Method for evaluating and optimizing performance of metal seal flange connection based on hierarchical model

Abstract

The application is based on the metal sealing flange connection performance evaluation and optimization method of hierarchical model, adopts I, II model to calculate the compression-rebound and contact performance of the sealing ring, adopts III, IV model to calculate the deformation and stress state of the sealing ring-flange-fastener structure in the pre-tightening and operating conditions. Based on the assumption that the sealing ring experiences the same compression-rebound process under different loading conditions, the contact state is the same, a method is proposed to accurately calculate the sealing ring contact pressure and contact width considering the sealing ring coating performance, which comprehensively evaluates the sealing performance from the compression-rebound response and contact state two sets of indexes; through three analysis iteration processes from simple to complex and from rough to detailed, the connection performance of the structure is evaluated and optimized, and the iteration number is reduced; the strategy of "two-dimensional analysis iteration + three-dimensional analysis verification" is adopted, which improves the evaluation and optimization efficiency.

Description

Technical Field

[0001] This invention relates to a method for evaluating and optimizing the performance of metal sealing flange connections based on a hierarchical model. Background Technology

[0002] The sealing ring-flange-fastener connection structure, as a detachable connection, is widely used in pressurized pipeline systems. It uses connecting bolts to press the sealing ring against the flange clamping surface, causing the sealing ring to undergo elastic or plastic deformation to fill gaps or defects between the flange clamping surfaces, achieving a seal. Its integrity and sealing reliability are crucial for the safe operation of pressurized pipeline systems. Flange connections are typically subjected to preload assembly loads as well as loads from temperature, medium pressure, additional axial forces and bending moments under operating conditions. Common failure modes of flange connections include seal leakage, insufficient connection stiffness, localized stress concentration leading to crack initiation, and insufficient bolt strength. Among these, sealing leakage occurs most frequently. The sealing performance is mainly determined by the compression-rebound characteristics of the sealing ring and the contact characteristics (contact pressure and width) between the sealing ring and the flange. The former depends on the stress-strain behavior of the sealing ring matrix (high-strength steel or high-temperature alloy), while the latter strongly depends on the mechanical properties and thickness of the sealing ring plating metal (usually soft metals such as copper and silver). When using finite element analysis, the plating must be included in the model. However, the plating thickness is usually tens of micrometers, which has a significant scale difference from the flange structure. It is impossible to characterize the sealing ring plating performance and the boundary load properties of the seal-flange-fastener connection structure in one model. Furthermore, when analyzing the connection performance of the sealing-flange-fastener system during the design phase, in addition to sealing performance, the stiffness and strength of the sealing ring, flange, and fasteners also need to be considered. This usually requires multiple rounds of iterative analysis to obtain a structural design scheme that meets the requirements. When using finite element analysis, there are problems such as the two-dimensional axisymmetric model not being able to reflect the actual load history of the pre-tightening process, not being able to simulate the circumferential pre-tightening load distribution, and not being able to evaluate the stiffness and strength of the fasteners, while the three-dimensional periodic symmetric model has a large computational scale (due to the complex structural contact relationship and the dimensional differences between the sealing ring and the flange), and the high cost of iterative analysis. Summary of the Invention

[0003] The technical problem solved by this invention is to provide a method for evaluating and optimizing the connection performance of metal sealing flanges based on a hierarchical model. A four-level finite element model is established, and the connection performance of the structure is analyzed and evaluated through three iterative analysis processes from simple to complex and from coarse to detailed. This overcomes the simulation calculation difficulties caused by the scale difference between the coating thickness and the flange structure, and improves the optimization iteration efficiency.

[0004] The technical solution of this invention is: a method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model, comprising:

[0005] 1) Using a two-dimensional model, calculate the compression-rebound response of the metal sealing flange structure under pre-tightening and working conditions to make a preliminary judgment on the sealing performance, and optimize the sealing ring structure, flange structure or adjust the pre-tightening force to obtain a structural design with reasonable values ​​for both compression and opening. When the compression-rebound response meets the sealing requirements and the sealing ring and flange meet the static strength requirements, proceed to step 2).

