| Double cone seal is a structure with some self-tightening,using widely on the petrochemistry industry due to the advantage of simple structure,easy manufacturing,flexible assembly or disassembly.But in the practical application for high pressure vessel,there are always leakage problem especially under pressure fluctuations or starting after repairing.If the sealing performance of chemical engineering device couldn’t be ensured,it would occur serious accidents.The important factors for ensuring the sealing performance are suitable bolt pre-tightening force and gasket contact pressure.Only the bolt pre-tightening force is applied appropriately,the gasket operating contact pressure could reach a certain amount and the double-cone sealing would be ensured.The design of double-cone ring is currently according to the Chinese criteria “pressure vessel”,following the gasket contact pressure “y”and the gasket coefficient “m” for traditional flange design,these gasket characteristic parameters was put forward for flat gasket seal structure in 1943.By the way,the relationships between Internal pressure acting on the inner cylinder and force acting on the cone under operating conditions were thought to be equal in the Chinese criteria,which is incorrect.Internal pressure may influent the force on the sealing surface,but there is no equilibrium relationship between them.Those questions are critical for the analysis of double-cone seal structure,it is necessary to set up more researches.The double-cone seal structure was studied with design pressure of 6.4MPa and internal diameter of 1000 mm in the thesis,and its structure characteristics,sealing mechanism,force under preloading and operating conditions were analyzed,which was compared with the flat gasket seal structure in the same conditions to discusses the difference and advantages between them.The concept of equivalent axial displacement was put forward by using the force-deformation relationships between the connector and the connected parts at elastic deformation allowance of materials.The double-cone ring structure under pre-tightening and operating conditions was analyzed by finite element method,and the curves of equivalent axial displacement varying with the axial force of sealing surface under different working conditions were obtained.The equivalent axial stiffness curves under pre-tightening and operating conditions for double-cone seal structure with the bolt stiffness curve were combined to obtain the pre-tightening bolt load and sealing contact pressure at the time when the gasket contact pressure reached the operating seal contact pressure.The applicability of the gasket contact pressure “y”proposed by the criteria was examined.By using the diagrams of equivalent axial force deformation and bolt force deformation under different working conditions obtained in this thesis,the axial component of force at sealing surface and the gasket contact pressure under operating conditions could be calculated by the bolt elongation measured,comparing with the minimum operating seal contact pressure to determine the sealing performance of double-cone seal and apply the suitable pre-tightening bolt load in the practical application.Gasket contact pressure is an important parameter.Axial component of force at sealing surface of surface is closely related to bolt stiffness,dimension parameters of double-cone ring,pre-tightening bolt load and internal pressure and so on.Through the analysis of various factors,the influence of those factors for the performance of double cone seal at elastic deformation allowance of materials have been got.The stress and finite element analysis in this thesis provide a reliable theoretical basis for the design of the double-cone sealing.It has practical significance for the proper application of bolt load.And it is a major component of the research on ensuring the sealing reliability of the double-cone system and the long-term safety operation of petrochemistry device. |
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