A method for optimizing the period of internal inspection of a pipeline containing corrosion defects

Abstract

The present application relates to the technical field of pipeline maintenance, and discloses a kind of corrosion defect containing pipeline internal detection cycle optimization method, comprising the following steps: corrosion defect containing pipeline internal detection cycle objective function is constructed;With the minimum pipeline maintenance total cost as the goal, with the maximum acceptable failure probability of pipeline as the constraint, the objective function is iteratively optimized, and the optimal solution corresponding internal detection cycle is the required result;The present application takes the maximum acceptable failure probability of different regional grade pipeline as the constraint condition, iteratively optimized, and the internal detection cycle calculated is more accurate, which can achieve the best balance between safety and cost control;By constructing the failure probability including pipeline burst and leakage, the typical failure mode of pipeline is considered, so that the annual failure probability calculation in the optimization model is more accurate;A pipeline maintenance cost calculation model under different maintenance criteria is constructed, accurately describing the relationship between variables, and improving the accuracy of risk assessment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pipeline maintenance, in particular to a corrosion defect-containing pipeline internal detection cycle optimization method. BACKGROUND

[0002] Oil and gas pipelines are critical infrastructure for energy transportation, and their safe and stable operation is of great importance. During service, pipelines may develop defects due to corrosion and other factors. If not detected and addressed in a timely manner, it may lead to leakage or even burst accidents, causing serious environmental, economic losses and casualties. Online detection is a key technology for assessing the geometric size of pipeline corrosion defects and ensuring pipeline safety. Common techniques include magnetic flux leakage detection and ultrasonic detection. In pipeline integrity management, determining a reasonable internal detection cycle (i.e., the time interval between two internal detections) is a core decision that directly affects the failure risk and maintenance cost of the pipeline. If the cycle is too long, dangerous defects may not be detected in time, leading to accidents. If the cycle is too short, it will significantly increase the cost of detection and maintenance, resulting in waste of resources.

[0003] Currently, the main problems of the existing pipeline internal detection cycle optimization technology are as follows:

[0004] 1) The corrosion defect growth model has insufficient prediction accuracy. For example, a simple linear model is used to describe the growth process of corrosion defects. However, corrosion itself is a complex electrochemical process with significant randomness and nonlinearity. The linear model cannot accurately capture this random cumulative degradation characteristic, resulting in a large deviation in the prediction of future defect size, and thus the calculated failure probability and optimal detection cycle are inaccurate, which cannot achieve the balance between risk and cost.

[0005] 2) The influence of regional grade on safety constraints is not systematically considered. The population density and environmental sensitivity of the geographical location where the pipeline is located determine the severity of the consequences of its failure. Different regions of the pipeline should follow different safety standards; however, existing optimization methods do not consider this factor, and generally use a unified and fixed acceptable failure probability as a constraint condition, or completely rely on the personal experience of engineers to set it. This approach cannot meet the higher safety requirements of high-grade areas (such as cities and densely populated areas), and may also lead to excessive detection in low-grade areas (such as uninhabited areas), resulting in unnecessary cost expenditure. SUMMARY

[0006] The present application provides a corrosion defect-containing pipeline internal detection cycle optimization method to solve the problems of the prior art.

[0007] The technical scheme adopted by the present application is: a corrosion defect-containing pipeline internal detection cycle optimization method, comprising the following steps:

[0008] Construct an objective function for the inspection cycle inside pipelines with corrosion defects;

[0009]

[0010] In the formula: For the first t Total annual pipeline maintenance cost For the first t Annual failure probability This represents the maximum acceptable failure probability of the pipeline.

[0011] Using the maximum acceptable failure probability of the pipeline as a constraint, the objective function is iteratively optimized, and the internal detection cycle corresponding to the optimal solution is the desired result.

[0012] The total cost of pipeline maintenance includes the cost of pipeline inspection, pipeline repair, and pipeline corrosion failure.

[0013]

[0014] In the formula: For the first t Annual pipeline inspection costs For internal testing costs, The discount rate is... For the first t Annual pipeline maintenance costs For the first i The repair cost of a defect. k For the first t The number of pipeline defects per year For indicator functions, For the first t Annual pipeline corrosion failure cost Costs associated with pipeline corrosion failure.

