of the soil; H is the soil depth above the center of the pipeline; is the i-th effective unit weight of the soil; α is the soil adhesion coefficient; f is the friction coefficient between the pipeline and the soil; is the i-th internal friction angle of the soil; K0 is the soil pressure coefficient; where i = 1, 2, 3…, n; n is the total number of samples;

[0094] The maximum soil lateral elastic force model per unit pipeline length is:

[0095]

[0096] Where: P u,i is the maximum soil lateral elastic force per unit pipe length; N ch is the horizontal bearing capacity coefficient of clay; N ch is the horizontal bearing capacity coefficient of sand.

[0097] (2) The seismic response model of corroded natural gas pipeline is established as follows:

[0098]

[0099]

[0100]

[0101] Where: ε ta,ij is the maximum axial strain of the corroded pipeline under instantaneous earthquake action; ε pa,ij is the maximum axial strain of the corroded pipeline under permanent ground deformation caused by earthquake; pb,ij is the maximum bending strain of the corroded pipeline under permanent ground deformation caused by earthquake; λ is the apparent wavelength of the seismic wave; is the jth equivalent outer radius of the corroded pipeline; is the jth equivalent inner radius of the corroded pipeline; is the i-th effective unit weight of soil; L is the area of ​​permanent ground deformation; is the jth equivalent corrosion growth of the corroded pipeline; wt is the wall thickness; E is the elastic modulus of the pipeline material; σ y is the yield stress of the pipeline material; W is the width of the displacement zone caused by the earthquake; δ d t Design for lateral displacement of the ground.

[0102] Step 3: Perform probability analysis on the seismic response results of the corroded natural gas pipeline to obtain the probability density function f(x) and the cumulative density function D(x):

[0103]

[0104]

[0105] Where: N is the total number of earthquake response samples; n represents the nth earthquake response sample; σ is the standard deviation of the earthquake response sample; d is the number of sample dimensions; x is the target earthquake response sample value; x n is the nth earthquake response sample value.

[0106] Step 4: Calculate the failure probability of corroded natural gas pipelines under earthquake action.

[0107] (1) Establish the structural limit state equation:

[0108] g(x)=xx a

[0109] Where: g(x) is the performance function in reliability analysis; x is the target earthquake response sample value, and x = ε ta,ij ,ε pb,ij ,ε pa,ij ;x a is the allowable strain corresponding to x, take x a =[ε ta,ij ],[ε pb,ij ],[ε pa,ij ];

[0110] (2) Calculate the failure probability of corroded natural gas pipelines using the following formula:

[0111]

[0112] Where: P fis the probability of failure of the corroded natural gas pipeline; P(F) is the probability of the final failure event; P(F1) is the probability of the first intermediate failure event; i represents the i-th intermediate failure event; m represents the number of intermediate failure events; P(F i+1 |F i ) represents the conditional failure probability; F i represents a series of intermediate failure events and is defined by the following formula:

[0113] F i ={g(x)≤g i}

[0114] Where: g i is the failure threshold value of the i-th failure intermediate event;

[0115] Assume that the independent and identically distributed sample points obtained using the cumulative density function D(X) are expressed as: P(F1) is calculated by the following formula:

[0116]

[0117] Where: is the probability estimate of the first intermediate failure event; N1 is the number of independent and identically distributed sample points corresponding to the first intermediate failure event; is the first indicator function, The j here represents the jth independent and identically distributed sample point.

[0118] Among them, the conditional failure probability P(F i+1 |F i ) is calculated by the following formula:

[0119]

[0120] Where: is the second indicator function; represents the jth independent and identically distributed sample point corresponding to the i+1th intermediate failure event; i represents the i-th intermediate failure event; N i+1 Represents the number of independent and identically distributed sample points corresponding to the i+1th intermediate failure event.

[0121] Embodiment 2:

[0122] A device for analyzing seismic probability of corroded natural gas pipelines comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method steps described in Example 1 are implemented.

[0123] The earthquake probability analysis device of this embodiment can be a computing device such as a desktop computer, a notebook computer, a palm computer, and a cloud server.

[0124] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0125] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

Claims

1. A seismic probability analysis method for corroded natural gas pipelines considering random spatial correlation of soil parameters, characterized in that: include: S1. Establish a soil random field model along the pipeline axis; S2. Based on the soil random field model, a seismic response model of the corroded natural gas pipeline is established to obtain a seismic response result; S3, performing probability analysis on the earthquake response results to obtain a probability density function and a cumulative density function; S4. Calculate the failure probability of corroded natural gas pipelines under earthquake action.

2. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 1 is characterized in that: Step S1 specifically includes: S101, establishing a random field model of any two soil parameters with potential correlation, and obtaining a correlation coefficient expression; S102. Randomly generate sample pairs of soil parameters with potential correlation.

3. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 2 is characterized in that: The correlation coefficient expression is: Where: a, b are two soil parameters with potential correlation; ρ a,b is the correlation coefficient of soil parameters a and b; l a,b is the correlation length of the random field model composed of soil parameters a and b.

4. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 2 is characterized in that: Sample pairs of soil parameters with potential correlation are randomly generated using the following formula: a ran =exp(u a +σ a N a,b ) b ran =exp(u b +σ b N a,b ) Where: a ran is a randomly generated sample of soil parameters a; b ran is a randomly generated sample of soil parameter b; u a and u b is the average value of the random field; σ a and σ b is the standard deviation of the random field; N a,b The product of the inverse function representing the probability function and the Cholesky decomposition is calculated by the following formula: N a,b =f -1 (a,b)U Where: f --1 (a, b) is the inverse of the bivariate normal probability density function f(a, b); U represents Cholesky decomposition; the bivariate normal probability density function f(a, b) is: Where: a,b is the correlation coefficient between soil parameters a and b.

5. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 2 is characterized in that: Step S2 specifically includes: S201. Based on soil parameters, a maximum spring force model per unit length along the pipeline axis and a maximum soil lateral elastic force model per unit pipeline length are established; S202. Establish a seismic response model of corroded natural gas pipelines.

6. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 5 is characterized in that: The maximum spring force model per unit length along the pipeline axial direction is: Where: T u,i is the maximum spring force per unit length of the pipeline axial direction; D is the outer diameter of the pipeline; c i is the i-th cohesion coefficient of the soil; H is the soil depth above the center of the pipeline; is the i-th effective unit weight of the soil; α is the soil adhesion coefficient; f is the friction coefficient between the pipeline and the soil; is the i-th internal friction angle of the soil; K0 is the soil pressure coefficient; where i = 1, 2, 3…, n; n is the total number of samples; The maximum soil lateral elastic force model per unit pipeline length is: Where: P u,i is the maximum soil lateral elastic force per unit pipe length; N ch is the horizontal bearing capacity coefficient of clay; N ch is the horizontal bearing capacity coefficient of sand.

7. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 6 is characterized in that: The earthquake response model is: Where: ε ta,ij is the maximum axial strain of the corroded pipeline under instantaneous earthquake action; ε pa,ij is the maximum axial strain of the corroded pipeline under permanent ground deformation caused by earthquake; pb,ij is the maximum bending strain of the corroded pipeline under permanent ground deformation caused by earthquake; λ is the apparent wavelength of the seismic wave; is the jth equivalent outer radius of the corroded pipeline; is the jth equivalent inner radius of the corroded pipe; is the i-th effective unit weight of the soil; L is the length of the permanent ground deformation zone caused by the earthquake; is the jth equivalent corrosion growth of the corroded pipeline; wt is the wall thickness; E is the elastic modulus of the pipeline material; σ y is the yield stress of the pipeline material; W is the width of the permanent ground deformation zone caused by earthquake; δ d t Design for lateral displacement of the ground.

8. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 1 is characterized in that: In step S3, the probability density function obtained is: Where: f(x) represents the probability density function; N is the total number of earthquake response samples; n represents the nth earthquake response sample; σ is the standard deviation of the earthquake response sample; d is the number of sample dimensions; x is the target earthquake response sample value; x n is the nth earthquake response sample value; The cumulative density function is: Where: D(X) represents the cumulative density function.

9. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 8, characterized in that: The method for calculating the failure probability of the corroded natural gas pipeline in step S4 includes: S401. Establish the structural limit state equation: g(x)=x-x a Where: g(x) is the performance function in reliability analysis; x is the target earthquake response sample value, and x = ε ta,ij ,ε pb,ij ,ε pa,ij ;x a is the allowable strain corresponding to x, take x a =[ε ta,ij ],[ε pb,ij ],[ε pa,ij ]; S402. Calculate the failure probability of corroded natural gas pipelines using the following formula: Where: P f is the probability of failure of the corroded natural gas pipeline; P(F) is the probability of the final failure event; P(F1) is the probability of the first intermediate failure event; i represents the i-th intermediate failure event; m represents the number of intermediate failure events; P(F i+1 |F i ) represents the conditional failure probability; F i represents a series of intermediate failure events and is defined by the following formula: F i ={g(x)≤g i } Where: g i is the failure threshold value of the i-th failure intermediate event; Assume that the independent and identically distributed sample points obtained using the cumulative density function D(X) are expressed as: P(F1) is calculated by the following formula: in: is the probability estimate of the first intermediate failure event; N1 is the number of independent and identically distributed sample points corresponding to the first intermediate failure event; is the first indicator function, The j here represents the jth independent and identically distributed sample point.

10. The method for seismic probability analysis of corroded natural gas pipelines considering random spatial correlation of soil parameters according to claim 9, characterized in that: The conditional failure probability P(F i+1 |F i ) is calculated by the following formula: Where: is the second indicator function; represents the jth independent and identically distributed sample point corresponding to the i+1th intermediate failure event; i represents the i-th intermediate failure event; N i+1 Represents the number of independent and identically distributed sample points corresponding to the i+1th intermediate failure event.

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