Original article Studies on joint strength and sealing behavior of single and twin-gasketed flange joints N Rino Nelson 1 , N Siva Prasad 2 and AS Sekhar 1 Abstract Leakage is the main mode of failure in gasketed flange joints used in nuclear and thermal power plants. The leakage occurs when the joint is not able to withstand the internal fluid pressure. To evaluate the leakage behavior of gasketed flange joint, it is important to incorporate gasket properties and interfacial contact behavior due to friction. However, for safe joint operation, the members also should be structurally sound without exceeding allowable limit of materials. In this study, the joint strength and sealing behavior of gasketed flange joint are investigated through experiments by carrying out leakage test. The joint strength is evaluated based on strains developed in flanges along longitudinal and tangential direction under both pretightening and pressurizing stages. Three-dimensional finite element simulation is also per- formed under both aforesaid stages, considering the nonlinear properties of gasket along with hysteresis during unload- ing. The finite element results of joint strength and leakage pressure are compared with experimental values and observed to be conservative. In addition, the performance of twin gaskets (two gaskets concentric to each other) through both experiment and simulation is also evaluated and compared with that of the single gasket. From the experiment and finite element analysis, it is found that the sealability of twin-gasketed joint is higher than that of single-gasketed joint. Keywords Twin gaskets, flange joint, leakage test, nonlinear, flange strains, leakage pressure Date received: 6 January 2017; accepted: 31 May 2017 Introduction Bolted flange joints with gaskets are widely used in pressure vessels in nuclear and thermal power plants and industrial pipelines. These joints are primarily subjected to bolt tightening torque and pressure load due to the internal fluid. The main concern in flange joint is its sealing performance and joint strength. Many research works have been carried out on flange joints to determine their behavior for deformation and leakage prediction with and without a gasket. Leakage problem in flange joint is mainly due to relaxation of bolt load, over compression of the gasket during assembly and difference in pressure between the inner and outer side of the gasket. The relaxation in bolt load is the primary reason for leak- age of internal fluid from bolted flange joint. Boqin et al. 1 developed a model to predict the gas leakage rate in connection with nonmetallic gasket sealant. The leakage rate obtained from a theoretical model based on laminar theory and molecular flow is vali- dated using leakage experiments. An analytical model was proposed based on deformation and flexibility of joint members to evaluate the relaxation in bolted flange joint by Bouzid and Nechache. 2 The optimum design of flange joint with tube spacers and disc springs is arrived to minimize the bolt relaxation in joint. In some applications, flanges are provided with conical faces having tapered sealing surface from flange inner diameter to outer diameter, in order to reduce the excessive gasket deformation along outer circumference. The strains in conical-faced flanges were measured to determine the joint behavior using strain gauges by Fessler et al. 3 In conical flange, the bolt preload required during assembly is more Proc IMechE Part E: J Process Mechanical Engineering 0(0) 1–13 ! IMechE 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954408917718598 journals.sagepub.com/home/pie 1 Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, India 2 GITAM University, Hyderabad, India Corresponding author: AS Sekhar, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India. Email: as_sekhar@iitm.ac.in