Method for optimizing detection period in pipeline with corrosion defect

Abstract

The invention relates to the technical field of pipeline maintenance, and discloses a corrosion defect-containing pipeline internal detection period optimization method which comprises the following steps: constructing a corrosion defect-containing pipeline internal detection period objective function; taking the minimization of the total pipeline maintenance cost as a target, taking the maximum acceptable failure probability of the pipeline as a constraint, carrying out iterative optimization on a target function, and taking an internal detection period corresponding to an optimal solution as a required result; according to the method, iterative optimization is carried out by taking the maximum acceptable failure probability of different regional grade pipelines as a constraint condition, the calculated internal detection period is more accurate, and the optimal balance can be obtained between safety guarantee and cost control; by constructing the failure probability including pipeline burst and leakage, the typical failure mode of the pipeline is considered, so that the annual failure probability calculation is more accurate in the optimization model; a pipeline maintenance cost calculation model under different maintenance criteria is constructed, the relationship between variables is accurately expressed, and the accuracy of risk assessment is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline maintenance, and in particular to a method for optimizing the internal detection cycle of a pipeline containing corrosion defects. Background Art

[0002] Oil and gas pipelines are critical infrastructure for energy transportation, and their safe and stable operation is of paramount importance. During their service life, pipelines may develop defects due to factors such as corrosion. If not discovered and addressed promptly, these defects can lead to leaks or even explosions, causing serious environmental and economic losses, as well as casualties. Online testing is a key technology for assessing the geometric dimensions of pipeline corrosion defects and ensuring pipeline safety. Commonly used techniques include magnetic flux leakage testing and ultrasonic testing. In pipeline integrity management, determining a reasonable internal inspection cycle (i.e., the time interval between two internal inspections) is a core decision that directly impacts the pipeline's failure risk and maintenance costs. If the cycle is too long, dangerous defects may not be discovered in time, leading to accidents. If the cycle is too short, the cost of inspection and maintenance will increase significantly, resulting in a waste of resources.

[0003] The current technologies for optimizing pipeline inspection cycles mainly have the following problems: 1) Corrosion defect growth models lack predictive accuracy. For example, simple linear models are used to describe the growth process of corrosion defects. However, corrosion itself is a complex electrochemical process with significant stochastic and nonlinear characteristics. Linear models cannot accurately capture this random, cumulative degradation, leading to significant deviations in predictions of future defect sizes. This in turn leads to inaccurate calculated failure probabilities and optimal inspection cycles, making it impossible to achieve a balance between risk and cost.

[0004] 2) Failure to systematically consider the differentiated impact of regional levels on safety constraints. Factors such as population density and environmental sensitivity in a pipeline's geographic location determine the severity of the consequences of its failure. Pipelines in different regions should adhere to different safety standards; however, existing optimization methods do not consider this factor, generally using a unified, fixed acceptable failure probability as a constraint or relying entirely on the engineer's personal experience. This approach fails to specifically meet the higher safety requirements of high-level regions (such as cities and densely populated areas) and may also lead to excessive testing in low-level areas (such as uninhabited areas), resulting in unnecessary costs. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a method for optimizing the internal detection cycle of a pipeline containing corrosion defects.

[0006] The technical solution adopted by the present invention is: a method for optimizing the internal detection cycle of a pipeline containing corrosion defects, comprising the following steps: Construct an objective function for the internal inspection cycle of pipelines containing corrosion defects;

[0007] Where: For the t Total annual pipeline maintenance cost, For the t The annual failure probability of is the maximum acceptable failure probability of the pipeline; Taking the maximum acceptable failure probability of the pipeline as a constraint, the objective function is iteratively optimized, and the internal inspection cycle corresponding to the optimal solution is the required result; The total pipeline maintenance cost includes pipeline in-line inspection cost, pipeline repair cost, and pipeline corrosion failure cost;

[0008] Where: For the t Annual in-pipeline inspection costs, is the internal inspection cost, is the discount rate, For the t Annual pipeline maintenance costs, For the i The cost of repairing a defect, k For the t The number of pipeline defects per year, is the indicator function, For the t Pipeline corrosion failure costs per year, is the pipeline corrosion failure cost.

