A method for predicting the leakage rate of the metal lens gasket sealing interface of ultra-high voltage equipment

Abstract

The present invention discloses a method for predicting the leakage rate of the sealing interface of a metal lens pad of an ultra-high voltage equipment, and belongs to the technical field of leakage rate prediction. The method comprises the steps of: S1, establishing a coupled damage cyclic elastic-plastic constitutive model of the metal lens pad material; S2, establishing a finite element model of an ultra-high voltage sealing structure, applying a cyclic load for simulation, and fitting a model of the attenuation law of the contact stress of the metal lens pad under the cyclic load; S3, establishing a single rough peak contact deformation finite element model, correlating it with the actual sealing structure, and fitting a relationship between the contact stress of the metal lens pad and the microscopic rough peak deformation under the cyclic load; S4, establishing a leakage model of the microscopic pore structure of the sealing interface, and combining steps S2 and S3 to obtain a leakage rate prediction model of the sealing interface; S5, using the prediction model to predict the leakage rate. The prediction method of the present invention can accurately predict the leakage rate of the metal lens pad sealing interface under cyclic load conditions.

Description

Technical Field

[0001] The invention relates to the technical field of pressure vessels, and in particular to a method for predicting the leakage rate of a metal lens gasket sealing interface of an ultra-high pressure device. Background Art

[0002] Leakage of the seal of pressure-bearing equipment will not only cause unplanned shutdowns, fires, explosions and other production accidents, but the volatile organic compounds (VOCs) it releases are also one of the main causes of air pollution. Due to the extremely high internal pressure, leakage is more likely to occur in ultra-high-pressure equipment and the leakage rate is high. For ultra-high-pressure equipment, metal lens gaskets are usually used for sealing in the flange sealing connection. In order to achieve long-term high-reliability ultra-high-pressure sealing, the sealing performance of the metal lens gasket must be considered when designing the structure. At present, most of the research on the sealing performance of metal lens gaskets at home and abroad uses the contact width and contact stress of the sealing interface as the basis for sealing performance evaluation and design, without considering the leakage rate, an important parameter, which can directly reflect the sealing performance of the metal lens gasket sealing interface. If the leakage rate of the metal lens gasket sealing interface in ultra-high-pressure equipment can be predicted, its sealing performance will be evaluated more accurately to ensure the long-term high-reliability operation of ultra-high-pressure equipment. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes a leakage rate prediction method for the sealing interface of a metal lens gasket of an ultra-high voltage device.

[0004] The present invention specifically adopts the following technical solutions:

[0005] A method for predicting the leakage rate of a metal lens gasket sealing interface of an ultra-high voltage device comprises the following steps:

[0006] S1. Analyze the deformation behavior and fatigue damage behavior of the metal lens pad in the sealing structure of ultra-high pressure equipment during service, establish a coupled fatigue damage cyclic elastic-plastic constitutive model for the metal lens pad material, and write a UMAT subroutine for the constitutive model;

[0007] S2. Establish a finite element model of the sealing structure of the ultra-high voltage equipment, introduce the coupled fatigue damage cyclic elastic-plastic constitutive model UMAT subroutine established in step S1, set the corresponding material properties and material physical parameters, apply cyclic loads for numerical simulation, and obtain a model of the attenuation law of the contact stress of the metal lens pad under the cyclic load according to the numerical simulation analysis results;

[0008] S3, establishing a single rough peak contact deformation finite element analysis model, applying the same cyclic load as step S2 and performing numerical simulation, fitting the relationship between the contact force of the single rough peak and the deformation of the microscopic rough peak according to the numerical simulation analysis results; and correlating the single rough peak contact deformation finite element model with the actual ultra-high pressure sealing structure, analyzing and obtaining the relationship between the contact stress of the metal lens pad in the actual ultra-high pressure sealing structure under the application of cyclic load and the deformation of the microscopic rough peak;

[0009] S4. Based on fractal theory and fractal porous media transport theory, a leakage model of the microscopic pore structure of the sealing interface is established, and combined with the attenuation law model of the contact stress of the metal lens pad under cyclic load obtained in step S2 and the relationship between the contact stress of the metal lens pad and the deformation of the microscopic roughness peak under cyclic load obtained in step S3, a leakage rate prediction model of the metal lens pad sealing interface is obtained;

[0010] S5. Based on the leakage rate prediction model of the metal lens gasket sealing interface obtained in step S4, the leakage rate of the metal lens gasket sealing interface of the ultra-high voltage equipment under service conditions is predicted.

