Pipe Bend Research Articles

Investigation on variation characteristics of bent tube axis and determination of bending die motion trajectory in free bending process

In free bending process, the axis shape of bent tube is determined by motion trajectory of bending die. The bent tubes with different bending radii and bending directions can be formed by continuously adjusting the position and posture of die. To accurately form the pre-designed bent tube, the formation mechanism of bending arc in free bending process was analyzed. The mathematical model between bending radius and deviation was established and the moving direction of bending die was also determined according to the plane space azimuth where the bending arc segment is located. The formation process of transition segments with variable curvature and variable bending direction is illustrated during the movement of bending die, and the influence of transition segment on the axis shape was also explored. By comparing the axis deviation of experimental and simulated bent tubes, the length of transition segment and the moving path of bending die can be optimized. Finally, the applicability of free bending forming technology in forming bent tubes with different axis features was verified by conducting free bending experiments on bent tubes with three typical shapes. Due to the high flexibility of free bending forming technology, the work in this paper could promote the engineering application of this technology in the precise control of axis shape of bent tube.

Differential flow velocities control method for push-bending of the thin-walled tube with a 0.9D bending radius by differential lubrication

The smaller the relative bending radius of the bent tube, the more difficult the tube blank is to be bent. In this paper, the push-bending process for the aluminum tube with a relative bending radius of 0.9D was analyzed through simulation. There was tangential tensile stress concentration occurring at the front endpoint of tube intrados, which increased the risk of cracking. That is because the bending tube’s extrados moves less angular distance than its intrados by the uniform lubrication method, causing excessive deformation of the cross-section. Therefore, a differential lubrication method using the lubricant with a larger friction coefficient at intrados and the lubricant with a smaller friction coefficient at extrados was proposed to increase the angular velocity of the tube’s extrados. It was found that the differential lubrication method helped avoid excessive thinning at the front endpoint of tube intrados through simulations. Furthermore, push-bending experiments of 5A02 aluminum alloy with a relative bending radius of 0.9D were carried out to investigate this effect. The experimental results showed that the differential lubrication method effectively avoided cracking, which agreed with the simulation results.

Influence of Asymmetrical Bending Pipe with Different Gating Systems on Low-Pressure Metal Mold Casting

Influence of Asymmetrical Bending Pipe with Different Gating Systems on Low-Pressure Metal Mold Casting

Numerical Investigation and Prediction of Side-By-Side Tunneling Effects on Buried Pipelines

With the fast development of underground space engineering, it is inevitable for buried pipelines to be crossed by twin tunnels. Previous studies mainly focused on the single-tunneling effects on pipelines. To emphasize the twin-tunneling effects on buried pipelines, we first examined the effectiveness of the ground settlement prediction method under twin-tunneling conditions. Then, the estimated ground settlement boundary condition was applied to the beam-on-spring finite element model. The numerical results show that with the decrease in tunnel depth and twin tunnel space, the values and positions of the maximum ground settlement and longitudinal pipe bending behavior both changed significantly. The biased distance of the maximum settlement position and the distance to the inflection point of the final ground settlement curve can be obtained by curve fitting. Based on that, a semi-empirical prediction method for the longitudinal pipe bending strain was proposed. The predicted values matched quite well with the numerical results, which can thus provide a quick and effective structural safety and integrity assessment approach for buried pipelines subjected to twin-tunneling conditions.

Interference Analysis of 5G NR Base Stations to Fixed Satellite Service Bent-Pipe Transponders in the 6425–7125 MHz Frequency Band

Future deployment of 5G NR base stations in the 6425-7125 MHz band raises numerous concerns over the long-term impact on the satellite transponders located in geostationary orbit. To study this impact and understand whether 5G NR may cause adverse effect to the spaceborne receivers, the research which estimated the interference levels to the satellite bent pipe links was done. The study presents the evaluation of aggregate interference from 5G NR base stations located inside the victim satellites' footprints using Monte-Carlo analysis and calculation of signal-to-noise degradation and bit error rates of the fixed-satellite service (FSS) bent-pipe transponders for each scenario. The results of the study showed the feasibility of co-existence between 5G NR and satellite systems in the 6425-7125 MHz bands, and that no negative impact on the performance of the satellite links is expected.