[0015] Furthermore, the process for determining the maximum acceptable failure probability of the pipeline is as follows:

[0016] Determine the pipeline safety level and obtain the associated failure rate under the corresponding safety level;

[0017] The maximum acceptable failure probability of the pipeline is obtained based on the associated failure rate.

[0018] Furthermore, the annual failure probability includes the pipeline rupture failure probability and the pipeline leakage failure probability.

[0019] Furthermore, the pipeline maintenance cost is calculated as follows:

[0020] First, establish maintenance guidelines.

[0021] Criterion one: the ratio of the maximum corrosion depth of the pipeline to the nominal wall thickness is greater than 0.4, or the ratio is between 0.1 and 0.4, and the failure pressure of the pipeline at the defect is less than 1.1 times the maximum operating pressure;

[0022] The pipeline repair cost calculation method is as follows:

[0023]

[0024] Criterion two: the corrosion defect depth is greater than 80% of the nominal wall thickness of the pipeline;

[0025]

[0026] In the formula: C e is the pipeline excavation cost, C b is the cost of installing a B-type sleeve, C p is the pipeline monitoring cost.

[0027] Further, the objective function is solved by using a Monte Carlo simulation method;

[0028] The mean value of the internal detection period T The calculation method is as follows:

[0029]

[0030] In the formula: N is the iteration number, j is the iteration number sequence, T j is the internal detection period corresponding to the i-th iteration; j

[0031]

[0032] In the formula: is the annual average total cost generated by the pipeline detection and repair in the maximum failure probability range in the i-th year, t is the total pipeline maintenance cost in the i-th iteration of the i-th year. t j

[0033] Further, the pipeline safety level includes a low safety level, a medium safety level, a high safety level, and an extremely high safety level, and the associated failure rate is set according to the safety level;

[0034] The pipeline maximum acceptable failure probability calculation process is as follows:

[0035]

[0036] In the formula:​​​​ for the associated failure rate under the safety level, for the pipe length, for the pipe operating pressure, D for the pipe operating outer diameter.

[0037] Further, the annual failure probability calculation method is as follows:

[0038]

[0039] In the formula: is the annual pipe leakage failure probability, t is the annual pipe burst failure probability; t

[0040] wherein,

[0041]

[0042]

[0043] In the formula: is the 0~ annual pipe cumulative leakage failure probability, t is the 0~ -1 annual pipe cumulative leakage failure probability, is the 0~ annual pipe cumulative total failure probability, t is the 0~ -1 annual pipe cumulative burst failure probability. t t t -1 year pipe cumulative burst failure probability.

[0044] Further, the iteration optimization process of the objective function is as follows:

[0045] The iteration number is set to n, and the inner detection cycle mean and the annual average total cost mean generated by the nth iteration are obtained; N N If the current acceptable failure probability is less than the maximum acceptable failure probability of the pipe, continue iteration until the updated acceptable failure probability is greater than or equal to the maximum acceptable failure probability of the pipe, and stop iteration;

[0046]

[0047] Compare the sizes of the annual average total costs of the pipe under the maximum acceptable annual failure probabilities of the pipe in different regions and levels, and select the minimum value. The inner detection cycle corresponding to the minimum value is the required inner detection cycle.

[0048] Further, the associated failure rate corresponding to the safety level of the pipe is as follows: ​​​​​​​​​

[0049] Low safety level is 5*10 -3 Medium safety level is 5*10 -4 High safety level is 5*10 -5 Very high safety level is 5*10 -6 .

[0050] Further, the calculation process of and is as follows:

[0051]

[0052]

[0053] In the formula: is the critical corrosion depth of burst failure in the t year, is the incomplete gamma function, a is the shape parameter of the gamma degradation process, is the scale parameter of the gamma degradation process, is the initial corrosion depth of the pipeline, is the gamma function, is the wall thickness of the pipeline.

