Evaluation method of ultimate bearing capacity of seawater pipelines with double-point defects

Abstract

The present invention provides a method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect, comprising the following steps: step S1: expressing the ultimate bearing capacity model of a pipeline containing an axial double-ball defect as the product of a distance influence factor #imgabs0# and an ultimate bearing capacity model of a pipeline containing a single-ball defect #imgabs1#; step S2: collecting the corrosion depth ratio of the seawater pipeline with the double-ball defect to be detected N , corrosion diameter #imgabs2# and the center distance of the axial double spherical defect l d ; Step S3: Input the data collected in step S2 into the ultimate bearing capacity model of the pipeline with axial double spherical defects to obtain the ultimate bearing capacity. Based on the ultimate bearing capacity model of the seawater pipeline with single point defects, considering the influence of the double point center distance, an ultimate bearing capacity assessment model of the seawater pipeline with double point defects is established, which has practical engineering value for accurately assessing the ultimate bearing capacity of the real corrosion defects of the seawater pipeline.

Description

Technical Field

[0001] The invention relates to the technical field of prediction of the ultimate bearing capacity of seawater pipelines, and in particular to a method for evaluating the ultimate bearing capacity of seawater pipelines containing double point defects. Background Art

[0002] Seawater pipelines work in a highly corrosive environment and are subject to very severe corrosion. The defects caused by corrosion in seawater pipelines will significantly reduce the bearing capacity of the pipelines. When the working pressure exceeds the bearing capacity of the seawater pipelines, the seawater pipelines will fail, which will result in failures in the main engine and related auxiliary mechanical equipment, affecting the navigation rate and the completion of the mission. For seawater pipelines with corrosion damage, the ultimate bearing capacity assessment work is carried out, and the research results are of great significance to the safe use of equipment and safe navigation.

[0003] At present, the load-bearing capacity assessment method of industrial oil and gas pipelines with defects is relatively mature. In the past 50 years, domestic and foreign scholars have conducted a large number of theoretical models and pipeline explosion test studies on the load-bearing capacity of industrial oil and gas pipelines after corrosion, and formed a series of specifications and standards. However, for ship seawater pipelines mainly made of copper-nickel alloy, there is no mature load-bearing capacity assessment method and standard.

[0004] Corrosion in seawater pipelines generally occurs in the form of group corrosion. Corrosion groups can be discretized into independent corrosion defects. Two independent corrosion defects will interfere with each other, resulting in the prediction of the ultimate bearing capacity of multi-point corrosion pipelines being different from that of single-point corrosion defect pipelines. The purpose of studying the ultimate bearing capacity of group corrosion defects is to solve the following two problems: (1) For pipelines with double corrosion defects, when the centers of the two corrosion defects are at what axial or circumferential distance, its ultimate bearing capacity is the same as that of pipelines with single defects of exactly equal size. That is, determine the minimum axial or circumferential distance between the double defects without mutual interference. (2) In the interval where the double defects interfere with each other, it has been confirmed that the mutual interference of the double defects will reduce the ultimate bearing capacity of the pipeline. However, as the distance between the defect centers changes, the existing methods are difficult to quantitatively evaluate the level of influence of the center distance on the ultimate bearing capacity of the pipeline, resulting in a large calculation deviation of the ultimate bearing capacity of seawater copper-nickel alloy pipelines.

[0005] Therefore, there is an urgent need for a method to calculate the ultimate bearing capacity of seawater copper-nickel alloy pipelines when double-point defects occur. Summary of the invention

[0006] The present invention proposes a method for evaluating the ultimate bearing capacity of a seawater pipeline containing double-ball defects, so as to solve the technical problem that the existing evaluation method does not consider the influence of the center distance of double-point defects in the seawater pipeline on the ultimate bearing capacity of the pipeline, resulting in a large deviation in the ultimate bearing capacity evaluation.