Development of an improved limit pressure equation for structurally distorted thin-walled pressurized 90 degree pipe bends

PurposeThis paper aims to present the approximate limit pressure solutions for thin-walled shape-imperfect 90° pipe bends. Limit pressure was determined by finite element (FE) limit analysis with the consideration of small geometry change effects.Design/methodology/approachThe limit pressure of 90° pipe bends with ovality and thinning has been evaluated by geometric linear FE approach. Internal pressure was applied to the inner surface of the FE pipe bend models. When von-Mises stress equals or just exceeds the yield strength of the material, the corresponding pressure was considered as the limit pressure for all models. The current FE methodology was evaluated by the theoretical solution which has been published in the literature.FindingsOvality and thinning produced a significant effect on thin-walled pipe bends. The ovality weakened pipe bend performance at any constant thinning, while thinning improved the performance of the bend portion at any constant ovality. The limit pressure of pipe bends under internal pressure increased with an increase in the bend ratio and decreased with an increase in the pipe ratio. With a simultaneous increment in bend radius and reduction in wall thickness, there was a reduction in limit pressure. A new closed-form empirical solution was proposed to evaluate limit pressure, which was validated with published experimental data.Originality/valueThe influences of structural deformation (ovality and thinning) in the limit pressure analysis of 90° pipe bends have not been investigated and reported.

Robotic laser directed energy deposition-based additive manufacturing of tubular components with variable overhang angles: Adaptive trajectory planning and characterization

The present work reports on an adaptive trajectory planning to build tubular components with variable overhang angles using a robotic Laser Directed Energy Deposition (LDED) based Additive Manufacturing process without utilizing support structures. The proposed technique uses a non-parallel slicing methodology to build complex components (e.g., bent pipes) and deploys adaptively varying scanning speed and tool orientation. The variation in scanning speed aids in having point-to-point variable layer height enabling non-parallel deposition while changing the tool orientation during deposition permits the manufacturing of support-free bent pipe parts. The bent pipes with 45° and 90° bents were built using an in-house developed LDED system and the built parts are characterized for geometry, density, microstructure, and microhardness. The geometrical analysis indicates a deviation in the range of + 0.5 mm to − 0.5 mm, with minimal roundness deviation at different sections. The density analysis of the segments extracted from the bent pipe reveals a density > 98%, with the presence of a few lack of fusion pores and gas pores at isolated locations. The microstructure and microhardness studies show that regions built with higher scanning speeds have a finer grain structure and higher average hardness. The study paves a path to build defect-free and dimensionally stable complex-shaped components with varying overhang angles using LDED.

Efficient CFD modelling of bulk condensation, fog transport and re-evaporation for application to containment scale

Formation of fog due to bulk condensation during a Beyond Design Basis Accident (BDBA) in a water-cooled nuclear reactor is of high safety relevance with regard to the flammability of the containment atmosphere and its interaction with several other safety relevant phenomena such as aerosol transport. Bulk condensation of steam in the presence of non-condensable gases is modelled using ‘return to saturation in constant timescale’ method in single-phase system as mass sink. The fog droplets formed as a result of condensation is transported as passive scalar in an Eulerian frame by considering the effects of convection by the gas mixture, turbulent and Brownian diffusion and droplet drift due to gravitation, drag and inertial forces. The model formulation is based on the assumption that fog volume fraction is fairly low (<1%) so that droplet–droplet interactions and the effect of droplets on the gas flow are negligible. The present work considers only spherical fog droplets of fixed diameter and evolution of droplet by coalescence and breakup is neglected. The effect of different droplet sizes is investigated in the validation cases to understand its consequence on the results. It is also assumed that the fog droplets are always in thermal equilibrium with the surrounding gas mixture. The re-evaporation of the transported fog droplets in regions where gas temperature is higher than saturation temperature is also incorporated into the solver. The model was numerically implemented to the containmentFOAM CFD package based on OpenFOAM. The verification of the phase change(condensation & evaporation) model by simulating the mixing of a cold and hot air–steam–fog mixture gave good agreement with Mollier diagram theory in terms of both final mixture temperature and quantity of steam and fog. The droplets drift transport model was validated by aerosol flow through a bent pipe investigating the effect of droplet Stokes number on deposition efficiency. The performance of the bulk condensation model was further validated and assessed by including the interaction with other relevant containment phenomena (e.g., wall condensation, multispecies transport) on SETCOM experimental facility (Forschungszentrum Jülich, Germany) and a technical scale THAI experiment (Becker Technologies, Germany). The results indicated that the inclusion of bulk condensation model improved the predictive capabilities of containmentFOAM, i.e., the consistency of simulation and measurements for these experiments.

