Contact Gasket Stress Distributions Research Articles

Finite Element Method Stress Analysis and Evaluation of the Sealing Performance in Box-Shape Flange Gasketed Connections Subjected to Internal Pressure

Bolted connections inserting gaskets such as box-shape flange connections have been widely used in mechanical structures, nuclear and chemical industry, and so on. They are usually used under internal pressure. In designing the box-shape flange connections with gaskets under internal pressure, it is important to clarify the gasket stress distribution for evaluating the sealing performance of these connections. However, no research in which the sealing performance of these connections is examined under internal pressure has been carried out. Thus, the design for box-shape connection such as thickness of flange cover, number of bolts, gasket width, and so on is not clarified. In this paper, the contact gasket stresses of these connections under internal pressure are analyzed using the finite element method (FEM), taking into account a hysteresis in the stress–displacement curve of the gasket. And then, using the contact gasket stress distributions obtained from FE analysis and the relationship between gasket stress and leak rate obtained from a gasket sealing test (JIS B2490), a method for estimating an amount of leakage is examined. Leakage tests were also conducted to measure an amount of gas leakage using an actual box-shape flange connection with a gasket. The estimated results are in reasonable agreement with the experimental results. In addition, the effect of gasket width, flange cover thickness, and flange cover material is examined on the sealing performances of box-shape flange connections under internal pressure. The effects of the above factors are discussed on the sealing performance in designing box-shape flange connections.

FEM Stress Analysis and Sealing Performance Evaluation of Pipe Flange Connection under Cyclic Internal Pressure and Thermal Changes

The effects of cyclic internal pressure and thermal changes on the sealing performance and mechanical behaviors in pipe flange connection are examined using the FEM analyses for pipe flange connections with spiral wound gasket (SWG). The contact gasket stress distributions and the axial bolt forces taking into account the cyclic internal pressure and thermal changes are demonstrated. The load (internal pressure, thermal changes) sequences are determined from the conditions for actual pipe flange connections used in petroleum and chemical plants. Furthermore, the effect of material differences between pipe flange and bolts on the contact gasket stress distribution are examined. From the FEM results, it is found that the contact gasket stress reduces to be the smallest when a plant is restarted. The reduced contact gasket stress should be taken into account in the sealing design of the connection. On the other hand, the leakage tests were carried out to verify the FEM results and the effect of number of cycles (for 21days). A fairy good agreement is seen between the estimated amount of leakage due to the contact gasket stress distributions obtained from the FEM and the measured amount of leakage. It is found that the contact gasket stress decreases when the plant is restarted and as the temperature decreases. At that time, the contact gasket stress is the smallest which may lead to a leakage accident.

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

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.

Stress Analysis and Sealing Performance Evaluation in Rectangular Box-Shape Bolted Flange Connection With Gasket Subjected to Internal Pressure

The contact gasket stress distributions in a rectangular box-shape bolted flange connection with a compressed sheet gasket subjected to internal pressure were analyzed using the finite element method. Leakage tests were also conducted for an actual rectangular box-shape bolted flange connection with a compressed sheet gasket under internal pressure. Using the obtained contact gasket stress distributions and the results of the leakage tests, the new gasket constants were calculated. The difference in the new gasket constants between the values obtained from the present study and those from the Pressure Vessel Research Council (PVRC) procedure was substantial. In addition, a method to determine the bolt preload for a given tightness parameter was demonstrated and the difference in the determined bolt preload was shown between the present study and the PVRC procedure. The characteristics of the rectangular box-shape bolted flange connection were demonstrated by comparing those of circular bolted flange connections.

FEM Stress Analysis and the Evaluation of Sealing Performance of the Box-Shaped Flange Connections with Gaskets Subjected to Internal Pressure (In the Case Where the Wavy Oil-Pan Shaped Flange Connection is Used)

The contact gasket stress distribution in a wavy oil-pan shaped flange connection under the internal pressure was examined using finite element method (FEM) for estimating a location where a principal leakage occurred and for calculating the amount of leakage. Leakage tests were also conducted to validate the estimated results using an actual connection under the internal pressure. The effects of flange shape on the contact gasket stress distributions were examined. The sealing performance for the difference types of inner fluid (gas/liquid) was evaluated from the contact gasket stress distributions. It was seen that the estimated amount of leakage was in a fairly good agreement with the measured results. The difference of the contact gasket stress distribution and the sealing performance were shown between the box-shaped flange and the wavy oil-pan shaped flange connections. In addition, a method how to determine the bolt preload taking into account the allowable amount of the leakage was demonstrated. Furthermore, discussion was made on the effect of the bolt pitch on the sealing performance.

