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1 Copyright 2011 by ASME Proceedings of the ASME 2011 Pressure Vessels & Piping Division Conference PVP2011 July 17-21, 2011, Baltimore, Maryland, USA PVP2011-57813 STRESS AND DEFORMATION ANALYSES OF LARGE DIAMETER BLIND FLANGE CONNECTIONS SUBJECTED TO BOLT LOADS AND INTERNAL PRESSURE Takashi KOBAYASHI Numazu National College of Technology , Numazu , Shizuoka ,Japan kobayashnumazu-ct.ac.jp Masahiro KOGASAKA Numazu National College of Technology , Numazu , Shizuoka Japan Kengou NISHIURA Mitsubishi Chemical Corporation , Kurashiki , Okayama Japan Uchiyama KAZUAKI Nichias Corporation , Minato-ku , Tokyo Japan ABSTRACT Leakage problems caused in large diameter gasketed flanged connections in piping systems are closely related to deformation of flanges caused by the high thrust force and rather low rigidity of the flanges. Therefore, it is necessary to understand the deformation characteristics of flanged connections when they are tightened and pressurized. In this study, experiments were carried out using a 16-inch gasketed flanged connection to examine the stress and strain in the flanges. In order to clarify the deformation characteristics of the gasketed flanged connection, a method to analyze stresses and deformations of a gasketed flanged connection was demonstrated using the classical theory by Timoshenko. Recently, finite element analysis (FEA) has widely been used in the analysis of gasketed flanged connections. However, analyses of flanged connection based on the analytical method using strength of materials are still important when parametric calculations of flanged connection are necessary. The experimental results and the analytical ones were compared and discussed to clarify the sealing behaviors of large diameter gasketed flanged connection. INTRODUCTION Gasketed flanged connections have widely been used in refinery plants, power plants, chemical plants and other industrial plants. The sealing behaviors of gasketed flanged connections should be considered in design, assembly, use and maintenance of gasketed flanged connections. Furthermore, due to recent increase of environmental concern, the fugitive emission from the gasketed flanged connection becomes important issue. Large diameter gasketed flanged connections are widely used, as well as small diameter gasketed flanged connections. However, the sealing behaviors of the large diameter gasketed flanged connections have not been fully understood. Therefore, the effects of deformation characteristic of the gasketed flanged connection on the sealing behaviors must be clarified. A test method for the sealing behaviors of gaskets, JIS B 2490, was established in Japan 1. This method focuses on the sealing behaviors of small diameter gaskets. The sealing behaviors of the small diameter gasketed flanged connection have been tested using the results obtained by JIS B 2490 2. In the cases of large diameter gasketed flanged connection, the deformation characteristics such as flange rotation make this problem more complex. In this paper, the strain distributions in large diameter gasketed flanged connection were measured using strain gauges. Two kinds of PTFE gaskets were used for the tests. It is found that the strain in large diameter gakseted flanged connection is low when a stiff gasket is used. Stresses and deformations of a large diameter gasketed flanged connection were calculated using the classical theory by Timoshenko. The experimental results were verified by the analysis. EXPERIMENT Gasket test using platens (JIS B 2490) Firstly, the characteristics of gasket were tested in accordance with the gasket test method JIS B 2490. In this test, a gasket is compressed between the upper and lower platens. The size of the test gaskets is 10K 50A (JIS B 2404). The pressure-temperature rating and nominal diameter approximately correspond to ASME B16.5 Class150 NPS2. The platens have raised faces of 96 mm OD and the surface Proceedings of the ASME 2011 Pressure Vessels & Piping Division Conference PVP2011 July 17-21, 2011, Baltimore, Maryland, USA PVP2011-57813 Downloaded From: / on 01/20/2016 Terms of Use: /about-asme/terms-of-use 2 Copyright 2011 by ASME roughness of the platens is 1.63.2 mRa. Two kinds of