Contact Gasket Stress Research Articles

Study on the sealing performance of high-pressure flanges by a magnetic measurement method of bolt axial force

Under high-pressure conditions, flange sealing often fails due to inadequate bolt pre-tension, leading to unstable pressurization or leakage. Assessing the integrity of high-pressure flange sealing presents challenges, constrained by operational conditions, complex equipment integration, and associated costs. This study introduces a method to evaluate flange sealing using magnetic measurements of bolt axial forces. A novel device developed using the magnetoelastic method efficiently and conveniently measures these forces under various internal pressures. The results show a linear relationship between magnetic signals and bolt axial forces at nominal pressures, whereas excessively high pressures cause anomalous changes in magnetic signals, indicative of bolt plastic deformation. Finite element simulation analyzed the changes in bolt axial force and gasket contact stress due to internal pressures, leading to an empirical formula that correlates these variables under varying pressures. The study also explored the impact of uneven pre-tensioning and gasket material on sealing contact stress. A sealing contact surface model, established based on actual roughness profile parameters, enabled the simulation and formulation of an exponential relationship between contact stress and sealing clearance. This foundation facilitated the creation of a leakage prediction model that incorporates bolt axial force parameters, thus enabling a quantitative assessment of flange sealing performance. This research provides a practical approach to evaluating the sealing performance of operational high-pressure flanges.

Reducing the urban environment impact of joint leakage of underground prefabricated structures: Waterproof performance improvement of WSR-EPDM gasket

Composite cross-section gaskets with ethylene propylene diene monomer (EPDM) and water swelling rubber (WSR) have been adopted for specific underground prefabricated structures to prevent water leakage. Research on the sealant behavior and waterproof failure mechanism of WSR-EPDM gaskets needs to be strengthened, and this paper presents a combined experimental and computational study to investigate the leakage behavior of WSR-EPDM gaskets. The mechanical performance of the WSR-EPDM gasket based on the 3-stages load-deformation relationship was detected using the electronic universal testing machine. And the waterproof performance of the WSR-EPDM gasket was tested based on the developed waterproof capacity test setup to monitor the water leakage pressure of joints under various combinations of joint openings and offsets. Three groups of mechanical tests and 12 groups of waterproof tests were carried out. Then, a series of finite element models were developed using the coupled Eulerian-Lagrangian method to reveal the failure mechanism of the WSR-EPDM gasket. The hyperelastic behavior of the WSR-EPDM gaskets was described using the two-coefficient Mooney-Rivlin hyperelastic model and verified against the gasket-in-groove mechanical test results. A supplementary parametric study investigated the effect of joint opening and offset. The correlation between gasket contact stress and supplied water pressure was analyzed. Finally, an improved gasket was developed, and the mechanical and waterproofing behavior was evaluated. The results indicated that the joint opening and offset negatively influenced the gasket waterproof behavior. The water-leakage path of the WSR-EPDM gasket was more likely to happen via the gasket-groove interface when the joint offset was larger. Furthermore, the mean contact pressure ratio to the water leakage pressure of 1:1 can be used as the criteria for a preliminary estimate of the potential water leakage path. The improved WSR-EPDM gasket showed excellent waterproof performance, with a maximum increasing ratio of 127.6%. The developed test setup and numerical methodology provide novel insights into the waterproof performance improvement of composite cross-section gaskets in complex situations.

Calculation Model of Mechanical and Sealing Properties of NiTi Alloy Corrugated Gaskets under Shape Memory Effect and Hyperelastic Coupling: I Mechanical Properties.