[0009] Furthermore, the process of determining the maximum acceptable failure probability of the 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.

[0010] Furthermore, the annual failure probability includes the failure probability of pipeline burst and the failure probability of pipeline leakage.

[0011] Furthermore, the pipeline maintenance cost is calculated as follows: Establish maintenance guidelines first Criterion 1: 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 maintenance cost is calculated as follows:

[0012] Criterion 2: The depth of the corrosion defect is greater than 80% of the nominal wall thickness of the pipe;

[0013] Where: C e is the pipeline excavation cost, C b Cost of installing type B casing, C p Monitoring costs for pipelines.

[0014] Furthermore, the objective function is solved using a Monte Carlo simulation method; Mean value within the detection period T The calculation method is as follows:

[0015] Where: N is the number of iterations, j is the iteration number, T j For the j The inner detection cycle corresponding to the iteration;

[0016] Where: For the pipeline t The annual average total cost of inspection and maintenance within the annual maximum probability of failure is For pipeline t Year j The total pipeline maintenance cost for iterations.

[0017] Furthermore, the pipeline safety level includes low safety level, medium safety level, high safety level and very high safety level, and associated failure rates are set corresponding to the safety levels; The calculation process of the maximum acceptable failure probability of the pipeline is as follows:

[0018] Where: is the correlation failure rate under the corresponding security level, is the pipe length, is the pipeline operating pressure, D is the operating outside diameter of the pipe.

[0019] Furthermore, the annual failure probability is calculated as follows:

[0020] Where: For the t Annual pipeline leakage failure probability, For thet Annual probability of pipeline burst failure; in,

[0021]

[0022] Where: 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 probability of pipeline burst failure.

[0023] Furthermore, the iterative optimization process of the objective function is as follows: Set the number of iterations N , get the N The mean of the internal detection period and the mean of the annual average total cost generated by the iterations; 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; Compare the average annual total cost of the pipeline under the maximum acceptable annual failure probability of pipelines in different regions and grades, select the minimum value, and the corresponding internal inspection cycle is the required internal inspection cycle.

[0024] Furthermore, the associated failure rates corresponding to the pipeline safety levels are as follows: The low security level is 5×10 -3 , the medium safety level is 5×10 -4 , the high security level is 5×10 -5 , the highest security level is 5×10 -6 .

[0025] Further, among them and The calculation process is as follows:

[0026]

[0027] Where: For the t Critical corrosion depth for burst failure, 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 pipe wall thickness.

[0028] The beneficial effects of the present invention are: (1) The present invention uses the total cost of pipeline maintenance as the objective function and the maximum acceptable failure probability of pipelines in different regions and grades as the constraint condition to perform iterative optimization. The calculated internal inspection period is more accurate and can achieve the best balance between ensuring safety and controlling costs. (2) The present invention considers typical failure modes of pipelines by constructing failure probabilities including pipeline burst and leakage, making the calculation of annual failure probability in the optimization model more accurate; (3) The present invention 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 THE DRAWINGS

[0029] Figure 1 Schematic diagram of the process of the present invention.

[0030] Figure 2 Schematic diagram of the simulation solution method in an embodiment of the present invention.

[0031] Figure 3 The average annual total cost in the iterative process of the embodiment of the present invention changes with the acceptable failure probability of the pipeline P a 's changing trend.

[0032] Figure 4 The acceptable failure probability of the pipeline and the detection cycle in the pipeline during the iteration process of the embodiment of the present invention are T relationship. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] The present invention uses minimizing the total cost of pipeline maintenance as the objective function and the maximum acceptable failure probability of pipelines of different regional grades as the constraint condition. Through modeling and iterative optimization, the solution is obtained by minimizing the internal inspection cycle corresponding to the total cost consisting of pipeline inspection cost, repair cost and failure cost. This solution can achieve the optimal balance between ensuring safety and controlling costs.

