Spiral Wound Gaskets Research Articles

To The Extreme

Spiral wound gaskets can operate in the harsh environments where standard gaskets would fail. Dobson Gaskets explores the qualities that make them so resistant.

Preliminary Experimental Quantification of Helium Leakages from Flanged Connections at HCPB TBS Operative Conditions

The HCPB TBS (Helium-Cooled Pebble Bed Test Blanket System) is one of the two European TBSs that will be installed and tested in the ITER reactor. The use of flanged connections in the Helium Coolant System and the Tritium Extraction System of the HCPB TBS would make the remote maintenance operations easier and faster. Therefore, investigating the helium leakage from flanges becomes a fundamental step toward the control of the tritium activity in the Port Cell, as the helium flow will contain a variable but not negligible amount of tritium. The first set of experiments on helium leakages from flanged connections is described in this paper. The experiments were performed in a HeFUS3 facility, an eight-shaped helium loop designed to work at HCPB-TBS-relevant conditions. The facility can provide a helium mass flow rate in the range of 0.27–1.4 kg/s and can reach a pressure as high as 80 bar and a temperature up to 530 °C. Two types of gaskets were tested in this campaign: a spiral-wound gasket and an oval ring joint. The gasket/flange assemblies are described in detail in this paper, together with the test section that hosts them and the performed commissioning tests. The tests were carried out at 500 °C and 80 bar. In these conditions, the leak rate from the flange with the oval ring joint resulted in being, on average, 1.42·10−6 mbar∙L/s, while the leak rate from the flange with the spiral-wound gasket resulted in being, on average, 3.73·10−3 mbar∙L/s.

Design method of enhancing the tightness of a spiral wound gasket with PTFE filling

The paper presents the experimental research results and numerical computations of two constructions of a spiral wound gasket with a PTFE filling. The first construction was a standard one in which the shape of the spiral’s windings in a cross section view resembles the shape of the letter ‘V.’ The second solution has an original, asymmetric shape of windings’ profile. Based on the vast experimental research tests, it was proved that the gasket with an asymmetric shape of windings is characterized with larger stiffness than the standard design, as well as increased tightness. Numerical calculations and a topography analysis of the contact surface of the gaskets showed that the asymmetric gasket under load is characterized with a larger effective contact surface when compared to the standard gasket. The gasket of an asymmetric construction can have a special application at small contact stress, which allows to avoid an excessive stress of flanges and bolts.

Numerical evaluation of effective compression behaviour of spiral wound gasket under loading and unloading

ABSTRACTGaskets are used as interfacing element between the mating surfaces, to seal the flange joint. The interfacing elements are usually subjected to compression during loading and relaxation during unloading. The unloading behaviour of the gasket material, when subjected to internal fluid pressure, controls the residual deformation in gasket. A methodology is proposed to obtain the homogenised behaviour of heterogenous gasket by volume averaging the response from micromechanical analysis. The response includes both loading and unloading characteristics of the gasket material. Here, the individual constituents’ characteristics in the spiral wound gasket is modelled using their respective elasto-plastic behaviour. But the unloading behaviour is more affected by the plastic properties. Therefore, the anisotropic Hill’s plastic parameters are evaluated by analysing the representative volume element of the gasket under different loading conditions. The compressive behaviour of the spiral wound gasket from homogenisation is compared with the experimental values for both loading and unloading conditions. An improved unloading behaviour is obtained using the proposed methodology.

Spiral wound gaskets with fiber Bragg grating sensors

Modern sealing components are used in a wide range of industrial processes. The recent global attention for reducing emission of environmentally harmful substances motivates gasket manufacturers to quantify the performance of sealing gaskets. We investigate the use of fiber Bragg grating sensors for measuring seating stress on a spiral wound gasket. The fiber-optic sensors are integrated in the gasket, following a particular instrumentation strategy. The instrumented gaskets are first installed in a standardized flange following a state-of-the-art installation protocol. Then, the gaskets are unloaded with a particular unloading strategy to simulate sealing performance loss. We compare the load in the mounting bolts during the (un)loading procedure with the response of the FBG sensors in the gasket and find a high correlation. We thus evidence the potential of fiber-optic sensors for measurements during installation as well as monitoring of sealing gaskets serving the accountability of these components.