[0007] In order to solve the above technical problems, the present invention provides a method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect, comprising the following steps:

[0008] Step S1: The ultimate bearing capacity model of the pipeline with axial double spherical defects is expressed as the distance influence factor The ultimate bearing capacity model of pipeline with single spherical defect The product of

[0009] Step S2: Collect the corrosion diameter of the seawater pipeline with double ball defects to be detected The center distance l of the axial double spherical defect d ;

[0010] Step S3: input the data collected in step S2 into the ultimate bearing capacity model of the pipeline containing axial double spherical defects to obtain the ultimate bearing capacity.

[0011] Preferably, in step S1, the ultimate bearing capacity model of the pipeline containing a single spherical defect The expression is:

[0012] ;

[0013] In the formula, Indicates the ultimate bearing capacity of lossless pipeline; represents the defect impact factor item; It represents the corrosion depth ratio; Indicates the length correction factor; Indicates the material yield strength ratio; Indicates wall thickness; Indicates the tensile strength of the material; Indicates the outer diameter of the pipe; Indicates the length of pipeline defects.

[0014] Preferably, the distance influence factor in step S1 is is the center distance l of the axial double spherical defects d The exponential function of the exponent , and when the center distance is minimum , follow l d Increase The value of gradually converges to 1.

[0015] Preferably, the distance influence factor The expression is:

[0016] .

[0017] Preferably, the distance influence factor In the index, the defect depth, i.e., the corrosion depth ratio, is added as the second linear tuning target, and the weight coefficient , and Make corrections.

[0018] Preferably, after adding the defect depth, the distance influence factor The expression for:

[0019] ;

[0020] In the formula, Indicates the corrosion depth ratio.

[0021] Preferably, the weight coefficient , and The least square method is used to solve the problem by taking the sum of squares of the difference between the finite element results and the ultimate bearing capacity model of the pipeline with axial double spherical defects, e(r), as the optimization target.

[0022] Preferably, the expression of the optimization objective e(r) is:

[0023] ;

[0024] In the formula, Represents the simulation results.

[0025] Preferably, the ultimate bearing capacity model of the pipeline containing axial double spherical defects is The expression is:

[0026] ;

[0027] In the formula, l d represents the center distance of the axial double spherical defect; N represents the corrosion depth ratio; Indicates the ultimate bearing capacity of lossless pipeline; represents the defect impact factor item; Indicates the length correction factor; Indicates the length of pipeline defects; Indicates the outer diameter of the pipe; Indicates the material yield strength ratio; Indicates the tensile strength of the material; Indicates wall thickness.

[0028] The beneficial effects of the present invention include at least: In order to accurately evaluate the bearing capacity of seawater pipelines containing double-point corrosion defects, the present invention establishes an evaluation model for the ultimate bearing capacity of seawater pipelines containing double-point defects based on the ultimate bearing capacity model of seawater pipelines with single-point defects according to simulation results, and verifies the accuracy of the evaluation model through a water pressure bursting test. The present invention has found that the ultimate bearing capacity increases slowly with the increase of the center distance between the two defects, and as the center distance between the two defects increases, the value tends to the ultimate bearing capacity of a single-defect pipeline with equal depth and diameter; the ultimate bearing capacity model established by the present invention has a good evaluation effect, with a maximum error within 3%, and is applied to the prediction of the ultimate bearing capacity of seawater pipelines containing double-point defects, which has practical engineering value for accurately evaluating the ultimate bearing capacity of real corrosion defects of seawater pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of a method flow of an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of the burst morphology of a double-point corrosion defect according to an embodiment of the present invention;

[0031] Figure 3 This is a cloud diagram of equivalent stress under different internal pressures of the AP8# pipeline of an embodiment of the present invention;

[0032] Figure 4 It is a schematic diagram of three units selected along the wall thickness direction of the AP8# pipeline according to an embodiment of the present invention;

[0033] Figure 5 for Figure 4 Schematic diagram of the variation curves of equivalent stress and equivalent plastic strain of the three selected units under the action of pressure in the pipe;

[0034] Figure 6 for Figure 5 The stress cloud diagram and strain state corresponding to the three state points in the curve;

[0035] Figure 7 The stress cloud diagrams of the two sections of the AP8# pipeline in the embodiment of the present invention when the internal pressure of the pipeline is 27.41 MPa after the pipeline is cut in the circumferential direction and the axial direction;

