Method for calculating ultimate bearing capacity of copper-nickel alloy pipeline containing single spherical defects

Abstract

The present invention provides a method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect. The method characterizes the defect projected area of ​​a single spherical defect in the copper-nickel alloy pipeline as a semi-ellipse with the major axis as the defect diameter and the minor axis as the defect depth, projected on an axial cross-section, to correct the defect projected area ratio. A length correction factor and a defect impact correction term are set based on the allowable stress method and the defect projected area, and an ultimate bearing capacity model for the copper-nickel alloy pipeline containing the spherical defect is constructed, incorporating the length correction factor and the defect impact correction term. A corrected ultimate bearing capacity model is obtained based on numerical simulation results of single spherical defects at various corrosion depths and lengths. Physical quantities of the copper-nickel alloy pipeline containing the single spherical defect to be tested are collected and evaluated using the corrected ultimate bearing capacity model to obtain the ultimate bearing capacity. This method has excellent evaluation accuracy for single spherical defects in submarine copper-nickel alloy pipelines.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of seawater pipeline ultimate bearing capacity prediction, and particularly relates to a copper-nickel alloy pipeline ultimate bearing capacity calculation method containing single spherical defects. BACKGROUND

[0002] The problem of evaluating the strength of the pipeline after corrosion has always been a hot research topic. With the increase of the age, the inner wall surface of the seawater pipeline forms defects in the form of metal loss under the erosion of seawater. The existence of defects reduces the bearing capacity of the seawater pipeline and seriously affects the reliability and safety of the equipment. The failure analysis of BRITOIL, a British offshore engineering operating company, shows that 33% of all ship facility failures are caused by corrosion. The corrosion of the seawater pipeline may cause corrosion leakage at the lightest and threaten the safety of navigation at the heaviest. The reason for the burst of the engine room seawater pipeline is that the pressure in the pipeline rises sharply, and the bearing capacity of the pipeline in the defect area containing corrosion, cracks, sand holes and the like exceeds the bearing capacity of the pipeline and bursts.

[0003] The corrosion leakage of the seawater pipeline often occurs at the elbow of the pipeline, is mostly local corrosion, and generally starts from the inside of the pipeline and gradually expands to the outside. The corrosion in the pipeline cannot be monitored by the conventional maintenance of the ship, and when there is dripping, seepage or even rupture, the pipeline has no repairability.

[0004] The working load of the seawater pipeline is the internal pressure of the pipeline, and the corrosion defect can cause the local thinning of the wall thickness of the pipeline. The bearing capacity of the pipeline containing defects is reduced under the action of the internal pressure. When the bearing capacity is reduced to a certain critical value, if it is not replaced and maintained in time, the pipeline will have the risk of bursting under the normal working pressure. Some scholars equivalent the pipeline containing complex defects to the pipeline containing single defects to calculate the ultimate bearing capacity. The maximum depth in the complex defect is taken as the equivalent defect corrosion depth, and the outer contour width and length in the complex defect are taken as the equivalent defect corrosion width and length, but this method does not consider the uncorroded area between the defects, so the evaluation result is conservative. On the basis of this, the DNV-RP-F101 standard projects the complex corrosion defects, so as to consider the influence of the uncorroded area in the axial direction of the interacting defects, but still does not consider the influence of the uncorroded area in the circumferential direction, is still conservative and has certain limitations.

[0005] The complex marine conditions cause the corrosion of the copper-nickel alloy pipe, and the defects generally appear in the form of metal loss in the pipeline and have irregular shapes. The premise of strength evaluation is that the defect size is measurable, so the irregular corrosion defect model is modeled as a regular defect, which can be generally simplified into three types of uniform matrix, groove and sphere. Single spherical defects are commonly seen in pitting defects, and the spherical defects generally appear in the form of pitting of the pipeline. The electrochemical corrosion in the local area of the pipeline produces similar spherical corrosion pits, and generally there are fluffy corrosion products outside the pits to block them, which are relatively hidden. Therefore, the study on single spherical defects has practical engineering significance. SUMMARY

[0006] The application provides a method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline with a single spherical defect, to solve the technical problem that the existing method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline with a single spherical defect is too conservative for the calculation of the ultimate bearing capacity of the copper-nickel alloy pipeline under complex marine environments.

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

[0008] Step S1: The defect projection area of the single spherical defect of the copper-nickel alloy pipeline is characterized by a half-elliptical projection on the axial section, with the long axis being the defect diameter D P and the short axis being the defect depth d, to correct the defect projection area ratio.