[0011] Furthermore, the control equation of the cyclic elastic-plastic constitutive model of coupled fatigue damage established in step S1 is:

[0012] (1);

[0013] (2);

[0014] (3);

[0015] (4);

[0016] (5);

[0017] (6);

[0018] In the formula, is the total strain tensor; is the elastic strain tensor; is the plastic strain tensor; is the plastic strain rate; is the elastic modulus; is Poisson's ratio; is the principal stress tensor; is the unit tensor; For time; is the Mises yield function; is the deviatoric stress tensor; ; is the total back stress tensor, which is obtained by superimposing several kinematic hardening law back stress tensors. , is the serial number, is the total number of superimposable kinematic hardening laws, For the A kinematic hardening law stack stress tensor; and For the The kinematic hardening parameters under the back stress tensor need to be determined through uniaxial tensile tests of the material; is the isotropic hardening change rate; is the saturation value of the isotropic hardening variable; is the isotropic hardening index, i.e. elastic limit stress; is the material constant determined by uniaxial tension test of the material; is the equivalent plastic strain rate, and ; is the fatigue damage value; the “~” above each parameter in the formula indicates that it needs to be updated during the damage process.

[0019] Furthermore, the finite element model of the ultra-high pressure equipment sealing structure established in step S2 includes two relatively connected pipes and a metal lens pad arranged between the two pipes, and the outer circles of the two pipes are respectively provided with flanges, and the two pipes are fixed by flanges and bolts after being connected.

[0020] Furthermore, the attenuation law model of the contact stress of the metal lens pad obtained in step S2 under the applied cyclic load is:

[0021] (7);

[0022] In the formula, is the average contact stress of the metal lens pad; is the bolt preload; is the number of load cycles; , is a constant related to the applied load and the internal pressure of the equipment.

[0023] Furthermore, the relationship between the contact force of the single roughness peak obtained in step S3 and the deformation of the microscopic roughness peak is:

[0024] (8);

[0025] In the formula, is the microscopic roughness peak deformation; is the contact force of a single roughness peak; , is a constant related to the roughness peak size.

[0026] Furthermore, the relationship between the contact stress of the metal lens pad and the deformation of the microscopic roughness peak in the actual ultra-high pressure sealing structure under the applied cyclic load obtained in step S3 is:

[0027] (9);

[0028] In the formula, , is a constant related to the roughness peak size.

[0029] Furthermore, the microscopic leakage model of the microscopic pore structure of the sealing interface obtained in step S4 based on the fractal theory and the fractal porous media transport theory is:

[0030] (10);

[0031] In the formula, is the micro leakage rate of the microscopic pore structure of the sealing interface, is the fractal dimension of the pore space, which is related to the porosity of the pore space; is the tortuosity fractal dimension, is the straight length of the pore channel, is the maximum pore size of the pore channel; is the viscosity coefficient of the medium, is the pressure difference in the leakage channel.

[0032] Furthermore, the leakage rate prediction model of the metal lens pad sealing interface obtained in step S4 is:

[0033] (11);

[0034] In the formula, is the leakage rate of the metal lens gasket sealing interface; is the fractal dimension of the pore space, which is related to the porosity of the pore space; is the tortuosity fractal dimension; is the viscosity coefficient of the medium; is the pressure difference in the pore channel; is the perimeter of the sealing interface; is the sampling length, i.e. the length of the pore space; is the initial contact diameter between the pipe and the metal lens pad; is the contact width between the pipe and the metal lens pad, which is equivalent to the straight length of the pore channel; , which is the maximum pore size of the pore channel, is the effective thickness of the interface microporous structure, that is, the area where the medium can flow, is the root mean square deviation of the pore space surface profile, , is the height of the pore space surface profile, obtained by the bivariate WM fractal function, is a constant related to the machining method of the metal lens pad, is the microscopic roughness peak deformation.