Significant analysis of the influence of process parameters on the wrinkling of aluminum alloy double-wall gap tube in rotary draw bending

Aluminum alloy double-wall gap tube is prone to wrinke in the rotary draw bending because the rigidity of the inner and outer tubes of the thin-walled structure is low, the mechanical properties between the tubes and the polymer filling medium are different greatly, and the bending forming is a complex nonlinear process of multi-mold coordination and multifactor coupling. While the process parameters are the main factors that affect the wrinkling of inner and outer tube, there are many process parameters and there are interactions among them. Therefore, based on the platform of ABAQUS/Explicit, elastic-plastic 3D-FE model of double-wall gap tube’s bending is established to study the influence mechanism of process parameters on the wrinkling aluminum alloy double-wall gap tube in rotary draw bending. The results show that the clearance between mandrel and inner tube, clearance between pressure die and outer tube, the anti-wrinkle die and the outer tube have significant effects on the wrinkling of the inner tube. The clearance between inner tube and core die, filling medium and inner tube and clearance between anti-wrinkle die and outer tube have significant effects on the wrinkling of inner tube. The wrinkling of the outer tube is more obvious than that of the inner tube. The results can provide a theoretical basis for optimizing the process parameters to suppress the wrinkling of aluminum alloy double-wall gap tube in the rotary-draw bending.

Investigation on temperature uniformity control of titanium extrusion in hot stretch bending process

Regarding to the impact of temperature on springback in hot stretch bending (HSB) process, this work proposed an investigation on temperature uniformity control of titanium extrusion in HSB process based on the mould which can be elevated by resistance heating. Prior to the HSB test, mould structure was designed to fit for resistance heating. Coupled thermal electrical structural finite element model of HSB process was created in ABAQUS. Resistance heating and HSB tests were performed using displacement control electrically assisted stretch bending machine. The results of simulation indicate that the temperature uniformity of titanium extrusion and the forming accuracy of curved part can be effectively improved by increasing the initial temperature of mould. At last, the curved part of titanium extrusion with L-section was achieved, and the forming accuracy of which was measured and evaluated.

Strain distribution at the transition from bent to unbent regions in tube rotary draw bending: an in-situ, real-time measurement study

In tube bending processes, accurate control of springback is of crucial importance as this affects the dimensional accuracy of the final product and overall equipment efficiency. The distribution of stress and strain during bending is one of the most fundamental issues determining the springback magnitude of the product. In conventional analyses of rotary draw bending, the deformation behaviour along the bending direction is normally assumed to be uniform for constant-radius bends, following the contour of the die configuration. In practice, however, the stress-strain distribution is non-uniform, particularly at the transition between the bent and unbent regions of the formed component. The distribution makes a significant contribution to springback and its variations, especially for low bend-angle components. This research focuses on exploring the strain distribution at the end transition of the bend of aluminium tubes in rotary draw bending. An experimental test setup for strain measurements with a strain gauge glued to the unbent area has been designed and conducted to measure the strain distribution during bending. The characteristics of non-uniform strain distribution during tube bending, including the evolving transition behaviour at the transition between bent and unbent areas, are studied. The results enhance the understanding of deformation characteristics of bent tubes, and contribute to improved physically-based models and springback control routines in industrial practice.

Springback prediction model of Ti-6Al-4V tube warm bending based on modified JC model considering variable temperature field