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

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

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

[0012] Preferably, step S1 comprises: representing the spherical projection area of the single spherical defect as a half-elliptical projection on the axial section, with the long axis being the defect diameter D P and the short axis being the defect depth d, and correcting the defect projection area ratio to:

[0013]

[0014] In the formula, t represents the wall thickness, A represents the defect projection area, and A0 represents the initial projection area.

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

[0016]

[0017] In the formula, L Z represents the pipeline defect length, D represents the pipeline outer diameter, v P1 and v P2represents a constant term; 0.785N represents the ratio of the projected area of the defect after correction.

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

[0019]

[0020] wherein v P3 represents a constant term; 0.785N represents the ratio of the projected area of the defect after correction.

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

[0022]

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

[0024] Preferably, step S3 comprises:

[0025] Step S31: in numerical simulation, internal pressure load is applied to the pipeline at both ends of the pipeline;

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

[0027] Step S33: using an unconstrained multi-variable optimization method, the constant term of the length correction coefficient Q P and the defect influence correction term R are taken as design variables, an optimization objective is set for solving, and a corrected ultimate bearing capacity model is obtained.

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

[0029] Preferably, the length correction coefficient Q P The initial value of the constant term v 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, in step S33, the expression of the optimization objective e(r) is:

[0031]

[0032] wherein k represents the number of numerical simulation; p FEA represents the result of numerical simulation; v 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 defect length of the pipeline; D represents the outer diameter of the pipeline; 0.785N represents the ratio of the corrected defect projection area; and t represents the wall thickness.

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

[0034]

[0035] wherein L Z represents the defect length of the pipeline; 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; and t represents the wall thickness.

[0036] The present application has at least the following beneficial effects: single spherical defects are common in pitting defects, and the study of single spherical defects has practical engineering significance. On the basis of establishing the ultimate bearing capacity evaluation and prediction model of the copper-nickel alloy pipeline containing groove defects, the defect projection area of the single spherical defect of the copper-nickel alloy pipeline is characterized by the projection on the axial section as a semi-elliptical shape with the long axis as the defect diameter D P and the short axis as the defect depth d, the ratio of the corrected defect projection area is corrected, and the length correction coefficient Q P and the defect influence correction term R are also corrected, the influence law of each parameter of the pipeline on the ultimate bearing capacity is studied, the ultimate bearing capacity evaluation and prediction model of the copper-nickel alloy pipeline containing spherical defects is corrected, and the calculation formula obtained by the correction is applied 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. BRIEF DESCRIPTION OF DRAWINGS

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

[0038] Figure 2 FIG. 3 is a schematic diagram of the relationship between the defect depth and the ultimate bearing capacity of the embodiment of the present application;

[0039] Figure 3 FIG. 5 is a comparison diagram of the constant term in the length correction coefficient of the embodiment of the present application and the numerical analysis result when the constant term takes different values;

[0040] Figure 4The schematic diagram of the correction effect of the correction formula of the spherical defect under different defect diameters in the limit bearing capacity calculation method of the copper-nickel alloy pipeline with single spherical defect of the embodiment of the present application;

[0041] Figure 5 The schematic diagram of the pitting longitudinal section of the embodiment of the present application. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application are clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0043] Single spherical defects are common in pitting defects, and it is of practical engineering significance to study single spherical defects. The present application establishes a limit bearing capacity evaluation model of a copper-nickel alloy pipeline with single spherical defects by correcting the defect projection area, establishes a numerical calculation model close to the actual seawater pipeline characteristics based on the explicit dynamics finite element method, analyzes the burst failure characteristics of the pipeline under the action of the internal pressure of the pipeline according to the numerical simulation results, studies the influence law of each parameter of the pipeline on the limit bearing capacity, corrects the limit bearing capacity evaluation and prediction model of the copper-nickel alloy pipeline with spherical defects, and applies the corrected calculation formula to the limit bearing capacity calculation of the seawater pipeline.

[0044] The embodiment of the present application provides a limit bearing capacity calculation method of a copper-nickel alloy pipeline with single spherical defects, which comprises the following steps:

[0045] Step S1: the defect projection area of the single spherical defect of the copper-nickel alloy pipeline is characterized by a half-elliptical shape with a long axis as a defect diameter D P and a short axis as a defect depth d on the axial section, so as to correct the ratio of the defect projection area;

[0046] Step S2: based on the allowable stress method and the defect projection area, a length correction coefficient Q P and a defect influence correction term R are set, and a limit bearing capacity model of the copper-nickel alloy pipeline with spherical defects containing the length correction coefficient Q P and the defect influence correction term R is constructed;

[0047] Step S3: based on the numerical simulation results of the single spherical defect under each corrosion depth and length, a corrected limit bearing capacity model is obtained;

[0048] Step S4: after collecting the physical quantities of the copper-nickel alloy pipeline with single spherical defects to be detected, the corrected limit bearing capacity model is used for evaluation, and the limit bearing capacity is obtained.

