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Journal of Solid Mechanics and Materials Engineering

Vol. 6, No. 4, 2012

288

Elasto-Plastic FEM Stress Analysis and Mechanical Characteristics of Pipe Flange Connections with Non-Asbestos Gaskets

under Internal Pressure* (Effects of Flange Nominal Diameter)

Yoshio TAKAGI**, Yuya OMIYA***, Takashi KOBAYASHI**** and Toshiyuki SAWA***

**Material Engineering Group, R&D Center, Tokyo Electric Power Company 4-1 Egasaki-cho, Tsurumi-ku, Yokohama, Kanagawa, Japan

E-mail: [email protected] ***Graduate school of Engineering, University of Hiroshima

1-4-1 Kagamiyama, Higashihiroshima, Hiroshima, Japan

****Numazu College of Technology 3600 Ooka, Numazu, Shizuoka, Japan

Abstract The effects of the nominal diameter of pipe flange connections with non-asbestos spiral wound gaskets(SWG) under internal pressure on the mechanical characteristics such as the contact gasket stress distribution which governs the sealing performance, the load factor and the hub stress of the connections were evaluated. The stresses in the connections with the nominal diameters from 3 to 24 under internal pressure are analyzed using the elasto-plastic(EP) FEM analysis taking account the hysteresis and non-linearity of deformation behavior of the non-asbestos SWG. As a result, it is found that the variations in the contact gasket stress distributions are substantial due to the flange rotation in the connections with the larger nominal diameter. Leakage tests were conducted to measure the axial bolt forces (the load factor) and the hub stress. The results obtained from the EP-FEM analyses are fairly consistent with the experimental results concerning the variation in the axial bolt forces (the load factor) and the hub stress. Using the obtained contact gasket stress distributions and the fundamental relationship between the amount of leakage and the contact gasket stress, the amount of the leakage of the connections is estimated. It is observed that the sealing performance of the connections with larger nominal diameter is worse than that of the connection with smaller nominal diameter because of the flange rotation. The estimated results are in a fairly good agreement with the measured results. The difference in the hub stress between the EP-FEM and ASME code is demonstrated and the differences in the load factor and the sealing performance of the connections are shown between the asbestos and non-asbestos gaskets.

Key words: Bolted Joints, Stress Analysis, Load Factor, Non-Asbestos Gasket, Flange Nominal Diameter, Contact Problem

*Received 19 Oct., 2011 (No. 11-0630) [DOI: 10.1299/jmmp.6.288]

Copyright 2012 by JSME


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1. Introduction

Pipe flange connections with gaskets have been widely used in chemical plants, nuclear power plants and so on. Those connections are usually used under internal pressure as well as other loadings. In order to optimize the design of pipe flange connections with gaskets, it is necessary to understand the mechanical characteristics of the connections under internal pressure. The important issues in designing the pipe flange connections under internal pressure are the precise estimations about the actual reduced contact gasket stress distributions at the interfaces, the hub stress and a variation in the axial bolt force (the load factor) from the view point of sealing performance and structural flange design. Some studies(1)-(8) on pipe flange connections with asbestos gaskets have been carried out for the connections with the smaller nominal diameter such as the sealing performance, the contact gasket stress distribution, the hub stress and the load factor. In practice, a lot of pipe flange connections with larger nominal diameter have been used, too. However, some questions remain whether it is possible to apply the researched results to the connection with the smaller nominal diameter for estimating the behavior of the connections with the larger nominal diameter, such as leakage prediction and a method to determine the bolt preload.

In Japan, the usage of asbestos material such as gaskets has been prohibited since 2008(9). Thus the non-asbestos gaskets must be used in pipe flange connections. However, only a few research(10)(11) has been carried out on the characteristics of the connections with non-asbestos gaskets. Therefore, it is necessary to examine the characteristics of the connections with non-asbestos gaskets. Furthermore, it is desirable to know the difference in the characteristics, in particular, the sealing performance of the connections with between asbestos and non-asbestos gaskets to replace asbestos gasket to non-asbestos one.