NiTi alloy’s shape memory effect provides additional restoring force under temperature loads, making it an ideal material for gaskets. However, its yield stress is too large to form the initial seal. In this paper, by combining the advantages of corrugated structure and NiTi alloy’s shape memory effect, a NiTi alloy corrugated gasket is proposed. Its mechanical properties were studied using experiments and the finite element method. The influences of geometric parameters on gasket performance were discussed. The results show that the shape memory effect can greatly improve the contact stress of gaskets. The corrugation can effectively reduce the pre-tightening force. The contact stress of NiTi alloy corrugated gasket is significantly affected by plate thickness, gasket height, and corrugation pitch and shows a high nonlinear characteristic. The proposed finite element method (FEM) and the gasket contact stress prediction model are accurate and engineering available.

Behaviour of flange joints in Steam Generator under thermal loads

Pressure vessels such as steam generators are subjected to high temperature, in addition to high pressure during the operating condition. Flanges and bolts are made up of different materials whose coefficient of thermal expansion varies. Usually, thermal expansion in bolts is greater than that of flanges. At elevated temperatures bolts expand more than that of flanges, resulting in decrease of compression in connected members achieved during assembly stage, which in turn decreases the contact stress in gasket. This can lead to leakage of internal fluid. The loss in gasket contact stress due to differential thermal expansion can be nullified by using sleeves of higher thermal expansion between the flange-nut and flange-bolt head interfaces. At higher temperatures sleeves expand more than bolts and flanges, pushing the flanges closer towards each other, thus decreasing gap created due to differential thermal expansion. The behaviour of gasketed blind flange joint with and without sleeves is analysed and the performances are compared under thermal loads. The non-linear behaviour of gaskets is included by specifying the loading and unloading characteristics with hysteresis.

Leakage Analysis on Non-axisymmetric Gasket of the Shelltube Heat Exchanger Header

This paper focuses the flanged static sealing structure of shell-tube heat exchange header, builds an static sealing model based on FEM(Finite Element Method),studies the effect of bolt preload and working medium load on the gasket actual contact stress. The results indicate that: an approximately linear relationship exists among the gasket contact stress, bolt preload and working medium load. When the pressure is gradually increasing, the flat end-plate’s outward convex deformation results in the decreasing gasket stress in the center and even leakage. After locating the above leakage reason, the flange gasket structure is improved, and the bolt distribution and bolt preload is adjusted accordingly. The problem of leakage has been solved, approves that the calculating method of gasket sealing is an effective approach.

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.

Development and application of the integrated sealant test apparatus for sealing gaskets in tunnel segmental joints

An innovative apparatus has been developed in this study to investigate the coupled leakage and mechanical behaviors of gasketed segmental joints, subjected to the field loading conditions during the construction and operation stages. The basic principles and detailed configurations of this newly developed test setup are presented in detail. The test apparatus can be used to accurately monitor the water leakage pressure of segmental joints under various combinations of joint openings and offsets. A series of test sets, based on different characteristics of sealing gaskets used in segmental joints, were subsequently conducted to evaluate the functionality of the test setup. Testing apparatus was designed to evaluate the waterproof capacity of the three types of segmental joints (i.e., longitudinal/circumferential joint and T-joint (intersection of longitudinal and circumferential joints)) in the Nanjing Weisan Rd. Tunnel. The tested segments were cast with the identical gasket groove details and flanks to the practical tunnel segments. The correlation between gasket contact stress and supplied water pressure was analyzed. Comparison of the gasket sealant and mechanical behavior showed that there existed a “correlated zone”. The results showed that gasket-gasket interface, gasket-concrete gasket groove interface, damaged zones, and frame corners were the potential places of leakage in segmental joints. Finally, the results demonstrated that local concrete damages around the groove flank could serve as a water leakage channel and reduced the sealant performance of gasket.

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.

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.

Sealing behavior of twin gasketed flange joints

Sealing performance of gasketed flange joints depends mainly on the behavior of gasket. In the present work, a three dimensional finite element analysis has been carried on a gasketed joint with single and twin gaskets having nonlinear material properties, to find the influence of gasket contact stress and sealing performance of the joint. Bolt preload required for safe operation of twin gasketed joints has been formulated by modifying the ASME code. A comparison is made on sealing performance of gasketed joint with single and twin gaskets. The contact pressure of twin gasketed joint is examined by varying the design parameters such as individual gasket widths and space between the gaskets. Contact pressure in single and twin gasketed flange joints at different operating conditions, viz., bolt preload and internal pressure have been investigated. It is observed that the flange joint with twin gasket can withstand higher internal pressure.