[0006] 2) Using a two-dimensional model, calculate the contact response of the metal sealing flange structure under pre-tightening and working conditions, iterate the sealing performance, adjust the coating material or thickness of the sealing ring, increase the flange stiffness or pre-tightening force, and obtain a structural design with reasonable values ​​for the contact stress and contact width between the sealing ring and the flange under the compression given in the pre-tightening state and the opening given in the working state; when the contact response meets the sealing performance requirements, proceed to step 3).

[0007] 3) Using a three-dimensional model, the mechanical response of the seal-flange-fastener under pre-tightening and working conditions is fully calculated. The consistency between the sealing ring compression under pre-tightening state and the sealing channel opening under working state calculated by the two-dimensional model and the calculation results of the three-dimensional model is verified. It is determined whether the flange and fastener meet the static strength requirements. If there is any inconsistency or failure to meet the requirements, adjustments and optimizations are made until a structural design that meets the requirements of sealing performance, strength and stiffness is obtained.

[0008] The specific process of step 1) is as follows:

[0009] Step 101: Establish a Level I finite element model, extract the cross section of the sealing ring, disregard the soft metal coating, and establish an axisymmetric compression-rebound performance analysis model of the sealing ring being compressed by a pair of rigid surfaces.

[0010] Step 102: Conduct Level I analysis, apply compression to the rigid surface in the axisymmetric compression-rebound performance analysis model, calculate the load-displacement curve of the sealing ring during loading and unloading, and calculate the rebound amount of the sealing ring.

[0011] Step 103: Change the compression amount and repeat the process of step 102 N times to calculate the rebound amount of the sealing ring when loaded and unloaded with different compression amounts. Plot the calculation results as a rebound amount-compression amount curve of the sealing ring; the value of N is 4 to 6.

[0012] Step 104: Establish a Level III finite element model, extract the sealing ring and flange section, ignore the flange weight reduction hole and bolt hole, simulate the pre-tightening effect of the fasteners by a pair of distributed forces of equal magnitude, do not consider the soft metal coating, and establish a two-dimensional axisymmetric sealing-flange model.

[0013] Step 105: Use a Level III finite element model to perform Level III analysis. Under given preload and operating loads, calculate the stress and strain distribution of the sealing ring and flange, the compression of the sealing ring under preload, and the opening of the sealing channel under operating conditions.

[0014] Step 106: Based on the sealing ring springback-compression curve obtained in Step 103, determine whether the compression of the sealing ring under the pre-tightened state obtained in Step 105 meets the sealing requirements; combining the sealing ring springback-compression curve obtained in Step 103 and the sealing channel opening amount under the working state obtained in Step 105, determine whether the flange stiffness meets the sealing requirements; based on the stress and strain distribution of the sealing ring and flange obtained in Step 105, determine whether the sealing ring and flange meet the static strength requirements.

[0015] Step 107: Based on the analysis conclusions of Step 106, if any of the three does not meet the requirements, then optimization and adjustment shall be performed;

[0016] Step 108 continues until all requirements are met, at which point the preliminary judgment process ends.

[0017] In step 107, optimization and adjustment are performed, specifically including:

[0018] A1) Adjust the sealing ring structure and return to step 101;

[0019] B1) Adjust the flange structure and return to step 104;

[0020] C1) Adjust the preload and return to step 105.

[0021] The specific process of step 2) is as follows:

[0022] Step 201: Establish a Level II finite element model, extract the cross section of the sealing ring, construct the soft metal coating, and establish an axisymmetric contact performance analysis model of the sealing ring being compressed by a pair of rigid surfaces.

[0023] Step 202: Conduct Level II analysis, apply compression to the rigid surface in the axisymmetric contact performance analysis model, calculate the distribution of contact pressure along the sealing lip during the loading process, and plot the contact pressure mean-compression curve and the contact width-compression curve.

[0024] Step 203: Combining the distribution of contact pressure along the sealing lip under different compression amounts obtained in step 202, the average contact pressure-compression amount curve, the contact width-compression amount curve, and the compression amount of the sealing ring under the pre-tightened state obtained in the preliminary judgment step, determine whether the current compression amount and contact pressure distribution meet the sealing requirements; if not, optimize accordingly.

[0025] Step 204 continues until the requirements of step 203 are met. At this point, the compression amount that meets the sealing requirements has been obtained. Level II analysis is carried out. The compression amount that currently meets the sealing requirements is applied to the rigid surface in the axisymmetric contact performance analysis model. The distribution of contact pressure along the sealing lip during the unloading process of the sealing ring is calculated, and the contact pressure mean - opening amount curve and contact width - opening amount curve are plotted.