[0036] Figure 8 for Figure 7 Schematic diagram of equivalent plastic stress of the units of the two paths under the internal pressure of the pipeline;

[0037] Fig. 9 Schematic diagram of the variation of Mises stress with internal pressure at different defect center distances under the corrosion depth ratios N=0.2 and N=0.8;

[0038] Fig.10Schematic diagram of the relationship between the double spherical defect depth and the ultimate bearing capacity of an embodiment of the present invention;

[0039] Fig.11 Schematic diagram of the relationship between the center distance of double defect centers and the ultimate bearing capacity at different defect depth ratios according to an embodiment of the present invention;

[0040] Fig.12 Schematic diagram of the relationship between the double spherical defect diameter and the ultimate bearing capacity according to an embodiment of the present invention;

[0041] Fig.13 Schematic diagram of the relationship between the center distance of double spherical defects and the ultimate bearing capacity at different defect diameters according to an embodiment of the present invention;

[0042] Fig.14 This is a schematic diagram of the correction result of the correction formula of Example 3. DETAILED DESCRIPTION

[0043] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0044] The ultimate bearing capacity of a double corrosion defect pipeline has an important relationship with the defect distance. The closer the distance, the greater the impact. If the distance exceeds the critical value, the two defects can be regarded as single spherical corrosion defects. Based on the single spherical corrosion defect, the embodiment of the present invention further analyzes the influence of the center distance between the two defects, establishes an axial double spherical corrosion copper-nickel alloy pipeline ultimate bearing capacity assessment prediction model, and applies the calculation formula obtained in the study to the seawater pipeline containing axial double spherical defects to obtain its ultimate bursting pressure.

[0045] Example 1

[0046] An embodiment of the present invention provides a method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect, comprising the following steps:

[0047] Step S1: The ultimate bearing capacity model of the pipeline with axial double spherical defects is expressed as the distance influence factor The ultimate bearing capacity model of pipeline with single spherical defect The product of

[0048] Step S2: Collect the corrosion diameter of the seawater pipeline with double ball defects to be detected The center distance l of the axial double spherical defect d ;

[0049] Step S3: input the data collected in step S2 into the ultimate bearing capacity model of the pipeline containing axial double spherical defects to obtain the ultimate bearing capacity.

[0050] Specifically, in step S1, for two axial double spherical defects of equal diameter and depth, when the defect center distance is large enough, the ultimate bearing capacity of the pipeline containing the defect is the ultimate bearing capacity of the single spherical defect; when the two axial defects are adjacent, it is considered that the defect influence reaches the maximum; this embodiment does not consider the case when the two defects overlap. According to the above description, the influence of the center distance between the two axial defects on the ultimate bearing capacity calculation model changes monotonically with the increase of the center distance, and can be expressed by a function containing a distance parameter The embodiment of the present invention will It is called the distance influence factor. The specific form of is determined according to the simulation results. Therefore, the ultimate bearing capacity of the pipeline with axial double spherical defects is expressed as a function The product of the ultimate bearing capacity of the pipeline containing a single spherical defect.

[0051] In the embodiment of the present invention, the ultimate bearing capacity model of the pipeline containing a single spherical defect is used The expression is:

[0052] (1)

[0053] In the formula, Indicates the ultimate bearing capacity of lossless pipeline; represents the defect impact factor item; It represents the corrosion depth ratio; Indicates the length correction factor; Indicates the material yield strength ratio; Indicates wall thickness; Indicates the tensile strength of the material; Indicates the outer diameter of the pipe; Indicates the length of pipeline defects.

[0054] According to the above description, the ultimate bearing capacity model of the pipeline with axial double spherical defects is obtained. The expression is:

[0055] (2)

[0056] Example 2

[0057] In this embodiment, based on the first embodiment, the distance influence factor is further considered. The influence of the ultimate bearing capacity of the pipeline with axial double spherical defects is studied by simulation to study the failure characteristics of the pipeline burst process and the distance influence factor Make further corrections.

