Bolted Flange Joints Research Articles

Nonlinear vibration characteristics of the rotor bearing system with bolted flange joints

As sophisticated mechanical equipment, the rotor system of aero-engine is assembled by various parts; bolted flange joints are one of the essential ways of joints. Aiming at the analysis of the nonlinear vibration characteristics of the rotor-bearing system with bolted flange joints, in this paper, a finite element modeling method for a rotor-bearing system with bolted flange joints is proposed, and an incremental harmonic balance method combined with arc length continuation is proposed to solve the dynamic solution of the rotor system. In order to solve the rotor system with rolling bearing nonlinearity, the alternating frequency/time-domain process of the rolling bearing element is deduced. Compared with the conventional harmonic balance method and the time-domain method, this method has the characteristics of fast convergence and high computational efficiency; solving the rotor system with nonlinear bearing force; overcome the shortcoming that the frequency–response curve of the system is too sharp to continue solving. By using this method, the influence of bearing clearance and stiffness on vibration characteristics of the rotor system with bolted flange joints is studied. The evolution law of the state of the rotor system with bolt flange is investigated through numerical simulation and experimental data. The results indicated that the modeling and solving method proposed in this paper could accurately solve the rotor-bearing system with bolted flange joints and analyze its vibration characteristics.

Measurement of small rotation angle of flange joints by a novel flexure magnifying mechanism

Bolted flange joints are indispensable components in process industries due to the good sealing, assemble and disassemble capacities. Generally, the flange rigidity characterized by the rotation angle is a key index to evaluate the sealing tightness of flange joints. However, the rotation angle of flange is usually too small (less than 1°) to monitor during the assemble and operation stages. Accordingly, a novel flexure magnifying mechanism is designed to measure the small rotation angle of flange joints under internal pressure and external bending moment. The magnification factor and calculation approach of the flexure amplification mechanism are deduced and verified by experimental data and finite element simulation. Results indicate that the proposed measuring apparatus has good performance to monitor the maximum rotation angle. It is of great interest that the measured location of the maximum rotation angle is in good agreement with that in the experiment, and the average error is 7.3%, which is acceptable for practical application. Additionally, the leakage rate at the top of flange joints slowly and almost linearly increases with the increment of external bending moment ascribing to the decrease the gasket stress near the top of flange joints.

A probabilistic approach for the detection of bolt loosening in periodically supported structures endowed with bolted flange joints

Abstract From the literature, only very limited research activities have been carried out for fault diagnose of periodic structural system following model-based approaches. This paper focuses on the development of a practical methodology for modeling and detecting bolt loosening on periodically supported beam-type structure endowed with bolted flange joints, representing typical supported pipeline system in industry, through using measured modal parameters. Within the framework of periodic system, an efficient analytical model of the complete periodic system is first developed for dynamic analysis in frequency domain. The highly accurate spectral element method is employed to formulate the supercell-based dynamic stiffness matrix (DSM) of periodic cell containing bolted flange connection in the midspan, and the transfer matrix-based method is also developed for assembling the system DSM of entire periodic structural system through the obtained DSM of each individual cell, where the computational effort required in dynamic analysis of the complete periodic system with a large amount of repeated cells is almost comparable to a single cell. Then, in the proposed methodology, the statistical detection of bolt loosening is accomplished through two phases. The most plausible model class with appropriate parameterization complexity is first recognized by following the Bayesian model class selection strategy in the first phase. In the subsequent phase, the posterior probability density function of the stiffness scaling parameters is identified following the particle filter-based approach. To demonstrate and validate the proposed methodology, this paper reports not only the theoretical development but also a comprehensive series of numerical and experimental case studies, and corresponding results achieved are very encouraging.

Real-time monitoring of bolt clamping force at high temperatures using metal-packaged regenerated fiber Bragg grating sensors

Inappropriate clamping force in bolted flange joints operated at high temperatures has been regarded as the main issue that endangers the reliability and safety of a plant. In order to accurately and reliably measure the bolt clamping force, an innovative technique is proposed using metal-packaged fiber Bragg grating (RFBG) sensors. A metal-packaged RFBG sensor is developed by a combination of magnetron sputtering and electroplating followed by spot-welding on a bolt, and calibrated by uniaxial tensile and thermal tests. The clamping force in a bolted steel-steel joint is monitored by the metal-packaged RFBG sensor spot-welded on the bolt and analyzed by a finite element model. The sensor exhibits good linear response to axial loads applied to the bolt when exposed to constant high temperatures up to 500 °C, as well as good stability and repeatability. Its thermal response is non-linear and can be expressed as a cubic-polynomial function of temperature. The variation of the clamping force in the bolted joint subjected to thermal loading is then monitored by the sensor, which is further verified by a comparison of the experimental results and the numerical predictions showing a satisfactory agreement. The results demonstrate that this technique provides a new possibility for real-time monitoring of bolt clamping force and structural health monitoring of bolt joint structures operating in high-temperature environments.