[0035] The present invention has the following beneficial effects:

[0036] The present invention provides a method for predicting the leakage rate of a metal lens pad sealing interface of an ultra-high voltage device. The prediction method takes into account the degradation law of material performance under long-term service, the microscopic contact deformation of the sealing interface and the flow characteristics of the leakage medium, thereby improving the accuracy of the leakage rate prediction result. The prediction method of the present invention can predict the leakage rate of the metal lens pad sealing interface under cyclic load conditions, thereby providing theoretical guidance for the design of ultra-high voltage metal lens pad sealing and ensuring the long-term high-reliability operation of the ultra-high voltage lens pad sealing structure. The method can also be used to predict the leakage rate of the metal lens pad sealing interface during service to prevent leakage accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the present invention;

[0038] Figure 2 A mesh diagram of a finite element model of a sealing structure of an ultra-high pressure device established in an embodiment of the present invention;

[0039] Figure 3 A distribution cloud diagram of the metal lens pad surface damage variables obtained by numerical simulation according to an embodiment of the present invention;

[0040] Figure 4 The curve showing the variation of the surface damage of the metal lens pad with respect to the number of cycles obtained by numerical simulation in an embodiment of the present invention;

[0041] Figure 5 A single roughness peak contact deformation finite element analysis model established for an embodiment of the present invention;

[0042] Figure 6 The leakage rate prediction model of the embodiment of the present invention is used to predict the leakage rate of the metal lens gasket sealing interface under cyclic conditions, thereby obtaining a cycle number-metal lens gasket interface leakage rate curve.

[0043] Labels in the figure: 1. Pipe; 2. Metal lens gasket; 3. Flange; 4. Bolt; 5. Nut. DETAILED DESCRIPTION

[0044] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and specific examples.

[0045] Reference Figure 1 The present invention provides a method for predicting the leakage rate of a metal lens gasket sealing interface of an ultra-high voltage device, which specifically includes the following steps S1-S5.

[0046] S1. Analyze the deformation behavior and fatigue damage behavior of the metal lens pad in the sealing structure of ultra-high pressure equipment during service, establish a cyclic elastic-plastic constitutive model of coupled fatigue damage of the metal lens pad material, and write an ABAQUS-UMAT user material subroutine and embed it into ABAQUS.

[0047] The governing equation of the cyclic elastic-plastic constitutive model of coupled fatigue damage established in the above step S1 is:

[0048] (1);

[0049] (2);

[0050] (3);

[0051] (4);

[0052] (5);

[0053] (6);

[0054] In the formula, is the total strain tensor; is the elastic strain tensor; is the plastic strain tensor; is the plastic strain rate; is the elastic modulus; is Poisson's ratio; is the principal stress tensor; is the unit tensor; For time; is the Mises yield function; is the deviatoric stress tensor; ; is the total back stress tensor, which is obtained by superimposing several kinematic hardening law back stress tensors. , is the serial number, is the total number of superimposable kinematic hardening laws, For the A kinematic hardening law stack stress tensor; and For the The kinematic hardening parameters under the back stress tensor need to be determined through uniaxial tensile tests of the material; is the isotropic hardening change rate; is the saturation value of the isotropic hardening variable; is the isotropic hardening index, i.e. elastic limit stress; is the material constant determined by uniaxial tension test of the material; is the equivalent plastic strain rate, and ; is the fatigue damage value; the “~” above each parameter in the formula indicates that it needs to be updated during the damage process.

[0055] The above-mentioned cyclic elastic-plastic constitutive model is coupled with fatigue damage. A reasonable damage evolution equation is crucial for establishing an accurate fatigue damage numerical model and then evaluating the fatigue life of the structure. A series of damage evolution equations proposed by French scholar Lemaitre are currently the most widely used in engineering. The low-cycle fatigue damage evolution equation is as follows:

[0056] Fatigue damage value The calculation formula is:

[0057] (12);

[0058] in:

[0059] (13);

[0060] (14);

[0061] (15);

[0062] In the formula, is the fatigue damage rate; is the material damage strain energy release rate; , is the material performance parameter; is the equivalent plastic strain accumulated inside the material, ; is the material damage threshold, that is, when the accumulated plastic strain inside the material reaches this value, damage begins to occur; is the equivalent stress; is the triaxial hydrostatic stress; is the triaxial stress function; is the crack closure parameter, =1, indicating that the material is in a tensile state. , indicating that the material is in a compressed state. The present invention studies the metal lens pad in a compressed state. When calculating its low-cycle fatigue damage, The value is 0.2; is the elastic modulus, is Poisson's ratio.