[0058] The double spherical defects in this embodiment are characterized by the dimensionless parameters of corrosion depth ratio N and corrosion diameter Describe the degree of corrosion and calculate the ultimate bearing capacity of copper-nickel alloy pipelines at different distances of defects by finite element method. Double spherical defects are defects with two equal diameters and depths. The defect parameters include corrosion depth ratio N, corrosion diameter The center distance l of the axial double spherical defect d The relationship between the spherical defects at different depths and the center distance between the axial double spherical defects and stress under constant corrosion diameter is studied. The sample pipeline parameters and numbers are shown in Table 1. For pipelines numbered AP1#~AP28#, the diameter D of the spherical corrosion defect is p Set to 12mm. The constant corrosion depth ratio, the relationship between the change of the center distance of the axial double spherical defects and stress under different corrosion diameters, the sample pipeline parameters of this paper are shown in Table 2. For the pipelines numbered AP29#~AP49#, the corrosion depth ratio N is set to 0.8. The explicit finite element method is used to perform 49 simulations to complete the numerical simulation of the 49 pipelines in Tables 1 and 2.

[0059] Table 1: Pipeline numbering table with axial double spherical defects

[0060]

[0061] Table 2: Pipeline numbering table with axial double spherical defects

[0062]

[0063] Trial calculations show that the axial double spherical defect center distance is greater than 40 mm, and the influence of the defect center distance on the ultimate bearing capacity has tended to be stable; the minimum defect center distance set in this embodiment is the sum of the two defect radii, and the closer the two defects are, the greater the degree of influence, so the defect center distance range is between 13 mm and 40 mm, and the distance interval is denser when the center distance is smaller, and the distance interval is sparser when the center distance is larger.

[0064] According to the parameters of each numbered pipeline given in Table 1, the simulation results are obtained through numerical simulation. Figure 2 The isometric drawings of the pipeline numbered AP8# in Table 1 are given at the beginning of pressurization and at the moment of bursting. Figure 2 As can be seen in (b), the pipeline will bulge significantly under the action of internal pressure, but no obvious bulging can be seen at the defect. Figure 3The cloud diagram shows the process of the AP8# pipeline defect area bursting under the action of internal pressure. As the pressure inside the pipe increases, the two defects in the center and the middle area between the two defects show obvious stress concentration. The two defects do interfere with each other on the line connecting the defect centers. The two defects and the middle area units undergo elastic deformation to plastic flow stage and finally reach the tensile limit. Figure 3 From (c) in the figure, it can be seen that the stress cloud diagram at the center of the defect begins to shrink at the same time at the two defects, indicating that the unit has entered the stress degradation stage at this time, and the stress degradation starts at the same time from the central area of ​​the two defects. Figure 3 The defect (d) in the figure has completely completed stress degradation along the wall thickness direction. After necking, the pipeline will be depressurized, and a crack will appear along the axial direction of the pipeline. After depressurization, whether the axial cracks formed by the two defects will be connected in the central connection area cannot be directly predicted.

[0065] Figure 4 The three units along the wall thickness direction of the defective part of AP8# pipeline are marked. Figure 5 The changes of von Mises equivalent stress and equivalent plastic strain of these three units under the pressure in the tube are described. Figure 6 Describes Figure 5 The pipeline states corresponding to the three state points in the curve are Figure 6 From the change from state 1 to state 2, the wall thickness at the weakest part of the defect is getting thinner. Comparing the calculation results of the pipeline with groove defects, it can be seen that the changes in the von Mises equivalent stress and equivalent plastic strain of the central area unit of the axial double spherical defect are consistent with those of the groove defect unit, and this embodiment will not be described in detail here.

