Service applicability evaluation method for fillet weld defect of B-type sleeve

Abstract

The invention discloses a service applicability evaluation method for fillet weld defects of a B-type sleeve, and belongs to the field of oil and gas pipeline transportation. The service applicability evaluation method is based on a finite element simulation means and is combined with a defective oil and gas pipeline evaluation standard SY / T 6477-2017'defective oil and gas conveying pipeline residual strength evaluation method '; finite element software and a linear regression method are used for obtaining a theoretical formula of a B-type sleeve fillet weld crack tip stress intensity factor, the B-type sleeve fillet weld crack stress intensity factor KI is calculated, and the service applicability of B-type sleeve fillet weld defects is evaluated in combination with B-type sleeve fillet weld fracture toughness Kmat. And technical support is provided for judging the service applicability of the fillet weld defect-containing B-type sleeve.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas pipeline transportation, and particularly relates to a service applicability evaluation method for defects of a B-type sleeve fillet weld. Background Art

[0002] Pipeline transportation is a long-distance transportation method that uses pipelines as carriers to transport liquids and gases. Pipelines can transport smoothly and uninterruptedly, optimizing the efficiency of modern production. Due to the underground tightness of pipelines, they can transport oil and gas resources safely and with quality, while having excellent economic benefits. However, during operation, pipelines are affected by factors such as terrain, soil quality, and natural disasters, and cracks may occur, leading to pipeline rupture and failure, resulting in safety hazards and even oil and gas leaks and explosions, endangering social and economic benefits. Therefore, evaluating the service reliability of oil and gas pipelines is of great significance to the long-term operation of pipeline transportation.

[0003] Since crack defects cause the largest proportion of oil and gas pipeline accidents, and cracks at fillet welds are more likely to cause major oil and gas leakage in pipelines, it is necessary to conduct in-depth research on the fracture mechanism of B-type sleeve fillet weld defects, especially for the most serious fillet weld crack type defects, the ratio of the stress intensity factor at the crack tip to its fracture toughness should be strictly calculated, and a defect applicability assessment method should be given. At present, there are calculation methods and related research on the stress intensity factor at the crack tip of the girth weld, but there are few related studies on the stress intensity factor at the crack tip of the B-type sleeve fillet weld, and there is no corresponding calculation formula and influencing factor assessment method. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a service suitability evaluation method for B-type sleeve corner weld defects, which is used to solve the technical problems of the existing evaluation methods such as long calculation time and cumbersome analysis steps.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The invention discloses a service applicability evaluation method for a B-type sleeve fillet weld defect, comprising the following steps:

[0007] S1: Collect the crack data of B-type sleeve fillet weld and convert the defect data into elliptical crack defect data;

[0008] S2: A pipeline model containing fillet weld crack data is established based on the elliptical crack defect data, and the stress intensity factor at the crack tip of the sleeve fillet weld under different parameters is calculated based on the model;

[0009] S3: According to the stress intensity factor at the crack tip of the sleeve fillet weld under different parameters obtained in S2, the calculation formula of the stress intensity factor at the crack tip of the sleeve fillet weld is regressed;

[0010] S4: The calculation formula of the stress intensity factor at the crack tip of the sleeve fillet weld is used to obtain the stress intensity factor under different parameters, and the influence of different parameters on the stress intensity factor at the crack tip of the sleeve fillet weld is analyzed;

[0011] S5: Calculate the stress intensity factor according to the influencing law and the calculation formula of the stress intensity factor at the crack tip of the sleeve fillet weld, and then compare it with the fracture toughness of the fillet weld material to determine whether the fillet weld crack of the B-type sleeve is acceptable.

[0012] Further, in S1, the B-type sleeve fillet weld crack data includes the geometric structure of the crack, the position parameters of the crack in the fillet weld, and the sleeve characteristics.

[0013] Furthermore, the geometric structure of the crack includes the crack height 2c, the circumferential length 2a, and the angle θ between the crack and the pipeline radial direction.

[0014] Furthermore, the position parameters of the crack in the fillet weld include the transverse coordinate Dx and the longitudinal coordinate Dy of the crack center in the fillet weld.

[0015] Further, in S2, the pipeline model containing fillet weld crack data is established based on the elliptical crack defect data by using the finite element method, and the steps of establishing are:

[0016] First, assign material parameters, then set the analysis step, insert the crack, divide the mesh and set the load, submit the calculation and perform post-processing, and calculate the stress intensity factor K at the crack tip of the fillet weld by the finite element method. I .

