Bolted Flange Joints Research Articles

Bolted flange joints equipped with FBG sensors in industrial piping systems subjected to seismic loads

The vulnerability of major-hazard industrial plants to natural hazards has been recognized as an emergent issue whose importance is underlined by the Sendai Framework, established immediately after the Tohoku earthquake of 2011, in Japan. Hence, seismic risk analysis is of paramount importance as testified by the intense research activity that characterized the last years. In this respect, structural health monitoring can represent a valuable tool able to strongly help the decision-making phase. Along this main vein, optical fibers (OFs) represent a class of sensors able to both monitor critical conditions, as leakage of hazardous material, and activate safety barriers, if any. More precisely, optical fibers represent an economic solution, whose characteristics appear particularly suitable for dangerous environments like major-hazard plants. However, investigations relevant to their use for seismic monitoring of chemical/petrochemical plants are rather limited, especially when subject to strong dynamic excitations. As a result, this paper deals with the analysis of optical fiber Bragg gratings (FBGs) applied to bolted flange joints (BFJ) under cyclic loadings. More precisely, two experimental programs, i.e., a cyclic test on a single BFJ and a series of shaking table tests on BFJs of a multicomponent system, demonstrated the effectiveness of the proposed monitoring systems in detecting hazardous conditions and, thus, their potential use in conjunction with safety barriers.

Numerical and experimental study of electromagnetic induction heating process for bolted flange joints

As a promising metalwork processing technology, electromagnetic induction heating (EMIH) method has been applied in dealing with bolted flange joints in turbomachinery. In this study, a 3-D finite element model of electromagnetic induction heating system for the bolted flange joint is established, and the specific governing equations are derived based on Maxwell’s principle. The alternately-coupled magneto-thermal analysis is carried out considering temperature-dependent material properties to obtain the temperature distribution, followed with the uncoupled thermal-mechanical analysis to acquire the axial stress and deformation in EMIH process. The magnetic induction intensity mainly concentrates at the inner wall region, attenuates seriously along the radial direction, and reduces to almost zero at the outer wall. Due to the skin effect, the heat transfers radially and axially outward, indicating a diamondlike-shaped development from the center to the surrounding region. The axial stress with and without initial pretension are also discussed respectively. Then the corresponding experiments are introduced and carried out to validate the reliability of numerical simulation results. By comparing the results of the center point of inner surface and outer surface, the numerical simulation is proved reliable with a 5∼10% reasonable deviation. Further, the induction heating process has been improved through the optimization method based on pattern search algorithm. By adopting the stepped input current density optimized in the study, the optimal thermal stress tends to be constant and the final heating time reduces by 20.5% in the safe range of stress.

A METHOD TO REDUCE THE NUMBER OF ASSEMBLY TIGHTENING PASSES IN BOLTED FLANGE JOINTS

Abstract Bolted flange joints are extensively used in the pressure vessels and piping equipment and rotating machinery. Achieving a uniform bolt preload during the assembly process is particularly important to satisfy in bolted flange connection of oil and gas and fossil and nuclear applications. However, it is a very difficult task when tightening all bolts one by one due to elastic interaction. The risk of leakage failure under service loading is consequently increased because of the scatter of the bolt preload. This paper takes the advantage of a developed analytical model based on the theory of circular beams on linear elastic foundation that simulate the elastic interaction of bolted flange joints to reduce the number of passes while achieving bolt load uniformity. As such, a novel methodology for the optimization of the tightening sequence strategies is suggested to obtain uniform bolt tension while avoiding yield under minimum tightening passes. In this regards, based on the target preload, the load applied to each bolt in each pass is suggested. The developed approach is validated both numerically using FEM (finite element method) and experimentally on a NPS 4 class 900 welding neck flange joint using the criss-cross tightening and sequential patterns.

