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This work investigated the influence of bend curvature on turbulent flow parameters through a 90° pipe bend using the numerical CFD method implemented in ANSYS Fluent. The numerical predictions were validated to be in good agreement with existing experimental measurements. The turbulence of the secondary motion was found to be generally stronger at the outer end of the pipe bend, with the most adverse effect recorded at about 45° along the bend. It was also observed that the RMS velocity is larger near the wall, especially at the outer wall region, and it is highest at 45° due to an increase in the circulation of dean vortices, indicating a turbulence generation. In addition, the RMS velocity increases downstream due to an additional mean strain resulting from secondary flow formation as the flow travels through the bend. Furthermore, larger static pressure and turbulent viscosity were observed at the outer wall due to the flow deceleration and swirling. Therefore, it can be established that the bend curvature affects the stability of the flow field inside a pipe bend. [ABSTRACT FROM AUTHOR]

In conveying concentrated liquid–solid mixtures in pipelines oriented horizontally, gravitational settling promotes a concentration-rich layer of solids at the pipe invert that degrades the wall due to sliding (abrading) action against the wall. The current study investigates near-wall flow field characteristics and then obtains flow and geometry conditions using a response surface methodology (RSM) that minimizes the maximum sliding frictional power developed in the vicinity of a 90° horizontal bend for transporting a dense solid–liquid mixture. The liquid–solid flow field is mathematically modeled with a Eulerian–Eulerian approach using the realizable k − ε model with standard wall functions for turbulence modeling. The effect of several operating parameters such as solid concentration, mixture velocity, particle sizes, pipe diameters, and bend ratios on the near-wall flow field in the bend reveals useful insight relevant to the bend wall degradation by solid particles. A reduction of 28% in the maximum sliding frictional power is achieved with the optimized flow conditions within the operating range considered. The novel approach could be utilized in an apriori estimation of the erosion in bends for any particle-pipe wall material combination in the hydro transport of dense solids. [Display omitted] • Water-sand flow characteristics are investigated for estimating frictional power. • Sliding frictional power is computed based on the energy approach. • Response surface methodology is used for optimizing frictional power. • Optimized flow conditions resulted in reduction in frictional power by 28%. • A priori estimation of bend erosion for any particle-pipe material combination. [ABSTRACT FROM AUTHOR]

This work investigated the influence of bend curvature on the parameters of turbulent flow through a 90° pipe bend using the numerical CFD method, implemented in ANSYS Fluent. The numerical predictions were validated to be in good agreement with existing experimental measurements. The turbulence of the secondary motion was found to be generally stronger at the outer end of the pipe bend, with the most adverse effect recorded at about 45° along the bend. It was also observed that the RMS velocity is larger near the wall, especially at the outer wall region, and it is highest at 45° due to an increase in the circulation of dean vortices, indicating a turbulence generation. In addition, the RMS velocity increases downstream due to an additional mean strain resulting from the creation of secondary flow as the flow travels through the bend. Furthermore, larger static pressure and turbulent viscosity were observed at the outer wall due to the flow deceleration and swirling. Therefore, it can be established that the bend curvature affects the stability of the flow field inside a pipe bend.

Non-Newtonian fluid flow in pipe bends is inevitable in industrial applications. Previous researchers have extensively explored Newtonian flow through curved ducts. However, the non-Newtonian counterpart gets little attention. We study the turbulent flow of shear-dependent fluids obeying the Power-Law model in a pipe manifold containing an in-plane double bend. Ostwald–de Waele's power law is used to model the fluid's rheology. We utilize computational fluid dynamics (CFD) to solve Reynolds-averaged Navier–Stokes (RANS) equations with the k-ε turbulence model. We validate our numerical results with previous experimental results. The in-plane double bend perturbs the flow in the pipe manifold to develop a Prandtl's secondary flow of the first kind. A fully developed flow at the bend upstream is disturbed due to the bend's curvature and regains its fully developed characteristics upon a certain downstream length after the exit of the bend. We study the rheological characteristics of the secondary flow within the bend and the evolution of fluid flow at the bend downstream. We demonstrate that the centrifugal force-dominated secondary flow increases with a decrease of the non-Newtonian power-law index. We capture the camel's-back-shaped velocity profiles within the bend due to accelerating-decelerating flow. The study reveals that the average flow velocity increases along the bend with a corresponding pressure head loss. We quantify this velocity rise by a newly introduced non-dimensional number, viz. enhancement ratio. The double bend's enhancement ratio decreases with an increase in n.