PVRC(11)(12) (Pressure Vessel Research Council) proposed the new gasket constants (Gb, a, Gs) and the tightness parameter Tp and it also proposed a method for evaluating the sealing performance and for determining the bolt preload using the new gasket constants and the tightness parameter Tp. However, the PVRC test method is based on the hypotheses, in which the gasket stress SG the tightness parameter TP relationship is the linear and the values converge to the new gasket constant Gb in Part B. The hypothesis is sometime incorrect. Therefore, a rational pipe flange design method based on a test method by which the gasket sealing performance can be evaluated such as JIS B 2490(13) is needed.

Thus, in this paper, the contact gasket stress distributions in the pipe flange connections with the different nominal diameters from 3 to 24 under internal pressure are analyzed using elasto-plastic finite element method (EP-FEM) by taking account a non-linearity and a hysteresis in the stress-strain curves of a non-asbestos spiral wound gasket (SWG) obtained from JIS B 2490(13) which is the test method for characterizing the mechanical properties of gaskets. In addition, the differences in the characteristics mentioned above of the connections with between asbestos and non-asbestos gasket are examined. The effects of the nominal diameters of the connections on the contact gasket stress distributions, the variations in the axial bolt force (the load factor) and the hub stress are analyzed using the EP-FEM (7)(8). The obtained hub stresses are compared with the values obtained from ASME code(14). An amount of gas leakage using the obtained contact gasket stress distributions and gasket property according to JIS B 2490(13) are estimated. Furthermore, the leakage tests and the measurements concerning a variation in an axial bolt force are performed for the connections with 3 and 20 nominal diameters (ANSI/ASME)(15) using helium gas to confirm the EP-FEM results and the estimated amount of gas leakage (leak rate). Discussion is made on the differences in the contact gasket stress, the load factor and the hub stress between asbestos and non-asbestos gasket.


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2. Nomenclature

2a1: inner diameter of pipe 2a3: inner diameter of gasket 2b1: outer diameter of pipe 2b3: outer diameter of gasket 2h1: pipe flange thickness 2h3: gasket thickness A: gasket contact area in the analysis C: bolt pitch circle diameter D: outer diameter of pipe flange Fc: force eliminated from the contact surfaces (=(1-g)W/N) Ff: bolt preload Ft: increment in axial bolt force P: internal pressure L: amount of gas leakage LS: fundamental leak rate N: numbers of bolt W: axial force due to internal pressure (=a12P) W: total axial force due to internal pressure (=a32P) X: outer diameter of hub Y: hub thickness : gasket displacement : the circumferential angle of gasket g: load factor (=Ft/W) zm: initial average contact gasket stress z: contact gasket stress

3. Elasto-plastic Finite Element Analysis (EP-FEM)

Figure 1 shows a pipe flange connection with a gasket, in which two pipe flanges including the gasket are fastened with N bolts and nuts with a bolt preload Ff, subjected to internal pressure P. When the internal pressure P is applied to the connection, a tensile load W (=a12P) acts on the end part of the connection in the axial direction, and an increment in axial bolt force Ft occurs in the bolts and the contact force Fc (per bolt) is eliminated from the gasket contact surfaces, that is, the total axial force W/N (=a32P/N) (per bolt) due to the internal pressure P equals to the sum of Ft and Fc (W/N=Ft+Fc), where the inside diameter of the gasket is designated as 2a3 and that of the pipe as 2a1. In predicting the sealing performance of the connection, the actual reduced contact gasket stress of the connection under internal pressure P must be estimated exactly. The ratio Ft to W/N is called as the load factor(4) g (=Ft /(W/N). When the value of the load factor g is obtained, the force Fc is obtained by the equation Fc=(1-g)W/N and the actual reduced average contact gasket stress is obtained from the equation (Ff -Fc)/A, where A is the contact gasket area per bolt. The cylindrical coordinate (r, , z) is used in the EP-FEM analysis. The contact gasket stress distributions, the hub stresses and the load factor g of the pipe flange connections with the different nominal diameters from 3 to 24 (3, 8, 16, 20 and 24) are analyzed using the EP-FEM. The flanges used are the class 300 while 3 pipe flanges are the class 600 in the ANSI/ASME B16.5 (15) (in the experiments, the connections with 3 of the class 600, and the connections with the 20 of the class 300 were used).

