Flange Rotation Research Articles

On the Strength and Tightness of ASME B16.5 and B16.47 Series A Standard Flanges

Abstract ASME flanges are extensively used in the pressure vessels and piping industry. The origin of their class and size is not based on the amount of initial bolt load they can carry nor the level of tightness they can achieve. Their PV rating does not give an indication on the level of stress they are subject to and little is known on their ability to withstand the maximum bolt stress level they can be subjected to during initial bolt-up or under operation. The integrity and leak tightness of ASME B16.5 and B16.47 series A flanges made of SA105 material need to be analyzed individually in order to identify the flange classes and sizes that are more vulnerable to the bolt stress level. This paper proposes the use of an accurate analytical model to appropriately address the integrity and leakage tightness of the complex statically indeterminate weld neck standard flange connections based on the flexibility and the elastic interaction between the different joint elements. As such, the most critical standard flanges in terms of class and size will be identified in order to avoid failure. The model is first tested and validated using finite element method simulations on different sizes of class 900 flanges. The study investigates the effect of the initial bolt preload on parameters such as flange rotation and stresses in the flange, gaskets, and bolts. The most critical size and class flanges and their highly stressed locations will be revealed.

Stress Analysis of ASME Section X Flanges Using Classical Lamination Theory

AbstractThe increased usage of fiber reinforced plastic (FRP) composite pressure vessels and piping components in the past decades in the residential and industrial sectors is attributed to the FRP material resistance to corrosion and chemical attacks. FRP composite flanges are, however, known for their anisotropic behavior. In the ASME code section X, FRP composite flanges are treated using an analytical approach derived from that metallic flanges in addition to the fact that the geometries are made to fit them as much as possible and not designed independently. This is known to have caused structural flaws for certain FRP flange classes and sizes. Using a recently developed anisotropic FRP flange approach, it is proposed to identify the most critical flanges by analyzing the flange parameters such as flange ring rotation and stresses in their different parts; gasket, flange ring, hub, and shell subjected to pressure loading. The study on the strength of flanges described in ASME section X RD-620.1 table, will reveal the most critical size and class flanges and their highly stressed locations. To conduct such a study, the selected flange material is an E glass/Vinyl Ester laminate composite. The study shows that FRP flanges of classes 25 and 50 are most vulnerable and should comparatively be less loaded. The stresses are found to reach 50 MPa in the shell and 58 MPa in the flange ring while the maximum flange rotation is 0.83 deg.

A Method Based on the Principle of Critical Energy for Calculating Flange Joints

An analysis has been made of the behavior of flange joint components under initial stress loading (pre-clamping) and in service. There have been highlighted the drawbacks in calculating flange joints to be found in currently acknowledged methods that do not take into account: - the influence of the bending moment produced by the total hydrostatic end force on bolt strength and flange rotation; - the presence of cracks in the welding or in its thermal influence zone; - the residual stresses; � the relaxation of the sealing gasket over time. The calculation method proposed in the paper takes into account all these particularities of loading. Furthermore, alongside the strength calculation of bolts and flanges, a proposal has been put forth for the calculation of the flange joint leak-tightness.

Design and analysis of the flange-bolted joint with respect to required tightness and strength

Abstract The paper presents the method of design and strength analysis of the flange-gasketed-bolted joint. In the first part, analytical calculations were carried out. Their purpose was to determine the assembly torque of nuts to achieve the desired tightness. The flanged joint designated as DN100 PN40 with two different gaskets was taken into consideration. The analytical calculations were performed in accordance with the algorithm included in PN EN 1591-1. In the further step, the numerical calculations were carried out to support the analytical results. The outcome of these calculations were maps of the contact stress distribution on the gasket surface, estimation of safety factors of individual joint elements as well as determination of the flange rotation. Data from the numerical calculations were compared with the analytical results, which confirmed their satisfactory compliance. In the last stage, the experimental tests of the joint were carried out. The main results of the test were the measured values of the leakage level, tightening force of the bolt and estimated safety factors. An indirect result of the experimental measurements were maps of the stress distribution on the contact surface of the gasket, which were determined by means of the measuring film. Ultimately, based on the experimental results, it was found that the proposed analytical method of calculation and simulation of the joint by means of the finite element method was a very good tool for the design of the joint at the required tightness level.

Pretightening Range of Flange Joints in Pipeline Considering Nonlinear Compression Resilience of Gaskets

AbstractThe analytical pretightening force range of flange joints in a pipeline was deduced based on the allowable gasket stress and flange rotation angle considering the nonlinear compression resi...