Design and Application of Spiral Wound Gasket Sealing for Big Opening Flange for High Temperature and Pressure Vessel

Metallic spiral-wound gasket sealing are generally applicable for the service conditions, which are subject to the periodic temperature and pressure changes, shocks or vibrations. The nominal size of the largest spiral wound gasket of flanges is according to the provisions of HG/T 20631; those more than this specification are in the scope of non-standard parts, which require customization and manufacturing. This paper aims for introducing the successful experience of the first application of customized for non-standard spiral-wound gasket sealing of the large opening flange used for pressure vessel which bears high temperature and high pressure. The paper demonstrated the basic principle and critical points for the design and application of customized non-standard spiral-wound gasket sealing for the large opening flange and provided the valuable reference of actual application experience for the design and manufacturing of similar components. This paper presents the experiences summary in the study field and provides valuable reference of actual application experience for the design and manufacturing of similar components.

Metal-to-metal contact gaskets for nuclear power stations in France

This article discusses various types of gaskets and allied technology that are used in the nuclear industry in France. After initially covering spiral-wound gaskets, with asbestos winding as the sealing element, it looks at what are referred to as “Graphite Expanse Matrice” gaskets, and their sealing characteristics. In addition, it also explains how calculations for metal-to-metal contact gaskets are done in accordance with the RCC-M® nuclear code, the French standard for the design and construction of pressurised equipment relating to the nuclear island of pressurised water reactor power plants. It concludes with a summary of the types, power-ratings and location of pressurised water reactor facilities in France that are in use or under construction.

Effective modeling of spiral wound gasket with graphite filler in gasketed flange joint subjected to bending loads

Abstract The flange joints with gasket are used in automobile, aircraft, pressure vessel and pipelines. The gasket deformation behavior controls the leakage phenomenon of the joint. The stress in spiral wound gasket with graphite filler is analyzed using micromechanical approach and axisymmetric finite element analysis. The material characteristics of individual constituents in gasket are modeled using their elasto-plastic behavior. The uniaxial compressive behavior of gasket is observed to be in good agreement with experimental values. The flange joint is analyzed for leakage by using 3D finite element model with individual constituents of gasket. A realistic distribution of contact stress in gasket is obtained using micromechanical approach. The contact stress distribution in the compression and tension side, when subjected to external bending load is also evaluated. The effective gasket width for sealing is contributed by filler tape alone, rather than combination of metal and filler tape in spiral wound gasket.

Failure analysis of outer ring of spiral wound gasket

Failure of spiral wound gaskets rarely occurs due to its outer ring. This paper presented a failure case of a spiral wound gasket owing to the rupture of the outer ring. A series of inspections including chemical, mechanical, metallographic and fractographic analysis were carried out to explore the failure mechanism of that ring. The results show that chemical compositions and mechanical properties of material agree with standard requirements and failure is related to multi-source fatigue fracture. Serious plastic deformation is found near the fracture region. It is owing to squeeze between the bolt and the outer ring, causing a high local circumferential stress. Fatigue fracture occurs when the outer ring is subjected to alternating loads under the high stress. The factors causing fracture of the outer ring were discussed and suggestions were also given for avoiding this failure.

Modeling of the elastic properties of compressed expanded graphite - A material used in spiral wound gaskets

The paper presents the method of modeling the elastic deformations of expanded graphite, a material used as flexible filling in spiral wound gaskets. Five methods (from A to E) were proposed, by means of which the mean values of the effective elasticmodulus were determined on the basis of the experimentally determined stress-strain characteristics of expanded graphite. The values determined in this way constituted the data set into the isotropic material model, reflecting the elastic properties of the expanded graphite tape in the numerical spiral wound gasket model. A different way of modeling the graphite's elastic properties using the numerical model was method F, in which a nonlinear hyperelastic material model proposed by Blatz-Ko was adapted. The basic purpose of the numerical calculations was to determine both the compression curve of the gasket and the stress distribution in the gasket's windings. The obtained numerical results of the gasket's compression were compared with the experimental test, which allowed the assumptions of the numerical models to be validated. The best way to reflect the elastic behavior of expanded graphite in the gasket's numerical model turned out to be the nonlinear material model presented in method F.