[0035] A method for optimizing the detection cycle of pipelines containing corrosion defects, such as Figure 1 As shown, the following steps are included: Construct an objective function for the internal inspection cycle of pipelines containing corrosion defects; (1) Where: For the t Total annual pipeline maintenance cost, For the t The annual failure probability of is the maximum acceptable failure probability of the pipeline; The total pipeline maintenance cost includes pipeline in-line inspection cost, pipeline repair cost, and pipeline corrosion failure cost; (2) Where: For the t Annual in-pipeline inspection costs, is the internal inspection cost, is the discount rate, For the t Annual pipeline maintenance costs, For the i The cost of repairing a defect, k For the t The number of pipeline defects per year, is an indicator function related to the corrosion pipeline maintenance criteria, For the t Pipeline corrosion failure costs per year, is the pipeline corrosion failure cost. It should be noted that all costs are relative values.

[0036] in: (3) (4) (5) The pipeline corrosion failure cost is the economic loss converted from the environmental damage and property loss caused by pipeline corrosion failure.

[0037] The process of determining the maximum acceptable failure rate of the 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.

[0038] This confirmation method directly links safety constraints with the geographical environment and regulatory requirements of the pipeline, overcoming the defects of existing technologies that do not distinguish between regions.

[0039] First, according to GB / T24259-2023 "Petroleum and Natural Gas Industry Pipeline Transportation System", determine the pipeline regional level, and combine the fluid type and regional level to obtain the corresponding pipeline safety level. As shown in Table 1: Table 1. Corresponding pipeline safety levels for different regions

[0040] According to the pipeline safety level, determine the associated failure rate under different safety levels , as shown in Table 2 Table 2. Correlation failure rates for different security levels

[0041] Combining the associated failure rate, pipeline operating pressure, and outer diameter, the maximum acceptable failure probability of the natural gas pipeline is calculated: (6) Where: is the correlation failure rate under the corresponding safety level (km -1 ·a -1 ), is the pipeline length (km), is the pipeline operating pressure (bar), D is the operating outer diameter of the pipeline (m).

[0042] The calculation process of annual failure probability is as follows: A random process model is used to describe the evolution of corrosion defects to predict the change of pipeline risk over time. In the target model, within the detection cycle t Annual failure probability It is the basic parameter for evaluating the cost of pipeline corrosion failure. Considering the typical failure modes of pipelines, including leakage and burst caused by corrosion, the internal inspection cycle t The annual failure probability is expressed by the following formula: (7) Where: For the t Annual pipeline leakage failure probability, For the t The annual probability of pipeline failure due to bursting is defined as the probability of pipeline failure due to bursting. t -No expiration occurs before 1 year, only t -1 year to t The probability of failure in a year. To facilitate calculation, the cumulative failure probability of the corroded pipeline can be used, as shown in Equations (8) and (9).

[0043] in, (8) (9) Where: 0~ t Annual cumulative pipeline leakage failure probability, 0~ t -1 year cumulative pipeline leakage failure probability, 0~ t The annual cumulative total failure probability of the pipeline is and The sum of 0~ t Annual cumulative pipeline burst failure probability, 0~ t -1-year cumulative probability of pipeline burst failure.

[0044] Different cumulative failure probabilities of corroded pipelines 、 、 The time-varying nature of the corrosion defect is mainly caused by the change in the corrosion rate, such as the depth and length of the corrosion defect. The gamma degradation process and linear model are used to describe the growth process of the defect. The corrosion depth increment follows the gamma distribution. d k ( t ), corrosion length increases L k ( t ) is expressed using a linear model.

[0045] in and The calculation process is as follows: (10) (11) Where: is the critical corrosion depth at the moment of burst failure (referring to the t Critical corrosion depth at the time of burst failure (years), is the lower incomplete gamma function; is the initial corrosion depth of the pipeline, mm; is the gamma function, is the pipe wall thickness, mm (0.8 is the critical corrosion depth for leakage failure, usually 80% of the wall thickness is taken as the leakage criterion); t For time, a and b are the shape and scale parameters of the gamma degradation process, .in: COV vt is the coefficient of variation of the corrosion depth growth rate; μis the average corrosion depth growth rate, mm / a.