Figure 2 shows an example of mesh divisions of the connection with 3 nominal diameter in the EP-FEM analyses. Taking account the symmetry of the connection, one-eight part of the connection is analyzed. The code of the EP- FEM employed is ANSYS. In this study, a


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non-linearity and a hysteresis of gasket are taken into consideration in the EP-FEM. Table 1 shows the dimensions of the pipe flange connection with the SWG. Figure 3 shows the designations of pipe flange connections shown in Table 1. Figure 4 shows a stress-strain curve of non-asbestos SWG (expanded graphite) which is market sold. The ordinate is the contact gasket stress z, and the abscissa is displacement of the gasket. This relationship was obtained according to JIS B 2490(13).

3inch 8inch 16inch 20inch 24inch2a1 74 196 378 476 574.92b1 89.1 216.3 406.4 508 609.6D 210 381 648 775 915 C 168 330 571.5 686 812.8R 127 270 470 584 692.2X 117 260 483 587 702 h1 32 41.5 57.2 63.5 71.6 Y 82.6 111.1 146 161.9 168.1

2a3 101.6 233.4 422.4 525.5 314.32b3 120.6 263.6 463.6 577.8 342.92h3 4.5 4.5 4.5 4.5 4.5 N 8 12 20 24 24

Bolt M20 M24 M33 M33 M39

Fig.1 A pipe flange connection with a gasket subjected to internal pressure

(Bolt number, N=8 for 3 pipe flange)

Z

r

o

Hub

Gasket

Bolt

Fig.2 A model for the elasto-plastic finite element analysis of a pipe flange connection

and mesh divisions

Table.1 Dimensions of the pipe flange connections (15) with the spiral wound gasket

used in the present EP-FEM (unit: mm)

Fig.3 Designations of the connection

Fig.4 Stress-displacement curve of non-asbestos SWG used in this study


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4. Experimental Method

An amount of gas leakage (leak rate LS: Pam3/s/m) in the connections with the 3 and the 20 nominal diameter under internal pressure P are measured at room temperature for verifications of the estimated amount of the leakage which is obtained from the contact gasket stress distribution and the fundamental data of the SWG according to JIS B 2490(13).

Figure 5 shows a schematic of the experimental setup of the pipe flange connection with the 20 nominal diameter to measure the amount of gas leakage, an increment of axial bolt force (the load factor g) and the hub stresses. The material of pipe flanges, the bolts and the nuts are all mild steel. The outer ring of the SWG is the stainless steel SUS304 (Japanese Industrial Standard: JIS). The nominal diameter of bolts used is M33 and the size of the gasket is 20 in ANSI/ASME Class 300(15). After fastening two pipe flanges including the SWG by 24 (=N) bolts and nuts with a bolt preload Ff, an internal pressure P was applied to the connections using helium gas shown as in Fig.5. Then, the magnitude of the internal pressure was measured with a pressure transducer and a variation in the axial bolt force was measured by the strain gauges attached to the bolt shank. The bolt preload was controlled monitoring the attached strain gauge outputs. The strain gauges were calibrated prior to the experiment. The outputs were recorded by an analyzing recorder through dynamic amplifiers. The mass leakage was measured from a variation in the pressure during certain time interval. In order to reduce the inner volume of the pipe flange connection a hollow cylinder was inserted in the pipe flange connection (20) as shown in Fig.5. The leakage tests were also carried out for the connection with the 3 nominal diameter as well as the connection with 20 nominal diameter.

5. Results of Elasto-Plastic Finite Element Method

5.1 Contact Gasket Stress Distribution EP-FEM analyses were carried out for the pipe flange connections with the different

nominal diameters from 3 to 24. Youngs modulus and Poissons ratio of mild steel pipe flange were 205GPa and 0.30, respectively. Youngs modulus and Poissons ratio of stainless steel of 3 pipe flange were 193GPa and 0.30, respectively.