Measured and investigated nonlinear dynamics parameters on bolted flange joints of combined rotor

The complex micro-slip phenomenon of the contact interface will lead to the nonlinear stiffness of the connection structure, as well as the structural damping and energy dissipation. As the most important connection structure of the combination rotor, the mechanical properties of bolted flange joint interface are needed in the dynamic analysis of the combined rotor. Therefore, it is urgent to model and test the friction contact interface in the nonlinear dynamic analysis of rotor. In this paper, two sets of mechanical characteristics test system were built to test the dynamic parameters of tangential and bending directions of the bolted flange joint interface. Then, the mechanical behavior and the change regularities of dynamics parameters were studied under different external excitation, bolt distribution and tightening torque. The results show that once the bolt preload is above the rated torque, stiffness softening behavior is not significant; and then the tangential stiffness of the joint interface tends to be stable, with the variation range of 8.08∼8.96e8 N/m; the equivalent bending stiffness coefficient is about 3.38∼3.83e6 N·m/rad. With the decrease of bolt preload, the external excitation and the number of bolts have a significant effect on the stiffness reduction of the joint. Finally, the change interval of the dynamics parameters of the interface obtained by the experiment provide basis for the uncertainty dynamic analysis and optimization of the rotor.

Dynamic modelling and vibration characteristics analysis for the bolted joint with spigot in the rotor system

The bolted flange joints with spigot (short for bolted joints) are widely used in the rotor system of aero-engine. The current models of the bolted joint usually ignore the spigot, therefore cannot account for the effect of spigot on joint's mechanical characteristics. In this paper, a new analytical model of bolted joint is proposed to describe its nonlinearity under bending moment. The model takes into account the sticking and sliding statuses of spigot by introducing a Jenkins element, therefore is able to describe the joint's damping effectively. By performing a comparison study with the finite contact element model, the accuracy of the proposed model is validated. Meantime, the comparison study highlights the important role of spigot on the hysteresis nonlinearity of the bolted joint. After that, a dynamical model of the bolted rotor is developed, in which the proposed bolted joint model is introduced by considering the influence of rotor's whirl motion. Based on the dynamical model, the dynamic characteristics of the bolted rotor are investigated in detail. The results show that the bolted joint mainly produces stiffness loss and damping nonlinearity into the rotor system. The stiffness loss occurs in any loading conditions and leads to a decrease of the rotor's critical speed. While the damping nonlinearity is mainly excited under large unbalance, it may induce a self-excited components in rotor's response at super-critical speed. The influence of the bolted joint on rotor dynamics can be reduced by decreasing flange length, friction coefficient and interference fit of the spigot.

Axial compression behaviour of bolted-flange composite column–column connection

Reliable column–column connection contributes to a reduction in waste materials and enables structures to be demountable after their service life. This paper demonstrates the feasibility of using a bolted-flange connection with concrete-filled steel tube (CFST) columns subjected to axial compression load. Compression capacity, ductility, axial stiffness and toughness, as well as failure modes are discussed. The specimens are grouped into two categories: group I—connection without stiffeners and group II—connections supported by stiffeners. Three thicknesses of 2, 4 and 6 mm were used to manufacture the bolted flanges and stiffeners. The results showed that the proposed connection was effective to avoid a reduction in compression capacity. The various thicknesses of bolted flanges in group I specimens had a slight influence on the axial stiffness value and that influence was doubled in group II specimens. The stiffeners played a significant role in the toughness value and this was reduced with a reduction in the thickness of the stiffeners. In addition, an improvement in ductility was noticeable in stiffened specimens. Consequently, it can be inferred that bolted-flange joints have the potential to produce reliable and economical designs for CFST columns.

Influence of Structural Parameters of Shape Memory Alloy Corrugated Gaskets on the Contact Pressure of Bolted Flange Joints

Shape memory alloy corrugated gaskets (SMA‐CGs) can adapt to fluctuating working conditions due to their pseudoelasticity (PE) and shape memory effect (SME), which make them excellent sealing components. In this study, the deformation mechanism of SMA‐CGs was examined according to their structural properties under installation and operating conditions to establish an SMA‐CG thermal‐mechanical coupling model with the finite element analysis (FEA) method, which has been verified through experimentation. Based on this, a thermal‐mechanical coupling FEA model was built for a bolted flange joint with SMA‐CG. The influence of the SMA‐CG structure parameters on compression‐rebound mechanical properties was also studied under installation and operating conditions. The conclusions are as follows: a thermal‐mechanical coupling finite element analysis method was established for NiTi alloy corrugated structures. Through comparison with the experimental results, the maximum error of the maximum compression load was 5.78%, the maximum error of the rebound rate was 8.85%, and the maximum error of the maximum compaction force in the heat recovery stage was 12.2%, all of which were within the <15% acceptable error range of engineering fields. According to the related experiments and finite element results, the maximum compressive force of gasket thermal recovery after unloading was not less than 40% of the initial maximum compressive load. The application of shape memory alloy to corrugated gasket significantly improved its ability in coping with fluctuating load temperatures. The contact pressure of corrugation increased with the increase of sheet thickness (T) and corrugated gasket height (H) under installation and operating conditions, showing a decreasing trend with the increase of pitch (P), of which the order of factors influencing the average contact pressure of corrugated gasket was sheet T > H > P, and when structural parameters of SMA‐CG were T = 0.6 mm, H = 4 mm, and P = 2.5 mm, the contact pressure of corrugated gasket was the highest under operating conditions.

