As a critical connection component in piping systems, the rationality of stress distribution in a flange connector directly affects its load-bearing capacity and sealing performance. Under high-pressure conditions, flange connectors often fail due to stress concentration, material yielding, or bolt deformation. Finite element analysis (FEM) provides a scientific basis for optimized design by simulating the mechanical behavior under actual working conditions. This paper systematically explains how to optimize the stress distribution of a flange connector using FEM from seven aspects: model establishment, contact state definition, boundary condition application, material parameter setting, mesh generation, result analysis, and optimization design.
The finite element model is the foundation of the analysis and must accurately reflect the geometric characteristics and connection relationships of the flange connector. A flange connector typically consists of a flange ring, bolts, nuts, and gaskets. Modeling requires considering the geometric dimensions, material properties, and assembly relationships of each component. For example, the conical neck, cylindrical structure, and ring plate structure of the flange ring need to be modeled according to actual dimensions; the threaded pairs of bolts and nuts can be simulated through binding contact or frictional contact; and the gasket requires a suitable material model based on its nonlinear characteristics. When simplifying the model, a portion of the model can be analyzed using symmetry, but it is crucial to ensure that the boundary conditions are consistent with actual operating conditions to avoid distortion of stress distribution due to simplification.
The definition of contact states directly affects the stress transmission path of the flange connector. Multiple contact pairs exist within the flange connector, including nut and flange face, bolt and nut, flange and gasket, etc. The contact between the nut and flange face requires particular attention, as insufficient contact area under high-pressure conditions can easily lead to localized stress concentration. Finite element analysis can simulate the impact of different nut and washer sizes on the contact area, revealing that appropriately sized nuts and washers can significantly increase the contact area, reduce peak contact stress, and thus improve load-bearing capacity. Furthermore, the threaded contact between the bolt and nut should employ a friction contact type to simulate torque transmission and stress distribution during actual tightening.
The application of boundary conditions must accurately reflect the actual stress state of the flange connector. Under high-pressure conditions, the flange connector primarily bears the axial force generated by internal pressure, bolt preload, and external loads (such as bending moment and torque). In the finite element model, internal pressure can be simulated by applying a pressure load to the inner surface of the flange, while bolt preload is applied using preload elements or temperature load methods. External loads need to be converted into equivalent pressures or moments based on actual working conditions and applied at appropriate locations. For example, external bending moment can be simulated by applying a couple to the end face of the nozzle, and seismic loads require consideration of inertial forces caused by acceleration. Appropriate application of boundary conditions is crucial to ensuring accurate analysis results.
Material parameters must be set consistent with actual material properties. The materials for each component of the flange connector must be selected according to design requirements; for example, flange rings commonly use high-strength alloy steel, while bolts must possess sufficient tensile and yield strength. In the finite element analysis, parameters such as the material's elastic modulus, Poisson's ratio, density, and yield strength must be input. For gaskets, due to their nonlinear characteristics, hyperelastic or elastoplastic material models must be used, and the corresponding stress-strain curves must be input. The accuracy of material parameters directly affects the calculation results of stress distribution, thus affecting the reliability of the optimization design.
The fineness of the mesh determines the accuracy and efficiency of the finite element analysis. Stress concentration areas of the flange connector (such as the flange conical neck and around bolt holes) require finer meshing to capture local stress gradients. For contact areas, the mesh needs further refinement to ensure accurate transmission of contact pressure. Simultaneously, mesh independence verification is necessary; this involves progressively refining the mesh and comparing the calculation results to ensure that the stress distribution does not significantly change with mesh refinement. A reasonable meshing method can improve analysis efficiency while maintaining computational accuracy.
After the finite element analysis, the results need in-depth analysis to identify stress concentration areas and potential failure risks. Stress contour plots provide a visual overview of the stress distribution in the flange connector, identifying high-stress areas (such as the flange conical neck transition and bolt bending points). Furthermore, stress values along the critical path can be extracted, stress curves plotted, and stress variation trends analyzed along the path. Additionally, deformation contour plots allow observation of the overall deformation of the flange connector, assessing whether its stiffness meets design requirements. Based on the analysis results, targeted optimization schemes can be proposed.
Optimized design must be based on the finite element analysis results, improving stress distribution by adjusting geometric or material parameters. For example, to address stress concentration at the flange conical neck transition, the conical neck radius can be optimized or the transition fillet radius increased to reduce stress peaks. For bolt bending deformation, the bolt diameter can be increased or high-strength materials used to improve bending resistance. Furthermore, adjusting the size or material of the nut and washer can further optimize contact stress distribution and improve sealing performance. After optimization, a new finite element analysis is required to verify the optimization effect and establish a closed-loop design process. Through continuous iterative optimization, the load-bearing capacity and reliability of the flange connector can be significantly improved.