[0049] Specifically, in step S1, the difference between spherical defects and conventional groove defects is that the projected areas of the two are inconsistent. The projected area of ​​spherical defects is calculated using D p ·d means, if Figure 1 As shown, the calculation error is large. The projection of the spherical defect on the axial section is the long axis of the defect diameter D P , a semi-ellipse with a short axis of the defect depth d. In the embodiment of the present invention, the area of ​​the semi-ellipse is used to represent the projected area of ​​the spherical defect, and the ratio of the defect projected area is corrected to:

[0050]

[0051] Where t represents the wall thickness, A represents the defect projection area, and A0 represents the initial projection area.

[0052] In step S2, based on the allowable stress method, DNV provides a length correction factor Q to correct the effect of the axial length of the defect. However, we note that the DNV standard does not distinguish between defect types, and the correction object of the length correction factor is the defect with a larger length. Often, the corrosion length of such defects is longer than that of the axial length. It can reach 50 or even 100. However, for the spherical defects targeted by the embodiments of the present invention, the corrosion length ratio Z is generally smaller than the defect diameter D. P =12mm is taken as an example, and its corrosion length ratio Z is This is far smaller than the correction range of the length correction factor Q provided by DNV, so the length correction factor Q needs to be re-established.

[0053] In the embodiment of the present invention, the form of Q in the DNV standard is quoted, and Q P To express it, suppose Q P The form is as follows, including v P1 ,v P2 Two constant coefficients, re-establish the coefficients through numerical analysis results to determine Q P The value of .

[0054]

[0055] Where, L Z Indicates the length of pipeline defects; D indicates the outer diameter of the pipeline;

[0056] Compared with the DNV standard, equations (1) and (2) correct the errors of the projected area and defect morphology respectively, but factors such as the difference in corrosion position are not taken into account. P3 Correct all other factors in the reduction ratio R, which is the defect effect correction term. Then the R term is corrected as follows:

[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, the modified ultimate bearing capacity model is obtained by studying the burst process failure characteristics of the pipeline with single spherical defects, and the specific method includes:

[0062] The corrosion depth ratio N and the corrosion diameter D P describe the extent of corrosion, and the ultimate bearing capacity values of the copper-nickel alloy pipeline under different defect parameters are calculated by the explicit dynamics-based finite element method. Pitting corrosion of seawater pipelines generally occurs in the form of small corrosion pits, so the defect diameter is considered to be between 3mm and 12mm when designing the defect size. It is found that when the corrosion depth is greater than the defect radius, the designed defect will be buried in the pipe wall, and it is difficult to mesh the defect, so the finite element method is difficult to solve, so such defects are avoided in design. The parameter design of single spherical corrosion defects is shown in Table 1, and 17 times of simulation are provided according to the defect parameters in the table, and 17 times of explicit finite element simulation of the pipeline are completed.

[0063] Table 1 Number table of pipeline with spherical defects

[0064]

[0065]

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

[0067] According to the results of the 17 numerical simulations in Table 1, the relationship between the corrosion defect depth ratio N and the ultimate bearing capacity of all simulated corrosion defects can be obtained, as shown in Figure 2 The depth ratio of the defect and the ultimate bearing capacity is approximately negatively related, and the deeper the corrosion defect depth, the greater the slope of the tangent on the curve, i.e. the greater the influence 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 increases with the increase of the depth. When the corrosion depth is shallow, the three curves are close, indicating that the diameter has a small influence on the strength, and the ultimate bearing capacity decreases with the increase of the diameter; when the corrosion depth is deep, the three curves gradually separate, indicating that the defect diameter has a more obvious influence on the strength when the corrosion depth is 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 under 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 is set to P The constant term in the defect impact 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, using the parameters of the 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 results. Therefore, we choose v 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 method, 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, e(r), is used as the optimization target.

