Calculation method for ultimate bearing capacity of copper-nickel alloy pipeline with single spherical defect

Abstract

The invention provides a method for calculating ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect, which comprises the following steps of: representing the defect projection area of the single spherical defect of the copper-nickel alloy pipeline by using a semi-ellipse with a long axis as a defect diameter and a short axis as a defect depth on an axial section to correct the ratio of the defect projection area; based on an allowable stress method and the defect projection area, setting a length correction coefficient and a defect influence correction term, and constructing an ultimate bearing capacity model, containing the length correction coefficient and the defect influence correction term, of the copper-nickel alloy pipeline containing the spherical defect; obtaining a corrected ultimate bearing capacity model based on the numerical simulation result of the single spherical defect under each corrosion depth and length; and after the physical quantity of the to-be-detected copper-nickel alloy pipeline containing the single spherical defect is collected, the corrected ultimate bearing capacity model is adopted for evaluation, and the ultimate bearing capacity is obtained. The method has good evaluation precision on the single spherical defect of the seabed copper-nickel alloy pipeline.

Description

Technical Field

[0001] The present invention relates to the technical field of predicting the ultimate bearing capacity of seawater pipelines, and particularly relates to a method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline with a single spherical defect. Background Art

[0002] The problem of strength assessment of pipe systems after corrosion has always been a hot research topic. With the increase of years, metal loss form defects are formed on the inner wall surface of seawater pipelines under the erosion of seawater. The existence of defects reduces the bearing capacity of seawater pipelines, seriously affecting the reliability and safety of equipment. The failure analysis of the British offshore engineering operating company BRITOIL shows that: among all the examples of ship facility failures, 33% are caused by corrosion. The corrosion of seawater pipe systems can cause corrosion leakage at best, and threaten navigation safety at worst. The reason for the bursting of the engine room seawater pipeline is the sharp rise in the internal pressure of the pipeline, which exceeds the bearing capacity of the pipeline in the areas containing defects such as corrosion, cracks, and sand holes and bursts.

[0003] The corrosion leakage of seawater pipelines mostly occurs at the elbows of the pipelines, mostly local corrosion, and generally starts from the inside of the pipelines and gradually expands outwards. The corrosion inside the pipelines is usually impossible to monitor during the regular maintenance of ships. By the time of dripping, seeping, or even bursting, the pipelines are no longer repairable.

[0004] The working load of seawater pipelines is the internal pressure of the pipelines. Corrosion defects will cause local thinning of the pipeline wall thickness, and the bearing capacity of the pipelines with defects will decrease under the action of internal pressure. When the bearing capacity decreases to a certain critical value, if there is no timely replacement and repair, there is a risk of bursting of the pipelines under normal working pressure. Some scholars equivalent the pipeline with complex defects to the pipeline with a single defect to calculate its ultimate bearing capacity. Take the maximum depth in the complex defects as the equivalent defect corrosion depth, and take the outer contour width and length in the complex defects as the equivalent defect corrosion width and length. However, this method does not consider the uncorroded area between defects, so the evaluation result is on the conservative side. On this basis, the DNV-RP-F101 standard projects the complex corrosion defects, thus considering the influence of the uncorroded area in the axial direction of the interacting defects, but still does not consider the influence of the circumferential uncorroded area, is still on the conservative side, and has certain limitations.

[0005] Complex marine conditions lead to the corrosion of copper-nickel alloy pipes. Defects generally appear in the form of metal loss inside the pipes, and the shape is irregular. The premise of strength evaluation is that the defect size can be measured. Therefore, the irregular corrosion defect is modeled into a regular defect, which can generally be simplified into three types: uniform rectangle, groove, and sphere. Single spherical defects are common in pitting defects, and spherical defects generally appear in the form of pipeline pitting. Electrochemical corrosion in local areas of the pipeline produces similar spherical corrosion pits. Generally, there are fluffy corrosion products covering outside the corrosion pits, which are relatively hidden. Therefore, the study of single spherical defects has practical engineering significance. Summary of the Invention

[0006] The present invention provides a method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline with a single spherical defect, so as to solve the technical problem that in the existing ultimate bearing capacity calculation method, for the single spherical corrosion of copper-nickel alloy pipes in a complex marine environment, the calculation of the ultimate bearing capacity is too conservative and thus inapplicable.