[0066] Figure 7 It shows the stress cloud diagram of the two sections after the pipeline is cut along the circumferential direction and axial direction when the pressure inside the AP8# pipe is 27.41MPa. Figure 8 It shows the equivalent plastic stress of the units along the two paths under the internal pressure of the pipeline, where the horizontal axis of the coordinate is sorted from left to right along the path. Figure 7 and Figure 8 It can be seen that the equivalent stress at the defect is much greater than that in other areas of the pipeline, indicating that the defect is the stress concentration area of ​​the pipeline. Figure 8 The stress of middle path 2 shows a local trough in the middle area between the two defects, indicating that the stresses of the two defects do interfere in the middle area. Similar to a single spherical defect, this type of defect has low stress areas near the stress concentration area, on the inner surface on both sides of the annular direction, and on the outer surface on both sides of the axial direction. However, at the same time, there are high stress areas on the inner surface on both sides of the axial direction, which gradually connect with the defect. It can also be analyzed that the burst of the pipeline will crack along the axial direction.

[0067] Fig. 9The figure shows the variation of Mises stress with internal pressure at different defect center distances for two corrosion depth ratios N=0.2 and N=0.8. The numbering method of pipelines is from Table 1. Fig. 9 The similarities between the pipes numbered AP1#, AP9#, AP17#, and AP25# in (a) are that their diameters are all 9 mm, their defect depth ratios are all 0.2, and only the defect center distance increases with the increase of the number. Fig. 9 In (b), the pipes numbered AP4#, AP12#, AP20#, and AP28# also have the same diameter and depth, all of which are 9 mm and have a defect depth ratio of 0.8. Only the defect center distance increases with the number. By comparing the two figures, we can draw the following conclusions:

[0068] 1) For defective pipelines of equal size but different defect center distances, the growth of pipeline equivalent stress under internal pressure is consistent with elasticity and yield, and only shows differences at the end of plastic flow, which is that the smaller the defect center distance, the faster the stress growth at the end of plastic flow.

[0069] 2) Fig. 9 (b) The middle line and Fig. 9 Compared with the line in (a), the four stress growth curves are more divergent and diverge earlier, indicating that the thinner the wall thickness at the defect, the earlier the difference in stress of defective pipes with the same wall thickness and different center distances begins.

[0070] To further determine the degree of influence, this embodiment sets the double defects to be equal diameter and equal depth defects. The axial double spherical defect parameters include the corrosion depth ratio N, the corrosion diameter and the distance between the two defects The control variable method is used to explore the influence of three parameters. The bursting process and ultimate bearing capacity data of all pipelines designed in Table 1 and Table 2 are obtained by using the dynamic explicit finite element method.

[0071] According to the ultimate bearing capacity data of 28 pipelines designed in Table 1, the relationship between the corrosion defect depth ratio N and the ultimate bearing capacity is obtained, as shown in Fig.10 As shown. Fig.10 It can be seen that the defect depth ratio N is approximately negatively correlated with the ultimate bearing capacity. And as the defect depth increases, the slope of the curve gradually increases, indicating that the effect of the defect depth on the ultimate bearing capacity of the copper-nickel alloy pipeline gradually increases.

[0072] Similarly, according to the simulation results of the pipeline in Table 1, the center distance between the two defects is The relationship with the ultimate bearing capacity is as follows: Fig.11As shown in the figure, the ultimate bearing capacity increases slowly with the increase of the center distance between the two defects: when the center distance between the two defects is small, the increase of the center distance makes the ultimate bearing capacity increase faster, but as the center distance between the two defects increases, the increase of the ultimate bearing capacity tends to be gentle and converges to a stable value. This value is the ultimate bearing capacity of the pipeline with a single spherical defect corresponding to the double spherical defect parameters. Fig.11 The two curves of N=0.2 and N=0.8 show that as the distance between the centers of defects decreases, the difference in the ultimate bearing capacity between the pipeline with a larger corrosion defect depth and its corresponding isolated defect (single spherical defect) is greater than that of the pipeline with a shallower corrosion defect depth. This indicates that the deeper the defect depth, the stronger the effect of the distance between the centers of the two defects on the ultimate bearing capacity.

[0073] According to the ultimate bearing capacity results calculated by the finite element method of the 28 pipes designed in Table 2, the relationship between the defect diameter and the ultimate bearing capacity is obtained, as shown in Fig.12 Defect diameter It is approximately negatively correlated with the ultimate bearing capacity. However, unlike the influence of corrosion defect depth ratio, as the defect diameter increases, the slope of the curve gradually decreases, indicating that the effect of defect depth on the ultimate bearing capacity of copper-nickel alloy pipelines gradually weakens.