Adaptation of a highly compressible elastomeric material model to simulate compressed expanded graphite and its application in the optimization of a graphite-metallic structure

The paper presents simulations of mechanical properties of compressed expanded graphite. To model the stress and strain states of compressed expanded graphite, a hyperelastic material model formulated by the Blatz–Ko was adapted. The idea of using this model resulted from the assumptions that compressed expanded graphite exhibits similar mechanical properties to polyurethane foam with high density. The material constant of the Blatz–Ko model was determined by numerical calculations where deformation energy equation was parameterized with the shear modulus. Such material model used in a compressed expanded graphite simulation was experimentally validated. Subsequently, the Blatz–Ko model was used in a numerical simulation of the graphite-metallic structure in the form of a spiral wound gasket which is composed of metallic and elastic tapes. This structure was subjected to an optimization process which included the reduction of stress in the elastic graphite tape obtaining the appropriate axial stiffness of the gasket. In the final stage, the optimal design of the gasket was experimentally tested. The experimental results were compared with the data obtained numerically, which allowed to verify the adapted material model and boundary conditions of the numerical gasket model.

Study on strength and sealing of a bolted flange joint under complex working conditions

Bolted flange joints are widely used in petrochemical equipment and pipelines, while the problem of its leakage is a serious threat to the environment and safety. In order to study the strength and sealing of the bolted flange connection, a three-dimensional finite element model of the bolted flange joint with a flexible graphite spiral wound gasket is developed by using APDL in ANSYS. Considering the nonlinear compression rebound constitutive relation of gasket material, the indirect coupling method of temperature and structure is used to simulate the whole process of the bolted flange joint from installation to maintenance. The stresses of the flange, bolt and gasket under different operated conditions are investigated in detail. The results show that the stress distribution of the bolted flange joint is not uniform along the circumference due to the tightening sequence of bolts. The stress of each part of the bolted flange joint changes slightly under pressure condition, but the stress distribution is greatly affected by high temperature and creep at high temperature for 1000 hours. And the possibility of leakage of the bolted flange connection is increased with the application of transient cooling and heating up and additional bending moment and torque. After the application of various loads in turn, the bolted flange joint is likely to leak on the tension side.

Sealing Performance Evaluation for Bolted Flange Joint with Spiral Wound Gasket Based on the Bolt Force

Leakage accidents often occur at the bolted flange joints, which are widely used in the petro-chemical plant. This is mainly resulted by the reduction of bolt force during operation. Therefore, bolt force is very important for sealing performance of the joints in service. Based on the leakage rate parameter, the relationship between the bolt force and gasket stress was derived. Moreover, the leakage rate model was established on the basis of bolt force. With this model, the leakage rate can be directly calculated through the bolt force, and the sealing performance can be evaluated. In order to verify this model, corresponding experiments have been performed. It shows that with the internal pressure increasing, the bolt force increases and the gasket stress reduces. There exists a monotonic relationship between the bolt force and gasket stress. The theoretical gasket stress value corresponds well with the experimental value. The calculated leakage rates for the joints also agree well with the experimental value. Then, it is feasible to evaluate the sealing performance for the bolted flange joints based on the bolt force.

Fretting friction and wear behaviors of spiral wound gasket (SWG) sealing surface

Abstract The vibration of the pipeline act on the gasket sealing surface in the form of fretting wear, reducing the sealing performance. In this paper, an experimental study was described on the fretting wear and frictional mechanism of interface between spiral wound gasket (SWG) and flange. The results showed that the gasket winding structure affects the variation of the friction coefficient fluctuation. Moreover, only the fretting behavior of mixed friction regime (MFR) and slip regime (SR) can be expressed stably. Additionally, fretting wear is dominated by abrasive and adhesive wear, and plastic deformation occurs under high load. The intense wear behavior mainly presented in the circumferential direction of small displacement and the radial friction process of large displacement.