Non-Newtonian fluid flow in pipe bends is inevitable in industrial applications. Previous researchers have extensively explored Newtonian flow through curved ducts. However, the non-Newtonian counterpart gets little attention. We study the turbulent flow of shear-dependent fluids obeying the Power-Law model in a pipe manifold containing an in-plane double bend. Ostwald-de Waele's power law is used to model the fluid's rheology. We utilize computational fluid dynamics (CFD) to solve Reynolds-averaged Navier-Stokes (RANS) equations with the k-ε turbulence model. We validate our numerical results with previous experimental results. The in-plane double bend perturbs the flow in the pipe manifold to develop a Prandtl's secondary flow of the first kind. A fully developed flow at the bend upstream is disturbed due to the bend's curvature and regains its fully developed characteristics upon a certain downstream length after the exit of the bend. We study the rheological characteristics of the secondary flow within the bend and the evolution of fluid flow at the bend downstream. We demonstrate that the centrifugal force-dominated secondary flow increases with a decrease of the non-Newtonian power-law index. We capture the camel'sback-shaped velocity profiles within the bend due to accelerating-decelerating flow. The study reveals that the average flow velocity increases along the bend with a corresponding pressure head loss. We quantify this velocity rise by a newly introduced non-dimensional number, viz. enhancement ratio. The double bend's enhancement ratio decreases with an increase in n. [ABSTRACT FROM AUTHOR]

The stability of pressure pipe bends is evaluated by the equilibrium between the thrust force and resistance forces in the current design, and the behavior of pipe bends is not considered. Force–displacement (F–D) relationships, which are used for predicting the displacement of pipe bends, include the performance of pipe joints in the design of pipe bends and shift the design method to a performance-based approach. However, F–D relationships have been proposed only under plane-strain conditions. The behavior of pipe bends cannot be represented in two dimensions. Therefore, in this study, the prediction method of the F–D relationship for buried structures is extended to a three-dimensional condition to improve the design method of pipe bends with thrust restraint. Lateral loading experiments on thrust restraint, using rigid thrust blocks and flexible thrust restraints with geogrids and gravel, were conducted in dry sand to investigate the lateral behavior of rigid and flexible thrust restraints and to obtain F–D curves with different dimensions of thrust restraint. The experimental results revealed that the deformation of the flexible thrust restraint had little effect on the lateral resistance force if proper dimensions of the thrust restraints were determined. Using the experimental results, the F–D relationship was formulated based on a hyperbolic curve. The proposed equations were able to predict the resistance force relatively well at small lateral displacements. In addition to the formulation of the F–D relationship, a new design procedure considering the pipe displacement and performance of pipe joints was developed by combining the proposed F–D prediction method and the joint separation model proposed in previous studies. [ABSTRACT FROM AUTHOR]

The investigation of the turbulence statistics for single-phase turbulent flow around pipe bends have mainly been experimental. Considering the cost-effectiveness of the numerical computational fluid dynamics (CFD) compared to experimental measurement, this work aims to study the accuracies of different CFD models, and establish their functionality and limitations. This paper investigates the capabilities of different numerical turbulence models and spatial discretization schemes for CFD analysis of a pipe bend. The pipe has a curvature radius which is seven times the inside diameter and a Reynolds number of 34132. The numerical modelling was developed on the commercial CFD software, ANSYS Fluent, evaluating the following viscous models:,, Spalart-Allmaras and Reynolds Stress Models. The streamwise velocities of the flow at cross-stream planes along the bend at 45º and 75º were computed for each of the turbulence models under different discretization schemes. The numerical results were compared against the existing experimental data for streamwise velocity, in order to investigate the accuracies of the different models. The results showed that the realizable K-E and Spalart-Allmaras models exhibited the best agreements with the experimental measurements, with respective average errors of 3.83% and 3.27% under the first-order spatial discretization scheme. It was also observed that the velocity profiles obtained through the K-W models (Standard and BSL), Transition SST and Reynolds Stress models exhibited better correlation with the experimental velocity profiles within the velocity transition region.