Hysteretic behavior and simplified simulation method of high-strength steel end-plate connections under cyclic loading

In this study, an experiment with four high-strength steel (HSS) end-plate connections was conducted. Compared with mild steel end-plate connections, the pinching effect of HSS end-plate connections is more obvious. Based on the comparison between the experiment results and the results of EC3 formulae, the requirement in EC3 could not be directly used in the design of the HSS end-plate connection. Given that the resistance and the prying forces of the idealized HSS T-stub are usually larger than that of mild steel T-stub, the effect of the bolt bending deformation and the beam flange rotation on the connection behavior of HSS end-plate connections could not be neglected. Hence, considering the aforementioned factors, the traditional multilinear model was modified in this study. Then, based on the modified multilinear model and the experiment result, a simplified hysteresis model was introduced to simulate the hysteresis properties of HSS end-plate connections. A validation was performed to prove that the modified multilinear model and the simplified hysteresis model can be used to predict the connection behavior of the HSS end-plate connection under cyclic loading. Furthermore, similar with the HSS T-stub, there are cracks in the heat-affected zone (HAZ) of the weld between the end plate and the beam. To investigate the damage accumulation and cracking problem of the HSS end-plate connection, a weighted value β determined by the experiment results and an ultimate plastic strain of HAZ were introduced in the damage cumulative model.

The Analysis of Bolted Flange Joints under Internal Pressure at High Temperature

Working temperature, internal pressure and the creep of bolted flange joints are the direct factors that influencing the gasket stress of bolted flange joints, the tightness of the whole system will be reduced because of these factors. thus the security level of bolted flange connection will be affected. In this paper, the deformation coordination equation of bolted flange connection system, the gasket compressive and resilient performance, as well as the gasket creep equation are combined to study the effect of internal pressure on bolted flange connections under a certain bolt preload and operating temperature, the equation about the relationship of the gasket force and internal pressure is simplified, and the main objective of the work is the calculation of the time-correlated gasket force, flange rotation and gasket unloading deformation under the different internal pressure. The results show that when the internal pressure is greater, the gasket force is smaller, on the contrary, the leakage rate are greater. Through the relevant conditions, in a period of the safe operation time, the maximum working internal pressure is got when reaching the condition of corresponding level of tightness.

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.

Behavior of bolted joints with metal-to-metal contact type gaskets under bolting-up and loading conditions

A floating-type joint applies the entire bolt load to the gasket to generate sealing contact stress, and is prone to leak due to the bolt load loss. Different with the floating type one, a metal-to-metal contact type joint applies only part of the bolt load to the gasket to achieve seating stress, and applies the additional bolt load to the metal-to-metal contact to compensate for the unloading effects due to internal and external loadings. Due to this advantage, metal-to-metal contact type joints are gradually used in chemical industries, nuclear power industries, etc. A flange joint together with a metal-to-metal contact type gasket forms the metal-to-metal contact type joint studied in this article. A three-dimensional nonlinear finite element model is developed to highlight the complex behavior of the flange joint under bolting-up, pressure loading and thermal loading conditions. Despite the common perception that gasket stress in a metal-to-metal contact type joint stays constant, reduced gasket stress is concluded due to flange rotation and joint thermal expansion.

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.

Effect of Growth Pressure and Gas-Phase Chemistry on the Optical Quality of InGaN/GaN Multi-Quantum Wells

ABSTRACTBlue light-emitting diodes (LED's), utilizing InGaN-based multi-quantum well (MQW) active regions deposited by organometallic chemical vapor epitaxy (OMVPE), are one of the fundamental building-blocks for current solid-state lighting applications. Studies [1,2] have previously been conducted to explore the optical and physical properties of the active MQW's over a variety of different OMVPE growth conditions. However, the conclusions of these papers have often been contradictory, possibly due to a limited data set or lack of understanding of the fundamental fluid dynamics and gas-phase chemistry that occurs during the deposition process.Multi-quantum well structures grown over a range of pressures from typical low-pressure production processes at 200 Torr, up to near-atmospheric growth conditions at 700 Torr, have been investigated in this study. At all growth pressures, clear trends of gas-phase chemical reactions are observed for increased gas residence times (lower gas speeds from the injector flange and lower rotation rates) and increased V/III ratios (higher NH3 flows).Confocal microscopy, excitation-dependent PL (PLE), and time-resolved photo-luminescence (TRPL) have been employed on these MQW structures to investigate the carrier lifetime characteristics. Confocal emission images show spatially-separated bright and dark regions. The bright regions are red-shifted in wavelength relative to the dark regions, suggesting microscopic spatial localization of high indium content regions. As the growth pressure and gas residence times are reduced, a larger difference in band-gap between bright and dark regions, longer lifetimes, and higher average PL intensities can be obtained, indicating that higher optical quality material can be realized. Optimized MQW's grown at high pressure exhibit higher PLE slope intensities and IQE characteristics than lower pressure samples. Results on simple LED structures indicate that the improvement in MQW optical quality at high pressures translates to higher output power at a 110 A/cm2 injection current density.

