Spiral Wound Gaskets Research Articles

552 うず巻形ガスケットにおける膨張黒鉛の酸化に伴うシール寿命推定法(フランジガスケット締結体の力学と密封性能評価III)

552 うず巻形ガスケットにおける膨張黒鉛の酸化に伴うシール寿命推定法(フランジガスケット締結体の力学と密封性能評価III)

652 低レーティングフランジへのうず巻形ガスケット適用のための密封特性比較(フランジガスケット締結体の力学と密封性能評価V)

652 低レーティングフランジへのうず巻形ガスケット適用のための密封特性比較(フランジガスケット締結体の力学と密封性能評価V)

THEORY AND TECHNOLOGY OF CLASSIFICATION DESIGN AND MANUFACTURE OF SPIRAL WOUND GASKETS

By selecting appropriate metallic strip and nonme-tallic filling strip materials, and adopting reasonable structure sizes and production technological parameters, spiral wound gaskets with good performances can be fabricated, which are suitable for the diverse rigorous operating conditions such as high and low temperature, high pressure, vibration, corrosion medium and so on. The concept of the classification design and manufacture of spiral wound gaskets is put forward. The corresponding theory and technology are investigated, which based both on the optimization of the structure sizes and production technological parameters of gaskets and on the tightness analysis method of bolted flanged connections. This technology will contribute the design, manufacture and use of spiral wound gaskets.

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.

Bolt-Up Guideline for Pipe Flange Connections

Numerical simulations are systematically executed for pipe flanges with wide variety of nominal size by using finite element analysis, which can simulate the bolt-up process of a pipe flange connection. Effects of the gasket modeling method on the bolt-up simulation and the bolu-up procedure which can prevent open up deformation are evaluated. It is indicated that the simplified linear modeling of gasket, in which two different Young's moduli are used in loading and unloading, is valid for estimating the variations, of mean bolt preloads during bolting up operations. The bolt-up procedure, in which four bolts located 90 degrees apart each other are tightened uniformly with the target bolt preload at the installation process, is effective to prevent the open up deformation. Finally, the methodical guideline for bolt-up operation of pipe flange connections with joint sheet gasket or spiral wound gasket is proposed.

Finite Element Simulation of Bolt-Up Process of Pipe Flange Connections With Spiral Wound Gasket

It is well known that a large amount of scatter in bolt preloads is observed when bolting up a pipe flange connection, especially in the case of using a spiral wound gasket. In this study, a numerical approach is proposed, which can simulate the bolt-up process of a pipe flange connection with a spiral wound gasket inserted. The numerical approach is designed so as to predict the scatter in bolt preloads and achieve uniform bolt preloads at the completion of pipe flange assembly. To attain the foregoing purposes, the stress-strain relationship of a spiral wound gasket, which shows highly nonlinear behavior, is identified with a sixth-degree polynomial during loading and with an exponential equation during unloading and reloading. Numerical analyses are conducted by three-dimensional FEM, in which a gasket is modeled as groups of nonlinear one-dimensional elements.

Effect of Surface Characteristics on Compressive Stress and Leakage Rate in Gasketed Flanged Joints

The effect of surface characteristics on compressive stress and leakage rate in gasketed flanged joints is discussed qualitatively and quantitatively based on experimental verifications. The sensitivity of the sealing phenomenon to the sealing surface characteristics, gas pressure and stress level is presented. Sealing surfaces produced with grinding, turning and milling procedures of different roughness values were the subject of the tests with three types of gasket, namely, PTFE (polytetrafluoroethylene), graphite, and spiral wound. The experimental results indicated that the roughness value Ra (average arithmetic height) has no effect on the sealing performance of the gasket, except for the ground type sealing surfaces. The platen (flange) surface forms were found to be the determining factor on the leakage rate and flow regime for gasketed flanged joints. It is shown that the surface characteristics have no effect on the leakage rate and on the gasket performance for the PTFE gasket at high stress levels. However, at low stress levels the rougher ground and milled sealing surfaces having radial channels on the surface produce larger leakage rates. The effect of surface characteristics, stress level, and gas pressure was more evident on the graphite and spiral wound gasket types, at both low and high stress levels. It is also shown that the leakage rate follows an exponential law as a factor of surface stress and gas pressure, for all sealing surface characteristics and gasket types. While there is little difference in the leakage rate for the PTFE gasket when the gasket stress level is increased by a factor of two, from S3 to S5, a substantial leakage rate reduction by a ratio of 17.5 times was observed for the graphite and spiral wound gaskets for most sealing surfaces. On the other hand, when increasing the helium gas pressure from 200 to 800 p.s.i., the leakage rate increased by 5 times for the PTFE, and up to10 times for the graphite and the spiral wound gaskets. It was determined that while molecular flow regimes can be achieved for the PTFE gasket for all sealing surfaces, the two other gasket types provided laminar flow under the same operating conditions.