Figure 6 shows the contact gasket stress distributions in the pipe flange connection with 8 nominal diameter in the circumferential-direction (-direction) at the distance r=116.7mm (the inner radius of the gasket), and 131.85mm (the outer radius of the gasket). The ordinate is the contact gasket stress z, and the abscissa is the circumferential angle (=0~90). The initial average contact gasket stress zm is 100MPa. Internal pressure P applied is 5MPa. Black solid line and dotted line show the initial clomping state. Purple solid line and dotted line show the pressurized state. Since the uniform axial bolt force is applied, the variations of the contact gasket stress distributions in the -direction are small. In the connections with another different nominal diameter (from the 3 to the 24), the variations of the contact gasket stress distributions in the -direction are also observed to be small. Thus, hereinafter, the contact gasket stress distributions in the radial direction are shown at = 0 (at the middle of bolt pitch). In Fig.6, the contact gasket stress distributions of the connections with asbestos gasket are described(8) as the red sold lime and dotted line. It is seen that the reduction in the contact gasket stress is larger for the connection with the


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asbestos gasket than that with non-asbestos gasket. According to Fig.6, the sealing performance is better for the connection with non-asbestos gasket than that with asbestos gasket.

Figure 7 shows the effects of the flange nominal diameter on the contact gasket stress distributions in the r-direction in case of initial clamping state. The ordinate is the normalized contact gasket stress z/zm, and the abscissa is the ratio of the distance r to the inner radius of the gasket a3, where zm is the initial average contact gasket stress. The nominal diameters of the connections calculated are 3, 8, 16, 20 and 24, where the initial average contact gasket stress zm is 100MPa for all nominal diameter connections. It is shown that the variations in the contact gasket stress distributions of the connections with the larger nominal diameter are larger than those with the smaller nominal diameter. Since the flange rotation in the connections with the larger nominal diameter tends to be larger than that with the smaller nominal diameter, the main reason of this fact is due to the flange rotation.

Figure 8 shows the effects of the flange nominal diameter on the contact gasket stress distributions in the r-direction in case of internal pressurized state at 5MPa. From the EP-FEM results, it is observed that the reduction in the contact gasket stress of the connections with the larger nominal diameter is larger than that with the smaller nominal diameter when the internal pressure is applied to the connections. It is because that the flange rotation of the connection occurs easily for the connections with larger nominal diameter. Another reason is that the value of the load factor of the connections decreases as the flange nominal diameter increases.

5.2 The load factor Figure 9 shows the comparisons of an increment in axial bolt force (load factor g). The

ordinate is the axial bolt force Ff +Ft and the abscissa is the total axial force W/N (=a32P/N). The solid line shows the results obtained from the EP-FEM. The dotted line shows the experimental results. The bolt preload Ff is 41.4kN for 3 and 189kN for 20. Red lines show the results for the connection with the smaller nominal diameter (3). Black line shows the case of the larger nominal diameter (20). The axial bolt force in the connection with the larger nominal diameter decreases linearly as the total axial force W/N increases while that in the connection with the smaller nominal diameter it increases linearly as the total axial force W/N increases. A fairly good agreement is observed between the results obtained from the EP-FEM and the experimental results. From the present

Fig.5 Schematic of experimental setup for 20 pipe flange connection

Fig.6 The contact stress distributions in the -direction for 8 pipe flange

connection


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analysis, the value of the load factor g in the connections with 3 nominal diameter was obtained as g=0.162 and, for the connections with 20 nominal diameter, it was as g= -0.148.