[0063] S2. Establish a finite element model of the sealing structure of the ultra-high voltage equipment, introduce the coupled fatigue damage cyclic elastoplastic constitutive model established in step S1, set the corresponding material properties and material physical parameters, apply cyclic loads for numerical simulation, and obtain the attenuation law model of the contact stress of the metal lens pad under the application of cyclic loads based on the numerical simulation analysis results.

[0064] The finite element model of the sealing structure of the ultra-high pressure equipment established in the above step S2 includes two relatively connected pipes and a metal lens pad arranged between the two pipes, and the outer rings of the two pipes are respectively provided with flanges, and the two pipes are fixed by flanges and bolts after being connected; and an external load of a cyclic amplitude is added to the side of the pipe in contact with the metal lens pad to simulate the cyclic load condition, simulate the deformation process and damage process of the metal lens pad under the cyclic load, and fit the attenuation law model of the contact stress of the metal lens pad under the applied cyclic load through simulation analysis:

[0065] (7);

[0066] In the formula, is the average contact stress of the metal lens pad; is the bolt preload; is the number of load cycles; , , is a constant related to the applied load and the internal pressure of the equipment.

[0067] S3. Based on the fact that the contact surface between the metal lens pad and the pipeline is a rough surface, the surface of the metal lens pad is set to a rough surface with a rough peak, and the contact surface of the pipeline is set to a smooth surface, and a single rough peak contact deformation finite element analysis model is established, wherein the rough peak is simplified to a triangular pyramid peak body, and the pipeline contact surface is set to a rigid body, and then a cyclic load the same as step S2 is applied and a numerical simulation is performed to simulate the deformation process of the single rough peak under the cyclic load, and the contact force exerted on the single rough peak is obtained, and the relationship between the contact force of the single rough peak and the deformation of the microscopic rough peak is fitted according to the numerical simulation analysis results; and the single rough peak contact deformation finite element model is associated with an actual ultra-high pressure sealing structure, and the relationship between the contact stress of the metal lens pad and the deformation of the microscopic rough peak in the actual ultra-high pressure sealing structure under the application of cyclic load is analyzed.

[0068] The relationship between the contact force of a single roughness peak and the deformation of the microscopic roughness peak obtained in the above step S3 is:

[0069] (8);

[0070] In the formula, is the microscopic roughness peak deformation, is the contact force of a single roughness peak, , is a constant related to the roughness peak size.

[0071] In order to link the single roughness peak contact deformation model with the actual ultra-high pressure sealing structure, it is assumed that the roughness peaks on the surface of the metal lens pad are consistent, and the contact surface between the pipe and the metal lens pad has a total of Rough peaks, among which is the total contact area between the pipe and the metal lens pad, , is the initial contact diameter between the pipe and the metal lens pad, is the contact width between the pipe and the metal lens pad, , It can be obtained by numerically simulating the deformation process of the metal lens pad under cyclic load in step S2, is the bottom area of ​​a single rough peak, , is the diameter of a single roughness peak; the contact force on a single roughness peak can be expressed as: ,in, is the total macroscopic contact force between the pipe and the metal lens pad, ; The relationship between the contact stress of the metal lens pad and the deformation of the microscopic roughness peak in the actual ultra-high pressure sealing structure under the applied cyclic load is obtained as follows:

[0072] (9);

[0073] In the formula, , is a constant related to the roughness peak size.

[0074] S4. Based on fractal theory and fractal porous media transport theory, a leakage model of the microscopic pore structure of the sealing interface is established. Combined with the attenuation law model of the contact stress of the metal lens pad under cyclic load obtained in step S2 and the relationship between the contact stress of the metal lens pad and the deformation of the microscopic roughness peak under cyclic load obtained in step S3, a leakage rate prediction model of the metal lens pad sealing interface is obtained.

[0075] Specifically, in this step, the contact between the two rough surfaces during the contact deformation of the metal lens pad is simplified to the contact between a rigid smooth surface and a surface with a composite roughness; the smooth surface is subjected to a load and undergoes displacement deformation, and the displacement deformation amount is the rough peak deformation amount in step S3 , taking the interface microporous structure formed between the surface roughness peak of the metal lens pad per unit length and the pipeline surface, the interface microporous structure parameters change with the load, and its leakage rate also changes accordingly.