[0007] To solve the above technical problem, the present invention provides a method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline with a single spherical defect, including the following steps:

[0008] Step S1: Characterize the defect projection area of the single spherical defect of the copper-nickel alloy pipeline as a semi-ellipse with the long axis being the defect diameter D P and the short axis being the defect depth d in the axial section projection, so as to correct the ratio of the defect projection areas;

[0009] Step S2: Based on the allowable stress method and the defect projection area, set a length correction coefficient Q P and a defect influence correction term R, and construct an ultimate bearing capacity model of a copper-nickel alloy pipeline with a spherical defect containing the length correction coefficient Q P and the defect influence correction term R;

[0010] Step S3: Based on the numerical simulation results of the single spherical defect at each corrosion depth and length, obtain a corrected ultimate bearing capacity model;

[0011] Step S4: After collecting the physical quantities of the copper-nickel alloy pipeline with a single spherical defect to be detected, use the corrected ultimate bearing capacity model for evaluation to obtain the ultimate bearing capacity.

[0012] Preferably, Step S1 includes: representing the spherical projection area of the single spherical defect as a semi-ellipse with the long axis being the defect diameter D P and the short axis being the defect depth d in the axial section projection, and correcting the ratio of the defect projection areas to:

[0013]

[0014] where t represents the wall thickness, A represents the defect projection area, and A 0 represents the initial projection area.

[0015] Preferably, in Step S2, the expression of the length correction coefficient Q P is:

[0016]

[0017] where L Z represents the pipeline defect length; D represents the pipeline outer diameter; v P1 and vP2 represents a constant coefficient.

[0018] Preferably, in step S2, the expression of the defect influence correction term R is:

[0019]

[0020] In the formula, v P3 represents the constant term; 0.785N represents the ratio of the corrected defect projection area.

[0021] Preferably, in step S2, the expression of the ultimate bearing capacity model is:

[0022]

[0023] In the formula, p CP represents the ultimate bearing capacity of the copper-nickel alloy pipeline with spherical defects; η represents the yield ratio of the material; σ b represents the tensile strength of the material;

[0024] Preferably, step S3 includes:

[0025] Step S31: Avoid applying internal pressure load to the pipeline at both ends during numerical simulation;

[0026] Step S32: Analyze the simulated numerical values of the ultimate bearing capacity to determine the initial values of the length correction coefficient Q P and the defect influence correction term R;

[0027] Step S33: Use the unconstrained multi-variable optimization method, taking the length correction coefficient Q P and the constant term of the defect influence correction term R as design variables, setting the optimization goal for solution, and obtaining the corrected ultimate bearing capacity model.

[0028] Preferably, in step S32, by setting different length correction coefficients Q P and defect influence correction terms R, the ultimate bearing capacity curve is obtained, and compared with the ultimate bearing capacity curve of the numerical simulation to obtain the initial values.

[0029] Preferably, the initial value of the constant term v P in the length correction coefficient Q P1 is set to 1.1, and the initial value of v P2 is set to 1.2; the initial value of the constant term v P3 in the defect influence correction term R is set to 1.07.

[0030] Preferably, the expression of the optimization goal e(r) in step S33 is:

[0031]

[0032] In the formula, k represents the number of numerical simulations; p FEA represents the result of the numerical simulation; ν P3 represents the constant term of the defect influence correction term R; η represents the yield ratio of the material; σ b represents the tensile strength of the material; L Z represents the length of the pipeline defect; D represents the outer diameter of the pipeline; 0.785N represents the ratio of the corrected defect projection area; t represents the wall thickness.

[0033] Preferably, in step S3, the expression of the corrected ultimate bearing capacity model is:

[0034]

[0035] In the formula, L Z represents the length of the pipeline defect; D represents the outer diameter of the pipeline; 0.785N represents the ratio of the corrected defect projection area; η represents the yield ratio of the material; σ b represents the tensile strength of the material; t represents the wall thickness.