Table 2 shows the values of the load factor g of the connections with the different nominal diameters from 3 to 24 obtained from the EP-FEM. The load factor g of the connections with 3 nominal diameter is the biggest. As the nominal diameter of the connections increases, the value of the load factor g decreases. The force Fc, which eliminates the contact gasket stress due to the internal pressure, is obtained as Fc =(1-g) W/N. Thus, the force Fc increases as the value of the load factor g of the connections decreases. In particular, when the value of the load factor is negative, the value of Fc increases. Thus, it can be concluded that the sealing performance of the connections with the larger nominal diameter is to be worse. In determining the bolt preload Ff of the pipe flange connections with the larger nominal diameter (more than 8 flange), it is necessary to take into account that the value of the load factor g which becomes negative. In Table 2, the values of the load factor for the connections with conventional asbestos gasket (SWG) are

Nominal diameter

Load Factor (Calculation)

3inch 0.162(0.161(8))

8inch -0.003(-0.06(8))

16inch -0.134(-0.197(8))

20inch -0.148(-0.226(8))

24inch -0.161

Fig.7 The contact stress distribution in the r-direction (in initial clamping state)

Fig.8 The contact stress distribution in the r-direction (in pressurized state)

Table.2 The values of the load factor obtained from FE-FEM (the values in the

brackets are the load factor o the connections with asbestos SWG(8))

Fig.9 The variation in axial bolt force of connections (3 and 20)


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described by the brackets(8). It is found that the values of the load factor for the connections with non-asbestos gasket are larger than those with asbestos gaskets. The result reveals that the average reduced gasket stress in the connection with non-asbestos gasket is smaller than that with asbestos gasket. Therefore, the sealing performance of the connections with non-asbestos gasket would be expected to be better than that with asbestos gasket.

5.3 The hub stress Figure 10 shows the effects of the nominal diameter in the pipe flange connections on the

hub stress (stress component in z-direction z(hub)) at the circumferential angle =0, where the initial average contact gasket stress is zm =100MPa and the internal pressure is P=5MPa. The ordinate is the stress component in the z-direction z(hub), and the abscissa is the nominal diameter (inch) of the pipe flange. Purple lines show the EP-FEM results, and the red lines show the results obtained from ASME code(14). Solid lines show the case of initial clamping state, and the dotted lines show the case of pressurized state. In the EP-FEM results, it is shown that the values of the hub stress of the connections with the smaller nominal diameter under internal pressure are larger than that in the initial clamping state. However, as the nominal diameter of the connections increases, the values of the hub stress of the connections in the case where the internal pressure is applied decreases more than that in the initial clamping state. The effect of the nominal diameter of the connection on the hub stress is seen to be small from the obtained results. The difference is found to be substantial between the results obtained from ASME code and the EP-FEM results. The hub stress obtained from ASME code is about 5.6 times larger than the hub stress obtained from the EP-FEM in the case where the nominal diameter is 24. The bolt preload Ff must be determined smaller due to the hub stress based on ASME code(14). This leads leakage accident to occur easily. From the EP-FEM result, the bolts should be tightened with the larger bolt preload. The hub stress in the z-direction was measured using the strain gages in the leakage experiment for verification of the EP-FEM result. The strain gages of which the length was 2mm were attached to flange hub. The hub stress was measured as 88.5MPa, while the EP-FEM result was 85.5MPa. A fairly good agreement was observed between the EP-FEM results and the experimental results. The hub stresses of the connections with asbestos gaskets are compared with those with non-asbestos gaskets. The difference is found to be small between asbestos and non-asbestos gaskets.

Fig.10 The effects of the nominal diameter of the pipe flange connections on the hub stress at =0


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6. Comparison of the leakage between the estimated and the measured results