[0026] Step 205: Based on the distribution of contact pressure along the sealing lip, the average contact pressure-opening curve, and the contact width-opening curve obtained in step 204, determine whether the opening of the sealing channel under the working state obtained in the preliminary judgment step meets the sealing requirements; if not, optimize accordingly.

[0027] Step 206 continues until the requirements of step 205 are met. At this point, a structural design that meets the requirements for sealing performance, flange stiffness, and sealing ring stiffness and strength has been obtained, and the rapid iteration process ends.

[0028] The compression applied to the rigid surface in the axisymmetric contact performance analysis model shall not be less than 1.2 times the compression determined in the preliminary judgment step.

[0029] In step 203, if the conditions are not met, optimization is performed, specifically including:

[0030] A2) Optimize the flange structure to increase the compression amount, return to step 104;

[0031] B2) Adjust the preload to increase the compression, then return to step 105;

[0032] C2) Change the coating material and thickness of the sealing ring, then return to step 201.

[0033] If the conditions are not met in step 205, optimization will be performed, specifically including:

[0034] A3) Increase flange stiffness, return to step 104;

[0035] B3) Increase the preload and return to step 105;

[0036] C3) Change the coating material and thickness of the sealing ring, then return to step 201.

[0037] If there are any inconsistencies or non-compliance in step 3), adjustments and optimizations shall be made, specifically by changing the bolt specifications, increasing the number of bolts, or optimizing the flange structure.

[0038] The specific process of step 3) is as follows:

[0039] Step 301: Establish a Level IV finite element model. Cut out sectors containing one bolt in the flange and sealing ring respectively, and establish a three-dimensional periodic symmetric model containing the flange, sealing ring and fastener.

[0040] Step 302: Perform Level IV finite element analysis. Under given preload and working load, calculate the compression of the sealing ring, stress and strain of the sealing ring and flange under the preload condition; and the opening of the sealing channel, stress and strain of the sealing ring and flange, and axial load, stress and strain of the fasteners under the working condition.

[0041] Step 303: Verify whether the compression amount of the sealing ring under the pre-tightening state and the opening amount of the sealing channel under the working state calculated in step 302 are consistent with the compression amount and opening amount obtained at the end of the rapid iteration process.

[0042] Step 304: If there is no consistency, return to step 104, correct the Level II model, and make the error of the compression and opening calculated using the Level II model less than 5% relative to the calculation results using the Level IV model, and continue the evaluation process from step 104.

[0043] Step 305: Based on the stress and strain distribution of the flange, and the axial load, stress, and strain of the fastener obtained in step 302, determine whether the flange and fastener meet the static strength requirements; if the flange and fastener do not meet the static strength requirements, then optimize; until the flange and fastener meet the static strength requirements, at which point a sealing ring-flange-fastener connection structure that meets the requirements of sealing performance, strength, and stiffness is obtained.

[0044] In step 305, optimization is performed, specifically including:

[0045] A4) Change the bolt specifications and return to step 301;

[0046] B4) Increase the number of bolts and return to step 301;

[0047] B4) Optimize the flange structure and return to step 301.

[0048] The beneficial effects of this invention are as follows: This invention uses low-level models (Levels I and II) to obtain the compression-rebound and contact performance of the sealing ring itself, and constructs a soft metal coating in the finite element model to accurately describe the influence of the sealing ring's mechanical properties and thickness on contact characteristics. High-level models (Levels III and IV) are used to obtain the deformation and stress state of the sealing ring-flange-fastener structure under pre-tightening and operating conditions. Based on the assumption that the sealing ring's contact state is the same under different loading conditions (compressed by a rigid surface or by a flange), as long as the compression-rebound (opening) process is the same, a method is proposed that can accurately calculate the contact pressure and contact width of the sealing ring considering the coating performance, thus comprehensively evaluating the sealing performance using both compression-rebound response and contact state indicators. The connection performance of the structure is optimized through three iterative analysis processes, progressing from simple to complex and from coarse to detailed. The analysis process adopts the evaluation sequence of "compression-rebound performance → contact performance → strength" to minimize the number of iterations. Balancing the advantages and disadvantages of two-dimensional axisymmetric models and three-dimensional periodic symmetric models, a strategy of "two-dimensional analysis iteration + three-dimensional analysis verification" is adopted to improve the efficiency of the optimization analysis. Attached Figure Description

[0049] Figure 1 This is a flowchart for preliminary judgment.