[0046] The pipeline maintenance cost in the objective function considers different maintenance criteria, and the process is as follows: Considering the growth of 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: 1) The maximum corrosion depth is less than or equal to 10% of the nominal wall diameter of the pipeline; 2) When the maximum corrosion depth is greater than 10% and less than or equal to 40% of the nominal wall diameter of the pipeline, the residual strength is less than 1.1 times the maximum operating pressure.

[0047] When the above conditions are not met, the pipeline needs to be repaired.

[0048] Criterion 1: When 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 pipeline is considered to have burst and failed.

[0049] The burst failure limit state function LSF(b) of the pipeline with corrosion defects is as follows: (12) Where: is the failure pressure at the moment of pipeline burst (referring to the t Failure pressure corresponding to the moment of pipeline burst in 2017) MPa, is the pipeline operating pressure, MPa.

[0050] Criterion 2: If the depth of the corrosion defect exceeds 80% of the nominal wall thickness of the pipe, repairs can be performed using patching plates, B-type sleeves, and bolt-tightening fixtures. At this point, the pipe is considered leaking and failed.

[0051] The leakage failure limit state function LSF(d) of a pipeline with corrosion defects is as follows: (13) Where: is the maximum corrosion depth at the time of leakage failure, mm ( t the maximum corrosion depth corresponding to the moment of leakage failure in the year); is the pipe wall thickness, mm.

[0052] The pipeline maintenance cost is calculated as follows: (14) (15) Where: Ce is the pipeline excavation cost, C b Cost of installing type B casing, C p Cost of monitoring pipelines The maximum acceptable failure probability of the pipeline is used as a constraint (annual failure probability is less than the maximum acceptable failure probability of the grade of the area where the pipeline is located), the objective function is iteratively optimized, and the internal inspection cycle corresponding to the optimal solution is the required result.

[0053] Monte Carlo simulation is used to simulate the objective function N Iterative calculation, j is the number of iterations ( j =1,2,3…, N ), No. j The present value of the inspection cost, failure cost and maintenance cost within the iteration (i.e. the inspection cost, pipeline maintenance cost and pipeline corrosion failure cost in the objective function, which are only used here to distinguish the calculated values ​​obtained in the specific iteration process) are respectively 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 possible failure probability range is calculated using the following formula: C t,s (The total cost in the objective function here represents the real-time calculation result during the iteration process, which means the same thing), the mean of the optimal internal detection cycle T as the final output result.

[0054] (16) (17) Where: N is the number of iterations, j is the iteration number, T j For the j The inner detection cycle corresponding to the iteration; For the pipeline t The annual average total cost of inspection and maintenance within the annual maximum probability of failure is For pipeline t Year j The total pipeline maintenance cost for iterations.

[0055] The average annual total cost includes the average annual maintenance cost , average annual failure cost and the average annual testing cost (The annual average total cost is the total cost in the objective function, which is just the value calculated under different conditions and is represented by different symbols for distinction). The calculation process is as follows: (18) (19) (20) Example The following takes a natural gas pipeline as an example to illustrate the actual application process of the present invention.

[0056] The natural gas pipeline has a mileage of 11.9 km and is divided into three levels: Class I, Class II, and Class III. Based on the most recent in-pipeline inspection data, the pipeline has 179 corrosion defects. The parameter probability statistical characteristics are shown in Table 3.

[0057] Table 3. Probability statistics of natural gas pipeline parameters for internal inspection results

[0058] Relative costs were used to set the values ​​for pipeline in-service inspection, failure losses, and repair costs, as shown in Table 4. In actual operation, the pipeline undergoes in-service inspections every four years, with an average annual total pipeline cost of 0.864. The discount rate is 2%.