The amount of helium gas leakage L(Pam3/s/m) is estimated using the contact gasket stress distribution obtained from the EP-FEM. The procedure is described as follows. (1) The sealing test according to the test method for sealing behavior of gaskets for pipe flanges (JIS B 2490) is conducted using the same kind gasket of which the nominal diameter is 3. The gasket stress z -gasket displacement curve and gasket stress z-fundamental leak rate Ls (Pam3/s) curve are obtained in the test. Figure 11 shows the schematic of experimental set up according to JIS B 2490(13). Figure 12 shows the gasket stress z -gasket displacement curve and gasket stress z- fundamental leak rate Ls curve obtained from JIS B 2490(13). (2) The contact gasket stress distributions obtained from the EP-FEM calculation are divided by n in the circumferential direction. In this study, the n is equal to the number of bolt N because the variation of contact gasket stress distribution in the circumferential direction is small. (3) The averages of contact gasket stress in each divided area are calculated. (4) The amount of leakage is obtained using the relationship between the gasket stress z - fundamental leak rate Ls curve obtained above procedure and the averages of contact gasket stress in each divided area. (5) The estimated fundamental leakage from the pipe flange connection is obtained from the sum of the leakage in each divided area. (6) The shape factor k(13) (k=1/(do/di)-1)) and the value of (P/P*)m (13) are multiply by the estimated fundamental leakage Ls for taking into account the nominal diameter and difference in the internal pressure, where, do is the outer diameter of gasket, di is the inner diameter of

Fig.11 Schematic of experimental setup for measuring the sealing behavior of

gaskets (JIS B 2490)(13)

Fig.12 The relationship between gasket stress and leak rate of

non-asbestos SWG

(a) case of 3pipe flange (b) case of 20 pipe flange

Fig.13 Comparison of leak rate in the pipe flange connection with spiral wound gasket between estimation and experiment

(a) the smaller nominal diameter (3) (b) the larger nominal diameter (20)


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gasket and m is a value that describes the relationship between internal pressure and leakage. The value of m is usually chosen as 1.5(13).

Figure 13 shows the comparisons of the results between the estimated gas leakage and the experimental results. The ordinate is the amount of gas leakage per unit gasket diameter (Pam3/s/m), and the initial average contact gasket stress zm. Figure13(a) is the case of the connection with the smaller nominal diameter pipe flange connection(3), and Fig.13(b) is the case of the connection with the larger nominal diameter pipe flange connection (20). A fairly good agreement between the estimated results and the experimental results is observed. The leak rate per unit gasket diameter in the connection with the smaller nominal diameter (3) is smaller than that in the connection with the larger nominal diameter (20). From the results, it can be concluded that the bigger preload is needed for the connections with larger nominal diameter for getting the same sealing performance of the connection with smaller nominal diameter. In Fig.13(a), the estimated results for the pipe flange connection with asbestos gasket are shown as an orange line. It is found that the sealing performance of pipe flange connection with non-asbestos gasket is better than that with non-asbestos gasket.

7. Conclusions

This paper has dealt with the effect of the nominal diameter of pipe flange connection on the sealing performance and the difference in the mechanical characteristics of the connections with between asbestos and non-asbestos gaskets. The contact gasket stress distributions, the load factor and hub stress are obtained from EP-FEM taking into account the non-asbestos gasket property according to JIS B 2490. The leakage tests were also conducted to demonstrate the validity of the result of EP-FEM. The results obtained are as follows.

(1) The contact gasket stress distributions in the pipe flange connections with the different nominal diameter from 3 to 24 were calculated using the EP-FEM taking account the hysteresis and the non-linearity of the non-asbestos gasket. It is found that the variations of the contact gasket stress distributions in the pipe flange connections with the larger nominal diameter are larger than those with the smaller nominal diameter. When an internal pressure is applied to the pipe flange connections, it is observed that the reductions of the average contact gasket stress in the pipe flange connections with the larger nominal diameter are much larger than those with the smaller nominal diameter. It is also found that the reduction in the average contact gasket stress in the connection with asbestos is larger than that with non-asbestos gasket.

(2) An increment in axial bolt force (load factor g) of the connections are obtained from the EP-FEM. It is found that the load factor g of the connections with the larger nominal diameter is negative. A fairly good agreement is observed between the results of the EP-FEM and the experimental results in the connections with 3 and 20 nominal diameters. It is also found that the values of the load factor of the connections with non-asbestos gaskets are larger than those with asbestos gaskets. Thus, the sealing performance of the connection with non-asbestos gaskets is assumed to be better than that with asbestos gaskets.