Application of Plastic Region Bolt Tightening Method to Larger Flange Connections

The plastic region bolt tightening method has been applied to the smaller pipe flange connections and its advantages had been demonstrated. The scatter in axial bolt forces for the smaller pipe flange connections which applied the plastic region bolt tightening method was minimal and it was effective for the leak prevention. In addition it is possible that the bolt diameter is downsized due to an obtainment of the higher axial bolt forces. However, the behavior of the larger flange connections has not been investigated. The flange rotation of larger flanges increases when the internal pressure is applied. In addition, the gasket stress is not uniform and it may cause the leak accident. It is necessary to investigate the behavior of the larger flange connections. The present paper describes the behavior of the larger flange connections under the plastic region bolt tightening. Firstly, JPI 20-inch flange connections tightened to the plastic region by downsized bolt and superiority in the uniformity in the axial bolt forces is demonstrated. And then, the internal pressure is applied to the flange connections and the behavior of the additional axial bolt force is demonstrated. The axial bolt force decreases with an increase in the internal pressure, and the load factor is negative due to increase of the flange rotation. However, the load factor of flange connections tightened to the plastic region by using downsized bolt approached zero. Downsizing of the bolt acts on advantageously for the larger flange connections whose load factor is negative and it is effective to the leakage prevention. Moreover, the leak rate from the flange connections is measured and sufficient sealing performance is obtained.

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.

Comparative Modal Analysis of Gasketed and Nongasketed Bolted Flanged Pipe Joints: FEA Approach

It is widely known that resonance can quickly lead to failure in vibrating bolted flanged pipe joints. Condition monitoring is performed time to time in some industries for smooth operation of a system, whereas mostly trial-and-error tests are performed to control vibration. During all this process, the inherent design problems are not considered. A bolted flange joint in piping system is not a simple problem, being the combination of flange, gasket, bolts, and washers. The success of a bolted flanged pipe joint is defined by the “static mode of load” in the joint. However, it has been recognized that a “dynamic mode of load” governs in a gasketed bolted flanged pipe joint, which leads to its failure due to flange rotation, providing flange yielding, fatigue of bolts, and gasket crushing. This paper presents results of detailed 3D finite element and mathematical modal analysis under bolt up to determine natural frequencies and mode shapes of gasketed flanged joints with and without raised face in comparison to the nongasketed flange joint.

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.

A New Approach to Model Bolted Flange Joints With Full Face Gaskets

The poor leakage performance of flanges with full face gaskets is attributed to the low reliability of the existing design methods, and in particular, their lack of assessing accurately the bolt and gasket load changes. The prediction of tightness of bolted joints relies very much on the level of precision of the gasket contact stress during operation. The accurate evaluation of this stress requires a flexibility analysis of the joint that includes the flange, gasket, and bolts, and the interaction between them. This paper analyzes the distribution of gasket stress and the load change in bolted joints with full face gaskets. It proposes a simple analytical approach capable of predicting flange rotation and bolt load change during operation. The method is based on the gasket-bolt-flange elastic interaction, including flange rotational flexibility. The proposed model is supported by comparison with numerical finite element analysis of different size flanges.

Analytical Modeling of Flat Face Flanges With Metal-to-Metal Contact Beyond the Bolt Circle

Design rules for flat face flanges with metal-to-metal contact beyond the bolt circle are covered by Appendix Y of the American Society of Mechanical Engineers Code. These design rules are based on Schneider’s work (1968, “Flat Faces Flanges With Metal-to-Metal Contact Beyond the Bolt Circle,” ASME J. Eng. Power, 90(1), pp. 82–88). The prediction of tightness of these bolted joints relies very much on the level of precision of the self-sealing gasket compression during operation. The evaluation of this compression requires a rigorous flexibility analysis of the joint including bolt-flange elastic interaction. This paper analyses flange separation and the bolt load change in flat face bolted joints. It proposes two different analytical approaches capable of predicting flange rotation and bolt load change during operation. The first method is based on the beam theory applied to a continuous flange sector. This approach is an improvement of the discrete beam theory used in the Schneider model. The second method is based on the circular plate theory and is developed for the purpose of a more accurate assessment of the load changes. As in the Taylor Forge method, this approach is, in general, better suited than the beam theory for flat face flanges, in particular when the flange width is small. The proposed models are compared with the discrete beam theory and validated using numerical finite element analysis on different flange sizes.

Modeling of through-thickness stress state in adhesive joints connecting pultruded FRP bridge decks and steel girders

The through-thickness performance of adhesive joints connecting pultruded FRP bridge decks and steel girders subjected to loading in the transverse bridge direction was investigated. Deck-to-girder adhesive joints can be assumed as being loaded by uplift forces only (and not by additional bending moments) if the adhesive layer has a minimal thickness of approximately 10 mm. If possible, however, steel web stiffeners should not be connected to the upper flange in order to allow free flange rotation. The tensile stress distribution in the adhesive joint is non-uniform with high stress concentrations below the FRP webs of the cellular deck and above the steel girder web. Alternately inclined deck webs cause significantly higher stresses below the vertical webs. An analytical model allowing the calculation of a representative approximation of the complex uplift stress state in the joint is proposed and validated by numerical and experimental results. Based on this model, a design method for adhesive joints connecting FRP decks and steel main girders can be established.

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.