Sealing performance of gasketed bolted flanged joints: Effect of flange surface characteristics and application of fuzzy logic.

摘要

The objective of this thesis is to investigate the effect of surface characteristics on the leakage rate and on the leakage behavior of gasketed bolted flanged joints. This research considers the experimental study of the effect of surface characteristics on compressive stress, leakage rate and flow regimes. The sealing surfaces of the test platens of raised face types are produced with grinding, turning and milling procedures having different average arithmetic roughness values and are the subject of the experiments. Different types of gasket materials commonly used in industrial applications are considered, namely PTFE, flexible graphite G2 and spiral wound. The experiments are performed based on modified ROom Temperature Tightness Test (ROTT) procedure, as opposed to the conventional ROTT test procedure, in order to reduce the experimental test points. The experimental results showing the surface characteristics, gasket stress and deflection, leakage rates and flow regimes are presented in tables and graphical form.; The analysis of sealing surface characteristics is complex and is influenced by many parameters that cannot be measured in a precise manner. The assessment of contact properties, macro and microstructure of the surfaces, with the gasket material adds to the complexity of the joint sealing phenomena, leakage rate and flow regime. The leakage rate and the state of flow regime depend on the geometry of the interfacial leak paths and on the gasket porosity, which are influenced by flange surface characteristics, gasket properties, gasket compressive stress and gas pressure. The combined effect of such parameters adds to the complexity of the joint system and is assessed in this thesis based on the relative measurement analysis.; To facilitate the understanding and the analysis of the gasketed bolted flanged joints sealing phenomena and to provide a tool for better decision making on the required system's parameters, the fuzzy logic is applied. Fuzzy logic algorithms are developed for the selection of gaskets and sealing surfaces to obtain optimal tightness of the joints, based on the leakage rate. The fuzzy algorithms are a multivariate input and output system that considers parameters such as gas pressure, gasket deflection and leakage rate, gasket type, gasket stress and flange surface roughness. The system's fuzzy rules are developed based on the experimental results.; Other fuzzy logic algorithms are also developed based on limited test points from modified ROTT tests to predict the leakage rate, and to determine the new PVRC gasket constants, Gb, a, and Gs, which are then used to determine the gasket minimum seating stress. The results obtained from the fuzzy logic algorithms are very close to the results of the experiments.; Finally, the models developed with fuzzy logic adequately address the complex nature of gaskets and sealing surfaces, and predict the experimental results from real situations, since they are capable of dealing with complex, vague information and missing/incomplete data. Based on the evidence presented in this thesis, it is shown conclusively that leakage rate through gasketed joint is predictable. The fuzzy decision support system approach, if more developed and refined, could effect a radical change in the method of selecting gaskets and estimating leakage rate in the field of gasketed bolted flanged joints.