Effect of External Bending Moment on the Sealing Performance of Pipe Flange Connection

Since an external bending moment affected the sealing performance of pipe flange connection, it was important to investigate this effect. This paper analyzed the contact gasket stress distribution of pipe flange connections and evaluated the effect of external bending moment on the sealing performance from the viewpoint of changes in contact gasket stress. The study included the FE analyses and the experimental leakage tests. The FE analyses revealed the large decrease of contact gasket stress at tension side and small increase at compression side. The difference in change in contact gasket stress was caused by the non-linear hysterics characteristics of stress-displacement curve of gasket. The FE analyses also revealed that the loading order, internal pressure and external bending moment, also affected the sealing performance due to the non-linear deformation characteristic of the gasket. The experimental leakage tests using helium (He) gas were analyzed by the finite element method and discussed. This paper also evaluated the stress distribution in the pipe flange under external bending moment. The results suggested that the hub stress dominated the flange structure and the most important factor in designing the flange.

21510 内圧を受けるガスケット付き閉止型フランジ締結体の応力解析と密封性能評価(一般講演 応力解析)

The stresses of a blind flange connection with a spiral wound gasket under internal pressure are analyzed taking account a hysteresis of the gasket using axisymmetric theory of elasticity as a four-body contact problem. The leakage tests were also conducted using an actual blind flange connection with a spiral wound gasket. Using the contact gasket stress distribution of the blind flange connections with 3" nominal diameter under internal pressure, the values of the new gasket constants proposed by PVRC were estimated by taking account the changes in the contact gasket stress. A difference in the new gasket constants was small between the PVRC values and the estimated values that were obtained by using the actual contact gasket stress. In addition, a method for determining the bolt preload for a given tightness parameter was demonstrated. The discrepancy of the bolt preload was increased between the estimated values and those by the PVRC as the given tightness parameter was increased.

FEM Stress Analysis and an Evaluation of the Sealing Performance in Non-circular Box-shape Bolted Flange Connections with Gaskets Subjected to Internal Pressure

The contact gasket stress distribution of a non-circular box-shape flange connection with a compressed sheet gasket subjected to internal pressure was analyzed taking account a hysteresis of the gasket using finite element method (FEM). Leakage tests were also conducted using an actual non-circular box-shape flange connection with a compressed sheet gasket under internal pressure. By using the contact gasket stress distributions and the results of the leakage tests, the new gasket constants were calculated. The difference in the new gasket constants was substantial between the values obtained from the present study and those from the PVRC procedure. In addition, a method to determine the initial clamping bolt force (bolt preload) for a given tightness parameter was demonstrated. It was found that a higher bolt preload was needed for a given tightness parameter in the more safety design of box-shape flange connections.

New Development in Studies on the Characteristics of Bolted Pipe Flange Connections in JPVRC

This paper deals with some studies carried out in the bolted flanged connection committee (BFC) in Japan Pressure Vessel Council (JPVRC) on the stress analysis of a pipe flange connection using the elastoplastic finite element method. The characteristics of the connections with the different nominal diameters from 2in. to 20in. such as the contact gasket stress distribution, the hub stress, and the load factors were examined. The results from the finite element analyses were fairly consistent with the experimental results concerning the variation in the axial bolt force. By using the contact stress distributions and the results of the leakage test, the new gasket constants were evaluated. As a result, it was found that the variations in the contact stress distributions were substantial due to the flange rotation in the pipe flange connections with the larger nominal diameter. A method to determine the bolt preload for a given tightness parameter was demonstrated and the difference in the bolt preload between our research and PVRC was shown. In addition, the characteristics of pipe flange connection under a bending moment and internal pressure were also discussed and a newly developed bolt tightening method was demonstrated.