A Study on the Behavior of Single- and Twin-Gasketed Flange Joint Under External Bending Load

Gasketed flange joints are widely used in pressure vessels and piping systems. They are subjected to bending load due to differential thermal expansion, wind load, self-weight, etc., in addition to assembly and internal fluid load. Most of the flange designs are based on equivalent pressure method to include the effect of external bending loads. The behavior of gasketed flange joint is complex due to the nonlinear hysteretic behavior of gasket material and contact interfaces between joint members. It becomes more complex when the joint is subjected to bending load at elevated temperatures. In the present work, performance of a flange joint has been studied under internal pressure and external bending load at elevated temperatures. A 3D finite element model is developed, considering the nonlinearities in the joint due to gasket material and contact between its members along with their temperature-dependent material properties. The performance of joint under different bolt preloads, internal fluid pressures, and temperatures is studied. Flange joint with two gaskets (twin-gasketed flange joint, TGJ) placed concentric is also analyzed. The results from finite element analysis (FEA) are validated using four-point bending test on gasketed flange joint. The sealing and strength criteria are considered to determine the maximum allowable bending moment at different internal fluid temperatures, for both single- and twin-gasketed flange joints with spiral wound gasket. Twin gasket is able to withstand higher bending moment without leakage compared to single gasket. Results show that the allowable load on flange joint depends on operating temperature and gasket configuration.

STAMINA OF A GASKETED BOLTED FLANGED PIPE JOINT UNDER DYNAMIC LOADING

Gasketed bolted flange joints are the most critical components in pipelines for their sealing and strength under operating conditions. Most of the work available in literature is under static loading, whereas in industry, cyclic loads are applied due to the vibrating machinery such as motors, pumps, sloshing in offshore applications and in the ships etc. In this study a three dimensional finite element analysis of a gasketed joint is carried out using a spiral wound gasket under bolt up and dynamic operating conditions (internal pressure, axial and bending) singly and in combination. The cyclic axial loads are concluded relatively more challenging for both the sealing and strength of the joint. Higher magnitudes of loads and frequencies are also observed more challenging to the joints performance.

Effect of thermal loading on sealing behavior of single and twin-gasketed flange joints

Gasketed flange joints are usually subjected to internal pressure at high temperature. The most important requirement of flange joint is to provide leak-free joint under operating condition. In the present study, temperature-dependent nonlinear gasket properties of spiral-wound gasket at elevated temperatures are obtained experimentally and included in the analysis. The relaxation of gasket contact stress in both single and twin-gasketed joints at elevated temperatures is compared. It is observed that the ability to withstand internal pressure decreases with increase in temperature in both single and twin-gasketed flange joints. But, the twin-gasketed flange joint is found to withstand higher internal pressure than single-gasketed joint at a given bolt preload and temperature. The influence of gasket seating surface rotation on the distribution of gasket radial contact stress at elevated temperature is studied. The effect of elevated temperature on flange stresses of twin-gasketed joint is also examined.

FLiNaK compatibility studies with Inconel 600 and silicon carbide

A small liquid fluoride salt test apparatus has been constructed and testing has been conducted to examine the compatibility of silicon carbide (SiC), Inconel 600 and a spiral wound gasket material in FLiNaK, the ternary eutectic alkaline metal fluoride salt mixture. These tests were conducted to evaluate materials and sealing systems that could be used in fluoride salt systems. Three months of testing at 700°C was conducted to assure that these materials and seals would be acceptable when operating under prototypic operating conditions. The SiC specimens showed little or no change over the test period, while the spiral wound gasket material did not show any degradation except that salt might have been seeping into the outermost spirals of the gasket. The Inconel 600 specimens showed regions of voiding which penetrated the specimen surface to about 250μm in depth. Analysis indicated that the salt had leached chrome from the Inconel surface, as was expected for this material.

On the Buckling of Spiral Wound Gaskets

The buckling of spiral wound gaskets (SWGs) causes turbulence of the fluid flow inside flanges and may result in leakage failure over time due to the unwinding of the spirals. A few limited studies on the lateral forces generated by axial compression of the gasket sealing element which cause this phenomenon are available in the literature. The lateral forces are generated during initial tightening and are not distributed uniformly in the circumferential direction. Hence, there is an introduction of concentrated forces in small areas. The nonuniform gasket contact stress caused by the tightening sequence makes the problem more complex. It is suggested to study experimentally the buckling of SWGs by developing a special test bench designed for this purpose. This test bench is able to measure the lateral loads and winding inward displacement during the tightening process. The experimental results are to be compared to those obtained by numerical finite element simulation for the purpose of extrapolating for other size gaskets.

The study of the loose flange connection with spiral wound gasket

The study of the loose flange connection with spiral wound gasket