Flange Joint Characteristics Of Consider Gasket Nonlinear Characteristics

Flanged joints are widely used in petrochemical equipments, power appliances and other industrial equipments. Gasket is one of the important seal components, and its performance directly affects the joints sealing performance. The Bolted flanged joint is considered as a system which consists of bolts, flanges and gaskets.Fitting methods for compression and spring curves of gaskets are discussed in this paper. According to non-linearity and non-conservative for gasket materials, two stages-loading and unloading for gaskets working process are respectively discussed. In the research of flanged joints, the flanged joint is taken as a system and mutual effects among every component are studied considering the non-linearity features of gaskets. A parametric 3-D finite element model of the 1/8 bolted flanged joints is established. It came true that gasket material non-linearity and stress-strain non-keeping are analyzed by using INTER194 and GASKET material in ANSYS software.As a result, distortion and stress distribution for joints and every component have been obtained. The influences of the important parameters-geometry dimension, such as the bolt pre-loading intensity, the internal pressure and the thickness of the gasket are analyzed. The main conclusions are as follows:(1) The regress coefficient of compression phase and spring phase were obtained through fitting compression and spring curves of gaskets. Forecasting can be obtained with the spring curves in different pre-loading condition according to the regress coefficient and stress-strain at uninstalling point, which will offer a reference for flange design with the criterion of leakage in some extent.(2) Whether pre-loading or loading conditions, stress distribution on gasket was asymmetric in circumference and radial and it is comparatively uniformity with the gasket thickness increasing.(3) The bend stress of bolt can't be neglected in pre-load condition. Stretch stress and bend stress of bolt increased with pre-load force. When pre-load force of bolt added to 7×10~4N,the bend stress are at 49.1% of average stretch stress. Therefore stretch stress and the bend stress must be considered when designing the flanged bolted joints. When the bend stress of bolt is big, it can result in invalid flanged bolted joints in normal design. In order to make sure the accuracy of design, the bend stress of bolt should be reduced, such as enhancing stiffness and diameter of the bolt.(4) Increasing gasket thickness can reduce the maximal stress intensity of flange loop where the stress level was higher in flanged jointed system.