An equivalent model of a nonlinear bolted flange joint

The dynamic response of individual components in an assembled structure shows high accuracy compared to experimental measurements of the system response. However, when it comes to assemblies, the conventional linear approaches fail to deliver good accuracy, due to the uncertain linear and nonlinear mechanisms in the contact interface of the joints. Therefore, the inherent dynamics of the contact interfaces needs to be considered in modeling assembled structures. In this paper the prediction of the nonlinear dynamic response in a bolted flange joint was obtained in two ways. First, a 3D detailed finite element model capable of representing the micro-slip mechanism was made using a quasi-static time stepping analysis. The linear characteristics and nonlinear mechanisms developing in the contact interface of a bolted joint are investigated by using the 3D detailed model. Moreover, the natural frequencies of the assembled structure (representing the linear response) and the micro-slip behavior in terms of hysteresis loops (representing the nonlinear response) are obtained using the detailed model. Second, an equivalent model composed of beam elements and an appropriate joint model is then constructed for the assembled structure. An identification approach is proposed, and the parameters of the joint model are identified using both linear and nonlinear characteristics, i.e. natural frequencies and hysteresis loops. Comparing the hysteresis loops obtained from the detailed and equivalent models verifies the accuracy of the joint model used to represent the contact interface and the identification approach proposed for parameter quantification.

A numerical investigation of the sealing performance and the strength of a raised face metallic bolted flange joint

The development of leakage and strength of a metallic bolted flange joint are investigated in this work. Finite element analyses in 2D and 3D have been developed using ANSYS to study a steel flange and bolt with an aluminium gasket. The pressure-penetration criterion (PPNC) in ANSYS has been used to model fluid leakage propagation between the flange and the gasket. Validation was performed with a benchmark test, using published study of a bolted metallic flange joint; the agreement between the results is excellent. Results showed that the finite element method using PPNC is a good method to study leakage behaviour compared to other methods, which are relatively time-consuming and expensive. The influence of the flange dimensions on the maximum stresses and leakage propagation has been investigated in this study. Furthermore, the agreement between the 3D and axisymmetric 2D FEA models is very good, so the latter can be used to save computational time. This study was undertaken as a preliminary to a larger project about bolted flange joints made of composite materials.

Analytical modeling of FRP hubbed flanges

In spite of the increasing use of FRP composites in bolted flange joints and the good knowledge of these structures and their material behavior the procedure used for their design is that of metallic flanges. There is a major concern to appropriately address the anisotropic behavior of composite materials in FRP flange design. Therefore, it is necessary to revisit this procedure by implementing a more suitable model to analyse the stresses and strains of FRP bolted flange joints.This paper presents an analytical model that treats FRP bolted flange joints integrity and tightness based on anisotropy and a flexibility analysis of all joint elements including the gasket, bolts and flanges. The theories that treats all parts of the flange are described in details. Finally, the developed analytical model is validated with experimental testing and numerical modeling of different size FRP flanges.

Seismic Vulnerability Analysis of a Coupled Tank-Piping System by Means of Hybrid Simulation and Acoustic Emission