[0076] The rough peaks on the surface of the metal lens pad are analogized to the pores of a porous medium and have fractal characteristics. Based on this assumption, the present invention uses the bivariate WM fractal function of the fractal theory to describe the morphological characteristics and laws of the sealing surface profile, and then obtains the microscopic leakage model of the microscopic pore structure of the sealing interface based on the fractal porous medium transport theory:

[0077] (10);

[0078] In the formula, is the micro leakage rate of the microscopic pore structure of the sealing interface, is the fractal dimension of the pore space, which is related to the porosity of the pore space; is the tortuosity fractal dimension, is the straight length of the pore channel, is the maximum pore size of the pore channel; is the viscosity coefficient of the medium, is the pressure difference in the leakage channel.

[0079] Based on the microscopic leakage model of the microscopic pore structure of the sealing interface, combined with the attenuation law model of the contact stress of the metal lens pad under cyclic load obtained in step S2 and the relationship between the contact stress of the metal lens pad under cyclic load and the deformation of the microscopic roughness peak obtained in step S3, the leakage rate prediction model of the metal lens pad sealing interface is obtained as follows:

[0080] (11);

[0081] In the formula, is the leakage rate of the metal lens gasket sealing interface; is the fractal dimension of the pore space, which is related to the porosity of the pore space; is the tortuosity fractal dimension; is the viscosity coefficient of the medium; is the pressure difference in the pore channel; is the perimeter of the sealing interface; is the sampling length, i.e. the length of the pore space, and the present invention takes the unit length; is the initial contact diameter between the pipe and the metal lens pad; is the contact width between the pipe and the metal lens pad, which is equivalent to the straight length of the pore channel; , which is the maximum pore size of the pore channel, is the effective thickness of the interface microporous structure, that is, the area where the medium can flow, is the root mean square deviation of the pore space surface profile, , is the height of the pore space surface profile, obtained by the bivariate WM fractal function, , represents the fractal dimension of a three-dimensional rough surface, is the scale factor that reflects the amplitude. represents the spatial frequency of the random contour, is the spatial frequency coefficient of the random profile, When it follows a normal distribution, its value is 1.5; is a constant related to the machining method of the metal lens pad, is the microscopic roughness peak deformation.

[0082] S5. Based on the leakage rate prediction model of the metal lens gasket sealing interface obtained in step S4, the leakage rate of the metal lens gasket sealing interface of the ultra-high voltage equipment under service conditions is predicted.

[0083] Specifically in the implementation case of the present invention, the leakage rate prediction model is used to predict the leakage rate of the sealing interface of the metal lens gasket of the ultra-high voltage equipment.

[0084] Reference Figure 2 In this embodiment, the finite element model of the sealing structure of the ultra-high pressure equipment under the cyclic load condition is established by using ABAQUS software, and the mesh is divided. The model includes two pipes 1 connected to each other and a metal lens pad 2 arranged between the two pipes, and the outer rings of the two pipes 1 are respectively provided with flanges 3. After the two pipes 1 are connected, they are fixed by flanges 3, bolts 4 and nuts 5. The lower pipe is fixed in the model to limit the movement of the model, and the upper pipe is a free end; the model adopts C3D8R (8-node hexahedral linear reduced integration unit) unit mesh, and the mesh density of the pipe-metal lens pad sealing interface area meets the principle of main density and sparseness, and the mesh size of the metal lens pad contact area is 0.03mm.

[0085] In the above model, the materials of the metal lens gasket, flange and pipe are GCr15, 42CrMoA and 40CrNi2MoA respectively, and the materials of the bolts and nuts are 35CrMoA.

[0086] The dimensions of the metal lens gasket, flange, pipe, bolts and nuts in the above model are shown in Table 1 below.

[0087] Table 1 Dimensional parameters of metal lens gaskets, flanges, pipes, bolts and nuts

[0088]

[0089] The material property parameters of the metal lens pad in the above model are shown in Table 2 below.

[0090] Table 2 Material property parameters of metal lens pad

[0091]

[0092] The finite element model of the sealing structure of the ultra-high pressure equipment is combined with the ABAQUS-UMAT user subroutine, and a 320kN bolt preload, 160MPa internal pressure condition, and 50MPa cyclic external load (equivalent to the load generated by the internal pressure fluctuation in the range of 120MPa~200MPa) are applied. The ABAQUS / Standard solver is used to calculate the contact deformation and fatigue damage of the metal lens pad under the cyclic load condition. When the damage in the contact area between the pipeline and the metal lens pad reaches the critical value of fatigue damage When , the damage will no longer change, indicating that failure has occurred in the area and the calculation ends.