Finite Element Analysis of Bolted Flanged Joints Subjected to External Loads

Since external loads affect the sealing performance of bolted flanged joints, this paper calculated external loads of bolted flanged joints by using CAESAR II software and evaluated the effects of external loads on the sealing performance from the viewpoint of changes in contact gasket stress and flange rotation by using ANSYS software. The FE results showed that the contact gasket stress decreases a lot at the tension side and increases a little at the compression side. The paper also evaluated the stress distribution in bolted flanged joints subjected to external loads. The results suggested that the flange rotation and the overall stress increased compared with that of flange without external loads. External loads can induce unexpected leakage and strength failure of the bolted flanged joints during operation.

Tightness Assessment of Bolted Flange Connections Considering the Creep Effect of Gasket

The tightness of bolted flange connections is the important guarantee to meet the safety operation for a long period, the creep effect of gasket may affect the tightness of bolted flange connections under high temperature conditions due to its creep deformation. Considering the creep effect of metal flexible graphite composite gasket under high temperature, the deformation compatibility equation of bolted flange connection system was deduced. The time-dependence of flange rotation, the gasket deformation and the gasket contact stress were studied systematically. Moreover, the influencing factors of leakage rate were analyzed in detail. Finally, based on the theory of tightness, the safety assessment method due to leakage rate was constructed under high temperature. Results presented the gasket stress increases linearly from inside to outside and the gasket stress became lower and lower with the creep time extended. The time-dependent leakage rate of bolted flange connections was deduced, and the tightness assessment can be made conveniently according to the proposed method.

Application of Orthogonal Experimental Method in the Sealing Design of a Bolted Flange Connections

The paper aims to provide a theoretical method of multi-parameter optimization collocation for sealing structure design. Based on the tightness analysis method, the paper analyzed the effects of several major influence factors on the maximal gasket contact stress. Some sensitive parameters were chosen according to the tightness analysis results. Orthogonal experiment method was applied in the current work to find the optimum combination of parameters which will contribute to a better sealing performance of the connections. The theoretical way proposed in this paper can effectively shorten the design period and is helpful to improve the quality of the design and reduce the design cost.

Comparative study of bolt spacing formulas used in bolted joint designs

Bolted flange joints are the most popular type of connection between pressure vessels and piping equipment. They are very attractive type of connection because they are simple to mount and offer the possibility of disassembly. However, they are very complex structures to design and analyze and often result in leakage failure. One of the raisons is the loss of tightness that results from the uneven distribution of the gasket contact stresses in the radial and circumferential direction. Many factors contribute to such a failure; bolt load non-uniformity, inadequate flange to gasket stiffness, inappropriate bolt spacing requirements or a combinations of some of these.The variation of the contact stress in the circumferential direction between any two bolts is dictated by bolt spacing. This paper is an extension of the work in which the more accurate analytical solution based on the theory of circular beams resting on a linear elastic foundation is used to validate some existing flange bolt spacing formulas and in particular the TEMA formula, Robert's formula and the one recently developed by Koves. The relationship between bolt spacing and the gasket compression modulus, flange thickness and size is deduced from an analysis that considers a maximum tolerated gasket contact stress difference obtained at the bolt and between two bolts. Comparison between these different methods is also provided.

