Flange Joints Research Articles

Flange joint monitoring based on strain measurement with fiber optic sensors embedded in gaskets

Flange joint monitoring based on strain measurement with fiber optic sensors embedded in gaskets

A unified nonlinear dynamic model for bolted flange joint disk-drum structures under different interface states: Theory and experiment

Bolted flange joint disk-drum structures (BFJDDSs) are key components in aero-engines, however, bolt looseness inevitably occurs due to extreme service conditions. This can cause the bolted joint interface to exhibit complex contact behaviors, which significantly complicate the vibration characteristics of BFJDDSs. Existing dynamic models for BFJDDSs have not considered the effect of bolt looseness (slip and separation), so their vibration behaviors are not well understood. In this study, a unified nonlinear dynamic model for BFJDDSs considering different interface states (stick, slip, and separation) is proposed, which is effective under both bolt looseness and non-looseness (stick) conditions. The bi-linear hysteretic model combined with the piecewise linear model is used to simultaneously consider different interface states. The Kirchhoff plate theory, the Sanders’ shell theory, and the Euler-Bernoulli beam theory are used to derive the energy functions of the disk, drum, and flange, respectively. Then, the Lagrange equations are employed to derive the governing equations of BFJDDSs. Modal and nonlinear forced vibration experiments are carried out on a BFJDDS to prove the correctness of the proposed mathematical model. Research results show that the proposed mathematical model is able to achieve good predictions of nonlinear dynamic properties of BFJDDSs under both bolt looseness and non-looseness conditions. This model is also able to well predict the jumping phenomenon observed in the experiment.

Calculation Method of New Assembled Corrugated Steel Initial Support Structure of Highway Tunnel

The assembled corrugated steel initial support structure is a new prefabricated structure in highway tunnel engineering, achieving a balance between economy and safety. This study proposes a simplified calculation method and elucidates the mechanical mechanisms of assembled corrugated steel initial support structures. Firstly, the stiffness characteristics of corrugated steel plates were studied based on full-scale tests. A general equivalent stiffness coefficient table was established. Numerical simulations of corrugated steel flange joints were conducted to explore their bending mechanical properties. A two-stage rotational stiffness model for corrugated steel flange joints was proposed. Finally, a plane strain-spring simplified calculation method for the assembled corrugated steel initial support structure was developed, and the monitoring data from the Qipanshan Tunnel validated the correctness and reliability of the proposed method. The results demonstrate that (1) the plane strain-spring simplified model consists of the planar strain equivalent calculation method for corrugated steel plates and the two-line stiffness equivalent spring of the corrugated steel flange joint. The simplified model was validated as effective by monitoring data. (2) Corrugated steel plates exhibit two stages under loading, namely gap elimination and elastic stages. The elastic stage stiffness of corrugated steel plates decreases with increasing ratio of depth to pitch (RDP), positively correlating with plate thickness when the RDP exceeds 0.333 and otherwise negatively correlated. (3) Corrugated steel lining flange joints exhibit distinct elastic and plastic stages in their linear moment–rotation curves under loading.

Experimental Study on Mechanic Behavior of Flange Joint for Steel Tube Under Axial Tension

The flange joint is an important connection in steel tube structures. In this paper, 11 groups of flange joint tests were conducted to investigate the influences of tube diameter, flange plate thickness, the distance from the bolt to the tube centroid, bolt numbers and material strength on the mechanical behavior. One of two failure modes in tests is that the excessive plastic deformation on the flange plate makes the flange plate lose the bearing capacity; the other is that the steel tube yield makes the joints fail. The results show that the calculating method for flange joint in Chinese design code is so safe that amplifying the calculating results of the code by 1.2 times would be closer to the bearing capacity of specimens. For a flange joint with different tube diameters, thickening the flange plate of thinner tube or thinning the flange plate of another tube are effective to ensure the deformations on both sides of the flange plates are equivalent. The ratio of the bearing capacity of the steel tube to that of flange plate should be greater than 1.7. And the thickness of the flange plate should be thicker than 14mm to reduce the deformation caused by cutting, drilling and welding during manufacturing.