[0017] Further, in S3, according to the several sleeve fillet weld crack tip stress intensity factors obtained in S2, the step of regressing the calculation formula of the sleeve fillet weld crack tip stress intensity factor is as follows:

[0018] The stress intensity factors at the crack tip of the sleeve fillet weld under different parameters obtained in S2 were sorted out, and the fitting equations of different parameters and maximum stress intensity factors were regressed. The stress intensity factor K at the crack tip of the sleeve fillet weld was regressed based on the results of SY / T6477-2017 standard and finite element simulation. I The calculation formula for .

[0019] Furthermore, in S4, the influence of different parameters on the stress intensity factor of the crack tip of the sleeve fillet weld is analyzed to verify the reliability of the finite element method combined with the SY / T 6477-2017 standard in evaluating the stress intensity factor of the crack tip of the fillet weld.

[0020] Furthermore, the different parameters include crack length, crack height, crack angle and crack position.

[0021] Further, in S5, the criteria for judging whether the crack of the fillet weld of the type B sleeve is acceptable are: comparing the stress intensity factor K at the crack tip of the fillet weld of the sleeve I Fracture toughness K of fillet weld material mat , determine whether the fillet weld crack of type B sleeve is acceptable.

[0022] Furthermore, when K I <K mat When K I >K mat Defects are unacceptable.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention discloses a service suitability evaluation method for a B-type sleeve fillet weld defect. Based on the calculation results of the crack stress intensity factor of the fracture mechanics evaluation standard SY / T 6477, theoretical calculations are carried out again on the basis of the results of numerical simulations, and a method is provided for calculating the stress intensity factor of the crack tip of the pipeline fillet weld. An accurate calculation formula for calculating the stress intensity factor of the crack tip of the sleeve fillet weld is regressed, and the stress intensity factor K of the B-type sleeve defect under specific parameters can be directly calculated by the formula. I , thus obtaining the distribution of crack stress intensity factor, analyzing the influence of various parameters on the crack stress intensity factor of sleeve fillet weld, and providing technical support for judging whether the pipeline with defective fillet weld sleeve can continue to be used, how to use it and how long to use it. In practical applications, this method can be directly evaluated, avoiding the use of finite element methods to simulate calculations one by one, saving a lot of calculation time, simplifying the analysis steps, helping to improve the production efficiency of oil and gas transportation, reducing unnecessary replacement of B-type sleeves, and providing technical support for the repair and maintenance of oil and gas pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of the service suitability evaluation method of the B-type sleeve fillet weld defect of the present invention;

[0026] Figure 2 The pipe model of the B-type sleeve fillet weld, the schematic diagram of the prefabricated crack and the mesh model diagram of the crack location;

[0027] Wherein: a-pipeline model schematic diagram; b-prefabricated crack schematic diagram; c-grid model diagram of crack location;

[0028] Figure 3 Schematic diagram of the stress field distribution model of crack-free and cracked pipes - L1-10v3 model;

[0029] Among them: a-no cracks; b-with cracks;

[0030] Figure 4 It is the stress distribution image of L1-10v3;

[0031] Figure 5 The maximum stress intensity factor fitting curve under different crack lengths;

[0032] Figure 6 is the maximum stress intensity factor fitting curve at the same crack depth;

[0033] Figure 7 It is the stress distribution image of L1-30v3v30°;

[0034] Figure 8 It is the fitting curve of maximum stress intensity factor under different crack angles;

[0035] Fig. 9 Schematic diagram of the crack center position at the fillet weld;

[0036] Fig.10 This is the stress distribution image of L2-30v3;

[0037] Fig.11 Fitting curve of maximum stress intensity factor at different crack positions. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the 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 should fall within the scope of protection of the present invention.

[0039] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0040] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0041] like Figure 1 As shown, the present invention discloses a method for evaluating the service suitability of a B-type sleeve fillet weld defect, comprising the following steps:

[0042] 1) Collect pipeline and fillet weld defect data

[0043] The parameters of commonly used oil and gas pipelines in recent years were collected to investigate the common distribution of cracks in the fillet weld of the pipeline (B-type sleeve), such as the geometric structure of the crack (the height 2c and the circumferential length 2a of the elliptical crack itself, the angle θ between the crack and the pipeline radial direction), the position parameters of the crack in the fillet weld (the transverse and longitudinal coordinates Dx and Dy of the crack center in the fillet weld) and the characteristics of the B-type sleeve (sleeve steel grade / wall thickness t s ), etc., to facilitate the subsequent evaluation of the influencing factors of the stress intensity factor at the crack tip of the pipeline fillet weld.