In order to shed light on the seismic response of complex industrial plants, advanced finite element models should take into account both multicomponents and relevant coupling effects. These models are usually computationally expensive and rely on significant computational resources. Moreover, the relationships between seismic action, system response and relevant damage levels are often characterized by a high level of nonlinearity, which requires a solid background of experimental data. Vulnerability and reliability analyses both depend on the adoption of a significant number of seismic waveforms that are generally not available when seismic risk evaluation is strictly site-specific. In addition, detection of most vulnerable components, i.e., pipe bends and welding points, is an important step to prevent leakage events. In order to handle these issues, a methodology based on a stochastic seismic ground motion model, hybrid simulation and acoustic emission is presented in this paper. The seismic model is able to generate synthetic ground motions coherent with site-specific analysis. In greater detail, the system is composed of a steel slender tank, i.e., the numerical substructure, and a piping network connected through a bolted flange joint, i.e., the physical substructure. Moreover, to monitor the seismic performance of the pipeline and harness the use of sensor technology, acoustic emission sensors are placed through the pipeline. Thus, real-time acoustic emission signals of the system under study are acquired using acoustic emission sensors. Moreover, in addition to seismic events, also a severe monotonic loading is exerted on the physical substructure. As a result, deformation levels of each critical component were investigated; and the processing of acoustic emission signals provided a more in-depth view of the damage of the analysed components.

Creep-Relaxation Modeling of HDPE and Polyvinyl Chloride Bolted Flange Joints

AbstractSimilar to many polymer materials, high-density polyethylene (HDPE) and polyvinyl chloride (PVC) show a clear creep behavior, the rate of which is influenced by temperature, load, and time. Most bolted flange joints undergo relaxation under compression, which is caused by the creep of the material. However, the creep property of the two polymers is different under tension and compression loading. Since the sealing capacity of a flanged gasketed joint is impacted by the amount of relaxation that takes place, it is important to properly address and predict the relaxation behavior due to flange creep under compression and thereby reducing the chances of leakage failure of HDPE and PVC bolted flange joints. The main objective of this study is to analyze the compressive creep behavior of HDPE and PVC flanges under normal operating conditions. This is achieved by developing a respective creep model for the two materials, based on their short-term experimental creep test data. Both numerical and experimental simulations of the polymeric flange relaxation behavior are conducted on an NPS 3 class 150 bolted flange joint of dissimilar materials, where one of the flanges is made of HDPE or PVC material and the other one is made of steel SA105. The study also provides a clear picture on how the compression creep data of ring specimen may be utilized for predicating the flange bolt load relaxation over time at the operating temperatures.

Cyclic performance of splice connections for hollow section fibre reinforced polymer members

This study investigates the cyclic performance of splice connections developed for hollow section fibre reinforced polymer (FRP) members. Splice connection specimens, each consisting of a steel bolted flange joint between two hollow section steel-FRP bonded sleeve joints, are prepared in three configurations with difference in bolt arrangement or bond length. Correspondingly, detailed finite element (FE) models are constructed with consideration of yielding of the steels, damage in the adhesive bond, pre-tensioning of the bolts and contact between the bolt-fastened parts. Tested under a cyclic flexural loading, the specimens experience different levels of yielding in the steel flange-plates before ultimate failure in the FRP member or in the steel flange-plate. Excellent ductility and energy dissipation capacity are demonstrated in a specimen where plastic deformation of the steel flange-plates is fully developed. The strain responses are also analysed to identify damage in the adhesive bond and yielding in the flange-plates. The FE modelling agrees well with the experimental results in terms of moment-rotation and load-strain responses, and can also predict the initiation of the ultimate failure in the FRP using the Tsai-Wu failure criterion.

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.

New Simplified Dynamic Modeling Method of Bolted Flange Joints of Launch Vehicle

Abstract The bolted flange joint is an important source of nonlinearity in dynamical analysis of launch vehicles, which will lead to both longitudinal and transversal responses simultaneously subject to transversal dynamic loads, and may result in the failure of the connection structure. In this paper, a novel simplified dynamic modeling method via structural static analysis is proposed to simulate dynamical response of nonlinear bolted flange joints of launch vehicle, in which only static analysis of the detailed finite element model or static experiment is used for parameter identification of the model. Two types of nonlinear springs are designed for different tensile and compressive stiffness of the bolted flange joint, which affect longitudinal dynamic behaviour of the connection, and a shear spring is used to modify the transversal stiffness. The sections of launch vehicle are modeled as linear beams for efficiency. Effectiveness of the proposed modeling method is confirmed by a typical connection structure, bolted flange connected cylindrical shells, whose finite element models are verified with dynamic experiments. Superiority of the simplified dynamic model from the proposed method is demonstrated by comparing with the previous simplified model. The connection structures with different numbers of bolts are studied, and most of the dynamic responses calculated from the proposed model agree well with those from the finite element model. The coupling vibration of the connection structure is predicted successfully, in which longitudinal response of the structure is excited by the transversal load.