Vibration of bolted composite cylindrical-cylindrical flanged shells considering contact characteristics

A semi-analytical model for bolted composite cylindrical-cylindrical flanged shells (BCCFS) considering the influence of the flange and the connection characteristics of the bolted flange joint is established. In the model, flanges are treated as annular plate structures and modeled using Kirchhoff plate theory. To simulate the connectivity performance of the bolted flange joint, a surface-spring model considering the pressure distribution characteristics is developed and applied to the model of the bolted structure. A method based on fractal contact theory is proposed to identify stiffness-related parameters of the surface-spring model, which avoids additional tensile experiments of the bolted joint. Sufficient modal tests are performed to validate the accuracy of the model. Furthermore, the effects of flange thickness, length ratio of two shells, and quantity of bolts on the free vibration characteristics of the structure are studied. The frequency veering phenomenon with the variation of size parameters is found and analyzed in depth.

Multi-weld Quality Optimization of Friction Stir Welding for Aluminium Flange Using the Grey-based Taguchi Method

Friction stir welding (FSW) is gaining traction as a preferred technique due to its potential to reduce heat input and enhance the mechanical properties of welded joints. However, the path to commercializing FSW for flange joints is not without challenges. Two primary obstacles are the complexity of the welding path and the intricate design requirements for the fixtures. These factors contribute to the difficulty in determining the ideal weld settings and process parameters, which are critical for achieving optimal results. The current study addresses these challenges by applying FSW to flange joints using custom-engineered fixtures. These fixtures are meticulously designed to hold the pipes and plates securely during the welding process. The focus of the research is on optimizing the multi-performance characteristics of FSW for Al 6063 flange joints through the hybrid Grey-based Taguchi method. The integrity of the weld joint is assessed by examining various mechanical properties within the weld zone, including rotation speed, travel speed, tool profile, and shoulder diameter. The study identifies the optimal parameter settings for the FSW process: a rotation speed of 3000 rpm, a travel speed of 3 mm/min2, a shoulder diameter of 20 mm, and a conical tool profile. Under these ideal conditions, the welded material exhibited a tensile strength of 170.169 MPa, a hardness of 63.7709 HV, and a corrosion rate of 0.022 mm/year. These findings underscore the effectiveness of the optimized FSW process in producing robust and durable flange joints.

Analysis of variance and grey relational analysis application methods for the selection and optimization problem in 6061-T6 flange friction stir welding process parameters

A study was carried out to investigate and enhance the effects of friction stir welding on the mechanical characteristics of a flange composed of 6061-T3 aluminum alloy. The pipes possess an outer diameter and wall thickness of 6 mm, while the plates are sized at 100 x 100 × 6 mm. Nine unique experiments were planned using the Taguchi orthogonal array method, with the welding tool remaining constant. Three independent variables (travel speed, rotation speed, and shoulder diameter) were altered at three different levels for each variable. The research analyzed the influence of various FSW factors on the weld flange joint. Analysis of variance (ANOVA) and grey relational analysis (GRA) were employed to determine the impact of each FSW underwater parameter. Moreover, the statistical Taguchi technique (TM) was used to predict the optimal combination of welding parameters to improve tensile properties, including tensile strength (UTS), yield strength (YS), elongation (EI%), and bending load (BL) of welded joints. Additionally, the actual tests demonstrated a high level of agreement with the results obtained from the proposed mathematical model. The validation results obtained indicate that the optimization method is a dependable tool for enhancing the quality responses of friction stir welding.

Influence of geometric imperfections of flange joints on the fatigue load of preloaded bolts

In an ideal flange joint configuration, the fatigue endurance of preloaded bolts is contingent upon factors such as the magnitude of preload, applied working load, and the geometric dimensions of the flange. However, real-world flanged joints often deviate from this ideal geometry, introducing imperfections that can markedly escalate the fatigue burden on bolts. This study endeavors to simulate the geometric imperfections inherent in a standard DN40 flange and ascertain their impact on bolt fatigue through a combination of empirical measurements and finite element (FE) analysis. The investigation reveals that even minor deviations in flange geometry, such as non-parallelism on the order of 0.03 mm, can exert a considerable influence on bolt fatigue, particularly when the flange gap aligns with the applied eccentric working load (same side). To mitigate the deleterious effects of these imperfections, the proposal and evaluation of employing filler material between the flanges are made. Specifically, it is demonstrated that a thin layer of liquid metal filler (KemisKit Fe21), substantially alleviates the fatigue burden on bolts. Empirical findings illustrate that this corrective measure enhances the fatigue life of bolts by a factor of more than 30 under the highest applied working load condition.