The safety of the piping systems used in any nuclear or thermal power plant is essential to the environment and also to the people involved. Pipe bends are one of the critical components of the piping system. Hence, fatigue life estimation becomes primary focus when the designing pipe bends for their safety limits. The current study uses finite element analysis and the revised manson universal slope method to estimate the life of elbows under in-plane opening and closing cyclic bending moment. The estimated fatigue life was compared with low-cycle fatigue tests in the literature. The displacement of 20 mm was given as input to estimate the number of cycles. The principal stresses were obtained on the highly strained node of the finite element model to locate the crack and its direction accurately. The elbows with thinning have a reduction in the fatigue life of about 19%. [ABSTRACT FROM AUTHOR]

Piping systems in nuclear power plants normally operate under high pressure and high temperature. To efficiently manage space within these systems, pipe bends are extensively used. However, the welded joints connecting these pipes may be susceptible to flaws due to weld residual stress, transient loads, and operating environments. When flaws are present in such areas, analytical evaluation of flaws is to be carried out based on fracture mechanics parameters such as stress intensity factor. To calculate the stress intensity factor, distributions of the elastic stress are required. Therefore, this paper presents closed-form approximations of elastic stress in the junction between a pipe bend and a straight pipe under internal pressure. Review of the existing elastic stress solutions for estimating the stresses in pipe bends was carried out analyzing their limitations. Based on those limitations elastic stress solutions for thick to thin wall pipe bends were proposed and were validated against finite element (FE) analysis for thick-wall to thin-wall pipe bends under internal pressure and combined loading (i.e. internal pressure, in-plane bending, out-of-plane bending inflicted simultaneously). 90 ° pipe bend, U-bend and double-bend pipe configurations were considered and showed good agreement with the FE results exhibiting less than 5.8 % discrepancies. The accuracy of the elastic stress solutions for pipe bends provided in the existing code are summarized and validated in the appendix as well. [Display omitted] • Elastic stress solutions for estimating the stresses in the junction between a pipe bend and a straight pipe are proposed. • Existing elastic stress solutions for pipe bends were reviewed, and their limitations and accuracies were checked via finite element analysis. • The applicable range of the existing elastic stress solutions (RCC-MRx A16) was re-evaluated through FEA. • The proposed elastic stress solution was validated by comparing estimated stresses with results from finite element analysis. [ABSTRACT FROM AUTHOR]

In this work, extended finite element method (XFEM) is used to simulate the fracture mechanics problems of part-through semi-elliptical circumferential crack in functionally graded pipe and pipe bend. Part-through semi-elliptical circumferential crack present in functionally graded pipe and pipe bend at different location has been subjected to internal pressure. Higher order shape function is used to model the crack with level set functions. The inner surface of the functionally graded pipe/pipe bend contains 100% steel alloy and outer surface contains 100% alumina ceramic. The material property gradation is followed by exponential law from inner surface to outer surface of the pipe and pipe bend in radial direction. Domain-based interaction integral approach has been used to determine the stress intensity factor at different location of the crack front. [ABSTRACT FROM AUTHOR]

Aircraft pipelines are mainly used for the storage and transportation of fuel, hydraulic oil and water, which are mostly bent pipes of non-ferromagnetic materials. We used PPM (Periodic Permanent Magnet) EMAT (Electromagnetic Acoustic Transducer) to detect the defects at 90-degree bends. A simulation model was established by finite element software to study the propagation characteristics and defect detection capability of T (0, 1) mode-guided wave in aluminum pipe bend. In terms of propagation characteristics, the energy of the guided wave was focused in the extrados of the bend, and the guided waves in the intrados and extrados of the bend were separated due to the difference in propagation distance. Regarding defect detection capability, T (0, 1) mode-guided wave had the highest detection sensitivity for the defect in the extrados of the bend and the lowest detection sensitivity for the defect in the middle area of the bend. We designed a PPM EMAT for 320 kHz to verify the simulation results experimentally, and the experimental results are in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

This paper deals with material and dimensional bending analysis of bimetallic pipes with defined bending radii. Basic characteristics of selected nickel superalloys with analysis of Inconel 625 and 16Mo3 steel in terms of primary mechanical properties and chemical composition are presented. In the practical part where the bimetallic tube is analyzed in terms of material properties is also performed geometric dimensional analysis, for which test specimens with different bending radii are made. The capillary test preceded dimensional analysis to remove cracks on the outer bend surfaces of the bimetallic tube. The geometric dimensional analysis itself is carried out using a 3D scanner and also includes external dimensional inspection in longitudinal section with changes in the curvature of bimetallic pipe bends for different bending radii. The article concludes with an overall evaluation of the achieved results, especially with regard to the deviations of rounding in individual sections of the external dimension.