[0054] The beneficial effects of the present application are:

[0055] (1) The present application takes the total pipeline maintenance cost as the objective function, takes the maximum acceptable failure probability of the pipeline in different regions as the constraint condition, and performs iterative optimization, so that the internal detection period calculated is more accurate, and the best balance between safety and cost control can be achieved;

[0056] (2) The present application considers the typical failure mode of the pipeline by constructing the failure probability including pipeline burst and leakage, so that the annual failure probability calculation in the optimization model is more accurate;

[0057] (3) The present application constructs a pipeline maintenance cost calculation model under different maintenance criteria, accurately describes the relationship between variables, and improves the accuracy of risk assessment. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a flowchart of the method of the present application.

[0059] Figure 2 is a schematic diagram of the simulation solving method in the embodiment of the present application.

[0060] Figure 3 is the change trend of the annual average total cost with the acceptable failure probability of the pipeline P a in the iterative process of the embodiment of the present application.

[0061] Figure 4 The relationship between the acceptable failure probability of the pipeline and the internal detection period of the pipeline in the iteration process of the embodiment of the present application. T DETAILED DESCRIPTION

[0062] The present application will be further described below in conjunction with the drawings and specific embodiments.

[0063] The present application takes the minimum total cost of pipeline maintenance as the objective function, takes the maximum acceptable failure probability of the pipeline in different regions as the constraint condition, and obtains the corresponding internal detection period which minimizes the total cost composed of the detection cost, the repair cost and the failure cost of the pipeline as the solving result, so as to achieve the best balance between safety and cost control.

[0064] An internal detection period optimization method for a pipeline containing corrosion defects, as shown in FIG. 1, comprises the following steps: Figure 1

[0065] Constructing an objective function of the internal detection period of the pipeline containing corrosion defects;

[0066] (1)

[0067] In the formula: is the total cost of pipeline maintenance in the year of the t , is the annual failure probability in the year of the , and is the maximum acceptable failure probability of the pipeline. t Among them, the total cost of pipeline maintenance includes the internal detection cost of the pipeline, the repair cost of the pipeline and the corrosion failure cost of the pipeline.

[0068]

[0069] (2) In the formula:

[0070] is the internal detection cost of the pipeline in the year of the , is the internal detection cost, is the discount rate, is the repair cost of the pipeline in the year of the t , is the repair cost of the th defect, is the number of defects of the pipeline in the year of the , is an indicator function related to the repair criterion of the corrosion pipeline, and is the corrosion failure cost of the pipeline in the year of the t i k t t ​​​​​​​​​​​​The pipeline corrosion failure cost. It should be noted that all costs are relative values.

[0071] Wherein:

[0072] (3)

[0073] (4)

[0074] (5)

[0075] Wherein the pipeline corrosion failure cost is the economic loss converted from the environmental damage and declared property loss caused by pipeline corrosion failure.

[0076] The determination process of the maximum acceptable failure rate of the pipeline is as follows:

[0077] Determine the safety level of the pipeline to obtain the associated failure rate under the corresponding safety level;

[0078] Obtain the maximum acceptable failure probability of the pipeline according to the associated failure rate.

[0079] This confirmation method directly links safety constraints with the geographical environment and regulatory requirements of the pipeline, overcoming the defects of the prior art caused by not distinguishing between regions.

[0080] First, according to GB / T 24259-2023 "Pipeline Transportation System for Petroleum and Natural Gas Industry", determine the pipeline region level, and combine the fluid type and region level to obtain the corresponding pipeline safety level. As shown in Table 1:

[0081] Table 1. Different region levels corresponding to pipeline safety levels

[0082]

[0083] Determine the associated failure rate under different safety levels according to the pipeline safety level As shown in Table 2

[0084] Table 2. Associated failure rates corresponding to different safety levels

[0085]

[0086] Combine the associated failure rate, pipeline operating pressure and outer diameter to calculate the maximum acceptable failure probability of the natural gas pipeline:

[0087] (6)

[0088] Wherein: is the associated failure rate under the corresponding safety level (km -1 ·a -1 ), is the pipe length (km), is the pipe operating pressure (bar), D is the pipe operating outer diameter (m).

