Gasketed Flange Joint Research Articles

Investigation of Sealing Performance with Bolted Flange Joints with Gasket using FEA Method

In pressure vessel and pipe systems, gasketed flange joints are quite frequent and are also used in oil and gas wellheads and trees as spool end connections. Flanges are most commonly employed when a joining or disassembling junction is required. The process industry has long been concerned about leakage in gasketed flanged junctions. The installation and stress factors of a gasketed flange joint directly affect its sealing effectiveness. API 6A type 6B flange with a maximum pressure rating of 20,000 psi is examined in this study using API design procedures. Due to the symmetricity of the 8 bolted flange, a 45 section is taken for analysis. The findings of a parametric analysis of flange behaviour and bolt stresses are investigated by altering the bolt preload and internal pressure while keeping other flange independent variables constant.

Methodology of Leakage Prediction in Gasketed Flange Joints at Pipeline Deformations.

The paper presents the proposal of a leakage prediction method in flange joints, after pipeline deformation, based on FEM (Finite Element Methods). The stages of developing the design are discussed, and a complex, multi-stage method of applying the loads is presented in detail. Moreover, the gasket material data obtained in experiments were used. The paper also presents the results of calculations on a non-uniform stress distribution in the radial direction of the gasket. In addition, it has been shown that the deflection of the pipeline with a minor displacement causes an increase in the diversification of the circumferential pressure of the gasket, and also has a significant influence on the determination of the actual state of stress to which the gasket is subject. Moreover, it was found that the distribution of contact pressure on the deflection of the pipeline has a significant influence on the level of leakage. The results of tests are compared to the results of the numerical calculations of the stress in bolts. By comparing the bolt tension changes obtained by numerical and experiment analyses, it has been shown that the assumptions made in developing the numerical model are correct.

Stress distribution and performance of threaded bolts in gasketed flange joints

AbstractThe performance of the flange joint depends on the relaxation of load in bolts. This in turn affects the gasket stress and control of leakage. A finite element model of flange joint with threaded bolt‐nut fastener having zero helix angle is developed and analyzed for stress distribution in the threaded bolt. The stress concentration factor at the thread root region is observed to be non‐uniform along the circumference due to the bending behavior of the bolt in the flange joint. The maximum stress is observed in the first engaged thread. The variation in bolt load due to internal fluid, thermal and external loads are also investigated for both single and twin‐gaskets (two concentric half‐sized single gaskets). The gasket material and gasket configuration are observed to be potential factors causing variation in the distribution of load in the flange joint. In a flange joint subjected to external bending load, the maximum stress concentration in the bolt is observed to be in the first thread, instead of the first engaged thread. Under external bending load, the flange joint loses its structural integrity before the traces of leakage occur in the joint.

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.

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.

Studies on joint strength and sealing behavior of single and twin-gasketed flange joints

Leakage is the main mode of failure in gasketed flange joints used in nuclear and thermal power plants. The leakage occurs when the joint is not able to withstand the internal fluid pressure. To evaluate the leakage behavior of gasketed flange joint, it is important to incorporate gasket properties and interfacial contact behavior due to friction. However, for safe joint operation, the members also should be structurally sound without exceeding allowable limit of materials. In this study, the joint strength and sealing behavior of gasketed flange joint are investigated through experiments by carrying out leakage test. The joint strength is evaluated based on strains developed in flanges along longitudinal and tangential direction under both pretightening and pressurizing stages. Three-dimensional finite element simulation is also performed under both aforesaid stages, considering the nonlinear properties of gasket along with hysteresis during unloading. The finite element results of joint strength and leakage pressure are compared with experimental values and observed to be conservative. In addition, the performance of twin gaskets (two gaskets concentric to each other) through both experiment and simulation is also evaluated and compared with that of the single gasket. From the experiment and finite element analysis, it is found that the sealability of twin-gasketed joint is higher than that of single-gasketed joint.

Behavior of gasketed bolted pipe flange joint under combined internal pressure, axial, and bending load: Three-dimensional numerical study

Optimized performance of joint is categorized by its “structural integrity” and “sealing capability”. In literature, limited data are available regarding the performance of gasketed bolted flanged joint under combined internal and external loading; hence an optimized joint performance cannot be addressed. In this paper, a detailed three-dimensional nonlinear finite element analysis of bolted gasketed flange joint is performed, to study its performance under combined internal (pressure) and external (axial and bending) load. Results of the finite element analysis are compared with the experimental results available in literature providing the validation of the numerical approach developed.