Flange joining using friction stir welding and tungsten inert gas welding of AA6082: A comparison based on joint performance

Expanding the use of 6xx aluminum alloy series in various industries is challenging due to the need for cost-effective welding processes and optimal settings to ensure high-quality joints. The present research focused on the comparison of joint performance of the pipes and plates using tungsten inert gas (TIG) and friction stir welding (FSW) The AA6082 alloy material is used for pipes and plates used in the study. Various techniques were utilized, including hardness and tensile tests, and microstructural examinations. Using a scanning electron microscope (SEM), the surface fracture of the specimens that failed under tensile tension was also examined. The present research also included the economic impact on the welding processes used. Results demonstrated that the weld obtained using FSW was defects free whereas, internal flaws were seen in TIG welded samples. The hardness value increased over the base material (BM) for the FSW and TIG by 31–35% and 46-40%, respectively. The FSW joint was welded at a maximum UTS of 3 mm/min and a rotational speed of 3000 rpm. FSW can create the AA60682 flange joints more efficiently and effectively than fusion welding procedures like TIG processes in pipeline applications. For AA6082 flange joints, overall total cost comparisons between FSW and TIG were also made.

Image-Based Bolt-Loosening Detection Using a Checkerboard Perspective Correction Method.

In this paper, a new image-correction method for flange joint bolts is proposed. A checkerboard is arranged on the side of a flange node bolt, and the homography matrix can be estimated using more than four feature points, which include the checkerboard corner points. Then, the perspective distortion of the captured image and the deviation of the camera position angle are corrected using the estimated homography matrix. Due to the use of more feature points, the stability of homography matrix identification is effectively improved. Simultaneously, the influence of the number of feature points, camera lens distance, and light intensities are analyzed. Finally, based on a bolt image taken using an iPhone 12, the prototype structure of the flange joint in the laboratory is verified. The results show that the proposed method can effectively correct image distortion and camera position angle deviation. The use of more than four correction points not only effectively improves the stability of bolt image correction but also improves the stability and accuracy of bolt-loosening detection. The analysis of influencing factors shows that the proposed method is still effective when the number of checkerboard correction points is reduced to nine, and the average error of the bolt-loosening detection result is less than 1.5 degrees. Moreover, the recommended camera shooting distance range is 20 cm to 60 cm, and the method exhibits low sensitivity to light intensity.

Effect of gasket material on flange face corrosion

Bolted flanged joints play a crucial role in connecting pressure vessels and piping systems. The corrosion of the flange surface is one of the most common causes of leakage failure in bolted flanged joints. This research investigates the effect of three gasket materials on the corrosion behavior of 321 stainless steel flange material using a novel setup specially designed for corrosion quantification of such assemblies. The results show that graphite gaskets cause more corrosion to flange surfaces under the same working conditions compared to graphite gaskets with metal foil inserts and virgin polytetrafluoroethylene (PTFE) gaskets. The mechanism of flange face corrosion is that, for PTFE gaskets, corrosion propagation mainly occurs at the gasket inner diameter and propagates through the depth of the flange while, for graphite gaskets, corrosion occurs on the whole contact surface of the flange and the gasket.