[0036] The beneficial effects of the present invention at least include: Single spherical defects are common in pitting defects, and studying single spherical defects has practical engineering significance. Based on the establishment of the ultimate bearing capacity evaluation and prediction model of copper-nickel alloy pipelines with groove defects, by taking the defect projection area of the single spherical defect of the copper-nickel alloy pipeline, and representing the projection on the axial section as a semi-ellipse with the major axis being the defect diameter D P and the minor axis being the defect depth d to correct the ratio of the corrected defect projection area, and at the same time, relatively assist in correcting the length correction coefficient Q P and the defect influence correction term R, study the influence law of each parameter of the pipeline on the ultimate bearing capacity, correct the ultimate bearing capacity evaluation and prediction model of the copper-nickel alloy pipeline with spherical defects, and apply the obtained calculation formula to the calculation of the ultimate bearing capacity of the seawater pipeline, which is more accurate for the calculation of the ultimate bearing capacity of the single spherical defect of the copper-nickel alloy pipeline in the marine environment. Description of the Drawings

[0037] Figure 1 is a schematic diagram of the projection area method of the single spherical defect of the embodiment of the present invention;

[0038] Figure 2 is a schematic diagram of the relationship between the defect depth and the ultimate bearing capacity of the embodiment of the present invention;

[0039] Figure 3 is a schematic diagram of the comparison between the numerical analysis results when the constant term in the length correction coefficient of the embodiment of the present invention takes different values;

[0040] Figure 4Schematic diagram of the correction effect of the correction formula for different defect diameters of the spherical defect in the calculation method of the ultimate bearing capacity of a copper-nickel alloy pipeline with a single spherical defect according to an embodiment of the present invention;

[0041] Figure 5 Schematic longitudinal section of pitting corrosion according to an embodiment of the present invention. Specific embodiments

[0042] The following combines the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0043] Single spherical defects are commonly found in pitting corrosion defects, and studying single spherical defects has practical engineering significance. The present invention corrects the defect projection area to establish an evaluation model for the ultimate bearing capacity of a copper-nickel alloy pipeline with a single spherical defect, establishes a numerical calculation model close to the characteristics of an actual seawater pipeline based on the finite element method of explicit dynamics, analyzes the bursting failure characteristics of the pipeline under the action of internal pressure according to the numerical simulation results, studies the influence law of each parameter of the pipeline on the ultimate bearing capacity, corrects the evaluation and prediction model for the ultimate bearing capacity of a copper-nickel alloy pipeline with a spherical defect, and applies the corrected calculation formula to the calculation of the ultimate bearing capacity of a seawater pipeline.

[0044] An embodiment of the present invention provides a calculation method for the ultimate bearing capacity of a copper-nickel alloy pipeline with a single spherical defect, including the following steps:

[0045] Step S1: Characterize the defect projection area of the single spherical defect of the copper-nickel alloy pipeline as a semi-ellipse with the projection on the axial section having a major axis as the defect diameter D P and a minor axis as the defect depth d to correct the ratio of the defect projection area;

[0046] Step S2: Based on the allowable stress method and the defect projection area, set a length correction coefficient Q P and a defect influence correction term R, and construct a model for the ultimate bearing capacity of a copper-nickel alloy pipeline with a spherical defect containing the length correction coefficient Q P and the defect influence correction term R;

[0047] Step S3: Based on the numerical simulation results of single spherical defects at each corrosion depth and length, obtain a corrected ultimate bearing capacity model;

[0048] Step S4: After collecting the physical quantities of the copper-nickel alloy pipeline with a single spherical defect to be detected, use the corrected ultimate bearing capacity model for evaluation to obtain the ultimate bearing capacity.

[0049] Specifically, in step S1, compared with conventional groove defects, the difference between spherical defects is that their projected areas are inconsistent. The projected area of a spherical defect is represented by D p ·d, as shown in Figure 1 , but the calculation error is relatively large. The projection of a spherical defect on the axial section is a semi-ellipse with a major axis equal to the defect diameter D P and a minor axis equal to the defect depth d. In the embodiment of the present invention, the projected area of the spherical defect is represented by the area of this semi-elliptical shape, and the ratio of the defect projected areas is corrected to:

[0050]

[0051] In the formula, t represents the wall thickness, A represents the defect projected area, and A 0 represents the initial projected area.