[0044] 2) Finite element method to calculate the stress intensity factor K at the crack tip of the fillet weld I

[0045] Finite element simulation software such as ABAQUS or ANSYS is used to establish a sleeve model with a fillet weld, assign material parameters, set analysis steps, insert cracks, divide the mesh and set loads, submit the calculation for post-processing, and calculate the stress distribution field on the crack surface of the sleeve fillet weld by the finite element method, and calculate the stress intensity factor K at the crack tip of the sleeve fillet weld. I .

[0046] 3) Obtain the stress intensity factor K at the crack tip of the sleeve fillet weld I The calculation formula

[0047] The simulation results in 2) are sorted out, and the fitting equations of different influencing factors and the maximum stress intensity factor are regressed. The stress intensity factor K at the crack tip of the sleeve fillet weld is regressed based on the SY / T6477-2017 standard combined with the results of finite element simulation. I The calculation formula for .

[0048] 4) Evaluate the stress intensity factor K at the crack tip of the sleeve fillet weld I Influencing factors:

[0049] The stress intensity factor K under different parameters is directly calculated using the regression formula I After comparative analysis, the distribution law of stress intensity factor under four parameters, namely crack length, crack height, crack angle and crack position, was evaluated, and the reliability of finite element method combined with SY / T 6477-2017 standard in evaluating the stress intensity factor at the crack tip of sleeve fillet weld was verified.

[0050] 5) Compare K by calculation I The value of the fracture toughness (K mat )

[0051] Determine whether the corner weld defect of type B sleeve is acceptable. I <K mat When K I >K mat Defects are unacceptable.

[0052] Example 1

[0053] A method for evaluating the service suitability of a B-type sleeve fillet weld defect comprises the following steps:

[0054] Collect relevant parameters of fillet weld cracks and analyze the effect of crack annular length 2a and crack height 2c on stress intensity factor K I The impact produced.

[0055] The finite element model is established. The pipe diameter is 1219mm, the wall thickness is 18.4mm, and the sleeve thickness is 28.5mm. For the convenience of calculation, the 1 / 2 model is used. In addition, in order to eliminate the marginal effect, the length from the fillet weld to the end is 3000mm. The interval between the sleeve and the pipe is 3mm. The fillet weld area is an isosceles right triangle. The geometric model of the pipe with fillet weld and the schematic diagram of the prefabricated crack are shown in the figure. Figure 2 (a) and Figure 2(b) As shown; different material properties are assigned to different pipes, welds, and sleeve positions, mainly elastic parameters, including elastic modulus 206GPa and Poisson's ratio 0.3. Boundary and load conditions are then applied to the pipeline, fixed constraints are applied to the two end faces respectively, axisymmetric constraints in the Y direction are used for the pipe section, and an outward internal pressure is applied to the inner wall of the pipe, with a load of 10MPa. In order to study the influence of cracks at the fillet weld, the mesh close to the fillet weld is densified, the mesh far away is relatively coarsened, and the mesh at the crack position is finer. The mesh model at the crack position is as follows: Figure 2 (c) as shown.

[0056] After the model is established, the calculation begins. The model with different parameters is expressed as LX-XvX. For example, L1-10v3 means that the crack position is L1, the crack length is 10mm, and the crack height is 3mm. To indicate the crack position, the fillet weld is divided into different blocks, as follows: Fig. 9 As shown, the coordinates of the center position of the elliptical crack are L1 position (8, 8) which is the 1 / 4 position in both the xy directions, L2 position (4, 25) which is near the 1 / 8 position in the x direction and the center of the maximum position in the y direction, L3 position (23.5, 4) which is near the center of the maximum position in the x direction and the 1 / 8 position in the y direction, L4 position (4, 20) which is near the 1 / 8 position in the x direction, and L5 position (20.5, 4) which is near the 1 / 8 position in the y direction; wherein the value ranges of the abscissa Dx and the ordinate Dy are both 0 to 25 mm.