[0074] The relationship between the center distance between two defects and the ultimate bearing capacity is as follows: Fig.13 As shown in the figure, the ultimate bearing capacity increases slowly with the increase of the center distance between the two defects: when the center distance between the two defects is small, the ultimate bearing capacity increases rapidly, but as the center distance between the two defects increases, the increase of the ultimate bearing capacity tends to be gentle and converges to a stable value. This value is the ultimate bearing capacity of the pipeline with a single spherical defect corresponding to the double spherical defect parameters. Fig.13 middle =6 and =12The two curves show that as the defect center distance decreases, the difference in ultimate bearing capacity between the pipeline with a larger corrosion defect diameter and its corresponding isolated defect (single spherical defect) is greater than that of the pipeline with a smaller corrosion defect diameter. This indicates that the larger the defect diameter, the stronger the effect of the center distance between the two defects on the ultimate bearing capacity.

[0075] After using the finite element method to study the ultimate bearing capacity of pipelines under various parameters, it was found that as the defect center distance increases, the difference between the numerical simulation results and the single defect of the same size gradually decreases; when the defect center distance is the same, the deeper the defect depth, the greater the difference. This shows that the influence of the defect center distance cannot be ignored. Therefore, this embodiment adds the distance influence factor based on Example 1. Make corrections. Represents the corrected distance influence factor.

[0076] Distance Impact Factor Need to satisfy the continuity function and satisfy the minimum center distance , as the center distance increases The value gradually converges to 1. Screening common functions, it is found that the exponential function has the property of convergence and is easy to deform. Therefore, the exponential function is deformed to meet the above conditions, and the distance influence factor is selected as follows:

[0077] (3).

[0078] Example 3

[0079] Based on Example 2, this example further modifies the function of the distance influence factor.

[0080] Directly applying equation (3) may not produce ideal correction results in some extreme cases, so further correction is needed. Fig.11 The results show that the deeper the defect depth, the stronger the effect of the distance between the two defect centers on the ultimate bearing capacity. Therefore, the defect depth parameter should be added to the distance influence factor. Assuming that the defect center distance is the same and the defect depth is different, the effect of the defect depth on the ultimate bearing capacity is linear. At the same time, considering that the influence of the defect center distance on the ultimate bearing capacity does not completely match the exponential function, a coefficient is added to the defect center distance parameter for scaling. The distance influence factor is defined as follows:

[0081] (4)

[0082] In the formula, , and Represents the weight coefficient.

[0083] Afterwards, in this embodiment, the sum of squares of the differences between the finite element results and the modified formula, e(r), is used as the optimization target:

[0084] (5)

[0085] Using the least squares method, As a design variable, when the e(r) value is the smallest, it is determined that the design variable has the best fitting effect. The optimal design variable is Based on this, the ultimate bearing capacity model of the pipeline with axial double spherical defects modified in this embodiment is obtained: The expression is:

[0086] (6)

[0087] Comparison between the modified formula of the ultimate bearing capacity of the pipeline with double spherical defects and the simulation results, such as Fig.14 As shown in the figure, it can be seen that the correction formula has a better correction effect when the defect depth is deeper; when the defect depth is shallow and the defect center distance is small, the correction deviation is about 1MPa.

[0088] The bursting of seawater pipelines is the limit state, so the ultimate bearing capacity is the bursting pressure of seawater pipelines. After the correction of numerical simulation results, the calculation formula of the ultimate bearing capacity of copper-nickel alloy pipes with axial double spherical defects was obtained. The calculation formula was applied to the calculation of the ultimate bearing capacity of two actual pipelines, and a specific calculation example was given.

[0089] Axial double spherical defects are common in the case of cavitation corrosion in pipelines. Under the impact of repeated bursting bubbles, the metal on the inner wall of the pipeline falls off, and spherical pits appear, which generally appear in the form of corrosion groups. The model is simplified here, and only the case where two defect pits are arranged along the axial direction is considered. This example elaborates on the process of calculating the ultimate bearing capacity of the obtained model.