FEM Stress Analysis and Sealing Performance Evaluation in Pipe Flange Connections with Spiral Wound Gaskets Subjected to External Bending Moments (Case where Internal Fluid is Liquid)

The leakage evaluation when gas is used is more severe than that when liquid is used in pipe flange connections. In a practical design, it is also necessary to examine the leakage in the connections under liquid internal pressure application. The contact gasket stress distributions in the connection with a spiral wound gasket subjected to internal pressure and bending moment were analyzed by using elasto-plastic finite element method (FEM) taking account hysteresis and nonlinearity in the stress-strain curve of the gasket. The effects of the initial clamping bolt force (bolt preload), the nominal pressure and the nominal diameter of the pipe flange and the equivalent pressure on the contact gasket stress distributions were examined. The leakage tests for the connections under the bending moment and the internal pressure were also conducted by using liquid (water). By using the results of the leakage tests and the calculated contact gasket stress distributions, the sealing performance of the connections was evaluated. It was found that the sealing performance of the connection can be estimated when liquid (water) was used. In addition, a method for determining the bolt preload in the connections under the bending moments was proposed for the reliable design.

Stress Analysis and Sealing Performance Evaluation of Pipe Flange Connections under Internal Pressure (Effects of Scatter in Bolt Preloads)

The effects of scatter in bolt preloads of pipe flange connections with gaskets subjected to internal pressure are examined. The scatter in the bolt preloads tightened by a torque wrench was measured in the experiments. The contact gasket stress distributions at the interfaces of the pipe flange connections with the gaskets were calculated under the measured bolt preloads using elastoplastic finite element method (FEM) taking into account hysteresis and non-linearity in the stress-strain curves of the gaskets. The effects of the scatter in the bolt preloads on the gas leakage were also exmained using actual pipe flange connections. As the result a difference in an amount of measured gas leakage was found to be substantial between our study and PVRC (ASME) procedure. By using the calculated contact gasket stress distributions in the connections under the internal pressure and the results of the leakage tests, the sealing performance was evaluated. The effect of the scatter in the bolt preloads is found to be substantial on the leakage. It is found that the sealing performance is worse in the actual pipe flange connection than that evaluated by PVRC procedure. The tightening efficiency was proposed taking account the leakage due to the scatter in bolt preloads.

大口径管フランジ締結体の応力解析と密封性能評価 : 初期締付け力のばらつきの影響(G03-4 応力解析(2),G03 材料力学)

The leakage tests were performed in the actual larger pipe flange connections tightened wit 20" nominal diameter with a target torque using helium gas. Then, the effects of the scatter in the axial bolt forces tightened by the torque control method on the gas leakage were also examined. In addition, the contact gasket stress distributions of the flange connection tightened with the measured axial bolt forces were analyzed by using the finite element method (FEM). By using the calculated contact stress distributions and the results of the leakage tests, the sealing performance of the connections was evaluated.

2537 内圧を受けるガスケット付き非円形容器締結体の有限要素解析と密封性能評価

The contact gasket stress distributions of a non-circular flange connection with a compressed asbestos sheet gasket subjected to internal pressure were analyzed taking account a hysteresis of the gasket by using finite element method (FEM). Leakage tests were also conducted using an actual non-circular flange connection with a compressed asbestos sheet gasket under internal pressure. By using the contact gasket stress distributions and the results of the leakage tests, the new gasket constants were calculated. A difference in the new gasket constants was substantial between the values obtained from the present study and those by the PVRC procedure. In addition, a method to determine the initial clamping bolt force (bolt preload) for a given tightness parameter was demonstrated.

FEM Stress Analysis and Sealing Performance Evaluation in Pipe Flange Connections with Gaskets Subjected to External Bending Moments

The stresses in a pipe flange connection with a gasket subjected to an internal pressure and an external bending moment are analyzed taking account the non-linearity and hysteresis of a spiral wound gasket and a joint sheet gasket by using an elasto-plastic finite element method (FEM). The effects of the internal pressure and the external bending moment on the contact gasket stress distributions are examined. Leakage tests were also conducted using an actual pipe flange connection with a gasket under an external bending moment. As a result, a difference in the new gasket constants is substantial between the PVRC values and the estimated values when the external bending moment is applied to the connection. The hub stress and variation in axial bolt force were also measured. Fairly good agreements are found between the calculated and experimental results. In addition, a method for determining the bolt preload in the pipe flange connection under the external bending moment is demonstrated for a given tightness parameter.