The plastic forming of titanium alloy tubes at room temperature exhibits strong anisotropy, low elongation, and large deformation resistance. Numerical control warm bending assisted forming technology can improve the stability of the titanium alloy tube bending process, increase the bending limit and reduce the springback angle. This technology promotes the wide application of high-precision titanium alloy bent tubes in many high-end fields such as aerospace, shipbuilding, chemical industry, and military industry. However, the titanium alloy tube bending at high temperatures involves complex material rheological behavior and microstructure characteristics. The coupling relationship between the stress-strain properties of the material and the temperature field makes it difficult to predict the springback behavior of titanium alloy tubes after warm bending. In this paper, based on the mechanical behavior of titanium alloy tubes at high temperatures, a constitutive model of titanium alloy suitable for local heating is improved. The theoretical model of springback for warm rotary draw bending of titanium alloy tube is established. The influence of warm bending strategies on the springback of bending is studied. The theoretical model is verified by establishing a thermal-mechanical coupling finite element model for the whole process of warm bending under the state of heat balance. The results show that the bending springback theory based on the modified John-Cook model can accurately simulate the temperature change of titanium alloy tube section, adapt to local heating strategies and provide high prediction accuracy of bending springback.

Three-dimensional modeling of joint kinematic of ductile iron pipelines subjected to normal faulting

Buried ductile iron (DI) pipelines are of paramount importance for urban water networks. The joint sealing performance can be seriously affected by fault offset, showing failures of axial pull-out of joint, joint crushing, joint rotation, and circular cracking caused by pipe bending. Analytical or beam-on-spring based numerical models and physical experiments have been done in the past, but the kinematic mechanism of DI pipes subjected to normal fault deserves to be understood using the three-dimensional (3D) finite element method. In this study, an explicit 3D numerical model is calibrated against a full-scale experiment, and is further adopted to analyze the impact of different parameters. It is demonstrated that joint rotation leakage dominates the failure mode, showing leakage at a single joint or two joints closest to the fault trace. The most unsafe fault-pipe crossing position is derived when the fault acts on one quarter of the rotated pipe barrel from the spigot, which can result in highly consistent pipe rotation pattern in the even configuration as proposed in existing theories. When the fault passes through the middle of the pipe barrel perpendicularly, the joints of DN 400 pipeline are more susceptible to leakage.

A Fast Conversion Method of Tube Coordinates

Inspired by the idea of the coordinate transformation of the robot arm, the tube structure is analogized to the robot arm structure, and the conversion method of the tube bend processing parameters LRA to the three-dimensional coordinate points is obtained. The method first regards the tube as a “mechanical arm”; then, using the similarity of the LRA processing parameters and D-H parameters, all the LRA parameters are converted into D-H parameters; finally, the D-H parameter method is applied to calculate the distance between each axis of the " mechanical arm ". If the first space coordinate point is defined as the origin of the base coordinate system , then the position of the origin of other coordinate systems in the base coordinate system can be obtained; It has been proved by experiments that this method fast and feasible.

Deformation behavior in tube bending: a comparative study of compression bending and rotary draw bending

As the first study in the field regarding CB, this paper investigates the implications of interchanging between RDB and CB through manufacturing bends with various angles and investigates the difference between the two methods in form of springback, cross section compression and widening, cross section shape and wall thinning/thickening. The experiments conducted consists of aluminum alloy 6060-T4 round tubes of 60 mm diameter and 3 mm wall thickness, bent around 222 mm radius tooling with various bend angles. In this case, we have found that CB is capable of manufacturing bends with quality near those manufactured by RDB with less springback, however with a dimensional penalty regarding increased deformation of the cross section.

On the buckling crossover of thick-walled pipe bend under external pressure

Pipe bend is a common junction in pipeline system. In this study, the post-buckling behavior of deep-sea thick-walled pipe bend under external pressure is studied by numerical simulation. A 4-node tetrahedron solid element based on vector form intrinsic finite element method (VFIFE) is introduced to simulate the whole buckling process. First, the VFIFE models of the thick-walled pipes are built and the results of the VFIFE method, traditional finite element method, and the experiments from other publications are compared to verify the proposed method. Then, collapse modes and collapse mechanism of the pipe bend when buckling propagates to the elbow under dynamic and quasi-static conditions are analyzed. Finally, the influence of different geometric parameters on the crossover pressure of the pipe bend is studied. These results can be used to support the buckling arrest design of pipe bends.