[0057] By simulating the stress distribution of L1-10v3 elliptical crack under load, the stress field distribution of the pipeline with / without crack is obtained, such as Figure 3 and Figure 4 As shown in the figure, the maximum Mises stress without cracks is 419.8MPa, and the maximum Mises stress with cracks is 544.4MPa. This is because cracks can affect the stress distribution of the pipeline, resulting in an increase in the maximum stress at a local location. The stress distribution at the crack of L1-10v3 after loading is shown in the figure. Figure 5 As shown in the figure, it is found that the stress in the elliptical crack area is slightly higher than that outside the area, but no obvious stress concentration is found. From the results of different principal stresses, it can be found that the different principal stresses in the peripheral area of ​​the crack tip are all large. The stress distribution results in other models are similar, and the main difference is reflected in the range of stress area. The numerical values ​​obtained by simulation are sorted out, and the stress intensity factor is calculated using the SY / T 6477-2017 standard. The results are shown in Table 1.

[0058] Table 1

[0059]

[0060] Based on the finite element results and the SY / T 6477-2017 standard, the fitting curve of crack length and maximum stress intensity factor is regressed, such as Figure 6 As shown, the calculation formula is:

[0061] y=46.48+0.52a-0.0112a 2 (1);

[0062] Among them, y represents the maximum stress intensity factor, and a represents half of the circumferential length of the crack. From the table and the regression equation, it can be seen that the crack length has an effect on the stress intensity factor K I It is found that when the crack position and crack depth are determined, the maximum stress intensity factor gradually increases with the increase of crack length, and the stress intensity factor K of a large number of pipeline fillet weld models with different crack lengths can be directly calculated by formula (1): I .

[0063] The same as the above steps, calculate the stress intensity factor value at different crack depths. The stress in the elliptical crack area in different depth models is slightly higher than that outside the area, and no obvious stress concentration is found. From the different principal stress results, it can be found that the different principal stresses in the peripheral area of ​​the crack tip are large. The difference between different models is the different stress ranges. The numerical values ​​obtained by simulation are sorted out, and the stress intensity factor is calculated using the SY / T6477-2017 standard. The results are shown in Table 2.

[0064] Table 2

[0065]

[0066] Based on the finite element results and the SY / T 6477-2017 standard, the fitting curve of the crack height and the maximum stress intensity factor is regressed, such as Figure 7 As shown, the calculation formula is:

[0067] y=29.04+13.76c+1.36c 2 (2);

[0068] Among them, y represents the maximum stress intensity factor, and c represents half of the crack height. From the table and regression equation, it can be seen that the crack height has a significant effect on the stress intensity factor K. I It is found that when the crack position and crack length are determined, the maximum stress intensity factor gradually increases with the increase of the crack height, and the stress intensity factor K at the crack tip of the sleeve fillet weld with a large number of different crack heights can be directly calculated by formula (2): I .

[0069] Example 2

[0070] A method for evaluating the service suitability of a B-type sleeve fillet weld defect comprises the following steps:

[0071] Collect relevant parameters of fillet weld cracks and analyze the effect of crack angle on the stress intensity factor K at the crack tip of sleeve fillet weld. I The modeling process, pipeline and fillet weld parameters in this embodiment are the same as those in Example 1, except that the crack length, its own height and crack position are kept unchanged, the stress distribution under different crack angles is simulated, and the influence of the radial angle θ between the crack and the pipeline on the maximum stress intensity factor is studied.

[0072] The stress distribution at the crack of the L1-30v3v30° model after loading is as follows Figure 8 As shown in the figure, it is found that the stress at the crack is relatively high, and there is local stress concentration. The first, second and third principal stresses are all large at the crack, and the maximum stress intensity factor at the crack is 67.44 MPa·m 1 / 2 The stress distribution results in other models are similar, and the main difference is reflected in the range of stress area. The numerical values ​​obtained by simulation are sorted out, and the stress intensity factor is calculated using the SY / T6477-2017 standard. The results are shown in Table 3.

[0073] Table 3

[0074]

[0075] Based on the finite element results and the SY / T 6477-2017 standard, the fitting curve of crack angle and maximum stress intensity factor is regressed, such as Figure 8 As shown, the calculation formula is:

[0076] y=0.9958+0.055 sin(θ)+0.886sin 2 (θ) (3);

[0077] Among them, y represents the maximum stress intensity factor, and θ represents the angle between the crack and the pipe radial direction. From the table and the regression equation, it is found that the crack angle has an effect on the stress intensity factor K at the crack tip of the sleeve fillet weld. I It is found that when the crack position, crack length and crack height are determined, as the crack and the pipe radial angle θ increase, the maximum stress intensity factor first increases and then decreases, reaching the maximum at 90°. In addition, the stress intensity factor K at the crack tip of a sleeve fillet weld with a large number of different crack inclination angles can be directly calculated by formula (1): I .