[0093] In the above numerical simulation process, the distribution of metal lens pad surface damage variables and the curve of the change of metal lens pad surface damage with the number of cycles are obtained, such as Figure 3 and Figure 4 As shown. Figure 3 and Figure 4 It can be seen that the surface damage of the metal lens pad is mainly concentrated at the initial contact position between the pipe and the metal lens pad, and increases with the increase of the number of external load cycles.

[0094] In addition, in the above numerical simulation process, the change data of the contact stress on the surface of the metal lens pad under cyclic load is also obtained, and the average contact stress on the surface of the metal lens pad is calculated. The average contact stress on the surface of the metal lens pad is fitted with the cyclic load cycle, and the attenuation law model of the contact stress of the metal lens pad under cyclic load is obtained:

[0095] .

[0096] In addition, through the above numerical simulation, it is also obtained that the initial contact diameter of the pipe and the gasket under this working condition is 46 mm, the initial contact width is 2 mm, and the contact width is 1.85 mm after the external load is applied.

[0097] Reference Figure 5 In this embodiment, a single rough peak contact deformation finite element analysis model is established by ABAQUS. The surface micromorphology of the metal lens pad is detected, and according to the detection results, the rough peak is simplified to a triangular pyramid peak with a height of 1.2 μm and a diameter of 8.2 μm. The pipeline contact surface is a smooth rigid body. A cyclic load is applied to the pipeline surface, and the relationship between the contact force on the micro rough peak and the deformation of the micro rough peak is obtained as follows:

[0098] ;

[0099] Then, the contact force on the microscopic roughness peak and the contact stress of the metal lens pad are related to each other. , the relationship between the contact stress of the metal lens pad and the deformation of the micro-roughness peak under the applied cyclic load is obtained as follows:

[0100] ;

[0101] Furthermore, the leakage rate prediction model of the metal lens pad sealing interface is obtained as follows;

[0102] .

[0103] The above formula can be used to predict the metal lens gasket sealing interface leakage rate under 320kN bolt preload, 160MPa internal pressure and 50MPa cyclic external load conditions, such as Figure 6 As shown. Figure 6 The prediction results can be used to obtain the metal lens gasket sealing interface leakage rate under different cycle times, so as to analyze the degradation of the metal lens gasket under long-term service and provide theoretical guidance for the sealing structure design of ultra-high pressure equipment.

[0104] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for predicting the leakage rate of a metal lens gasket sealing interface of an ultra-high voltage device, characterized in that: Includes steps: S1. Analyze the deformation behavior and fatigue damage behavior of the metal lens pad in the sealing structure of ultra-high pressure equipment during service, establish a coupled fatigue damage cyclic elastic-plastic constitutive model for the metal lens pad material, and write a UMAT subroutine for the constitutive model; S2. Establish a finite element model of the sealing structure of the ultra-high voltage equipment, introduce the coupled fatigue damage cyclic elastic-plastic constitutive model UMAT subroutine established in step S1, set the corresponding material properties and material physical parameters, apply cyclic loads for numerical simulation, and obtain a model of the attenuation law of the contact stress of the metal lens pad under the cyclic load according to the numerical simulation analysis results; S3, establishing a single rough peak contact deformation finite element analysis model, applying the same cyclic load as step S2 and performing numerical simulation, fitting the relationship between the contact force of the single rough peak and the deformation of the microscopic rough peak according to the numerical simulation analysis results; and correlating the single rough peak contact deformation finite element model with the actual ultra-high pressure sealing structure, analyzing and obtaining the relationship between the contact stress of the metal lens pad in the actual ultra-high pressure sealing structure under the application of cyclic load and the deformation of the microscopic rough peak; S4. Based on fractal theory and fractal porous media transport theory, a leakage model of the microscopic pore structure of the sealing interface is established, and combined with the attenuation law model of the contact stress of the metal lens pad under cyclic load obtained in step S2 and the relationship between the contact stress of the metal lens pad and the deformation of the microscopic roughness peak under cyclic load obtained in step S3, a leakage rate prediction model of the metal lens pad sealing interface is obtained; S5. Based on the leakage rate prediction model of the metal lens gasket sealing interface obtained in step S4, the leakage rate of the metal lens gasket sealing interface of the ultra-high voltage equipment under service conditions is predicted.

