Analysis Of The Stress Of The Connection Between Spherical Shell And Cylinder In Fully Welded Ball Valve

Along with the increasing progress of technology and manufacture, production of valves are developed to the direction of high parameter such as high temperature, high pressure, large caliber and high seal. The production of the valve industry are wanted to be more economic security.For fully welded ball valve with large diameter, it must be analyzed depend on the experimental research and be analysis contrasted the results because the aperture is gone beyond the scope of application of "Design by Rules". The cost will be increased and the design cycle will be extended. The safety will be guaranteed but the economy by what the products designed by analysis."Design by analysis" and "Finite Element Analysis" is the Important means of the Structure analysis nowadays. The different Failure criterion is put to use in the method of "Design by analysis" and "Finite Element Analysis". The influence of the overall stress by the local stress is considered. The stress is classified and limited by the different cause. The strength is ensured and the restrictive conditions of the stress is relaxed. The material and cost would be saved for the fully welded ball valve with large diameter.The fully welded ball valve with NPS56Class900will be taken as an example in this paper:First of all, the method "Design by analysis" will be used. The stress of the dangerous section will be analyzed and the relationship of the calculation between the stress and the wall thickness will be ensured by the basic formula of elastic mechanics and the theory of plate. Then results of the stress analysis will be divided into primary membrane stress Pm, primary bending stress Pb and the secondary stress Q. All types of stress strength well be limited according to the determine requirements which in JB4732-95<steel pressure vessels-design by analysis>. The wall thickness of the valve body will be determined when all types of stress strength satisfy the condition.Secondly, the method "Finite Element Analysis" will be used. The stress of body of the valve will be calculated by The finite element analysis software named ANSYS Workbench according to the wall thickness which was calculated before. The stress concentration position of the calculation results will be disposed with Stress linearization. All kinds of stress will be obtained and be judged for verifying if the wall thickness is meet the strength requirements which was gained by the method "Design by analysis"Finally, it will be compared the wall thickness gained by "Design by analysis" with the wall thickness gained by "Design by rules". The superiority of "Design by analysis" and "Finite Element Analysis" will be found in design of valve.