2536 内圧を受けるガスケット付き閉止型フランジ締結体の有限要素解析と密封性能評価

The stresses of a bolted flange connection with a cover of pressure vessel in which a spiral wound gasket is inserted, under internal pressure are analyzed taking account a hysteresis of the gasket by using the finite element method (FEM). The leakage tests were also conducted using an actual bolted flange connection with a cover of pressure vessel with a spiral wound gasket. Using the contact stress distribution of the bolted flange connection under internal pressure and the tightness parameter, the values of the new gasket constant were obtained by taking into account the changes in the contact stress. The sealing performance was evaluated by the new gasket constants.

Finite-element Stress Analysis and Characteristic Evaluations of Pipe Flange Connection with Spiral Wound Gasket under Internal Pressure

Finite-element Stress Analysis and Characteristic Evaluations of Pipe Flange Connection with Spiral Wound Gasket under Internal Pressure

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.

Stress Analysis and Determination of Bolt Preload in Pipe Flange Connections With Gaskets Under Internal Pressure

The stresses of a pipe flange connection with a spiral-wound gasket under internal pressure are analyzed taking account a nonlinearity and a hysteresis of the gasket by using an axisymmetric theory of elasticity and the finite element method (FEM). The leakage tests were also conducted using an actual pipe flange connection with a spiral-wound gasket. Using the contact stress distribution of the pipe flange connection with 3-in. nominal diameter under internal pressure and the tightness parameter, the values of the new gasket constants are obtained by taking into account the changes in the contact stress. A difference in the new gasket constants between the estimated values obtained from the actual pipe flange connection and the values obtained by the PVRC procedure is small. In addition, a method to determine the bolt preload for a given tightness parameter is demonstrated. The obtained results of the bolt preload for the pipe flange connection are in a fairly good agreement with those obtained by the PVRC procedure under a lower pressure application. However, a difference in the bolt preload is about 10% when an internal pressure is increased.

Stress Analysis and an Estimation of the Sealing Performance in Pipe Flange Connections with Spiral Wound Gasket Subjected to Internal Pressure.

The stresses of a pipe flange connection with a spiral wound gasket under internal pressure are analyzed taking account a non-linearity and a hysteresis of the gasket by using axisymmetric theory of elasticity and finite element method (FEM). The leakage tests were also conducted using the actual pipe flange connections with spiral wound gaskets. Using the contact stress distribution of the pipe flange connections with 3 nominal diameter under internal pressure, the values of the new gasket constants proposed by PVRG are estimated by taking account the changes in the contact stress. A difference in the new gasket constants is substantial between the PVRC values and the estimated results, which are obtained by using the initial clamping stress. However, the difference is small between the PVRC values and the estimated values which are obtained by using the actual gasket stress. In addition, a method for determining the bolt preload for a given tightness parameter is demonstrated. The obtained results for the pipe flange connection are in a fairy good agreement with those obtained by PVRG procedure.

Gasket characteristics for the design of bolted flange connections of metal-to-metal contact type

Frequently used joints in industrial plants are bolted flange connections of metal-to-metal contact type (MMC) especially where dynamic loadings are to be expected. Contrary to floating type flanged joints, where the total bolt load is transmitted through the gasket, only that part of the bolt load is taken over by the gasket which is necessary for MMC. Two basically different types of MMC joints have to be distinguished. In the first case, the gasket — mostly spiral wound gaskets (SWG) without distance rings — is implemented in a groove in one of the flanges, and during assembly flange contact has to be reached. If this type is used the most important parameter is the clearance on the outer diameter. If the difference between the outer diameters of the groove and gasket is too small, excessive gasket stress for MMC results which cannot be reached in practice. This effect is enhanced with increasing oversize of the gasket (difference between gasket thickness and groove depth). The acceptable range of radial clearance is between 1.0 and 1.5 mm, depending on the gasket thickness. Gaskets with small width (about 6 mm) show rather large leakage rates due to collapse and/or inward buckling. In the second case, flat face flanges and a gasket with a sealing element and distance ring (e.g. SWG with outer distance ring) is used. Tightening of the bolts leads to contact between the flanges and the distance ring. Depending on the width of the gasket the required gasket stress for MMC can be too high. The optimum width with respect to adequate MMC stress and tightness is about 10 mm or less.

