Stress Classification And Strength Estimate Of Valve Body

The valve is special pressure equipment with irregular shape. The valve design of domestic and international level is followed by pressure vessel design technology. As the valve shell and major component, the valve body occupies three-fifths of the total valve weight. The design level of the valve body has a decisive influence on the valve manufacturing cost, performance and service life. Many valves that conventional design can not meet the requirements, such as high parameters valves, special structure valves, nuclear valves, use stress analysis method to design the body.Stress classification is a major feature of the stress analysis design. The principles of classification and the classification results of some typical problems are given in ASME. But for practical engineering problems, the corresponding results are not necessarily can be found in the specification, and the definite classification ways are not provided. On the basis of the pressure vessels stress classification idea, how to make stress classification and assessment on the valve body use some techniques, is the core and difficult problems to achieve the valve analysis design.The paper first start with the conventional valve design, analyze the wall thickness formulas, the theoretical bases and stress simplified calculation formulas of valve body. Secondly, in accordance with conventional design methods, calculate the stress of examples of gate valve use simplified ways. Then create the finite element models of examples of gate valve body, set the boundary conditions, apply loads in design and hydrostatic test conditions to make statics analysis and calculation of the valve body with finite element software. The main research is the stress distribution, maximum stress value and the location of maximum stress. The results of simplified stress calculation and finite element stress calculation are compared.Then, start with the research of pressure vessel stress classification, the difference between stress classification and decomposition and various classification techniques and methods are discussed. Combined with the analysis of characteristics of the valve body stress distribution, the body stress is classified as primary stress, secondary stress and peak stress in accordance with stress classification guidelines. A typical body's stress classification table is provided.Finally, the body stress of the examples of gate valve is classified. Various types of stress and equivalent stress of the combination are given to different restrictions bases on the principle of equal safety margin, and the stress intensity evaluation is made according to the analysis design method.In the paper, the valve body stress is classified by the guidelines of pressure vessel stress classification based on the detailed valve body stress analysis, and for the first time, the valve body's stress classification table is provided, and the body strength estimate is made with different limits instead of the same allowable stress in traditional design. From the perspective of stress classification, with the purpose of "the material used in key positions", the research basis of theory and practice is made for the problem of "where should be thick, where to thinning" in the valve body. From a comprehensive point of view of security and economy, the gist for the optimization of valve body structure and wall thickness is provided.