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.

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.

Studies on gasketed flange joints under bending with anisotropic Hill plasticity model for gasket

The behavior of a gasketed flange joint under bending loads has been studied by three dimensional finite element analysis (FEA) and experiments. The in-plane and bending stiffness of spiral wound gaskets are considered using anisotropic Hill plasticity material model. The variation in bolt axial force of joints under bending load predicted by the finite element analysis compares well with the experimental results. The contact stress distribution obtained have significant variation in the pattern from the previous material models and consistent with the results of Bouzid [1] regarding flange rotation.

PERFORMANCE TESTING OF A GASKETED BOLTED FLANGE PIPE JOINT UNDER COMBINED PRESSURE AND THERMAL LOADING

From detailed experiments, the sealing performance of the ANSI 4 inch, Class 900# gasketed flange joint tightened to the target torque of 700 Nm applied according to ASME guidelines under combined pressure of 14 MPa and temperature of 100°C is concluded.

Relaxation behaviour of gasketed joints during assembly using finite element analysis

Gasketed bolted flange pipe joints are always prone to leakage during operating conditions. Therefore, performance of a gasketed flange joint is very much dependent on the proper joint assembly with proper gasket, proper gasket seating stress and proper pre-loading in the bolts of a joint. For a gasketed flange joint, the two main concerns are the joint strength and the sealing capability. To investigate these, a detailed three-dimensional nonlinear finite element analysis of a gasketed joint is carried out using gasket as a solid plate. Bolt scatter, bolt bending and bolt relaxation are concluded as the main factors affecting the joint’s performance. In addition, the importance of proper bolt tightening sequence, number of passes influence of elastic and elasto-plastic material modelling on joint performance are also presented. A dynamic mode in a gasketed joint is concluded, which is the main reason for its failure.

Performance testing of gasketed flange joint under combined loading

This technical note presents joint strength and sealing capability of a gasketed flange joint using extensive experimental studies with different load combinations. Actual joint load capacity is determined under both the design and proof test pressure with maximum additional external loading (axial and bending) that can be applied for safe joint performance. In addition, application of combined load is also discussed in the light of equivalent pressure approach.

Bolt preload scatter and relaxation behaviour during tightening a 4 in-900# flange joint with spiral wound gasket

Gasketed bolted flange pipe joints are found prone to leakage during operating conditions. Therefore, performance of a gasketed flange joint is highly dependent on the proper joint assembly with proper gasket, proper gasket seating stress, and proper preloading in the bolts of a joint. For a gasketed flange joint, the two main concerns are the joint strength and the sealing capability. To investigate these, a detailed three-dimensional non-linear finite-element analysis (FEA) of a gasketed joint is carried out using a spiral wound gasket. FEA results are compared with the experimental results and are found to be in good agreement, hence validating the FE model developed. Bolt scatter, bolt bending, and bolt relaxation are considered to be the main factors affecting the joint performance. In addition, the importance of proper bolt tightening sequence and number of passes and the influence of elastic and elasto-plastic material modelling on joint performance are also presented. Stress variation in the flange due to flange rotation highlighted joint strength, and gasket contact/seating stress variation highlighted the sealing performance during bolt up. Modelling the non-linearity of the spiral wound gasket using non-linear elements highlights reduced joint strength and sealing performance. Summarizing, a dynamic mode in a gasketed joint is concluded, which is the main reason for its failure.

Determination of optimized non-gasketed flange geometry for safe stress and no leak condition: Finite-element analysis approach

Performance of a flange joint is characterized mainly due to its ‘strength’ and ‘sealing capability’. Available design rules for flange joints are mainly concerned with the strength of the flanges and do not sufficiently consider for their sealing. Being continuous problems faced by the gasketed flange joints for strength and sealing based on concluded ‘dynamic mode of load’, non-gasketed joints are recommended as an alternative. The current paper presents three-dimensional non-linear finite-element analysis of non-gasketed flange joint with different flange surface profiles (positive taper, negative taper, and zero taper angles) to find out the most optimal flange geometry for safe stress and no-leak conditions under bolt up and internal pressure loading. Based on the results, optimum flange geometry is selected and further analysed under proof test pressure. A ‘static mode of load’ in positive taper angle flange is concluded, ensuring proper joint sealing, and strength.