[0059] Table 4. In-pipeline inspection, failure loss, and pipeline repair cost values ​​based on relative costs

[0060] The specific calculation process is as follows Figure 2 As shown: Step 1: Construct the optimal pipeline internal inspection cycle model, i.e., the objective function. Obtain the parameters listed in Tables 3 and 4 as input parameters for solving the model. These include the corroded pipeline's operating outer diameter, wall thickness, yield strength, tensile strength, operating pressure, corrosion length and depth, and the growth rates of corrosion length and depth, as well as the pipeline internal inspection cost, corrosion failure cost, excavation cost, pipeline monitoring cost, and the cost of installing a Type B sleeve.

[0061] Step 2: Combined with the regional grade of the pipeline with corrosion defects, the corresponding associated failure rate and the input parameters, the maximum acceptable failure probability of the natural gas pipeline is calculated to be 4.98×10 -3 .

[0062] Step 3: Set the initial iteration value of the iterative solution and record the acceptable failure probability of the pipeline as P a The initial value of the acceptable annual failure probability of the pipeline is recorded as Ps ( P s is 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 recorded as Δ P s , the value is 10 -5 .

[0063] Step 4: Based on the input parameters and the defect growth process, use equations (7), (8), (9) and the subset simulation method to obtain the annual failure probability of the corroded pipeline: .

[0064] Step 5: Calculate the pipeline k The time-varying values ​​of the length and depth of each corrosion defect are combined with the limit state functions (12) and (13) to determine the pipeline maintenance method and determine the maintenance cost of the pipeline during service life. C m,t .

[0065] Compare the calculated results in step 4 and the acceptable annual failure probability setting value of the pipeline P s The size of P sf ( t )≥ P s When , the iterative calculation of annual failure probability stops.

[0066] according to Calculated value to determine pipeline corrosion failure cost C f,t ; Calculate the average annual total cost in different corrosion time periods according to formula (16) C t,s ; Calculate the average annual maintenance cost according to equations (18), (19) and (20) , average annual failure cost and the average annual testing cost .

[0067] Step 6: Repeat steps 4 and 5 until the set number of iterations is met N ,Will N The mean of the internal detection cycle and the mean of the annual average total cost generated by the iteration C t,s As the current acceptable failure probability of the pipeline P aIf the acceptable failure probability is less than the maximum acceptable failure probability, proceed to the next step.

[0068] Acceptable initial value of annual failure probability of pipeline P s On the basis of P s , obtain the new acceptable failure probability of the pipeline P a ( P a = P s +Δ P s ); Repeat the iteration until the updated P a When the probability is greater than or equal to the maximum failure probability of the pipeline, the iterative calculation is stopped.

[0069] At this time, the average annual total cost of pipelines under the acceptable annual failure probability of regional grade pipelines is compared. C t,s The size of the filter is the minimum value, which corresponds to the internal detection cycle T That is the optimal value.

[0070] The optimization results of this embodiment are as follows Figure 3 and Figure 4 As shown in the results, it can be seen that when internal inspection is carried out under different service time and acceptable failure probability of pipeline, it is found that the average total cost in the year is P a 2.23×10 -4 The minimum value appears when , indicating that it is most economical to carry out pipeline inspection under this probability threshold. The corresponding annual average total cost and optimal inspection cycle are 0.701 and 9.8 years, respectively, which is about 14.9% lower than the cost of a fixed inspection cycle.

[0071] The present invention uses the maximum acceptable failure probability corresponding to pipelines of different regional grades as the objective function for constraint solving, which solves the defect of the existing technology using a unified failure probability threshold. By establishing differentiated safety constraints, the optimization results can balance the safety risks and economic costs of pipelines in different regions. Taking into account the randomness of corrosion defect growth, a multi-level maintenance decision criterion and cost function are established according to national standards. This analysis of multivariable relationships significantly improves the accuracy of risk assessment and makes the optimization model closer to engineering practice. Finally, a Monte Carlo simulation combined with iterative optimization solution method is used to obtain the optimal solution within a large feasible domain that meets safety constraints. The optimal internal detection period obtained by the method of the present invention is more accurate and more in line with engineering practice than existing optimization methods.