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

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

Evaluation of Interfacial and Permeation Leaks in Gaskets and Compression Packing

The quantities of leak rate through sealing systems are subjected to strict regulations because of the global concern on radiative materials. The maximum tolerated leak is becoming a design criterion in pressure vessel design codes, and the leak rate for an application under specific conditions is required to be estimated with reasonable accuracy. In this respect, experimental and theoretical studies are conducted to characterize gasket and packing materials to predict leakage. The amount of the total leak is the summation of the permeation leak through the sealing material and the interfacial leak generated between the sealing element and its mating surfaces. Unfortunately, existing models used to predict leakage do not separate these two types of leaks. This paper deals with a study based on experimental testing that quantifies the amount of these two types of leaks in bolted gasketed joints and packed stuffing boxes. It shows the contribution of interfacial leak for low and high contact surface stresses and the influence of the surface finish of 0.8 and 6.3 μm (32 and 250 μin) resulting from phonographic grooves in the case of a bolted flange joint. The results indicate that most leakage is interfacial, reaching 99% at the low stress while interfacial leak is of the same order of magnitude of permeation leak at high stresses reaching 10−6 and 10−8 mg/s in both packing and gaskets, respectively. Finally, particular focus is put on the technique of precompression to improve material sealing tightness.

Predicting Leak Rate Through Valve Stem Packing in Nuclear Applications

Leaking valves have forced shutdown in many nuclear power plants. The myth of zero leakage or adequate sealing must give way to more realistic maximum leak rate criterion in design of nuclear bolted flange joints and valve packed stuffing boxes. It is well established that the predicting leakage in these pressure vessel components is a major engineering challenge to designers. This is particularly true in nuclear valves due to different working conditions and material variations. The prediction of the leak rate through packing rings is not a straightforward task to achieve. This work presents a study on the ability of microchannel flow models to predict leak rates through packing rings made of flexible graphite. A methodology based on experimental characterization of packing material porosity parameters is developed to predict leak rates at different compression stress levels. Three different models are compared to predict leakage; the diffusive and second-order flow models are derived from Naiver–Stokes equations and incorporate the boundary conditions of an intermediate flow regime to cover the wide range of leak rate levels and the lattice model is based on porous media of packing rings as packing bed (Dp). The flow porosity parameters (N, R) of the microchannels assumed to simulate the leak paths present in the packing are obtained experimentally. The predicted leak rates from different gases (He, N2, and Ar) are compared to those measured experimentally in which the set of packing rings is mainly subjected to different gland stresses and pressures.

Internal pressure estimation of the leak free bolted flange joint (Second)

Internal pressure estimation of the leak free bolted flange joint (Second)

Leakage through gasket regarding rotated bolted-flange joint

Leakage through gasket regarding rotated bolted-flange joint

Performance of a gasketed joint under bolt up and combined pressure, axial and thermal loading – FEA study

In this paper the strength and sealing performance of a gasketed bolted flanged pipe joint is studied under bolt up and combined operating conditions using 3D nonlinear finite element analysis. The key combinations of internal pressure, axial and thermal loading are considered. The strength of the joint is seen to be affected by the axial and thermal loading combination whereas the joint sealing is seen to be dependent on the bolt up strategy during assembly and is slightly affected under pressure but only partially affected under axial loading in certain locations. Thermal loading was also considered and was found to have a significant effect on the sealing performance up to 100 °C, but beyond that no sealing was observed, resulting in the possibility of leakage and hence increasing the risk of overall joint failure. Finally, the joint load capacities are determined under various combined loadings showing its safe and unsafe operational limits.

Leak prediction through porous compressed packing rings: A comparison study

The Prediction of leak rate is a significant challenge in the design of bolted flange joints and valves. With the increase of the strict regulations on fugitive emissions appropriate leakage-based standard design procedures are required. Fluid flow through porous media is a very attractive theory that can be used to predict leak rates through gaskets and compression packings. Valves that are the major source of fugitive emissions in the category of pressurized equipment use compression packings and seals the design of which is not covered by a standard design procedure.In this study, three different models; capillary, concentric cylinders, and modified Darcy's models, are used to characterize the sealing behavior of graphite-based compression packing rings. Based on data from several experimental tests, the ability of each model to predict accurate leak rates is evaluated. The comparison between the predicted and the measured leak rates is conducted for different molecular size gasses and a wide range of gland stresses and gas pressures.