gaskets, PTFE with filler (Gasket A) and expanded PTFE (Gasket B), were used in the experiment. The thickness of the gaskets were 3.0 mm. Measurement of strain distributions of blind flange connections In order to measure the strain distributions of the gasketed flanged connection, a large diameter gasketed flanged connection (material: SS400), with pressure-temperature rating and the nominal diameter 10K 400A (JIS B 2404), were chosen for this experiment. The pressure-temperature rating and nominal diameter approximately correspond to ASME B16.5 Class150 NPS16. Figure 1 shows the experimental setup for the large diameter gasketed flanged connection (JIS 10K 400A). Sixteen bolts (material: SS400, size: M24) were used to tighten the flanged connection. For eight bolts out of the sixteen bolts, strain gages were installed at the center of the bolts to measure the bolt load. The bolt load was controlled using a torque wrench. Molybdenum lubricant was applied to the bolts, nut and contact surface of the flanged connection. The nut factor was determined by experiment to be 0.091. EXPERIMENTAL RESULTS AND CONSIDERATIONS Characteristics of gaskets (JIS B 2490) Figure 2 shows the stress-deflection curve for Gasket A and B obtained by gasket test method JIS B 2490. In the case of Gasket A, the deflection at step S8 is small compared with that of Gasket B. When the gaskets are unloaded from Step S8 to S9, the elastic recovery of gasket is small in the case of Gasket A. It can be said that Gasket A is stiff compared with Gasket B. Figure 3 shows the sealing behaviors for Gasket A and B. From the view point of sealing performance, Gasket A is approximately ten times tighter than Gasket B, namely the leak rate of Gasket A is small compared with Gasket B. The differences of gasket behaviors stems from the material properties. The material of the Gasket B is expanded PTFE and it has porous structure. Due to the porous structure of the gasket, the deformation of gasket is large and the leak rate becomes high. Figure 1 Experimental setup (a) Gasket A (b) Gasket B Figure 2 Stress-deflection curve of gasket (a) Gasket A (b) Gasket B Figure 3 Sealing behavior as a function of gasket stress S2S3S4S6S71.00E-061.00E-051.00E-041.00E-031.00E-021.00E-011.00E+0001020304050Gasket stress e N/mm2Leak rate L0 Pa m3/sS10S1S2S3 S4S5S6 S7 S8S11051015202530354045500.0000.400.500.60Thickness changes of gasket mmGasket stress e N/mm2S9S10S11 S8S7 S6 S4 S5 S3 S2S11.00E-061.00E-051.00E-041.00E-031.00E-021.00E-011.00E+0001020304050Gasket stress e N/mm2Leak rate L0 Pa m3/sS9 S10S11S8S7 S6 S4S5S3 S2S1051015202530354045500.0000.400.500.60Thickness changes of gasket mmGasket stress e N/mm2S8S9S10S1 S5 S11S2S3S4S6S7Downloaded From: / on 01/20/2016 Terms of Use: /about-asme/terms-of-use 3 Copyright 2011 by ASME Strain of flange Figure 4 shows the strain distributions in the flanged connection at initial tightening in the case of Gasket A, as an example. Figures 4 (a) and (b) are the radial strain r and the circumferential strain, respectively. With increasing the tightening torque, the strains increased. However, it is noted that the strain distributions are almost uniform. Figure 5 shows the strain distributions when pressurized in the case of Gasket A, as an example. The initial tightening torque was 100 Nm and the internal pressure was increased to 1.5 MPa. Figures 5(a) and (b) are the radial strain r and the circumferential strain, respectively. With increasing the internal pressure, the strains near the center of the gasketed flanged connection increased. This is because the flange was bent by the thrust force due to the internal pressure. In the case of Gasket B, as the tendencies were almost the same as those of Gasket A, the results are not shown. Stress of flange Based on the measured strains shown in Fig4 and 5, stresses r and were calculated using the following equation: rrrEE2211 (1) Furthermore, the von Mises stress can be calculated using the following equation: (2) Figure 6 demonstrates the von Mises stress near the center of gasketed flanged connection(r=25mm). The changes of stresses in the initial tightening state and the pressurized state(internal pressure 1.0MPa) in the cases of Gasket A and B are shown. It is noted that the von Mises stresses of