[0089] where the annual failure probability is calculated as follows:

[0090] A stochastic process model is used to describe the evolution of corrosion defects to predict the change of pipe risk over time. In the target model, the annual failure probability at the in-service inspection interval t is a basic parameter for evaluating the cost of corrosion failure of a pipe. Considering the typical failure modes of a pipe including corrosion-induced leakage and burst, the annual failure probability at the in-service inspection interval is expressed by the following equation: t

[0091] (7)

[0092] where: is the pipe leakage failure probability in the t th year, is the pipe burst failure probability in the t th year; it is defined as the probability that the pipe does not fail before t -1 years and only fails between t -1 years and t years. To facilitate calculation, the cumulative failure probability of a corroded pipe can be used, as shown in equations (8) and (9).

[0093] where:

[0094] (8)

[0095] (9)

[0096] where: is the cumulative pipe leakage failure probability from 0 to t -1 years, is the cumulative pipe leakage failure probability from 0 to t -1 years, is the cumulative total failure probability of a pipe from 0 to t years is the sum of and , and is the cumulative pipe burst failure probability from 0 to t -1 years, is the cumulative pipe burst failure probability from 0 to t -1 years.

[0097] The different cumulative failure probabilities of a corroded pipe , ,​​ The time-varying nature of the corrosion defects is mainly caused by changes in the corrosion rate, resulting in variations in the depth and length of the corrosion defects. The growth process of the defects is described using both gamma degradation and linear models, and the increment of corrosion depth follows a gamma distribution. d k ( t Corrosion length increases L k ( t It is expressed using a linear model.

[0098] in and The calculation process is as follows:

[0099] (10)

[0100] (11)

[0101] In the formula: The critical corrosion depth at the moment of burst failure (referring to the first...) t (Critical corrosion depth at the time of annual burst failure). The lower incomplete gamma function; The initial corrosion depth of the pipeline, in mm; For gamma function, For pipe wall thickness, mm (0.8) The critical corrosion depth for leakage failure is typically taken as 80% of the wall thickness (the threshold for leakage criterion). t For time, a and b The shape and scale parameters of the gamma degradation process. .in: COV vt Let be the coefficient of variation of the corrosion depth growth rate; μ The mean corrosion depth growth rate is expressed in mm / a.

[0102] The objective function considers different maintenance criteria for pipeline maintenance costs, as follows:

[0103] Considering the increase in corrosion defect size and changes in operating pressure inside the pipe, and referring to the national standard GB / T36701-2018 "Guidelines for Repairing Defects in Buried Steel Pipelines", the pipeline does not require repair when the corrosion depth and operating pressure meet the following conditions:

[0104] 1) The maximum corrosion depth is less than or equal to 10% of the nominal pipe diameter;

[0105] 2) When the maximum corrosion depth is greater than 10% of the nominal pipe diameter and less than or equal to 40%, the remaining strength is less than 1.1 times the maximum operating pressure.

[0106] If the above conditions are not met, the pipeline needs to be repaired.

[0107] Criterion 1: If the ratio of the maximum corrosion depth to the nominal wall diameter of the pipeline is greater than 0.4, or the ratio is between 0.1 and 0.4, and the failure pressure of the pipeline at the defect is less than 1.1 times the maximum operating pressure, the pipeline is considered to have ruptured and failed.

[0108] The limit state function LSF(b) for burst failure of a pipeline with corrosion defects is as follows:

[0109] (12)

[0110] In the formula: The failure pressure at the moment of pipe rupture (referring to the first...) t (failure pressure at the moment of pipeline rupture in [year], MPa) The pressure is the pipeline operating pressure, in MPa.

[0111] Criterion 2: If the depth of corrosion defects exceeds 80% of the nominal pipe wall thickness, repair can be performed using patch plates, type B sleeves, and bolt-fastened clamps. In this case, the pipe is considered to have leaked and failed.

[0112] The leakage failure limit state function LSF(d) for a pipeline with corrosion defects is as follows:

[0113] (13)

[0114] In the formula: The maximum corrosion depth at the moment of leakage failure, in mm (the first...). t (Maximum corrosion depth at the time of leakage failure in the year). The thickness is the pipe wall thickness, in mm.