Nonlinear behavior of single bolted flange joints: A novel analytical model

Flange joints are widely used in mechanical and civil structures. In this study joint deformations are investigated and a detailed model, which can demonstrate the actual joint behavior, is developed. This is done by modeling joint laps and bolts respectively as cantilever beams and springs. Then, an accurate relation between their load and deflection is obtained. It is shown that unlike the lap joints, the flange joints should be modeled using bilinear stiffness. Furthermore, the Euler-Bernoulli theory is used to model dynamic behavior of the beams, which are connected to the flange joint. An analytical procedure is introduced to calculate natural frequencies and mode shapes of two beams, which are connected by a single bolt flange joint. Two experimental setups consisting of a single bolt flange joint specimen and beam-flange system have been designed to investigate static and dynamic behavior of the system. One of the specimens is put into different loading configurations to obtain moment-slope curve. Another setup, consisting of freely suspended beams connected by a single bolt flange joint, is used to investigate natural frequencies of the system. Comparing the theoretical flange stiffness with the experimental and FEM results shows accuracy of the proposed model. Furthermore, dynamic behavior of the proposed beam-spring model is validated using empirical natural frequencies.

Analytical evaluation of elastic interaction in bolted flange joints

Bolted flange joints are the most popular type of connection of pressure vessels and piping equipment because of their ease of assembly and disassembly. However, the initial tightening of their bolts is a delicate operation because it is extremely difficult to achieve the target load and uniformity due to elastic interaction. This study consists of developing an analytical model to evaluate the elastic interaction of bolted flange joints subjected to multi-pass tightening patterns. The proposed analytical model is based on the theory of circular beams on elastic foundation. The parameters such as elastic compliance due to bending, twisting and bearing are involved to describe the effects of elastic interaction during the tightening sequence. The developed model based on the theory of circular beams on elastic foundation is compared to the straight beam on elastic foundation theory. The validity of the approach is supported by experimental tests conducted on a NPS 4 class 900 weld neck bolted flange joint and by finite element analysis on this bolted joint and a 52 heat exchanger flange joint using the criss-cross tightening and sequential patterns. This study provides an attractive alternative to evaluate the bolt tension scatter due to elastic interaction avoiding costly experimental tests and cumbersome FEA simulations.

Tensile resistances of bolted circular flange connections

A closed form solution for the ultimate tensile resistance of a bolted flange joint is derived considering yield line failure mechanisms developed by Igarashi et al. The position of the prying force is determined based on formulations previously developed by the authors. Under various simplified assumptions and approximations, a design approach similar to that of the Eurocode 3 for T-stubs is proposed. To validate this approach, experimental tests have been performed on six connections of circular hollow sections made of bolted ring flange. A finite element model considering the elastoplastic behaviour of steel and contact conditions has been developed and the results showed a good agreement with experimental results. Based on the FEM model, a parametric study shows that the proposed analytical model is valid for a wide range of connections.

Elastic Interaction in Bolted Flange Joints: An Analytical Model to Predict and Optimize Bolt Load

Bolted flange joints are widely used in the nuclear power plants and other industrial complexes. During their assembly, it is extremely difficult to achieve the target bolt preload and tightening uniformity due to elastic interaction and criss-cross talks. In addition to the severe service loadings, the initial bolt load scatter increases the risk of leakage failure. The objective of this paper is to present an analytical model to predict the bolt tension change due to elastic interaction during the sequence of initial tightening. The proposed analytical model is based on the theory of circular beams on linear elastic foundation. The elastic compliances of the flanges, the bolts, and the gasket due to bending, twisting, and axial compression are involved in the elastic interaction and bolt load changes during tightening. The developed model can be used to optimize the initial bolt tightening to obtain a uniform final preload under minimum tightening passes. The approach is validated using finite element analysis (FEA) and experimental tests conducted on a NPS 4 class 900 weld neck bolted flange joint.

Bolted fibre-reinforced polymer flange joints for pipelines: A review of current practice and future challenges

Metallic bolted flanges and pipes have both been increasingly replaced by fibre-reinforced polymer materials in many applications which deal with extreme harsh environments such as oil, chemical, marine, etc. This is not only due to the fibre-reinforced polymer material’s resistance to the chemical reaction but also due to their inherent mechanical properties of high strength to weight ratio. However, very little research has been published regarding bolted flange joints made of fibre-reinforced polymer materials. Also, the availability of standards and relevant design codes are very limited for bolted fibre-reinforced polymer flange joints. Hence, the design guidelines, dimensional considerations and selection of fabrication methods for the bolted fibre-reinforced polymer flange joints have yet to be optimized fully. For instance, the ASME Boiler and Pressure Vessel Code, section X and ASME PCC-1-2013 appendix O or other similar standards do not include specific rules for the design of the bolted fibre-reinforced polymer flange joints. As a result, it is difficult to understand the consequences on the reliability of fibre-reinforced polymer flanges made with parametric variations and dimensional alterations. This has led the authors to carry out research to maximise the performance of the bolted fibre-reinforced polymer flange joints through a series of experimenters and numerical simulations. The present article will focus on the available techniques to manufacture the bolted fibre-reinforced polymer flanges along with the associated issues and possible challenges compared to metallic flanges.