A study on the sealing performance of flange joints with gaskets under external bending using finite-element analysis

The effect of external bending on flange joints in pipelines, pressure vessels, and pressure vessel nozzles is significant and difficult to assess. In the current work, the sealing performance of a gasketed flange joint under external bending has been studied by using a three-dimensional finite element analysis, considering the non-linear material behaviour of the gaskets. Spiral wound gaskets and non-metallic gaskets with various sealing materials are considered. Results show that the allowable bending moment on a flange joint depends on the tightness required, type of gasket, and its deformation characteristics. Gaskets with elastomeric sealing materials show good performance against leakage under external bending.

Three-Dimensional Nonlinear Finite-Element Analysis of Gasketed Flange Joint under Combined Internal Pressure and Variable Temperatures

Performance of a flange joint is characterized mainly due to its and capabilit. A number of analytical and experimental studies have been conducted to study these characteristics only under internal pressure loading. The effect of steady state thermal loading is a well recognized problem and makes the problem more complex under combined application of internal pressure and temperature. To investigate fundamental joint characteristics, joint strength and sealing capability under combined internal pressure, and variable steady state thermal loading, a three-dimensional nonlinear finite-element analysis of gasketed flange joint is carried out using ANSYS commercial software. Reduced joint strength is concluded due to the flange rotation resulting in flange yielding under bolt up and applied operating conditions. Reduced joint sealing is concluded due to the variation in gasket seating or contact pressure due to bolt load variation. Flange rotation, bolt bending, and joint relaxation concluded fatigue and dynamic behavior in the gasketed joint. These effects are observed to be more pronounced at higher temperatures. Verification of finite-element model with available classical theories is also performed and discussed.

Design for Leakage in Flange Joints Under External Loads

This paper uses an analytical model based on the Pressure Vessel Research Council (PVRC) ROTT test gasket constants to compute leakage in gasketed flange joints subjected to internal pressure and external bending moments. The model results are compared to test data, and design recommendations are made, consistent with the ASME∕PVRC tightness-based methodology.

Determination of safe operating conditions for gasketed flange joint under combined internal pressure and temperature: A finite element approach

Performance of a flange joint is characterised mainly by its ‘strength’ and ‘sealing capability’. A number of analytical and experimental studies have been conducted to study these characteristics under internal pressure loading. However, with the advent of new technological trends for high temperature and pressure applications, an increased demand for analysis is recognized. The effect of steady-state thermal loading makes the problem more complex as it leads to combined application of internal pressure and temperature. The present design codes do not address the effects of temperature on the structural integrity and sealing ability. In addition, the available design solutions do not solve problems of failure of a gasketed flange joint even under bolt up and internal pressure loading conditions. To investigate joint strength and sealing capability under combined internal pressure and different steady-state thermal loading, a 3D nonlinear finite element analysis (FEA) of a gasketed flange joint is carried out and its behaviour is discussed. To determine the safe operating conditions or the actual joint load capacity, the joint is further analyzed for different internal pressures keeping the temperature constant.

Comparative study of the behaviour of conventional gasketed and compact non-gasketed flanged pipe joints under bolt up and operating conditions

Bolted flanged joints comprise an assembly of a number of important individual components, which are required to perform well together in service. The ideal requirement for a bolted flange joint is a ‘zero-leak’ condition. However, whilst recommended design procedures for bolted flange joints are available in international codes and standards, leakage problems are still faced by industry. These are common in both normal operating (internal pressure loading) and critical event conditions. The drive is, therefore, to find a flange joint assembly, which provides ‘zero-leak condition’ and requires little or no maintenance and handling. Considerable investigation in the area of optimised bolted joints has been in progress for the past 10 years comparing traditional gasketed joints and ‘compact non-gasketed’ joints, using both analytical and experimental approaches. In this present study, two-dimensional non-linear finite element studies have been performed for both gasketed and non-gasketed bolted flange pipe joints. Based on the stress results for the flange and the bolt and the flange rotation/displacement, compact non-gasketed flange joints are shown to be a viable and preferable alternative to the conventional gasketed flange joints. Recommendations are made for a best-fit flange model for static load conditions with ‘zero-leak’ sealing in a flange joint.