Claims

1. A method for optimizing the internal detection cycle of a pipeline containing corrosion defects, characterized in that: The following steps are involved: Construct an objective function for the internal inspection cycle of pipelines containing corrosion defects; Where: For the t Total annual pipeline maintenance cost, For the t The annual failure probability of is the maximum acceptable failure probability of the pipeline; Taking the maximum acceptable failure probability of the pipeline as a constraint, the objective function is iteratively optimized, and the internal inspection cycle corresponding to the optimal solution is the required result; The total pipeline maintenance cost includes pipeline in-line inspection cost, pipeline repair cost, and pipeline corrosion failure cost; Where: For the t Annual in-pipeline inspection costs, is the internal inspection cost, is the discount rate, For the t Annual pipeline maintenance costs, For the i The cost of repairing a defect, k For the t The number of pipeline defects per year, is the indicator function, For the t Pipeline corrosion failure costs per year, is the pipeline corrosion failure cost.

2. The method for optimizing the internal detection cycle of a pipeline containing corrosion defects according to claim 1, characterized in that: The process of determining the maximum acceptable failure probability of the 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.

3. The method for optimizing the internal detection cycle of a pipeline containing corrosion defects according to claim 1, characterized in that: The annual failure probability includes the pipeline burst failure probability and the pipeline leakage failure probability.

4. The method for optimizing the internal detection cycle of a pipeline containing corrosion defects according to claim 1, characterized in that: The pipeline maintenance cost is calculated as follows: Establish maintenance guidelines first Criterion 1: 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 maintenance cost is calculated as follows: Criterion 2: The depth of the corrosion defect is greater than 80% of the nominal wall thickness of the pipe; Where: C e is the pipeline excavation cost, C b Cost of installing type B casing, C p Monitoring costs for pipelines.

5. The method for optimizing the internal detection cycle of a pipeline containing corrosion defects according to claim 1, characterized in that: The objective function is solved by Monte Carlo simulation method; Mean value within the detection period T The calculation method is as follows: Where: N is the number of iterations, j is the iteration number, T j For the j The inner detection cycle corresponding to the iteration; Where: For the pipeline t The annual average total cost of inspection and maintenance within the annual maximum probability of failure is For pipeline t Year j The total pipeline maintenance cost for iterations.

6. The method for optimizing the internal detection cycle of a pipeline containing corrosion defects according to claim 2, characterized in that: The pipeline safety level includes low safety level, medium safety level, high safety level and very high safety level, and the associated failure rate is set corresponding to the safety level; The calculation process of the maximum acceptable failure probability of the pipeline is as follows: Where: is the correlation failure rate under the corresponding security level, is the pipe length, is the pipeline operating pressure, D is the operating outside diameter of the pipe.

7. The method for optimizing the internal detection cycle of a pipeline containing corrosion defects according to claim 3 is characterized in that: The annual failure probability is calculated as follows: Where: For the t Annual pipeline leakage failure probability, For the t Annual probability of pipeline burst failure; in, Where: 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 probability of pipeline burst failure.

8. The method for optimizing the internal detection cycle of a pipeline containing 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 , get the N The mean of the internal detection period and the mean of the annual average total cost generated by the iterations; 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; Compare the average annual total cost of the pipeline under the maximum acceptable annual failure probability of pipelines in different regions and grades, select the minimum value, and the corresponding internal inspection cycle is the required internal inspection cycle.

9. The method for optimizing the internal detection cycle of a pipeline containing corrosion defects according to claim 6, characterized in that: The associated failure rates corresponding to the pipeline safety levels are as follows: Low security level 5×10 -3 , medium safety level 5×10 -4 , high security level 5×10 -5 , extremely high security level 5×10 -6 .

10. The method for optimizing the internal detection cycle of a pipeline containing corrosion defects according to claim 7, characterized in that: in and The calculation process is as follows: Where: For the t Critical corrosion depth for burst failure, 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 pipe wall thickness.

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