[0090] Step 1: Determine the diameter of the seawater pipeline defect , defect depth d, pipe outer diameter , inner diameter , pipeline wall thickness t, defect center distance l d , the test data is shown in Table 3:

[0091] Table 3 Seawater pipeline size data

[0092]

[0093] Step 2: Obtain pipe material parameters. The raw materials for obtaining the material parameters come from the burst test pipeline, and the data are shown in Table 4:

[0094] Table 4 Measured values ​​of seawater pipeline tensile test

[0095]

[0096] Step 3: Take the 7# pipeline as an example to calculate the bursting pressure. The calculation unit shall be based on the International System of Units SI (mm).

[0097] Yield-to-strength ratio:

[0098] (7)

[0099] Corresponding intact pipeline bursting pressure value:

[0100] (8)

[0101] Corrosion length correction factor:

[0102] (9)

[0103] Corrosion depth ratio:

[0104] (10)

[0105] Distance influence factor:

[0106] (11)

[0107] The calculation result of the bursting pressure of the 7# pipeline with axial double spherical defects is:

[0108] (12)

[0109] Similarly, the bursting pressure of pipeline 8# is calculated to be 30.176MPa.

[0110] It can be seen that by applying the formula (6) obtained in this embodiment to the evaluation of the ultimate bearing capacity of seawater pipelines, the improved model of its bursting pressure is in good agreement with the numerical simulation results.

[0111] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, 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 more specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. As long as there is no contradiction in the combination of these technical features, they should be considered as the scope recorded in this specification.

[0112] It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect, characterized in that: The following steps are involved: Step S1: The ultimate bearing capacity model of the pipeline with axial double spherical defects is expressed as the distance influence factor The ultimate bearing capacity model of pipeline with single spherical defect The product of Step S2: Collect the corrosion diameter of the seawater pipeline with the double-ball defect to be detected and the center distance l of the axial double-ball defect d ; Step S3: input the data collected in step S2 into the ultimate bearing capacity model of the pipeline containing axial double spherical defects to obtain the ultimate bearing capacity; In step S1, the ultimate bearing capacity model of the pipeline containing a single spherical defect The expression is: ； In the formula, Indicates the ultimate bearing capacity of lossless pipeline; represents the defect impact factor item; It represents the corrosion depth ratio; Indicates the length correction factor; Indicates the material yield strength ratio; Indicates wall thickness; Indicates the tensile strength of the material; Indicates the outer diameter of the pipe; Indicates the length of pipeline defects; The distance influence factor described in step S1 is the center distance l of the axial double spherical defects d The exponential function of the exponent , and when the center distance is minimum , follow l d Increase The value of gradually converges to 1; The distance influence factor The expression is: 。 2. The method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect according to claim 1 is characterized in that: The distance influence factor In the index, the defect depth, i.e., the corrosion depth ratio, is added as the second linear tuning target, and the weight coefficient , and Make corrections.

3. The method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect according to claim 2 is characterized in that: After adding the defect depth, the distance influence factor The expression for: ； In the formula, Indicates the corrosion depth ratio.

4. The method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect according to claim 3 is characterized in that: The weight coefficient , and The least square method is used to solve the problem by taking the sum of squares of the difference between the finite element results and the ultimate bearing capacity model of the pipeline with axial double spherical defects, e(r), as the optimization target.

5. The method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect according to claim 4 is characterized in that: The expression of the optimization objective e(r) is: ； In the formula, Represents the simulation results.

6. The method for evaluating the ultimate bearing capacity of a seawater pipeline containing a double-ball defect according to claim 1, characterized in that: The ultimate bearing capacity model of the pipeline containing axial double spherical defects The expression is: ； In the formula, l d represents the center distance of the axial double spherical defect; N represents the corrosion depth ratio; Indicates the ultimate bearing capacity of lossless pipeline; represents the defect impact factor item; Indicates the length correction factor; Indicates the length of pipeline defects; Indicates the outer diameter of the pipe; Indicates the material yield strength ratio; Indicates the tensile strength of the material; Indicates wall thickness.

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