[0050] Figure 2 This is a flowchart illustrating a rapid iteration process. Detailed Implementation

[0051] First, perform the preliminary judgment process, as shown in the attached document. Figure 1 As shown, steps 101 to 110 are included:

[0052] (1) Step 101: Establish a Level I finite element model, extract the cross section of the sealing ring, and without considering the soft metal coating, establish an axisymmetric compression-rebound performance analysis model of the sealing ring being compressed by a pair of rigid surfaces.

[0053] (2) Step 102: Conduct Level I analysis, apply compression to the rigid surface in the axisymmetric compression-rebound performance analysis model, calculate the load-displacement curve of the sealing ring during loading and unloading, and calculate the rebound amount of the sealing ring.

[0054] (3) Step 103: Change the compression amount and repeat step 102 4 to 6 times to calculate the rebound amount of the sealing ring when loading and unloading with different compression amounts. Plot the calculation results as a rebound amount-compression amount curve of the sealing ring.

[0055] (4) Step 104: Establish a Level III finite element model, extract the sealing ring and flange section, ignore the flange weight reduction hole and bolt hole, and simulate the pre-tightening effect of the fastener by a pair of equal distributed forces, without considering the soft metal coating, and establish a two-dimensional axisymmetric sealing-flange model.

[0056] (5) Step 105: Use the Level III finite element model to carry out Level III analysis. Under the given preload and operating load, calculate the stress and strain distribution of the sealing ring and flange, the compression of the sealing ring under the preload state, and the opening of the sealing channel under the working state.

[0057] (6) Step 106: Based on the sealing ring rebound amount-compression amount curve obtained in step 103, determine whether the compression amount of the sealing ring under the pre-tightening state obtained in step 105 meets the sealing requirements.

[0058] (7) Step 107: Combine the sealing ring springback-compression curve obtained in step 103 and the sealing channel opening amount under working conditions obtained in step 105 to determine whether the flange stiffness meets the sealing requirements.

[0059] (8) Step 108: Based on the stress and strain distribution of the sealing ring and flange obtained in step 105, determine whether the sealing ring and flange meet the static strength requirements.

[0060] (9) Step 109: Based on the analysis conclusions of steps 106-108, if any of the three conditions is not met, optimization is performed, specifically including:

[0061] a) Optimize the sealing ring structure and return to step 101;

[0062] b) Optimize the flange structure and return to step 104;

[0063] c) Adjust the preload and return to step 105;

[0064] (10) Step 110, until the analysis conclusions of steps 106 to 108 all meet the requirements, the preliminary judgment process ends and the rapid iteration process begins.

[0065] Next, a rapid iteration process is executed, including steps 201–206:

[0066] (11) Step 201: Establish a Level II finite element model, extract the cross section of the sealing ring, construct the soft metal coating, and establish an axisymmetric contact performance analysis model of the sealing ring being compressed by a pair of rigid surfaces.

[0067] (12) Step 202: Conduct Level II analysis, apply a compression amount (not less than 1.2 times the compression amount determined in the preliminary judgment step) to the rigid surface in the axisymmetric contact performance analysis model, calculate the distribution of contact pressure along the sealing lip during the loading process, and plot the contact pressure mean - compression amount curve and the contact width - compression amount curve.

[0068] (13) Step 203: Combining the distribution of contact pressure along the sealing lip under different compression amounts obtained in step 202, the average contact pressure-compression amount curve, the contact width-compression amount curve, and the compression amount of the sealing ring under the pre-tightening state obtained in the preliminary judgment step, determine whether the current compression amount and contact pressure distribution meet the sealing requirements; if not, optimize accordingly, specifically including:

[0069] a) Optimize the flange structure to increase the compression amount, return to step 104;

[0070] b) Adjust the preload to increase the compression, then return to step 105;

[0071] c) Change the coating material and thickness of the sealing ring, then return to step 201;

[0072] (14) Step 204, until the analysis conclusion of step 203 meets the requirements. At this time, the compression amount that meets the sealing requirements has been obtained. Perform Level II analysis, apply the current compression amount that meets the sealing requirements to the rigid surface in the axisymmetric contact performance analysis model, calculate the distribution of contact pressure along the sealing lip during the unloading process of the sealing ring, and draw the contact pressure mean - opening amount curve and contact width - opening amount curve.