Topology optimization for rarefied gas flow problems using density method and adjoint IP-DSMC

In this paper, a topology optimization method based on direct simulation Monte Carlo (DSMC) is presented for rarefied gas flows. Distribution of fluid and solid in the design domain is characterized by a pseudo density. The traditional DSMC algorithm is extended to include the pseudo density by interpreting solid as an imaginary gas with fixed temperature and zero macroscopic velocity. Treating the pseudo density as the design variable, design sensitivity is obtained through the Lagrangian multiplier method and the adjoint state method. A discrete version of the adjoint equations is used, so that the adjoint variables can be evaluated using the information stored during the forward DSMC process. The information preservation (IP) method for subsonic flow is also considered in order to reduce random noise and simplify the discrete adjoint equations. The extended DSMC algorithm is verified by numerical examples, and optimized design for bent pipe is also included.

Influence of mandrel-cores filling on size effect of cross-section distortion of bimetallic thin-walled composite bending tube

Two new size factors of cross-section hollow coefficient and bending degree are introduced to reveal the size effect of bending forming of bimetallic composite tube. Hollow coefficient and bending degree can limit the commonly used bent tube to the size description range of (0, 2.00). The evolution laws of the cross-section distortion forms in the hollow coefficient-bending degree interval are revealed as well as the action of the mandrel-cores on the size effect. Results show the mandrel-cores filling can expand the forming limit of the bent tube, but also bring two other forming defects of wrinkle and rupture. The identification factor (hollow coefficient multiply bending degree) provides a method for querying the cross-section distortion forms of all composite bending tubes. In the identification factor interval (0, 1.00), the distribution area of bending forming defects of the composite tube is continuous. The thin-walled composite bending tube collapses when identification factor in (0, 0.39), wrinkles when identification factor in [0.39, 0.50), and ruptures when identification factor in [0.50, 1.00). The mathematical model of size effect is derived, by which the average cross-section distortion rate is found to distribute like a radial leaf in the hollow coefficient-bending degree qualified forming space. The best forming zone is hollow coefficient 0.46–0.68, and bending degree 0.25–0.47.

The vortex structures of the mean turbulent flow field in a 90-degree bend pipe

We analyse the vortex structures of the mean turbulent flow field in a 90-degree bend pipe at bulk Reynolds number 5300 and radius of curvature 2.5 times the pipe radius. The Reynolds averaged Navier–Stokes equations are solved for the mean turbulent flow field in the finite volume framework of ANSYS Fluent. The Reynolds stress model is adopted for closure of turbulence quantities. Notwithstanding any scale resolving simulation, we show that a detailed exploration of the flow, turbulence, and vortex structures in the mean turbulent flow field inside a pipe bend is possible, through the paradigm based on complex conjugate eigenvalues of the velocity gradient tensor. The convex contour of the inner side of the bend is found to be the key vortex-generating surface. We find that the vortices start to gain swirling strength just after entering the bend. The strength further decays, rather than getting enhanced, within the remaining part of the bend. The outer side of the bend, on the other hand, appears to maintain a straining flow regime. Fluid particles move between the vortex region and the straining region through the strain-dominated vortex regions, the structure of which is also unveiled through the eigenvalue-based vortex defining paradigm. Both the straining and the vortex zone inject turbulence. However, the vortex-induced turbulence suffers significant dissipation within the bend region. The vortices transported downstream of the bend help in generating turbulence to recover the loss of turbulence in the bend region.

Experimental and analytical studies on stability of ultra-strong thin-walled steel tube and coupler scaffolds

In this study, to improve the erection efficiency and reduce the weight of structures, an ultra-strong thin-walled steel tube and coupler scaffold (UTSTCS) is developed and investigated. Notably, the weight of this UTSTCS is ∼60% that of traditional scaffolds. Six ultra-high full-scale UTSTCS specimens are constructed and tested to determine the bearing capacity of the UTSTCS. A finite element model is built considering the initial member imperfection and semi-rigid behavior of right-angle couplers, based on which parametric studies are then conducted to investigate the method for determining the ultimate bearing capacity and influence of various geometric properties on the stability behavior of UTSTCSs. Compared with that of traditional scaffolds, the vertical bearing capacity of UTSTCSs does not decrease appreciably when the weight of the steel tube is reduced by 40%. Under a uniform vertical load, the main failure modes of UTSTCSs are top coupler slipping, top horizontal tube bending, and post bending. The joint type of the upper layer members, story height, and post spacing have evident influences on the bearing capacity. Moreover, the results of the proposed method for predicting the ultimate bearing capacity of UTSTCSs are in good agreement with the numerical simulation and experimental results.