[0078] Example 3

[0079] A method for evaluating the service suitability of a B-type sleeve fillet weld defect comprises the following steps:

[0080] Collect relevant parameters of fillet weld cracks and analyze the effect of crack position on the stress intensity factor K at the crack tip of sleeve fillet weld. I The modeling process, pipeline and fillet weld parameters in this embodiment are the same as those in Embodiment 1 and Embodiment 2, except that the crack length, crack height and the angle between the crack and the pipeline radial direction are kept constant, the stress distribution at different crack positions is simulated, and the influence of the crack position on the maximum stress intensity factor is studied.

[0081] In order to study the influence of cracks at different positions on the stress intensity factor, the fillet weld area is divided into different blocks in this embodiment, as follows: Fig. 9 As shown, the crack is elliptical, and its center position coordinates are respectively selected as L1 position (8, 8) which is 1 / 4 position in both xy directions of the fillet weld, L2 position (4, 25) which is 1 / 8 in the x direction and the center of the maximum position in the y direction, L3 position (23.5, 4) which is the center of the maximum position in the x direction and 1 / 8 in the y direction, L4 position (4, 20) which is 1 / 8 in the x direction, and L5 position (20.5, 4) which is 1 / 8 in the y direction.

[0082] Taking the L2-30v3 model as an example, the stress distribution at the crack after loading is as follows: Fig.10 As shown in the figure, it can be seen that there is obvious stress concentration at the crack tip, with a value of 1178MPa, which is close to the outer edge of the fillet weld. From the stress distribution at the crack position, the stress around the crack is significantly higher, especially the Mises stress, the first principal stress and the second principal stress. The overall stress distribution at the L1 position is significantly different, and the maximum stress intensity factor at the crack is 143.71MPa·m 1 / 2 When the crack characteristics are the same, the maximum stress intensity factors at different locations are very different. The values ​​obtained by simulation are sorted out, and the stress intensity factors are calculated using the SY / T6477-2017 standard. The results are shown in Table 4. Fig. 9 shown.

[0083] Table 4

[0084]

[0085] Based on the finite element results and SY / T 6477-2017 standard, the position of buried cracks is normalized:

[0086] x=((Dx-15.5) 2 + Dy 2 ) 0.5 (4);

[0087] The fitting curve of crack and maximum stress intensity factor is regressed, such as Fig.11As shown, the calculation formula is:

[0088] y=17.74+3.61x+0.026x 2 (5);

[0089] Among them, y represents the maximum stress intensity factor, x represents the normalized position, Dx represents the horizontal coordinate position, Dy represents the vertical coordinate position, and the coordinate range of Dx and Dy is 0 to 25 mm. From the table and the regression equation, it can be obtained that the crack position has an influence on the stress intensity factor K at the crack tip of the sleeve fillet weld. I It is found that when the crack inclination, crack length and depth are determined, the maximum stress intensity factor of different crack positions is quite different, and the maximum sleeve fillet weld crack tip stress intensity factor K of a large number of pipe fillet weld cracks at different positions can be directly calculated by formulas (4) and (5): I .

[0090] Through the analysis of the relevant data obtained in the above three embodiments, the stress intensity factor value predicted by SY / T 6477-2017 is used, and the crack angle and crack position analysis are further combined to regress the maximum stress factor model at the crack tip based on the predicted value of SY / T 6477-2017. The model considers the influence of the crack angle and crack position, and the calculation formula is as follows:

[0091] y=0.01654(159.59-0.14s+0.117s 2 )(0.9958+0.055sin(θ)+

[0092] 0.886sin 2 (θ))(17.74+3.61x+0.026x 2 )(6);

[0093] Among them, y represents the maximum stress intensity factor, x represents the normalized position, s is the stress intensity factor predicted by SY / T 6477-2017, and θ represents the angle between the crack and the pipe radial direction. Using this formula, the maximum stress intensity factor K at the crack tip of the sleeve fillet weld can be calculated by considering the crack angle and crack position and combining the stress intensity factor predicted by SY / T 6477-2017. I .

