| In order to ensure the safety and reliability of sealing structures in pressure vessels, enough preload must be kept for gaskets, however, if this value is too big or too small, there would be bad influences for sealing. Especially, with the development of manufacture and equipments, more and more sealing structures are getting to be used, such as heat exchangers used at petroleum refining process. They mostly adopt the complex sealing structure with screw rings as fasteners, which causes the difficulties of manufacture and assembly and leakage of materials.By using the finite element method and taking bolt material elastic-plasticity into consideration, the distribution laws of inner force, stresses and deformation of a standard coarse screwed bolt M12 under the action of axial force were numerically calculated and analyzed. Based on the mathematical models for elastic and plastic deformation of screw, equations for thread friction torque were gotten.An experiment was made on the relation between the load and the deformation of flexible graphite corrugate gaskets with metal frame. The load-deformation curves were used in later finite element calculation as material data. Based on the finite element calculation and analysis, the flexibility of each part and load-deformation curves of the sealing structure were gotten. Finally an improved method on determining proper value of fasteners preload was proposed.The steady temperature fields for a 2D axisymmetric model of a sealing structure were calculated. Moreover, thermoelastic deformations calculation under some kinds of combinations of preload, medium pressure, various temperature difference and different temperatures were carried out. The focus was paid on the influences of temperature difference stress on the tightness of the whole structure. No more than the difference of 5℃must be kept after the equipment was shut down under the design temperature of 450℃. |
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