Development of a New Bolt Spacing Formula

Bolted flange joints are extensively used to connect pressure vessels and piping equipment together. They are simple structures that offer the possibility of disassembly. However, they often experience leakage problems due to a loss of tightness as a result of a nonuniform distribution of gasket contact stresses in the radial and circumferential directions. Many factors contribute to such a failure; the flange and gasket stiffness, bolt spacing or a combination of them are to name a few. In our recent papers, the effect of bolt spacing was investigated based on the theory of circular beams on linear elastic foundation and on the theory of rings on nonlinear elastic foundation. The variations of the contact stress between bolts were of a concern. This paper is an extension of the work in which an analytical solution, based on the theory of circular beams resting in a linear elastic foundation, has been developed to determine a formulae for flange bolt spacing. The relationship between bolt spacing, gasket compression modulus, and flange thickness is deduced from an analysis that considers a maximum tolerated gasket contact stress difference between any two bolts.

The effect of bolt tightening methods and sequence on the performance of gasketed bolted flange joint assembly

This paper presents results of the effect of different bolt tightening sequences and methods on the performance of gasketed bolted flange joint using nonlinear finite element analysis. Bolt preload scatter due to elastic interactions, flange stress variation and bolt bending due to flange rotation and gasket contact stress variation is difficult to eliminate in torque control method i.e. tightening one bolt at a time. Although stretch control method (tightening more than one bolt at time) eradicates the bolt preload scatter, flange stress variation is relatively high. Flange joint\'s performance is compared to establish relative merits and demerits of both the methods and different bolt tightening sequences.

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.

On the Use of Theory of Rings on Nonlinear Elastic Foundation to Study the Effect of Bolt Spacing in Bolted Flange Joints

Bolted flange joints are extensively used to connect pressure vessels and piping equipment together. They are simple structures that offer the possibility of disassembly. However, they often experience leakage problems due to a loss of tightness as a result of a nonuniform distribution of gasket contact stresses in the radial and circumferential direction. Many factors contribute to such a failure; the flange and gasket stiffness and bolt spacing design combination being one of them. In our recent paper, the effects of bolt spacing were investigated based on the theory of circular beams resting on a linear elastic foundation (Do, T. D., Bouzid, A. H., and Dao, T.-M., 2011, “Effect of Bolt Spacing on the Circumferential Distribution of Gasket Contact Stress in Bolted Flange Joints,” ASME J. Pressure Vessel Technol., 133 (4), 041205). This paper is an extension of the work in which an analytical solution based on the real nonlinear gasket behavior is developed. This study focuses on the distribution of the gasket contact stress of two large diameter flanges, namely, a 52 in. and a 120 in. heat exchanger (HE) flanges. The nonlinear gasket behavior solution is compared to the Finite Element Analysis (FEA) and the linear gasket behavior solution for evaluation and comparison.

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.

Prediction of Time-Correlated Leakage Rates of Bolted Flanged Connections by Considering the Maximum Gasket Contact Stress

The leakage rates of bolted flanged connections change with service time due to the gasket contact stress relaxation and degradation of gasket material. The nonuniform distribution of gasket contact stress has significant influence on the leakage behavior of the connections. In order to predict the time-correlated leakage rates accurately, both appropriate approaches to dealing with the gasket residual contact stress and a corresponding time-correlated leakage model of sealing elements are needed. In this paper, an analytical model has been developed to determine the maximum contact stress at gasket outer diameter in consideration of creeps of flanges, bolts and gasket coupled to the axial deformation compatibility equation. The analysis was verified against the finite element numerical simulation considering the nonlinear behavior of gasket and material creep. The analytical results of the maximum contact stress of gasket and its change over time compared well with those obtained by finite element method. A time-correlated leakage model of nonmetallic gasket sealing connections based on the porous medium theory was established, in which the effects of the gasket material degradation and contact stress relaxation on the sealing performance were taken into consideration. Furthermore, a leakage rate prediction method was proposed. Some long-term sealing performance tests were performed on two types of gaskets to obtain the coefficients in the leakage model. The leakage rate prediction method proposed in this paper was also validated against the experimental data presented by other researchers, and the errors between the predicted values and the experimental results were within 18%.