A lightweight optimal design model for bolted flange joints without gaskets considering its sealing performance

The lightweight optimal design of bolted flange joint system without gaskets is still a challenging problem, mainly owing to two issues: the relatively large number of mutually dependent geometric design parameters and the complicated role played by the contact details between members. With these two issues properly addressed, this article aims for devising a concise formulation for lightweight optimal design of bolted joint systems without gaskets. After a systematic examination of the correlations between design parameters, the total number of free design variables is reduced to three: member thickness, bolt spacing, and bolt specification, respectively. Besides, a finite element analysis that can resolve more contact details between members is conducted, and the influencing factors on the pressure distribution at the member surface are thus identified, with a criterion for the system sealing failure incorporated. Based on the findings in this work, a novel design scheme for the joint system is proposed, and good agreement between our predictions and results obtained by a full three-dimensional finite element analysis is shown. The proposed approach can be used to optimize the design parameters of bolted joint systems considering sealing performance without heavy finite element computation and can find applications in many relevant engineering fields.

Compression Creep and Thermal Ratcheting Behavior of High Density Polyethylene (HDPE).

The characterization of thermal ratcheting behavior of high density polyethylene (HDPE) material coupled with compressive creep is presented. The research explores the adverse influence of thermal cycling on HDPE material properties under the effect of compressive load, number of thermal cycles, creep time period, and thermal ratcheting temperature range. The compressive creep analysis of HDPE shows that the magnitude of creep strain increases with increase in magnitude of applied load and temperature, respectively. The creep strain value increased by 7 and 28 times between least and maximum applied temperature and load conditions, respectively. The creep modulus decreases with increase in compressive load and temperature conditions. The cumulative deformation is evident in the HDPE material, causing a reduction in the thickness of the sample under thermal ratcheting. The loss of thickness increases with increase in the number of thermal cycles, while showing no sign of saturation. The thermal ratcheting strain (TRS) is influenced dominantly by the applied load condition. In addition, the TRS decreases with increase in creep time period, which is cited to the extended damage induced due creep. The results highlight the need for improved design standard with inclusion of thermal ratcheting phenomenon for HDPE structures particularly HDPE bolted flange joint.

Axial performance of steel splice connection for tubular FRP column members

A splice connection is proposed for connecting tubular fibre reinforced polymer (FRP) members. This connection consists of a steel bolted flange joint (BFJ) and two steel-FRP bonded sleeve joints (BSJs). The BFJ connects two steel hollow sections, each of which is telescoped into the targeted tubular FRP member through adhesive bond, forming a BSJ. To evaluate the performance of the proposed splice connection under axial loadings, BSJs of four different bond lengths and BFJs of two bolt configurations are tested individually. Finite element (FE) models are developed which feature a bilinear bond-slip relation, contact behaviours and bolt pre-tensioning. Comparisons are made between experimental and FE results in terms of load-displacement behaviours, ultimate capacities and strain responses. Besides being capable of identifying an effective bond length for the BSJ and modelling the yielding process of the BFJ, FE analysis provides insight into the distribution of adhesive shear stress over the bond area of the BSJs, and the steel yield line pattern on the flange-plate of the BFJs. Verified by experimental results, the FE modelling technique is then utilised to understand the integrated axial behaviours of a complete splice connection.

Reduced Order Modeling for Multistage Bladed Disks With Friction Contacts at the Flange Joint

Most aircraft turbojet engines consist of multiple stages coupled by means of bolted flange joints which potentially represent source of nonlinearities due to friction phenomena. Methods aimed at predicting the forced response of multistage bladed disks have to take into account such nonlinear behavior and its effect in damping blades vibration. In this paper, a novel reduced order model (ROM) is proposed for studying nonlinear vibration due to contacts in multistage bladed disks. The methodology exploits the shape of the single-stage normal modes at the interstage boundary being mathematically described by spatial Fourier coefficients. Most of the Fourier coefficients represent the dominant kinematics in terms of the well-known nodal diameters (standard harmonics), while the others, which are detectable at the interstage boundary, correspond to new spatial small wavelength phenomena named as extra harmonics. The number of Fourier coefficients describing the displacement field at the interstage boundary only depends on the specific engine order (EO) excitation acting on the multistage system. This reduced set of coefficients allows the reconstruction of the physical relative displacement field at the interface between stages and, under the hypothesis of the single harmonic balance method (SHBM), the evaluation of the contact forces by employing the classic Jenkins contact element. The methodology is here applied to a simple multistage bladed disk and its performance is tested using as a benchmark the Craig–Bampton ROMs of each single stage.