From the recent literature, it is revealed that pipe bend geometry deviates from the circular cross-section due to pipe bending process for any bend angle, and this deviation in the cross-section is defined as the initial geometric imperfection. This paper focuses on the determination of collapse moment of different angled pipe bends incorporated with initial geometric imperfection subjected to in-plane closing and opening bending moments. The three-dimensional finite element analysis is accounted for geometric as well as material nonlinearities. Python scripting is implemented for modeling the pipe bends with initial geometry imperfection. The twice-elastic-slope method is adopted to determine the collapse moments. From the results, it is observed that initial imperfection has significant impact on the collapse moment of pipe bends. It can be concluded that the effect of initial imperfection decreases with the decrease in bend angle from 150∘ to 45∘. Based on the finite element results, a simple collapse moment equation is proposed to predict the collapse moment for more accurate cross-section of the different angled pipe bends. [ABSTRACT FROM AUTHOR]

Bimetal pipes are highly stressed composite components that must resist corrosion in a chemically aggressive environment. They are made by welding resistive material to commonly available carbon steel pipes. The production of pipe bends with a supercritical bend of 0.7D, which are part of serpentine systems, is very complex and technologically demanding because very often undesired cracks occur. To increase the service life of these serpentine systems, the use of a 16Mo3 base steel pipe with a cladding layer of Inconel 625 material was proposed for their production in order to significantly increase their corrosion resistance. For this reason, an extensive analysis of the production of pipe bends with a supercritical bend of 0.7D from bimetal pipes with Inconel 625 cladding was performed, which addressed not only the bend but also the mechanical properties of the pipe with Inconel 625 cladding. It was found that the production of the bent pipes with a bend of 0.7D is feasible completely without defects with perfectly satisfactory mechanical properties, under appropriate technological conditions. [ABSTRACT FROM AUTHOR]

The erosive wear rate caused by slurry flow is the worst phenomenon associated with complex geometry like bend, curved cross section and rotating machinery. The numerous quantitative research is available in the past for findings of erosive wear rate through pipe bend, but findings of erosive wear rate through pipe bend using Fluent based various erosion models are not yet established. In the present work, erosion wear rate using four computational-based erosion models viz. Generic, Oka, Finnie and Mclaury through horizontal mitre pipe bend instigated by bottom ash particulates slurry has been investigated using Fluent code. The solid particulates of spherical shapes 162 µm, 300 µm and 445 µm having density 2219 kg/m3 were tracked to compute the erosion wear rate using Discrete Phase Model (DPM). The particulates were tracked using Eulerian–Lagrangian approach coupled with k−ɛ turbulent model at volume fraction ranging from 2.5 to 10% for wide range of velocities viz. 1–10 ms−1. Additionally, the results of DPM concentration, turbulence intensity, velocity and particle tracking using particulate residence time were predicted to analyze the erosive rate through pipe bend. The simulated outcomes show that the maximum erosion wear rate exists at the extrados of pipeline near the bend exit. Finally, the effects of particulate size, concentration and velocity were discussed on erosion wear rate. Furthermore, the simulated outcomes obtained through computational erosion models were verified with the available experimental data and findings show that the outcomes obtained with Generic model could be the benchmark for designing the slurry pipeline bend. [ABSTRACT FROM AUTHOR]