[0115] The method for calculating pipeline maintenance costs is as follows:

[0116] (14)

[0117] (15)

[0118] In the formula: C e For pipeline excavation costs, C b To reduce the cost of installing type B bushing, C p For pipeline monitoring costs

[0119] Using the maximum acceptable failure probability of the pipeline as a constraint (annual failure probability) The objective function is iteratively optimized by taking the probability of failure (which is less than the maximum acceptable failure probability of the region where the pipeline is located) and the internal detection cycle corresponding to the optimal solution is the desired result.

[0120] Monte Carlo simulation was used to perform the objective function. N The calculation is performed in the next iteration. j The iteration number ( j =1,2,3…, N ), No. j The present values ​​of the detection cost, failure cost, and maintenance cost in this iteration (i.e., the internal detection cost, pipeline maintenance cost, and pipeline corrosion failure cost in the objective function; these are just values ​​to distinguish them from the specific calculations obtained in this iteration) are as follows: C I,t,j , C f,t,j , C m,t,j The average annual total cost of pipeline inspection and maintenance within the maximum probability of failure range is calculated using the following formula. C t,s (The total cost in the objective function, which here represents the real-time calculation result during the iteration process, has the same meaning.) The average of the optimal internal detection cycle... T As the final output.

[0121] (16)

[0122] (17)

[0123] In the formula: N For the number of iterations, j This is the iteration number. T j For the first j The internal detection cycle corresponding to the next iteration; For the pipeline in the first t The average annual total cost of inspection and maintenance within the range of the maximum probability of failure per year. For the pipeline t Year j Total pipeline maintenance cost for each iteration.

[0124] Average annual total cost includes average annual maintenance cost. Average annual failure cost and average annual testing cost (The average annual total cost is the total cost in the objective function; it's just a value calculated under different conditions, and different symbols are used to represent it for distinction.) The calculation process is as follows:

[0125] (18)

[0126] (19)

[0127] (20)

[0128] Embodiment

[0129] The following illustrates the practical application process of the present application by taking a specific natural gas pipeline as an example.

[0130] The mileage of the natural gas pipeline is 11.9 km, and the area grades along the way include first-class areas, second-class areas and third-class areas. According to the statistical results of the latest pipeline internal detection data, the pipeline has a total of 179 corrosion defects, and the parameter probability statistical characteristics are shown in Table 3.

[0131] Table 3. Parameter probability statistics of natural gas pipeline internal detection results

[0132]

[0133] The relative cost is used to set the pipeline internal detection, failure loss and maintenance cost values, as shown in Table 4. Among them, the pipeline is actually operated once every 4 years, and the average total cost of the pipeline is 0.864 per year. The discount rate is 2%.

[0134] Table 4. Setting of pipeline internal detection, failure loss and pipeline maintenance cost values based on relative cost

[0135]

[0136] The specific calculation process is shown in Table 4. Figure 2

[0137] Step 1: Construct the pipeline optimal internal detection cycle model, that is, the objective function; obtain the parameters in Table 3 and Table 4, and take them as the input parameters of the model solution. Including the corrosion pipeline operating outer diameter, wall thickness, yield strength, tensile strength, operating pressure, corrosion length, depth and corrosion length and depth growth rate and pipeline internal detection cost, corrosion failure cost, excavation cost, pipeline monitoring cost, B-type sleeve installation cost.

[0138] Step 2: According to the area grade of the pipeline with corrosion defects and the corresponding associated failure rate and input parameters, the maximum acceptable failure probability of the natural gas pipeline is calculated to be 4.98×10 -3 .

[0139] Step 3: Set the initial iteration value of the iterative solution, and take the acceptable failure probability of the pipeline as P a , and the initial value of the acceptable annual failure probability of the pipeline is P s ​​P s (less than the maximum acceptable failure probability of the pipeline), with a value of 5×10 -5 The number of iterations for solving the mean value of the internal detection period is: N The value is 10. 4 The acceptable annual failure probability increment of the pipeline in the iterative solution process is denoted as Δ. P s The value is 10. -5 .