Evaluation of Marginal Nut Height and Width on Sealing Performance of Bolted Flange Joints

Evaluation of Marginal Nut Height and Width on Sealing Performance of Bolted Flange Joints

Tension–bend–shear capacity of bolted-flange connection for square steel tube column

In this study, the square steel tube column is connected by bolted flange instead of traditional welding. For multi-rise structure, tension, bending moment, and shear force may act on the connection under vertical and horizontal loads. To investigate the mechanical behavior of flange connections, full-scale model tests and finite element analyses of 10 bolted-flange joints were carried out. The mechanical properties of the specimens and the influence of the flange thickness, flange size, and bolt hole diameter under a tension–bend–shear combination were obtained. The size of the bolt hole and flange has little effect on the load-carrying capacity of the connection. With the increase of the thickness of flange, the flexural rigidity and load-carrying capacity of the connection increase obviously, and the yield mechanism of the specimen changes from flange yield to bolt yield. The influence of the axial tension ratio on the bolt tension was investigated by the experiment-verified finite element models. The axial tension ratio is the value that the axial force of column divided by the cross-sectional area and the material design strength of the column. Increasing the axial tension ratio may increase the bolt tension, which has a harmful effect on the bolts at the tension side of the flange. Using yield line theory, formulas for calculating the static load-bearing capacity resisting the bending moment, shear and tension were deduced and verified by comparing with the result of experiment and finite element analysis.

Failure Analysis of 304 Stainless Steel Components Used in Petrochemical Industry Applications

Type 304 stainless steel has been used to manufacture metal gaskets used as seals in bolted flange joints of hydrocarbon transfer pipeline in polyethylene plant and piping system used to distribute demineralized water in a polypropylene plant. During reassembling of ten joints after scheduled maintenance, heavy leakage has occurred in one joint. On the other hand, the water pipes have been drained and unused for about 2 months; however, after reuse, leakage has been detected. It is shown that the gasket has been crushed due to improper reassembling practice involving the application of excessive compressive preload generated by tightening the bolts. Most evidence pointed out that the water pipes have been degraded by pitting corrosion due to contamination of the water by chloride ions.

The elastic serrated gasket of the flange bolted joints

The paper presents the experimental as well as numerical research of a bolted flange joint with an elastic serrated gasket. Two constructions of a metal core were proposed. Their cross-section shapes were different in relation to the standard solution. Results of the experimental research showed that the elastic core provides a considerable increase of the joint tightness compared to the tightness of the joint sealed with a standard gasket. Next, numerical analysis was conducted whose aim was to determine contact pressure on the interfacing surface between the gasket and flange. It appeared that proper forming of the core cross-section provides quite regular distribution of contact pressure along the gasket width. The final part verified the numerical computation and explains the effect of the increased tightness of the joint with an elastic core.

Impact and usage of the shear thickening fluid (STF) material in damping vibration of bolted flange joints

Bolted flange joints in fuzes undergo high acceleration during penetration, along with nonlinear responses which are forced reaction, structural vibrations, and shock effects. Vibrations of high frequencies aggregate noises and make it harder for the signal processing of fuzes. This study proposed an effective and innovative method of suppressing vibrations of high frequencies caused by impact loading. Shear thickening fluids (STFs) were stuffed into bolted flange joints. A damper of 57 vol/vol% dense silica particle-ethylene glycol suspension was inserted into gaps between the surfaces of the incident bar and the flange. Based on a modified split Hopkinson pressure bar, pulse widths, amplitudes, and structural frequencies of both impact and vibrational response regions were evaluated to examine the effectiveness of the STF damper. The amplitude and pulse width in the vibrational response region were significantly reduced, since this suspension forms jamming clusters subjected to impulses, attenuating the shockwaves. The STF fillers under various lengths of projectiles from 50 mm–400 mm were discussed to validate effectiveness. Further comparisons with epoxy resin fillers with various curing times indicated that the STF inhibited high frequency oscillations as a protector, and damped the dominant frequency of the original structure. However, experimental data showed that the transmission pulse of the incident bar was similar to joints without protection, indicating that the force transmission ratio was not affected by the fillers. These results show the feasibility of STFs as energy absorbers for vibration reduction of bolted flange joints.