[0052] In step S2, based on the allowable stress method DNV, a length correction coefficient Q is provided to correct the influence caused by the axial length of the defect. However, we note that the DNV standard does not distinguish between defect types, and the correction object of this length correction coefficient is defects with a relatively large length. Usually, the corrosion length ratio of such defects can reach 50 or even 100. However, for the spherical defects targeted in the embodiment of the present invention, their corrosion length ratio Z is generally small. Taking the defect diameter D P = 12 mm as an example, its corrosion length ratio Z is which is much smaller than the correction range of the length correction coefficient Q provided in DNV. Therefore, it is necessary to re-establish the length correction coefficient Q.

[0053] In the embodiment of the present invention, the form of Q in the DNV standard is cited, and it is represented by Q P . Assuming the form of Q P is as follows, which includes two constant coefficients v P1 , v P2 . The value of Q is re-established through the numerical analysis results. P

[0054]

[0055] In the formula, L Z represents the pipeline defect length; D represents the pipeline outer diameter;

[0056] Compared with the DNV standard, equations (1) and (2) respectively correct the errors of the projected area and the defect morphology, but other factors such as the difference in corrosion position are not taken into account. All other factors are corrected by the correction coefficient ν P3 in the reduction ratio R, i.e., the defect influence correction term. Then the R term is corrected to:

[0057]

[0058] Finally, the expression of the ultimate bearing capacity model of the copper-nickel alloy pipeline with spherical defects is obtained as follows:

[0059]

[0060] In the above formula, p CP is the ultimate bearing capacity of the copper-nickel alloy pipeline with spherical defects.

[0061] In step S3, by studying the failure characteristics of the bursting process of the pipeline with a single spherical defect, a modified ultimate bearing capacity model is obtained. The specific method includes:

[0062] Taking the corrosion depth ratio N and the corrosion diameter D P to describe the degree of corrosion, and calculating the ultimate bearing capacity values of the copper-nickel alloy pipeline under different defect parameters by the finite element method based on explicit dynamics. Pitting corrosion of seawater pipelines generally appears in the form of small corrosion pits. Therefore, when designing the defect size, the case where the defect diameter is between 3 mm and 12 mm is considered. It is found that when designing the defect, when the corrosion depth is greater than the defect radius, most or even all of the designed defects will be buried in the pipe wall, which is difficult to mesh and difficult to solve by the finite element method. Therefore, the design of such defects is avoided. The parameter design of the single spherical corrosion defect is shown in Table 1. According to the defect parameters provided in this table, 17 simulations are completed, and the explicit finite element simulations of 17 pipelines are completed.

[0063] Table 1 Pipeline number table with spherical defects

[0064]

[0065]

[0066] Select the numerical simulation results of the pipeline numbered P9# in Table 1 for the analysis and description of the mechanical behavior and fracture characteristics as follows.

[0067] According to the results of the 17 groups of numerical simulations in Table 1, the relationship diagram between the corrosion defect depth ratio N and the ultimate bearing capacity of all simulations can be obtained, as Figure 2 shown. The depth ratio of the defect and the ultimate bearing capacity are approximately negatively correlated, and the deeper the corrosion defect depth, the greater the tangent slope of the curve, that is, the greater the impact on the ultimate bearing capacity of the copper-nickel alloy pipeline, indicating that the influence of the corrosion defect depth on the ultimate bearing capacity of the copper-nickel alloy pipeline gradually strengthens with the increase of the depth. When the corrosion depth is relatively shallow, the three curves are close to each other, indicating that the diameter has a small impact on the strength, and the ultimate bearing capacity decreases with the increase of the diameter; when the corrosion depth is relatively deep, the three curves gradually separate, indicating that the defect diameter has a more obvious impact on the strength when the corrosion depth is relatively deep.

[0068] The prediction model of the ultimate bearing capacity of copper-nickel alloy pipelines with single spherical defects was modified. The finite element method was used to perform numerical analysis and the ultimate bearing capacity of the pipelines at various corrosion depths and lengths was obtained. P1 ,v P2 ,v P3 The result of formula (4) is close to the numerical analysis result, and the unconstrained multivariate optimization method can achieve this effect.