[0140] Step 4: Based on the input parameters and the defect growth process, use equations (7), (8), and (9) and subset simulation method to obtain the annual failure probability of the corroded pipeline. .

[0141] Step 5: Calculate the amount of water in the pipeline. k The time-varying values ​​of the length and depth of each corrosion defect, combined with the limit state functions (12) and (13), determine the pipeline maintenance method and the maintenance cost over the pipeline's service life. C m,t .

[0142] Compare with the calculations in step 4 and the acceptable annual failure probability set value for pipelines P s The size, when P sf ( t )≥ P s At that point, the annual failure probability iterative calculation is stopped.

[0143] according to The calculated value determines the cost of pipeline corrosion failure. C f,t ; Calculate the average annual total cost over different corrosion periods using formula (16). C t,s Calculate the average annual maintenance cost according to equations (18), (19) and (20). Average annual failure cost and average annual testing cost .

[0144] Step 6: Repeat steps 4 and 5 until the set number of iterations is met. N ,Will N The average internal detection cycle and average annual total cost generated in each iteration C t,s As the current acceptable failure probability of the pipeline P aThe internal testing cycle and total cost value. If the acceptable failure probability is less than the maximum acceptable failure probability, proceed to the next step.

[0145] Initial value of acceptable annual failure probability for pipeline P s Based on this, add Δ P s To obtain the new acceptable failure probability of the pipeline. P a ( P a = P s +Δ P s Repeat the iteration until the updated version is reached. P a Stop iterative calculation when the probability of failure is greater than or equal to the maximum probability of failure of the pipeline.

[0146] At this point, we compare the average annual total cost of pipelines under the acceptable annual failure probability for regional-level pipelines. C t,s The size is selected, and the minimum value is chosen, along with its corresponding internal detection period. T That is the optimal value.

[0147] The optimization results of this embodiment are as follows: Figure 3 and Figure 4 As shown in the results, internal inspections conducted under different service times and acceptable failure probabilities reveal that the average total cost per year varies with the failure probability. P a 2.23 × 10 -4 The occurrence of the minimum value indicates that conducting pipeline internal inspection is most economical under this probability threshold. The corresponding average annual total cost and optimal internal inspection cycle are 0.701 and 9.8 years, respectively, which is about 14.9% lower than the cost of a fixed inspection cycle.

[0148] This invention uses the maximum acceptable failure probability corresponding to pipelines of different regional grades as the objective function for constraint solution construction, overcoming the shortcomings of existing technologies that use a uniform failure probability threshold. By establishing differentiated safety constraints, the optimization results can balance pipeline safety risks and economic costs in different regions. Taking into account the randomness of corrosion defect growth, multi-level maintenance decision criteria and cost functions are established based on national standards. This extended analysis of multivariate relationships significantly improves the accuracy of risk assessment, making the optimization model closer to engineering practice. Finally, a solution method combining Monte Carlo simulation and iterative optimization is used, which can obtain the optimal solution within a wide feasible domain that satisfies safety constraints. The optimal internal detection cycle obtained by the method of this invention is more accurate and more in line with engineering practice compared with existing optimization methods.

Claims

1. A method for optimizing the inspection cycle of pipelines with corrosion defects, characterized in that, Includes the following steps: Construct an objective function for the inspection cycle inside pipelines with corrosion defects; In the formula: For the first t Total annual pipeline maintenance cost For the first t Annual failure probability This represents the maximum acceptable failure probability of the pipeline. Using the maximum acceptable failure probability of the pipeline as a constraint, the objective function is iteratively optimized, and the internal detection cycle corresponding to the optimal solution is the desired result. The process for determining the maximum acceptable failure probability of a pipeline is as follows: Determine the pipeline safety level and obtain the associated failure rate under the corresponding safety level; The maximum acceptable failure probability of the pipeline is obtained based on the associated failure rate. Pipeline safety levels include low safety level, medium safety level, high safety level and very high safety level, with corresponding failure rates set for each safety level; The calculation process for the maximum acceptable failure probability of the pipeline is as follows: In the formula: The associated failure rate under the corresponding security level, For the length of the pipe, For pipeline operating pressure, D The outer diameter of the pipeline during operation; The total cost of pipeline maintenance includes the cost of pipeline inspection, pipeline repair, and pipeline corrosion failure. In the formula: For the first t Annual pipeline inspection costs For internal testing costs, The discount rate is... For the first t Annual pipeline maintenance costs For the first i The repair cost of a defect. k For the first t The number of pipeline defects per year For indicator functions, For the first t Annual pipeline corrosion failure cost Costs associated with pipeline corrosion failure.