Gasket B are high compared with those of Gasket A. This is related to the deformation characteristics of gaskets shown in Fig.2 and those of flanges. The gasketed flanged connection is deformed by the bolt load and the thrust force due to the internal pressure. As Gasket A is stiff compared with Gasket B, the gasket stress becomes high at the outer circumference of the gasket when the flanged connection is deformed. Because of this, the length of the lever arm becomes short and the stress in the case of Gasket B becomes less. (a) radial strain r (b) circumferential strain Figure 4 Strain distribution at initial tightening (the case of Gasket A) (a) radial strain r (b) circumferential strain Figure 5 Strain distribution when pressurized (the case of Gasket A, tightening torque 100Nm)-2000200400600800050100150200250300Distance from center r mmStrain r strain50N100Nm150NmTightening torque -2000200400600800050100150200250300Distance from center r mmStrain strain50N100Nm150NmTightening torque-2000200400600800050100150200250300Distance from center r mmStrain strain0MPa0.5MPa1.0MPa1.5MPaInternal pressure -2000200400600800050100150200250300Distance from center r mmStrain strain0MPa0.5MPa1.0MPa1.5MPaInternal pressurerreq22Downloaded From: / on 01/20/2016 Terms of Use: /about-asme/terms-of-use 4 Copyright 2011 by ASME Figure 6 Comparisons of von Mises stress near the center of the gasketed flanged connection Analysis of flange deformation In order to clarify the deformation characteristics of the gasketed flanged connection, an analysis using the classical theory by Timoshenko was carried out. Figure 7 shows the model for analysis of the gasketed flanged connection. Nomenclature is as follows: a : Inner radius of gasket b : Radius of center of width of gasket c : Radius of bolt pitch circle d : Radius of blind flange t : Flange thickness The flange is divided into four parts: Part I, II, III and IV. Each part can be analyzed by the theory of bending of plates3. Part I, II, III and IV are connected each other at points A, B and C. For simplicity, only the flange was modeled in this study. It is assumed that the flange is fixed at the center of the width of gasket (r=b) and that the bolt load is applied continuously on the bolt pitch circle. The boundary conditions are summarized in Table 1. The analytical method is based on the method by the authors 4. Figure 8 demonstrates the analytical result of deflection curve of the gasketed flanged connection. The tightening torque is 100 Nm. Then, the internal pressure 1 MPa is applied. The gasketed flanged connection is bent by the bolt load and the thrust force increases the deflection in the gasketed flanged connection. Due to this deformation, the gasket compression in the radial direction cannot be uniform. Thus, the deformation characteristics of gasketed flanged connection affect the sealing behaviors of gasketed flanged connections. Although the deformation characteristics of the gasket are not considered in this study, we need to consider those in our future studies. In Fig. 9, analytical results concerning strains of the gasketed flanged connection are compared with experimental ones in the case of Gasket B. The analytical results agree well with the experimental ones. In the future studies, we will examine the effects of the deformation characteristics of gasketed flanged connection on the sealing performance using the analytical method shown in this paper. Table 1 Matrix of boundary conditions considered w:deflection, M:moment Figure 7 Model for analysis of blind flange Connecting point Distance from center Boundary condition Deflection Slope Moment (radial) A r = a IIIww drdwdrdwIII IIIMM B r = b 0IIIIIww drdwdrdwIIIIIIIIIIMMC r = c IVIIIww drdwdrdwIVIIIIVIIIMMD r = d - - 0IVM 050100150200250050100150200Mises stress eq N/mm2Tightening torque T NmGasket AGasket BGasket AGasket BDownloaded From: / on 01/20/2016 Terms of Use: /about-asme/terms-of-use 5 Copyright 2011 by ASME Figure 8 Analytical result of deflection curve (Tightening torque 100Nm, Internal pressure 1MPa) (a) radial strain r (b) circumferential strain Figure 9 Strain distribution when pressurized (The case of Gasket B) CONCLUSION The deformation characteristic of gasketed flanged connection was discussed in this s