Plastic collapse behavior of plate to CHS connection under biaxially symmetric load

This study investigates the plastic collapse behavior of a non-diaphragm type connection with flange plates connected to a circular hollow section (CHS) column, where four flanges were joined from two orthogonal directions. The analysis was conducted using the finite element method (FEM). The focus was on determining the collapse load of the flange joint under a biaxially symmetric load from the four flanges. In an initial numerical analysis, the fundamental collapse behavior of the cylindrical wall was explored. Finite element models of CHS tubes with perfectly elasto-plastic material properties were employed. The analysis revealed that the plastic collapse mechanism of the cylindrical wall was influenced by the axial force in the transverse flanges. Prediction equations for the collapse load of the joint were formulated, assuming four representative collapse mechanisms and employing the principle of virtual work based on the numerical analysis results. Additionally, the ultimate strength of the joint, determined by the plastic collapse of the cylindrical wall, was computed using finite element models of CHS tubes with realistic hardening properties. A comparison between predictions from the equations based on perfectly elasto-plastic CHS tubes and numerical solutions through finite element analysis (FEA) of CHS tubes with realistic hardening properties validates the accuracy of the proposed prediction equations, even when applied to realistic steel tubes.

Nonlinear vibrations of bolted flange joint plate system considering the stick–slip–separation state: theory and experiment

Nonlinear vibrations of bolted flange joint plate system considering the stick–slip–separation state: theory and experiment

Effect of gap size on flange face corrosion

AbstractBolted flanged joints play a critical role in offshore wind turbine tower structures, serving as integral components that connect various sections of the tower. This research study employs electrochemical techniques to investigate the effect of gap dimensions, which determine the crevice gap thickness and crevice depth, on corrosion behavior of 321 stainless steel flange sample plates in a 3.5 wt% NaCl solution at 50°C. Gaskets are used in this study to create gaps between two flange surfaces. A novel fixture is utilized to simulate the applied stress on the gasket, fluid flow within the fixture, and the geometric aspects of the gasket and flange. The findings reveal that increasing the gap thickness from 1.58 to 6.35 mm results in a rise in the general corrosion rate of the flange surface from 0.09 to 1.03 mm y−1, and crevice corrosion initiation time increases from 0.23 to 3.12 h. Furthermore, reducing the crevice depth (d) from 7.49 to 0 mm leads to a decrease in the general corrosion rate from 0.09 mm y−1 to 0.04 µm y−1, and cases with d = 3.81 and d = 0 mm show no observable crevice corrosion after potentiostatic tests.

Performance study of eccentrically braced steel frames with core tube flange connection

This paper proposes a kind of assembly brace connections adapted to the core tube flanged column connection joint of the frame-brace structure, starting from the eccentrically braced frame structure in the steel frame system and designing and completing a set of proposed static tests of the eccentrically braced frame with the core tube flanged column connection joint. By conducting in-depth analysis and research at three levels, namely the seismic performance of the eccentrically braced frame system, the performance characteristics of the core tube type flanged column connection joints, and the performance of assembled brace connections, the study has yielded insights into the force mechanism and failure modes of the core tube type flanged column connection joints within the eccentrically braced frame system; the eccentrically braced frame system has been validated to possess good seismic performance by analyzing hysteresis curves, typical section strains, and bolt forces. These analyses have shown that the system can meet the seismic requirements. Moreover, the assembled brace joints were destroyed later than the braces, indicating that the assembled brace connection joints could fulfill the requirement of “strong joints.”

Optimization of the Mechanical Properties of Bolted Connections between Concrete-Filled Tubular Columns and Steel Beam with Reinforcing Rings

To study the mechanical performance of bolted connections with different structural forms of reinforced rings, based on the results of monotonic loading tests on two bolted connections between a concrete-filled steel tubular column and a steel beam with an outer reinforcing ring, this article uses ABAQUS v.2020 software to establish a three-dimensional refined finite element analysis model of such connections using appropriate constitutive models for concrete and steel. Subsequently, the effect of the dimensions of the steel beam, reinforcing ring, and cover plate on the load-bearing properties and the failure mechanism of the connections is investigated, and the numerical model is consistent with the verification test results. Then, the numerical simulations comparing bolted exterior reinforced rings under seven different construction measures (i.e., number of bolts, stiffeners) based on a conventional welded exterior reinforced rings with rigid connections (i.e., CGJ) are standardized. The research results indicate that when four rows of bolts are introduced on exterior reinforced rings, the web of steel beam is welded with stiffeners, and the top and bottom reinforced rings are also added with stiffeners; this bolted connection with an external reinforcing ring (i.e., GZ-7) can achieve the rigidity and load-bearing capacity of a fully welded external reinforcing ring rigid connection. At the same time, the reinforcing ring plate is bolted to the flange of the steel beam, and the force transmission path at the connection is changed to avoid the brittle fracture easily caused by the welded flange joints. It is also in line with the development trend of sustainable construction of “assembly” and “disassembly”.