[0073]

[0074] Where p FEA is the result of numerical analysis. When the e(r) value is the smallest, it is determined that this set of design variables has the best fitting effect. The optimal design variables are calculated to be 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] Taking P6# to P11# pipelines in Table 1, D P = 9mm; P12# to P17# pipelines, D P = 12mm, as shown in the following table, the comparison of DNV RP-F101 guideline allowable stress method calculation results, numerical analysis results and modified formula calculation results Figure 4 P = 3mm, D P = 6mm, two cases are not compared due to too little data. As can be seen from the table, taking the numerical analysis results as reliable results, the DNV RP-F101 guideline allowable stress method calculation results have errors in the wall thickness direction, which is manifested in that the error is larger as the defect depth of the pipeline increases; the modified formula has good evaluation accuracy. Figure 4

[0077] The seawater pipeline takes burst as the limit state, so the ultimate bearing capacity is the burst pressure of the seawater pipeline. Through the modification of the numerical analysis results, the evaluation model of the ultimate bearing capacity of the copper-nickel alloy pipe containing spherical defects is improved. The model is applied to the calculation of the ultimate bearing capacity of three actual pipelines, and specific calculation examples are given.

[0078] Spherical defects generally appear in the form of pipeline pitting. Similar spherical corrosion pits are produced by electrochemical corrosion in local areas of the pipeline, and there are generally fluffy corrosion products outside the pits, which are relatively hidden. The appearance and schematic diagram of the pitting defect that may appear are shown in the following table. This example elaborates the process of calculating the ultimate bearing capacity by the model of the embodiment of the application, i.e., formula (6). Figure 5

[0079] The calculation example is as follows:

[0080] Step one: determine the defect diameter D P , defect depth d, pipe outer diameter D, inner diameter D i , pipeline wall thickness t, and the test data are shown in the following table:

[0081] Table 2: Size data of seawater pipeline

[0082]

[0083] Step two: obtain the pipe material parameters. According to the parameters of the actual seawater pipeline, the material parameters are obtained from the burst test pipeline, and the data are as follows:

[0084] Step three: taking 4# pipe as an example, the formula (6) is used to calculate the ultimate bearing capacity, and the calculation unit is SI (mm).

[0085] Yield strength ratio:

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

[0087] Corresponding intact pipeline bursting pressure value:

[0088]

[0089] Corrosion length correction factor:

[0090]

[0091] Corrosion depth ratio:

[0092]

[0093] The calculation result of the bursting pressure of the 4# pipeline containing spherical defects is:

[0094]

[0095] =35.403MPa

[0096] Similarly, using formula (6), the bursting pressures of pipelines 5# and 6# are calculated to be 31.431MPa and 38.008MPa.

[0097] The present invention establishes an ultimate bearing capacity prediction model for a copper-nickel alloy pipeline containing a single spherical defect, performs a numerical simulation of the blasting of the spherical defect pipeline, and uses the numerical simulation results to correct the initial prediction model.

[0098] The technical features of the above embodiments may be combined in any manner. To simplify the description, not all possible combinations of the technical features in the above embodiments are described. Only preferred embodiments of the present invention are presented. While the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. As long as there are no contradictions in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] It should be noted that those skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on 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 by: 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 being the defect diameter D. P , a semi-ellipse with the minor axis being the defect depth d is used to characterize the defect in order to correct the ratio of the defect projected 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 containing spherical defects and the 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 inspected, the modified ultimate bearing capacity model is used for evaluation to obtain the ultimate bearing capacity; Step S1 includes: taking the long 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. 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; In step S2, the length correction coefficient Q P The expression is: Where, L Z Indicates the length of pipeline defects; D indicates the outer diameter of the pipeline; v P1 and v P2 represents a constant coefficient; In step S2, the defect impact correction term R is expressed as: Where, v P3 represents a constant term; 0.785N represents the ratio of the corrected defect projection area; In step S2, the expression of the ultimate bearing capacity model is: Where 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.

2. 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 the unconstrained multivariate optimization method, the length correction coefficient Q P The constant term of the defect effect correction term R is used as the design variable, and the optimization target is set to solve the problem, and the corrected ultimate bearing capacity model is obtained.

3. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 2, wherein: 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.

4. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 3, wherein: The length correction factor Q P The constant term v P1 The initial value is set to 1.1, v 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.

5. The method for calculating the ultimate bearing capacity of a copper-nickel alloy pipeline containing a single spherical defect according to claim 4, 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 defects; D represents the outer diameter of the pipeline; 0.785N represents the ratio of the corrected defect projection area; t represents the wall thickness.

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: In step S3, the expression of the revised 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 indicates the wall thickness.

Images