[0069] In order to set a good initial value to make the fitting effect of the unconstrained multivariate optimization method more ideal, the length correction coefficient Q P The constant term in the defect effect correction term R is analyzed as follows.

[0070] Based on multiple standard parameters, let v P1 =0.31, 0.6275, 0.8, 1.0, 1.1. Based on the parameters of pipelines P12# to P17# in Table 1, the results of formula (4) are compared with the results of numerical analysis. Figure 3 shown.

[0071] from Figure 3 It can be seen that v P1 The larger the value, the greater the slope of the curve, and the closer it is to the numerical simulation result. P1 The initial value of is 1.1. Similarly, determine v P2 The initial value is 1.2, v P3 The initial value is 1.07. Optimize v P1 ,v P2 ,v P3 The value of brings the value of formula (4) closer to the result of numerical analysis.

[0072] Using unconstrained multivariate optimization methods, v P =[v P1 ,v P2 ,v P3 ] T As the design variable, the sum of squares of the differences between the 17 sets of finite element results and the modified formula is used as the optimization target

[0073]

[0074] In the formula, p FEA is the result of numerical analysis. When the value of e(r) is the smallest, it is determined that this set of design variables has the best fitting effect. The optimal design variables calculated are x = [1.0 1.1834 1.0556] T Based on this, the formula of the revised ultimate bearing capacity model can be written as:

[0075]

[0076] Take the pipelines from P6# to P11# in Table 1, D P = 9 mm; for the pipelines from P12# to P17#, D P = 12 mm, compare the calculation results of the allowable stress method in DNV RP-F101 criterion, the numerical analysis results and the calculation results of the modified formula as Figure 4 shown, D P = 3 mm, D P = 6 mm, these two cases could not be compared due to too little data. From Figure 4 it can be seen that taking the numerical analysis results as the reliable results, there are errors in the calculation results of the allowable stress method in DNV RP-F101 criterion in the wall thickness direction, showing that the error is larger when the pipeline depth increases with the defect depth; the modified formula has good evaluation accuracy.

[0077] The seawater pipeline takes bursting as the limit state, so the ultimate bearing capacity is the bursting pressure of the seawater pipeline. Through the correction of the numerical analysis results, the evaluation model of the ultimate bearing capacity of the copper-nickel alloy pipe with spherical defects is improved. The present invention applies this model to the calculation of the ultimate bearing capacity of 3 actual pipelines and gives specific calculation examples.

[0078] Spherical defects generally appear in the form of pitting corrosion of pipelines. Electrochemical corrosion in local areas of pipelines produces similar spherical corrosion pits. Generally, there are fluffy corrosion products covering outside the corrosion pits, which are relatively concealed. The possible morphologies and schematic diagrams of pitting corrosion defects are as Figure 5 shown. This calculation example details the process of obtaining the ultimate bearing capacity model in the embodiment of the present invention, that is, calculating the ultimate bearing capacity by formula (6).

[0079] The calculation example is as follows:

[0080] Step 1: Determine the defect diameter D of the seawater pipeline P , defect depth d, outer diameter D of the pipe, inner diameter D i , pipeline wall thickness t, and the test data are shown in Table 2:

[0081] Table 2 Seawater pipeline size data

[0082]

[0083] Step 2: Obtain the pipe material parameters. According to the parameters of the actual seawater pipeline, the raw materials for obtaining these material parameters come from the bursting test pipeline, and the data are as follows:

[0084] Step 3: Take Pipe No. 4 as an example, use formula (6) to calculate the ultimate bearing capacity evaluation, and the calculation unit is based on the International System of Units SI (mm).

[0085] Yield ratio:

[0086] η = σs / σ b = 141 / 341 = 0.4135(7)

[0087] Corresponding intact pipeline burst pressure value:

[0088]

[0089] Corrosion length correction factor:

[0090]

[0091] Corrosion depth ratio:

[0092]

[0093] Then the calculated burst pressure result of the pipeline with spherical defect No. 4 is:

[0094]

[0095] = 35.403 MPa

[0096] Similarly, using formula (6) to calculate the burst pressures of pipelines No. 5 and No. 6 are 31.431 MPa and 38.008 MPa.