Dynamic modeling and vibration analysis of bolted flange joint disk-drum structures: Theory and experiment

Bolted flange joint disk-drum structures (BFJDSs) are key components in aero-engines, in which fatigue damage often occurs due to structural vibration. However, no study has so far given an effective theoretical dynamic model of BFJDSs. In this study, an effective dynamic model of BFJDSs is proposed. The present model considers the flange effect, non-uniform contact pressure of bolted joint, and bolt mass. The theoretical expression for describing the stiffness variation of bolted joints is presented. During the modeling process, the energy functions of disk, drum, and flange are obtained according to the Kirchhoff plate, Sanders’ shell, and Euler-Bernoulli beam theories, respectively. The non-uniform artificial spring technique is adopted to simulate the pressure distribution of bolted joint. This method is capable of taking into account the contact pressure, which is closer to real contact situation. The displacement functions of disk and drum are expanded by using the Chebyshev orthogonal polynomials, and the motion equations are obtained by employing the Lagrange equation. Then, the experimental studies are performed on BFJDSs to illustrate the effectiveness of the theoretical model. Finally, the frequency veering and coupling vibration phenomena are revealed. The comparison studies indicate that the established theoretical model can well predict the vibration characteristics of BFJDSs under both bolt looseness and no-looseness conditions. The maximum error can be reduced from 46.81% to 3.61% by using the present dynamic model.

Modeling of wear process of a sealing washer in a flanged joint during fretting

The influence of steel surface roughness parameters on the coefficient of sliding friction and wear of sealing material in flanged joints is investigated. The dependence of the friction coefficient on the parameter Ra of the surface roughness of the steel part and the pressing force is established. The critical shear stresses for the flange-washer interface are determined, causing failure of the surface layer of the washer and a violation of the tightness of the flanged joint. Keywords:fretting, flanged joint, surface roughness, vibration, friction coefficient, tangential stresses, cyclic deformation elaguina.o@gubkin.ru, dubinova.o@gubkin.ru

A Numerical Comparison of Different Methods for Evaluating Pipe Flanges Under External Loads

Abstract This paper presents a numerical comparison of seven different methods for evaluating external loads on flanged joints in a piping system. The comparison will demonstrate in tabular form the factor of safety of some widely used traditional methods. An explanation of the history and basis of each method will be made. Differences in the results will be discussed, and an attempt will be made to explain the discrepancies between the more rigorous methods.

Component-based models of beam-column joints exposed to fire in steel framed structures against progressive collapse

This paper is supplementary research following the previous experimental and numerical studies on the progressive collapse behaviors of beam-column substructures with different joint configurations under middle-column removal scenarios induced by fire. The component-based models (CBMs) of beam-column joints exposed to fire, which include the welded web-welded flange (WW) joint, as well as the bolted web-welded flange (BW) joint, were proposed based on refined FE models established in previous studies. Subsequently, the proposed CBMs with detailed spring arrangements and constitutive parameters were incorporated into the ABAQUS software to validate the collapse responses of beam-column joints obtained from both test results and refined solid FE models. A comparison investigation with experimental data indicates that the proposed CBMs can accurately reflect the nonlinear collapse behaviors of different fire-exposed beam-column joints with relatively high computational efficiency. Moreover, the validated CBMs are further incorporated into the collapse analysis of a multi-story planar steel framed structure exposed to fire, by compiling the VUSDFLD subroutine, to realize the component deletion process. The parameter effects of fire location, joint configurations, and loading ratios on collapse behaviors and force redistributions of framed structures exposed to fire were investigated. Based on analysis results, it is shown that the component failure temperature is quite sensitive to whether the specific joint configurations are considered in the analysis of fire-resistant progressive collapse in planar framed structures, which should be paid sufficient attention to in the performance evaluation of collapse resistance. For those planar framed structures with larger loading ratios, it is recommended to increase the section of the frame column or carry out fire protection to prevent the progressive collapse of the structure.