2. The method for predicting the leakage rate of the metal lens gasket sealing interface of ultra-high voltage equipment according to claim 1, characterized in that: The control equation of the cyclic elastic-plastic constitutive model of coupled fatigue damage established in step S1 is: （1）； （2）； （3）； （4）； （5）； （6）； In the formula, is the total strain tensor; is the elastic strain tensor; is the plastic strain tensor; is the plastic strain rate; is the elastic modulus; is Poisson’s ratio; is the principal stress tensor; is the unit tensor; For time; is the Mises yield function; is the deviatoric stress tensor; ; is the total back stress tensor, which is obtained by superimposing several kinematic hardening law back stress tensors. , is the serial number, is the total number of superimposable kinematic hardening laws, For the A kinematic hardening law stack stress tensor; and For the The kinematic hardening parameters under the back stress tensor need to be determined through uniaxial tensile tests of the material; is the isotropic hardening change rate; is the saturation value of the isotropic hardening variable; is the isotropic hardening index, i.e. elastic limit stress; is the material constant determined by uniaxial tension test of the material; is the equivalent plastic strain rate, and ; is the fatigue damage value; the "~" above each parameter in the formula indicates that it needs to be updated during the damage process.

3. The method for predicting the leakage rate of the metal lens gasket sealing interface of ultra-high voltage equipment according to claim 2, characterized in that: The finite element model of the ultra-high pressure equipment sealing structure established in step S2 includes two relatively connected pipes and a metal lens pad arranged between the two pipes, and the outer circles of the two pipes are respectively provided with flanges, and the two pipes are fixed by flanges and bolts after being connected.

4. The method for predicting the leakage rate of the metal lens gasket sealing interface of ultra-high voltage equipment according to claim 2, characterized in that: The attenuation law model of the contact stress of the metal lens pad obtained in step S2 under the applied cyclic load is: （7）； In the formula, is the average contact stress of the metal lens pad; is the bolt preload; is the number of load cycles; , is a constant related to the applied load and the internal pressure of the equipment.

5. The method for predicting the leakage rate of the metal lens gasket sealing interface of ultra-high voltage equipment according to claim 4, characterized in that: The relationship between the contact force of a single roughness peak obtained in step S3 and the deformation of the microscopic roughness peak is: （8）； In the formula, is the microscopic roughness peak deformation; is the contact force of a single roughness peak; , is a constant related to the roughness peak size.

6. The method for predicting the leakage rate of the metal lens gasket sealing interface of ultra-high voltage equipment according to claim 5, characterized in that: The relationship between the contact stress of the metal lens pad in the actual ultra-high pressure sealing structure under the applied cyclic load and the deformation of the microscopic roughness peak obtained in step S3 is: （9）； In the formula, , is a constant related to the roughness peak size.

7. The method for predicting the leakage rate of the metal lens gasket sealing interface of ultra-high voltage equipment according to claim 6, characterized in that: The microscopic leakage model of the microscopic pore structure of the sealing interface obtained in step S4 based on the fractal theory and the fractal porous media transport theory is: （10）； In the formula, is the micro leakage rate of the microscopic pore structure of the sealing interface, is the fractal dimension of the pore space, which is related to the porosity of the pore space; is the tortuosity fractal dimension, is the straight length of the pore channel, is the maximum pore size of the pore channel; is the viscosity coefficient of the medium, is the pressure difference in the leakage channel.

8. The method for predicting the leakage rate of the metal lens gasket sealing interface of ultra-high voltage equipment according to claim 7, characterized in that: The leakage rate prediction model of the metal lens pad sealing interface obtained in step S4 is: （11）； In the formula, is the leakage rate of the metal lens gasket sealing interface; is the fractal dimension of the pore space, which is related to the porosity of the pore space; is the tortuosity fractal dimension; is the viscosity coefficient of the medium; is the pressure difference in the pore channel; is the perimeter of the sealing interface; is the sampling length, i.e. the length of the pore space; is the initial contact diameter between the pipe and the metal lens pad; is the contact width between the pipe and the metal lens pad, which is equivalent to the straight length of the pore channel; , which is the maximum pore size of the pore channel, is the effective thickness of the interface microporous structure, that is, the area where the medium can flow, is the root mean square deviation of the pore space surface profile, , is the height of the pore space surface profile, obtained by the bivariate WM fractal function, is a constant related to the machining method of the metal lens pad, is the microscopic roughness peak deformation.

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