[0094] The present invention is based on the finite element simulation calculation results, refers to the stress intensity factor calculated by the SY / T 6477-2017 standard, and fits the calculation formula of the stress intensity factor of the crack tip of the sleeve fillet weld. The stress intensity factor of the fillet weld crack of a large number of models can be directly calculated by the formula method, and then the control variable method is used to study the influence of different variables on the stress intensity factor of the crack tip of the sleeve fillet weld, evaluate the influencing factors of the crack tip stress intensity factor, and judge whether the fillet weld defect is acceptable. Provide a basis for evaluating the service safety of the B-type sleeve containing fillet weld cracks in actual engineering applications.

[0095] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating the service suitability of B-type sleeve fillet weld defects, characterized in that: The following steps are involved: S1: Collect the crack data of B-type sleeve fillet weld and convert the defect data into elliptical crack defect data; S2: A pipeline model containing fillet weld crack data is established based on the elliptical crack defect data, and the stress intensity factor at the crack tip of the sleeve fillet weld under different parameters is calculated based on the model; S3: According to the stress intensity factor at the crack tip of the sleeve fillet weld under different parameters obtained in S2, the calculation formula of the stress intensity factor at the crack tip of the sleeve fillet weld is regressed; S4: The calculation formula of the stress intensity factor at the crack tip of the sleeve fillet weld is used to obtain the stress intensity factor under different parameters, and the influence of different parameters on the stress intensity factor at the crack tip of the sleeve fillet weld is analyzed; S5: Calculate the stress intensity factor according to the influencing law and the calculation formula of the stress intensity factor at the crack tip of the sleeve fillet weld, and then compare it with the fracture toughness of the fillet weld material to determine whether the fillet weld crack of the B-type sleeve is acceptable.

2. A method for evaluating the service suitability of a B-type sleeve fillet weld defect according to claim 1, characterized in that: In S1, the B-type sleeve fillet weld crack data includes the geometric structure of the crack, the position parameters of the crack in the fillet weld, and the sleeve characteristics.

3. The service suitability evaluation method for a B-type sleeve fillet weld defect according to claim 2 is characterized in that: The geometric structure of the crack includes the crack height 2c, the circumferential length 2a, and the angle θ between the crack and the pipeline radial direction.

4. The service suitability evaluation method for a B-type sleeve fillet weld defect according to claim 2 is characterized in that: The position parameters of the crack in the fillet weld include the transverse coordinate Dx and the longitudinal coordinate Dy of the crack center in the fillet weld.

5. The service suitability evaluation method for a B-type sleeve fillet weld defect according to claim 1 is characterized in that: In S2, the pipeline model containing fillet weld crack data is established based on the elliptical crack defect data by using the finite element method, and the steps of establishing are: First, assign material parameters, then set the analysis step, insert the crack, divide the mesh and set the load, submit the calculation and perform post-processing, and calculate the stress intensity factor K at the crack tip of the fillet weld by the finite element method. I .

6. The service suitability evaluation method for a B-type sleeve fillet weld defect according to claim 1 is characterized in that: In S3, according to the several sleeve fillet weld crack tip stress intensity factors obtained in S2, the steps of regressing the calculation formula of the sleeve fillet weld crack tip stress intensity factor are as follows: The stress intensity factors at the crack tip of the sleeve fillet weld under different parameters obtained in S2 were sorted out, and the fitting equations of different parameters and maximum stress intensity factors were regressed. The stress intensity factor K at the crack tip of the sleeve fillet weld was regressed based on the results of SY / T6477-2017 standard and finite element simulation. I The calculation formula for .

7. A method for evaluating the service suitability of a B-type sleeve fillet weld defect according to claim 6, characterized in that: In S4, the influence of different parameters on the stress intensity factor of the crack tip of the sleeve fillet weld is analyzed, and the reliability of the finite element method combined with the SY / T 6477-2017 standard in evaluating the stress intensity factor of the crack tip of the fillet weld is verified.

8. A method for evaluating the service suitability of a B-type sleeve fillet weld defect according to claim 7, characterized in that: The different parameters include crack length, crack height itself, crack angle and crack location.

9. A method for evaluating the service suitability of a B-type sleeve fillet weld defect according to claim 7, characterized in that: In S5, the criteria for judging whether the crack of the fillet weld of the type B sleeve is acceptable are: comparing the stress intensity factor K at the crack tip of the fillet weld of the sleeve I Fracture toughness K of fillet weld material mat , determine whether the fillet weld crack of type B sleeve is acceptable.

10. A method for evaluating the service suitability of a B-type sleeve fillet weld defect according to claim 9, characterized in that: When K I <K mat When K I >K mat Defects are unacceptable.

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