Overall finite element analysis of a 2000m3 large propylene spherical tank

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As a large-capacity and pressure-bearing efficient storage pressure vessel, the spherical tank has been widely used in petrochemical, night scene, city gas and other industries. The storage media covers (propane, butane, propylene, ethylene, liquefied petroleum gas, liquid ammonia, etc.), and can also be used as a storage tank for compressed gases (air, oxygen, nitrogen, etc.). The operating temperature is generally -50~50℃, and the operating pressure is generally below 3MPa. The maximum stress of the spherical tank structure generally occurs at the connection between the pillar and the shell, so the most important thing in the design of the spherical tank is to ensure that the stress assessment here is passed. This example takes a 2000m3 propylene spherical tank as an example to outline the overall finite element analysis of the propylene spherical tank in WB. When establishing the overall model of the spherical tank, it is considered that the various open nozzles of the spherical tank have a relatively small impact on the whole. From an overall perspective, their impact is only partial. In addition, the overall analysis focuses on examining the stress conditions at the joints between the pillars and the spherical tank under various load conditions. Therefore, various nozzles can be ignored when constructing the overall analysis model. The inner wall of the spherical shell is considered to have a corrosion allowance of 2mm, the negative deviation of the steel plate is 0.3, the inner diameter of the spherical shell is 15704mm, and the effective thickness of the spherical shell is 43.7mm. Loads considered include design pressure, operating medium liquid column static pressure, attachment weight, wind load, seismic load, snow load and weight of corrosion layer. The geometric model of the spherical tank in this example adopts a combination modeling method of various units. Because the model is large, the sphere uses the Solid185 enhanced strain unit. The calculation accuracy is equivalent to the Solid186 unit and the calculation accuracy can be guaranteed. * * Reduce the number of units and grid nodes to ensure calculation efficiency and calculation time. * * improve ； Pillar part: The connection between the pillars and the sphere is the key stress inspection area, so the upper half of the pillars also use Solid185 enhanced strain units, while the lower half of the pillars are not the focus of the inspection. The number of units and grid nodes can also be reduced by using Shell181 units. ； The tie rod part uses Link180 unit. It should be noted that: When modeling different unit combinations, it is necessary to consider the connection issues between different units. The rod unit has three degrees of freedom, the shell unit has six degrees of freedom, and the solid unit has three degrees of freedom. Although the rod unit and the shell unit have different degrees of freedom, the rod unit and the shell unit can share the grid nodes, while the shell unit and the solid unit cannot share the grid nodes. Therefore, binding contacts need to be used at the connection between the shell unit and the solid unit to connect the two. The detailed geometric model is shown in the figure below.: Mesh division Mesh division adopts full hexahedral mesh division. Compared with the solid part, the sphere part has a regular structure and can be divided into sweepable bodies. However, the connection part between the sphere and the pillar has a very irregular structure and is difficult to divide. However, a mesh dominated by hexahedrons can be drawn. , the meshing of the pillars and tie rods using shell elements and rod elements is relatively simple. At the same time, the mesh of the connection part between the pillar and the sphere is refined according to the requirements of stress analysis, while the mesh of other parts can be coarsened, which improves the calculation efficiency while ensuring the calculation accuracy. Load application Only one calculation case is listed in this example: Design pressure + weight of structural accessories and corrosion layer + operating medium liquid column static pressure + 25% wind load + seismic load + snow load, in which the weight of structural accessories and corrosion layer is used together with the weight of the sphere to adopt the density conversion method. The weight of the sphere and accessories is considered with the method of equivalent density and gravity velocity. The operating medium liquid column static pressure is applied with the liquid column static pressure function in WB, the wind load is applied in the form of concentrated force, the seismic load is applied in the form of horizontal acceleration, and the snow load is applied in the form of mass point. For more exciting content, you can search and follow the WeChat public account "ANSYS Analysis and Designer" - a gathering inn for pressure vessel analysis and designers. The calculation results show that: The stress value of the connection part between the lower pillar and the sphere is the largest on the windward side that bears the wind load and overlaps with the earthquake load, and the maximum stress is 396.82MPa.