[0073] (15) Step 205: Based on the distribution of contact pressure along the sealing lip, the average contact pressure-opening curve, and the contact width-opening curve obtained in step 204, determine whether the opening of the sealing channel under the working state obtained in the preliminary judgment step meets the sealing requirements; if not, optimize accordingly, specifically including:

[0074] a) Increase flange stiffness, return to step 104;

[0075] b) Increase the preload and return to step 105;

[0076] c) Change the coating material and thickness of the sealing ring, then return to step 201;

[0077] (16) Step 206, until the analysis conclusion of step 205 meets the requirements, at this time the structural design with the requirements of sealing performance, flange stiffness and sealing ring stiffness and strength has been obtained, the rapid iteration process ends and the detailed evaluation process begins.

[0078] Finally, a detailed evaluation process is performed, including steps 301 to 307:

[0079] (17) Step 301: Establish a Level IV finite element model. Cut out sectors containing one bolt in the flange and sealing ring respectively, and establish a three-dimensional periodic symmetric model containing the flange, sealing ring and fastener.

[0080] (18) Step 302: Perform Level IV finite element analysis. Under given preload and working load, calculate the compression of the sealing ring, stress and strain of the sealing ring and flange under the preload state; the opening of the sealing channel under the working state; stress and strain of the sealing ring and flange; and axial load, stress and strain of the fastener.

[0081] (19) Step 303: Verify whether the compression amount of the sealing ring under the pre-tightening state and the opening amount of the sealing channel under the working state calculated in step 302 are consistent with the compression amount and opening amount obtained at the end of the rapid iteration process (relative error less than 5%).

[0082] (20) Step 304, return to step 104, correct the Level II model, so that the error of the compression and opening calculated by the Level II model is less than 5% compared with the calculation results of the Level IV model, and continue the evaluation process from step 104.

[0083] (21) Step 305: Based on the stress and strain distribution of the flange, the axial load, stress and strain of the fastener obtained in step 302, determine whether the flange and fastener meet the static strength requirements.

[0084] (22) Step 306: If the flange and fasteners do not meet the static strength requirements, optimization shall be performed, specifically including:

[0085] a) Change the bolt specifications and return to step 301;

[0086] b) Increase the number of bolts and return to step 301;

[0087] b) Optimize the flange structure and return to step 301;

[0088] (23) Step 307, until the flange and fasteners meet the static strength requirements, at which point the sealing ring-flange-fastener connection structure that meets the requirements of sealing performance, strength and stiffness is obtained.

[0089] (1) Based on the hierarchical model, a four-level finite element analysis model for the performance optimization analysis of metal sealing flange connections is established:

[0090] Level I model: Axisymmetric compression-rebound performance analysis model (without considering the coating, the sealing ring is compressed by a pair of rigid surfaces);

[0091] Level II model: axisymmetric contact performance analysis model (considering the coating, the sealing ring is compressed by a pair of rigid surfaces);

[0092] Level III Model: Two-dimensional axisymmetric sealing ring-flange model (the model includes an uncoated sealing ring and a flange);

[0093] Level IV model: Three-dimensional periodic symmetrical sealing ring-flange-fastener model (the model includes an unplated sealing ring, flange, and fasteners).

[0094] (2) Using the above four-level finite element model, the following four-level numerical simulation analysis is carried out respectively. The calculation time for level I, II and III analysis is in the minute level, and the calculation time for level IV analysis is in the tens of hours level.

[0095] Level I Analysis: Using the Level I model, the compression-rebound characteristics of the sealing ring are analyzed and the load-displacement curves and the rebound-compression curves of the sealing ring under different compression amounts are calculated.

[0096] Level II Analysis: Using the Level II model, the contact characteristics of the sealing ring are analyzed, and the distribution of contact pressure along the sealing lip, the mean contact pressure-compression curve, and the contact width-compression curve are calculated under different compression amounts; the distribution of contact pressure along the sealing lip, the mean contact pressure-opening curve, and the contact width-opening curve are also calculated under different opening amounts.