2. The method for optimizing the inspection cycle of a pipeline with corrosion defects according to claim 1, characterized in that, The annual failure probability includes the probability of pipeline rupture failure and the probability of pipeline leakage failure.

3. The method for optimizing the inspection cycle of a pipeline with corrosion defects according to claim 1, characterized in that, The pipeline maintenance cost is calculated as follows: First, establish maintenance guidelines. Criterion 1: The ratio of the maximum corrosion depth of the pipeline to the nominal wall diameter is greater than 0.4, or the ratio is between 0.1 and 0.4, and the failure pressure of the pipeline at the defect is less than 1.1 times the maximum operating pressure; The method for calculating pipeline maintenance costs is as follows: Criterion 2: The depth of corrosion defects is greater than 80% of the nominal wall thickness of the pipe; In the formula: C e For pipeline excavation costs, C b To reduce the cost of installing type B bushing, C p For pipeline monitoring costs.

4. The method for optimizing the inspection cycle of a pipeline with corrosion defects according to claim 1, characterized in that, The objective function is solved using the Monte Carlo simulation method. Average of internal testing cycles T The calculation method is as follows: In the formula: N For the number of iterations, j This is the iteration number. T j For the first j The internal detection cycle corresponding to the next iteration; In the formula: For the pipeline in the first t The average annual total cost of inspection and maintenance within the range of the maximum probability of failure per year. For the pipeline t Year j Total pipeline maintenance cost for each iteration.

5. The method for optimizing the inspection cycle of a pipeline with corrosion defects according to claim 2, characterized in that, The method for calculating the annual failure probability is as follows: In the formula: For the first t Annual pipeline leakage failure probability For the first t Annual pipeline burst failure probability; in, In the formula: 0~ t Annual cumulative pipeline leakage failure probability 0~ t -1-year cumulative pipeline leakage failure probability 0~ t Annual cumulative total pipeline failure probability 0~ t Annual cumulative pipeline burst failure probability 0~ t -1 year cumulative pipeline burst failure probability.

6. The method for optimizing the inspection cycle of a pipeline with corrosion defects according to claim 1, characterized in that, The iterative optimization process of the objective function is as follows: Set the number of iterations N , obtained the N The average internal detection cycle and average annual total cost generated by each iteration; If the current acceptable failure probability is less than the maximum acceptable failure probability of the pipeline, continue iterating until the updated acceptable failure probability is greater than or equal to the maximum acceptable failure probability of the pipeline, then stop iterating. By comparing the average annual total cost of the pipeline under the maximum acceptable annual failure probability for different regions and grades of the pipeline, the minimum value is selected, and the corresponding internal inspection cycle is the required internal inspection cycle.

7. The method for optimizing the inspection cycle of a pipeline with corrosion defects according to claim 1, characterized in that, The associated failure rates corresponding to the pipeline safety levels are as follows: Low security level 5×10 -3 Medium security level 5×10 -4 High security level 5×10 -5 Extremely high security level 5×10 -6 .

8. The method for optimizing the inspection cycle of a pipeline with corrosion defects according to claim 5, characterized in that, in and The calculation process is as follows: In the formula: For the first t Critical corrosion depth for annual burst failure It is an incomplete gamma function. a The shape parameters for the gamma degradation process. The scale parameter for the gamma degradation process. This represents the initial corrosion depth of the pipeline. For gamma function, This refers to the pipe wall thickness.

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