(3) The effects of the nominal diameter in the pipe flange connections on the hub stress are calculated when the initial average contact gasket stress z is 100MPa. It is shown that the values of the hub stress of the connections with the smaller nominal diameter in the case where the internal pressure is applied to the connections are larger than that in the case of initial clamping state. However, as the nominal diameter of the pipe flange connections is increases, the values of the hub stress of connection in the case where the internal pressure is applied are smaller than that in the case of initial clamping state. The hub stresses obtained from the EP-FEM is different from those obtained from ASME code. Due to the


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EP-FEM result, the bolt preload is designed to be much larger. (4) The gas leakage is estimated using the contact gasket stress distributions obtained

from the EP-FEM and the relationship between gasket stress z and fundamental leak rate LS according to JIS B 2490. A fairly good agreement is observed between estimated gas leakage and experimental gas leakage. The sealing performance of the connection with smaller nominal diameter is better than that with larger nominal diameter. It is demonstrated that the sealing performance of the connection with non-asbestos gaskets are better than that with asbestos gasket.

References

1. Morohoshi, T., Sawa, T., On the Characteristics of Rectangular Bolted Flanged Connections With Gaskets Subjected to External Tensile Loads and Bending Moments, Transactions of the ASME, Journal of Pressure Vessel Technology, Vol.116, (1994), pp.207-215.

2. Bickford, J. H., Gaskets and Gasketed Joints, Marcel Dekker Inc., (1997). 3. Bouzid, A. H., Derenne, M., Analytical Modeling of the Contact Stress with Nonlinear

Gaskets, Transactions of the ASME, Journal of Pressure Vessel Technology, Vol.124, (2002), pp.49-53.

4. Sawa, T., Ogata, N., Nishida, T., Stress Analysis and Determination of Bolt Preload in Pipe Flange Connections with Gaskets under Internal Pressure, Transactions of the ASME, Journal of Pressure Vessel Technology, Vol.124, (2002), pp.385-396.

5. Takagi, T., Fukuoka, T., Three-Dimensional Finite Element Analysis of Pipe Flange Connections (In Case of Using Compressed Asbestos Sheet Gasket), Transactions of the Japan Society of Mechanical Engineers, Series A, Vol.68, No.665, (2002), pp.22-27.

6. Ando, F., Sawa, T., Ikeda, M., A New Design Method for Piping Components Against Leakage and Damage Subjected to High Level Earthquake Load, Proc. of ASME PVP Conference 2002, Vol.445, No.1, (2002), pp.113-118.

7. Nagata, S., Matumoto, M., Sawa, T., Stress Analysis and Sealing Performance Evaluation of Pipe Flange Connections under Internal Pressure (Effects of Scatter in Bolt Preload), Transactions of the Japan Society of Mechanical Engineers, Series A, Vol.70, No.699, (2004), pp.1595-1602.

8. SAWA, T., Nagata, S., Tsuji, H., New Development in Studies on the Characteristics of Bolted Pipe Flange Connections in JPVRC, Transaction of ASME, Journal of Pressure Vessel Technology, Vol.128, (2006), pp.103-108.

9. Ministry of Health. Labor and Welfare, Government ordinance in which a part of labor safety hygiene law enforcement order is revised (Government Ordinance Vol.349), (2008). (In Japanese).

10. Kobayashi, T., Nishiura, K., Hanashima, K., Study on the Tightening Criteria of bolts for Low Pressure Rating Flanges, Yamanashi District Conference, 504, (2008), pp.131-132.

11. Bouzid, A. H., Derenne, M., El-Rich, M., Effect of flange Rotation and Gasket Width on Leakage Behavior of Bolted Flanged Joints, Welding Research Council Bulletin, 496, (2004).

12. Pressure Vessel Research Council, Standard Test Method for GASKET CONSTANTS FOR BOLTED JOINT DESIGN, Draft 10.01, (2001).

13. Japanese Industrial Standards. JIS B2490 Test method for sealing behavior of gaskets for pipe flanges , (2008).

14. ASME Boiler & Pressure Vessel Code Section VIII Division 1 Rules for Construction of Pressure Vessels App.2, (2004).

15. ANSI/ASME B16.5, Pipe Flanges and Flanged Fittings, (1996).

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