[0097] Level III Analysis: Using a Level III model, rapid analysis of the mechanical properties of the sealing-flange joint is conducted, calculating the compression of the sealing ring, stress and strain of the sealing ring and flange under a given preload condition; and the opening of the sealing channel, stress and strain of the sealing ring and flange under working conditions.

[0098] Level IV Analysis: Using the Level IV model, a detailed analysis of the mechanical properties of the seal-flange-fastener joint is conducted. The compression of the sealing ring, stress and strain of the sealing ring and flange under a given preload condition are calculated; the opening of the sealing channel, stress and strain of the sealing ring and flange, and axial load, stress and strain of the fastener are calculated under the working condition.

[0099] (3) Three analysis iteration processes are adopted, from simple to complex and from rough to detailed, which significantly improves the efficiency of improving the performance of the sealing-flange-bolt joint connection in the structural design process.

[0100] The failure modes of the sealing-flange-bolted joint are mostly sealing leakage, with insufficient strength being less common. Considering that contact pressure and contact width need to be guaranteed by a certain residual compression (compression in pre-tightened state - opening in working state), a judgment sequence of "compression-rebound performance → contact performance → strength" was established to minimize the number of iterations. During the iterative analysis, a two-dimensional axisymmetric model was used as much as possible to obtain a sealing-flange joint structure that basically meets the requirements. Then, a more accurate and detailed three-dimensional periodic model was used for verification and supplementary checks.

[0101] ①Preliminary judgment: Based on the results of Level I and Level III analyses, make a preliminary judgment on whether the compression, opening, and sealing strength are reasonable. If they are not reasonable, optimize the sealing ring and flange structure or adjust the preload, and repeat the Level I and Level III analyses until the compression-rebound characteristics given by the Level I analysis and the compression and opening given by the Level III analysis are within a reasonable range, and the seal meets the static strength requirements.

[0102] ② Rapid iteration: Determine whether the sealing performance meets the requirements based on the results of Level II and Level III analysis; if not, optimize the coating properties of the sealing ring, the flange structure, or adjust the preload. Based on the changes, conduct Level I, II, or III analysis again until: a) the sealing performance of the sealing ring-flange structure meets the requirements; b) the flange stiffness meets the requirements.

[0103] Through a rapid iterative process, a structural design has been obtained that meets the requirements for sealing performance, flange stiffness, and sealing ring stiffness and strength. However, the Level III model does not include fasteners and uses a pair of equal forces to simulate the pre-tightening process. This cannot reflect the change in the clamping force of the fasteners on the upper and lower flanges from pre-tightening to the working state, as well as the differences in the circumferential compression, opening, stress, and strain of the sealing ring-flange structure (this difference is very small when the bolts are distributed densely along the circumferential direction). In addition, the difference in flange stiffness along the circumferential direction (caused by the weight reduction holes) and the strength of the fasteners themselves in the working state need to be considered using the analysis results of the three-dimensional model.

[0104] ③ Detailed assessment: The sealing performance is finally assessed based on the results of the Level II and IV analyses, and the flange strength and fastener strength are assessed based on the results of the Level IV analyses.

[0105] (4) A graded model is adopted to construct a soft metal coating in the model, taking into account the influence of the mechanical properties and thickness of the coating, so as to ensure the accuracy of the calculation results of the seal-flange contact performance.

[0106] The contact pressure and width of the sealing ring strongly depend on the mechanical properties and thickness of the coating metal (usually soft metals such as copper and silver). The sealing ring contact performance analysis model must include the coating; however, the coating thickness is typically tens of micrometers, a significant scale difference from the flange structure, making it impossible to simultaneously characterize the sealing ring coating performance and the boundary load properties of the seal-flange-fastener connection structure in a single model. Therefore, a set of rigid surface compression models of a two-dimensional axisymmetric sealing ring with coating (Level II model) is used to obtain the contact pressure and contact width of the sealing ring under different compression and opening amounts, i.e., the sealing ring contact characteristic curves. Then, the sealing flange joint model (Level III and IV models) is used to calculate the compression and opening amounts of the sealing ring under given preload and operating conditions. This accurately provides the contact state of the sealing ring under a given state, thus evaluating the sealing performance. It is assumed here that the sealing ring's contact state is the same under different loading conditions (compressed by a rigid surface or by a flange) as long as the compression-springback (opening) process is the same.

