Preface
The pressure vessel tube plate is an important part of the pressure vessel. According to the characteristics of the tube plate structure, it directly affects the pressure bearing capacity of the tube box. Its deformation and stress analysis play a decisive role in the stress analysis of the entire box and pipe structure. However, the analysis of stress and strain on the pressure vessel tube plate by the J-commissioning analytical method is too large. The ANSYS finite element analysis software was used to establish the finite element model of the pressure vessel tube plate. The stress solution was applied to the stress field analysis to calculate the maximum stress cleft of the pressure vessel tube plate. The finite element analysis and computer graphics functions of ANSYS were used to display the three-dimensional stress equivalent. The surface should be moved to the isosurface, which provides a sufficient theoretical basis for the optimal analysis of the pressure vessel tube plate mechanism.
1 basic sub-process
1.1 Creating a Finite Element Model
In this paper, a U-tube type pressure vessel is selected for modeling. The tube plate material is made of 20MuMo forgings. The spherical head material 16MnR, the material's elastic modulus E = 20E + 05MPa. The Poisson's ratio is 03, the density is 7.8t/m3, the design pressure P = 31.4MPa, the allowable stress is 196MPa.
In the stress analysis of the pressure vessel, the design of the pressure vessel component is concerned with the distribution law of the stress along the wall thickness and its size. A check line along the wall thickness direction can be used instead of the check surface. In addition, since the pressure vessel is an axisymmetric structure, half of the structure can be selected for modeling. In order to save time and storage space without affecting the analysis results, some details are omitted according to their structure. Where the tube hole weakens the strength of the tube sheet, the concept of the effective elastic modulus E1 and the effective Poisson's ratio V1 can be used to convert the tube sheet to an equivalent non-porous circular plate of the same thickness, so the tube plate area is divided into two major parts, 1 Zones are treated as equivalent circular plates, while Zone 2 is treated as actual quiet conditions. According to relevant literature, E1 = 054F and V1 = 0360 are summarized above. The simplified finite element analysis model obtained is shown in Figure 1.
Figure 1 Finite element analysis model
1.2 mesh division
There are usually two methods for meshing ANSYS: free partitioning and mapping partitioning. The free division grid is mainly used to divide the region with irregular boundary shapes. The analysis is slightly not high enough, but the required division area meets certain topological conditions.奕淞"The sub-grid is mainly suitable for helium bodies and has high analysis accuracy. In view of the structural characteristics of pressure vessel tubesheets, both methods are used in this paper. In the non-boundary area, the grid is divided by drunkenness, and the free mesh is used in the boundary area and areas where the shoot-through is not very demanding. The quadrilateral mesh cell uses 8-node SOLID 82. The trigonal mesh cell uses 6-node SOLID Triangle 6node2. SOLID82 has compatible displacement pillows for modeling of curved boundaries. They have three degrees of freedom at each node: translational movement in the direction of the node coordinates XYZ SOLID82 has the functions of plasticity, creep, stress intensification, large deformation and force change. The connection between the tube plate and the head is relatively concentrated, and the triangulation mesh is used here. There are 1265 cells and 3994 nodes.
1.3 Constraints and Applied Loads
Whether the application of boundary conditions is consistent with the actual project directly affects the correctness and rationality of the results. Since the stress analysis of the pressure vessel is based on a line instead of a face, and half of the analysis is performed, the X direction constraint is applied at the end face and the Y direction constraint is applied at the pipe hole. The entire tube process is under pressure, so the surface load applied on the wire is P = 31.4 MP, as shown in Figure 2:
1.4 Calculation Results and Analysis
In this step, ANSYS will discuss the nodes of each cell that are automatically divided. Many equations are established and it takes a certain amount of time. The results obtained are very large. After the structural analysis is completed, the analysis results can be viewed in a general-purpose postprocessor and a post-time processor. Figure 3 and Figure 4 show the stress distribution and displacement distribution of the pressure vessel tube plate, respectively.
From the strain distribution diagram of the node, the maximum deformation appeared at the top of the spherical head, and its value reached 0.547~0.549.
The next largest value appears at the left end of the tubesheet, which also reaches about 0.5mm. This is consistent with the actual deformation. In fact, this also reflects the deformation of the left end of the tube sheet, and the stress analysis of the whole box and tube structure plays a central role. The choice of the thickness of the tube sheet and the parameters of the outer radius of the tube sheet is very important for the optimization of the structure. significance. From the nodal stress distribution diagram, it can be seen that the maximum stress occurs at the joint between the tube plate and the ball head. The maximum equivalent stress is 144.16 MPa, and the stress conditions in other parts are relatively uniform. This is consistent with the actual situation. Based on the above analysis, the establishment and analysis results of the finite element model are objective and reflect the stress of the pressure vessel tube plate.
2 Summary
The significance of this article lies in:
2.1 Using finite element analysis to change the continuous structure into a discrete structure, replacing the traditional theoretical analysis. The ANSYS software can more accurately reflect the stress conditions of each point, and the structure of the pressure vessel is used to provide sufficient theoretical data.
2.2 Although the equivalent stress produced under the action of surface loads is less than the allowable stress value of its material (196 MPa), the stress concentration at the connection between the tube plate and the head is a dangerous part. The deformation of the head and the deformation of the left end of the tube sheet are more Because of its large size, it has defects of insufficient strength and rigidity. It is necessary to improve the structure of the pressure vessel tube plate to reduce weight, improve performance, and save costs.
2.3 dynamically demonstrate the process of deformation of the pressure vessel tube plate, and can draw a corresponding change curve by means of the post-processor, so that the needle setters clearly grasp the law of change and change characteristics.
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