[0097] The present invention establishes a limit bearing capacity prediction model for copper-nickel alloy pipelines with single spherical defects, conducts numerical simulations on the bursting of pipelines with spherical defects, and modifies the initial prediction model using the numerical simulation results.

[0098] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. Only the preferred embodiments of the present invention are expressed. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. As long as the combinations of these technical features do not conflict, they should be considered as within the scope described in this specification.

[0099] It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect, characterized in that: The following steps are involved: Step S1: The defect projection area of ​​the single spherical defect of the copper-nickel alloy pipeline is taken as the defect diameter D with the major axis of the projection on the axial section P , a semi-ellipse with a minor axis of the defect depth d is used to characterize the defect in order to correct the ratio of the defect projection area; Step S2: Based on the allowable stress method and the defect projection area, set the length correction coefficient Q P and the defect effect correction term R, and construct the length correction factor Q containing the P The ultimate bearing capacity model of copper-nickel alloy pipelines with spherical defects and defect effect correction term R; Step S3: based on the numerical simulation results of the single spherical defect at various corrosion depths and lengths, a revised ultimate bearing capacity model is obtained; Step S4: After collecting the physical quantities of the copper-nickel alloy pipeline containing the single spherical defect to be detected, the modified ultimate bearing capacity model is used for evaluation to obtain the ultimate bearing capacity.

2. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 1 is characterized in that: Step S1 includes: taking the major axis of the projection on the axial section as the defect diameter D P , the semi-ellipse with the short axis being the defect depth d represents the spherical projection area of ​​a single spherical defect, and the ratio of the defect projection area is corrected to: Where t represents the wall thickness, A represents the defect projection area, and A0 represents the initial projection area.

3. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 2 is characterized in that: In step S2, the length correction coefficient Q P The expression is: Where, L Z represents the length of pipeline defects; D represents the outer diameter of the pipeline; v P1 and v P2 represents a constant coefficient.

4. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 3 is characterized in that: In step S2, the defect impact correction term R is expressed as: In the formula, v P3 represents a constant term; 0.785N represents the ratio of the defect projection area after correction.

5. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 4 is characterized in that: In step S2, the expression of the ultimate bearing capacity model is: In the formula, p CP represents the ultimate bearing capacity of copper-nickel alloy pipelines containing spherical defects; η represents the material yield strength ratio; σ b Indicates the tensile strength of the material.

6. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 1, characterized in that: Step S3 includes: Step S31: applying an internal pressure load to the pipeline while avoiding both ends of the pipeline in the numerical simulation; Step S32: Analyze the simulated value of the ultimate bearing capacity to determine the length correction coefficient Q P and the initial value of the defect effect correction term R; Step S33: Using an unconstrained multivariate optimization method, the length correction coefficient Q P The constant term of the defect effect correction term R is taken as the design variable, and the optimization target is set to solve it, and the corrected ultimate bearing capacity model is obtained.

7. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 6 is characterized in that: In step S32, different length correction coefficients Q are set. P The ultimate bearing capacity curve is obtained by adding the defect influence correction term R, and compared with the ultimate bearing capacity curve of numerical simulation to obtain the initial value.

8. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 7 is characterized in that: The length correction factor Q P The constant term v P1 The initial value of v is set to 1.1, P2 The initial value is set to 1.2; the constant term v in the defect impact correction term R P3 The initial value is set to 1.

07.

9. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 8, characterized in that: The expression of the optimization target e(r) in step S33 is: Where k represents the number of numerical simulations; p FEA represents the result of numerical simulation; ν P3 represents the constant term of the defect effect correction term R; η represents the material yield strength ratio; σ b Indicates the tensile strength of the material; L Z represents the length of pipeline defect; D represents the outer diameter of the pipeline; 0.785N represents the ratio of the corrected defect projection area; t represents the wall thickness.

10. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 1, characterized in that: In step S3, the expression of the modified ultimate bearing capacity model is: Where, L Z Indicates the length of pipeline defects; D indicates the outer diameter of the pipeline; 0.785N represents the ratio of the corrected defect projection area; η represents the material yield strength ratio; σ b Indicates the tensile strength of the material; t represents the wall thickness.

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