Claims

1. A method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model, characterized in that... Includes the following steps: 1) Using Level I and Level III models, calculate the compression-rebound response of the metal sealing flange structure under pre-tightening and working conditions to make a preliminary judgment on the sealing performance, and optimize the sealing ring structure, flange structure or adjust the pre-tightening force to obtain a structural design that meets the requirements for compression and opening; when the compression-rebound response meets the sealing performance requirements, and the sealing ring and flange meet the static strength requirements, proceed to step 2). 2) Using a Level II model, calculate the contact response of the metal sealing flange structure under preload and working conditions. Iterate the sealing performance, adjust the coating material or thickness of the sealing ring, and increase the flange stiffness or preload to obtain a structural design where the contact stress and contact width between the sealing ring and the flange meet the requirements under the given compression in the preload state and the given opening in the working state. Once the contact response meets the sealing requirements, proceed to step 3). 3) Using a Class IV model, we comprehensively calculate the mechanical response of the seal-flange-fastener under pre-tightening and working conditions. We verify the consistency between the sealing ring compression under pre-tightening and the sealing channel opening under working conditions calculated by the two-dimensional model and the calculation results of the three-dimensional model. We determine whether the flange and fastener meet the static strength requirements. If there are inconsistencies or non-compliance, we make adjustments and optimizations until we obtain a structural design that meets the requirements for sealing performance, strength and stiffness. in, Level I model: axisymmetric compression-rebound performance analysis model, without considering the coating, the sealing ring is compressed by a pair of rigid surfaces; Level II model: axisymmetric contact performance analysis model, considering the coating, with the sealing ring compressed by a pair of rigid surfaces; Level III Model: Two-dimensional axisymmetric sealing ring-flange model, which includes an uncoated sealing ring and a flange; Level IV model: Three-dimensional periodic symmetrical sealing ring-flange-fastener model, which includes unplated sealing ring, flange and fastener.

2. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 1, characterized in that: The specific process of step 1) is as follows: Step 101: Establish a Level I finite element model, extract the cross section of the sealing ring, disregard the soft metal coating, and establish an axisymmetric compression-rebound performance analysis model of the sealing ring being compressed by a pair of rigid surfaces. Step 102: Conduct Level I analysis, apply compression to the rigid surface in the axisymmetric compression-rebound performance analysis model, calculate the load-displacement curve of the sealing ring during loading and unloading, and calculate the rebound amount of the sealing ring. Step 103: Change the compression amount and repeat the process of step 102 N times to calculate the rebound amount of the sealing ring when loaded and unloaded with different compression amounts. Plot the calculation results as a rebound amount-compression amount curve of the sealing ring; the value of N is 4~6. Step 104: Establish a Level III finite element model, extract the sealing ring and flange section, ignore the flange weight reduction hole and bolt hole, simulate the pre-tightening effect of the fasteners by a pair of equal distributed forces, do not consider the soft metal coating, and establish a two-dimensional axisymmetric sealing ring-flange model. Step 105: Use a Level III finite element model to perform Level III analysis. Under given preload and operating loads, calculate the stress and strain distribution of the sealing ring and flange, the compression of the sealing ring under preload, and the opening of the sealing channel under operating conditions. Step 106: Based on the sealing ring springback-compression curve obtained in Step 103, determine whether the compression of the sealing ring under the pre-tightened state obtained in Step 105 meets the sealing requirements; combining the sealing ring springback-compression curve obtained in Step 103 and the sealing channel opening amount under the working state obtained in Step 105, determine whether the flange stiffness meets the sealing requirements; based on the stress and strain distribution of the sealing ring and flange obtained in Step 105, determine whether the sealing ring and flange meet the static strength requirements. Step 107: Based on the analysis conclusions of Step 106, if any of the three does not meet the requirements, then optimization and adjustment shall be performed; Step 108 continues until all requirements are met, at which point the preliminary judgment process ends.

3. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 2, characterized in that: In step 107, optimization and adjustment are performed, specifically including: Adjust the sealing ring structure and return to step 101; Alternatively, adjust the flange structure and return to step 104; Alternatively, adjust the preload and return to step 105.

4. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 2, characterized in that: The specific process of step 2) is as follows: Step 201: Establish a Level II finite element model, extract the cross section of the sealing ring, construct the soft metal coating, and establish an axisymmetric contact performance analysis model of the sealing ring being compressed by a pair of rigid surfaces. Step 202: Conduct Level II analysis, apply compression to the rigid surface in the axisymmetric contact performance analysis model, calculate the distribution of contact pressure along the sealing lip during the loading process, and plot the contact pressure mean-compression curve and the contact width-compression curve. Step 203: Combining the distribution of contact pressure along the sealing lip under different compression amounts obtained in step 202, the average contact pressure-compression amount curve, the contact width-compression amount curve, and the compression amount of the sealing ring under the pre-tightened state obtained in the preliminary judgment step, determine whether the current compression amount and contact pressure distribution meet the sealing requirements; if not, optimize accordingly. Step 204 continues until the requirements of step 203 are met. At this point, the compression amount that meets the sealing requirements has been obtained. Level II analysis is carried out. The compression amount that currently meets the sealing requirements is applied to the rigid surface in the axisymmetric contact performance analysis model. The distribution of contact pressure along the sealing lip during the unloading process of the sealing ring is calculated, and the contact pressure mean - opening amount curve and contact width - opening amount curve are plotted. Step 205: Based on the distribution of contact pressure along the sealing lip, the average contact pressure-opening curve, and the contact width-opening curve obtained in step 204, determine whether the opening of the sealing channel under the working state obtained in the preliminary judgment step meets the sealing requirements; if not, optimize accordingly. Step 206 continues until the requirements of step 205 are met. At this point, a structural design that meets the requirements for sealing performance, flange stiffness, and sealing ring stiffness and strength has been obtained, and the rapid iteration process ends.

5. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 4, characterized in that: The compression applied to the rigid surface in the axisymmetric contact performance analysis model shall not be less than 1.2 times the compression determined in the preliminary judgment step.

6. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 4, characterized in that: In step 203, if the conditions are not met, optimization is performed, specifically including: Adjust the flange structure to increase the compression, then return to step 104; Alternatively, adjust the preload to increase the compression, and return to step 105; Alternatively, change the coating material and thickness of the sealing ring, and return to step 201.

7. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 4, characterized in that: If the conditions are not met in step 205, optimization will be performed, specifically including: Increase flange stiffness, return to step 104; Alternatively, increase the preload and return to step 105; Alternatively, change the coating material and thickness of the sealing ring, and return to step 201.

8. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 4, characterized in that: The specific process of step 3) is as follows: Step 301: Establish a Level IV finite element model. Cut out sectors containing one bolt in the flange and sealing ring respectively, and establish a three-dimensional periodic symmetrical sealing ring-flange-fastener model containing the flange, sealing ring, and fastener. Step 302: Perform Level IV finite element analysis. Under given preload and working load, calculate the compression of the sealing ring, stress and strain of the sealing ring and flange under the preload condition; and the opening of the sealing channel, stress and strain of the sealing ring and flange, and axial load, stress and strain of the fasteners under the working condition. Step 303: Verify whether the compression amount of the sealing ring under the pre-tightened state and the opening amount of the sealing channel under the working state calculated in Step 302 are consistent with the compression amount and opening amount obtained at the end of the rapid iteration process; if they are consistent, proceed to Step 304; if they are inconsistent, correct the Level II model. Step 304: Based on the stress and strain distribution of the flange, and the axial load, stress, and strain of the fastener obtained in step 302, determine whether the flange and fastener meet the static strength requirements; if the flange and fastener do not meet the static strength requirements, then optimize them. Until the flange and fasteners meet the static strength requirements, a sealing ring-flange-fastener connection structure that meets the requirements of sealing performance, strength and stiffness is obtained.

9. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 8, characterized in that: If there is a discrepancy in step 303, return to step 104 to correct the Level II model until the compression and opening values ​​calculated using the Level II model have an error of less than 5% relative to the calculation results using the Level IV model.

10. The method for evaluating and optimizing the performance of metal-sealed flange connections based on a hierarchical model according to claim 9, characterized in that: In step 304, optimization is performed, specifically including: Change the bolt specifications and return to step 301; Alternatively, increase the number of bolts and return to step 301; Alternatively, optimize the flange structure and return to step 301.

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