FEM Stress Analyses and a Sealing Performance Evaluation on Pipe Flange Connections with Larger Nominal Diameter Including Spiral Wound Gaskets Under Internal Pressure

FEM Stress Analyses and a Sealing Performance Evaluation on Pipe Flange Connections with Larger Nominal Diameter Including Spiral Wound Gaskets Under Internal Pressure

323 フランジ継手の挙動解析における渦巻きガスケットの応力-ひずみ関係の簡略モデル化(オーガナイズドセッション : フランジガスケット締結体の力学と密封性能評価1)

323 フランジ継手の挙動解析における渦巻きガスケットの応力-ひずみ関係の簡略モデル化(オーガナイズドセッション : フランジガスケット締結体の力学と密封性能評価1)

Generic issues effecting spiral-wound gasket performance

Spiral-wound gaskets (SWG) are used extensively as primary seals in critical joint applications of plant process piping systems in all industries, including petrochemical, paper and electricity generation. Despite widespread use and a long performance history, industry continues to experience significant operations and maintenance cost expenditures, conservatively estimated by some at more than 250 million US dollars per year, that are directly attributable to plant piping system leakage, of which SWG leaks appear to play a significant role. Recent works performed by the authors, in the area of improved plant leakage reduction techniques, strongly suggests that clearly definable gasket design, manufacturing and assembly factors are responsible. This work has also identified very effective preventive actions that have been proven experimentally, and in the field, to dramatically reduce incidents of piping system leakage caused by assembly failures in SWG joints. This paper discusses those generic issues effecting gasket performance, identifies those actions proven to mitigate leakage incidents, and offers suggestions for plant operators to generally improve their existing plant leakage reduction programs.

Evaluations of Bolt-up Process of Pipe Flange Connection Using Finite Element Analysis. In Case of Using Spiral Wound Gasket.

In multi-bolt system, the scatter in bolt tension is largely dependent on the method of tightening operation and elastic interaction due to the successive tightening of bolts. In this study, focuses are placed on effects of elastic interaction and a new bolt-up strategy using three-dimensional finite element analysis, in which a gasket is modeled as a nonlinear one-dimensional gasket element, is proposed. Two types of numerical procedures are presented here. One is to predict the final scatter in bolt tension when tightening all bolts one by one in arbitray order with target preload. The other is to predict the amounts of initial bolt loads needed to create uniform final preloads with one pass operation of bolt tightening. The effectiveness of the numerical approach proposed here is substantiated by comparing numerical results with experimental ones. Contact pressure distributions on the gasket bearing surface, which significantly affect the sealing performance of flange connections, are also evaluated. The objective connection is composed of bolts, pipe flanges and a spiral wound gasket with inner and outer rings.

Effect of structural and operational factors on the leakage of spiral-wound gaskets

Effect of structural and operational factors on the leakage of spiral-wound gaskets

Asbestos-free sheet material for spiral-wound gaskets: Lancaster, R.A., McKenzie, N.C. and Hargreaves, B. (T&N Materials Research Limited, Manchester, England) US Pat 4 529 662 (16 July 1985)

Asbestos-free sheet material for spiral-wound gaskets: Lancaster, R.A., McKenzie, N.C. and Hargreaves, B. (T&N Materials Research Limited, Manchester, England) US Pat 4 529 662 (16 July 1985)

Progress in Gasket Testing—Milestone Results

An extensive gasket test program, carried out under the auspices of the Pressure Vessel Research Committee and supported by over 30 sponsors from 6 countries, is nearing completion. The program was developed as part of the Long-Range Flanged-Joint Improvement Program of the PVRC at the request of the American Society of Mechanical Engineers and in response to the need for resolving complex gasket behavior questions. The test program was formulated in cooperation with cognizant ASME, API and ASTM Standards Committees. In these tests, complex load/pressure sequences are used to determine leakage performance and deformation response at room temperature of four types of commonly used gaskets. This paper presents an overview of the test program which investigates the effect of fluid pressure, type of fluid, flange facing surface finish, maximum gasket stress, gasket deformation and stress cycling. The results of the first two series of tests on spiral-wound asbestos-filled gaskets are presented to highlight some of the trends observed. Interpretation of the results is carried out with the aim of deriving meaningful design factors similar to the m and y factors of the ASME Pressure Vessel Code. It is shown, however, that such factors cannot have a unique value for a given gasket type. Instead, m and y are interrelated and their value depends on the level of specified tightness. They are also influenced by the various parameters aforementioned.