Laminar fluid-particle flows in bend geometries are present in many industrial, pharmaceutical, and biomedical applications. Particle deposition has been studied extensively; however, little attention has been paid to the effect of particle sedimentation on particle position and deposition in different pipe geometry combinations. This study presented a comprehensive analysis of sedimentation effects on particle flow behaviour in 90° circular pipe bends of micron particles in laminar pipe flows. Pipe geometry combinations consisted of eight pipe diameters, nine bend radii, and 30 particle diameters in a range of 1 to 100 μm. The results demonstrated the locations of particles that sedimented to the bottom half of the straight pipe section, and the particle positions upstream from the pipe bend entrance, which was no longer in a fully developed profile. These new locations represent the effects of gravity, pulling the particles down. While obtaining these positions can be found through CFD analysis, we proposed an analytical solution to predict the particle trajectory from different release locations that would help to identify the initial particle distribution at locations upstream to the bend, to obviate the need for long upstream straight pipe sections in the CFD analysis. [Display omitted] • The effect of particle sedimentation on pipe geometry combinations was studied. • The study emphasized the sedimentation for micron particles in laminar pipe flows. • Combinations: 8 pipe diameters, 9 bend radii, and 30 particle diameters in microns. • Sedimentation caused particle deposition on the inner wall side of the pipe bend. • To obviate the need for long upstream straight pipe sections in the CFD analysis. [ABSTRACT FROM AUTHOR]

In this study, a bidirectional fluid-structure interaction (FSI) method was proposed based on dynamic mesh technology to calculate the erosion defects of pipe bends under high pressure. In calculating the erosion rate of pipe bends, a stress erosion model was adopted, and the displacement and stress of the inner wall of pipe bend under high external pressure were considered. The influence of different parameters on the calculation results of erosion depth was discussed, and the buckling pressure and collapse mode of pipe bend under the erosion defect of liquid-solid flow were also studied. The proposed method can be used for predicting pipeline erosion defects under high pressure and evaluating the remaining limit load of pipelines with such erosion defects. • A bidirectional fluid structure interaction method was proposed to calculate the erosion of pipe bend under high pressure. • The deformation and stress of pipe bend under high pressure were considered in the fluid domain calculation. • A displacement field transfer method was proposed to update the solid mesh automatically based on erosion results. • The influence of erosion defects on pipe bend buckling was analyzed on the basis of erosion analysis. [ABSTRACT FROM AUTHOR]

The present study was carried out in an attempt to reduce head loss in 90° pipe bends for conveying coal-water slurry suspensions using computational fluid dynamics (CFD). Bend geometries were modified by altering the r/D ratios within the range of 1.5–3.0. Numerical simulations were performed using several turbulence models for a solid concentration range of 30–60% (by weight) and the results were validated with experimental data. An Eulerian multiphase model along with an SST k-ω turbulence scheme was found most appropriate and shows decent agreement with experimentation results. The mean sizes of coal particles were taken as 16 μm. Results show that head loss was increased with flow velocity and solid concentration. It was also observed that r/D ratio has a significant impact on head loss characteristics. The minimum drop in head loss was observed in a pipe bend having an r/D ratio of 2.0. The effect of flow separation and secondary flows on turbulence, flow velocity and distribution of the solid suspension inside the bend geometry was also studied with the help of contours. [ABSTRACT FROM AUTHOR]

In the present study turbulent flow in a circular cross-sectioned 90° smooth-walled pipe bend has been investigated numerically. The geometry of the model consisted of three sections: a straight inlet pipe of length 52 diameters, a 90° bend with radius of curvature 1 diameter, and a straight downstream pipe of length 52 diameters. Reynolds numbers from 5,000 to 120,000 were considered. The numerical model was developed using COMSOL Multiphysics and all turbulent flow simulations were performed using the standard k - ε turbulence model. The main objective of this work was to estimate the resistance coefficient of pipe bends using not only pressure drop but also information of the flow behavior far downstream in the outlet pipe. Wall static pressure and velocity fields of the secondary flow were illustrated to provide information of the flow behavior in the bend and downstream of the pipe bend. Furthermore, swirl intensity of secondary flow was presented in order to describe its behavior as the flow develops in the outlet pipe. Estimations of resistance coefficient were calculated and compared to other studies. It was found that the procedure used in this study is a viable method for a more accurate estimation of resistance coefficient values for turbulent pipe flows containing 90° bends. For best accuracy in either experimental or computational analyses, it is recommended that pressure in the downstream tangent be measured at no less than fifty diameters downstream of the bend to avoid influence of the secondary flow. [ABSTRACT FROM AUTHOR]

Results are provided for comprehensive research conducted in PJSC VTI on large diameter pipe bends prepared by electroslag melting (ESM) of steel 15Kh1M1F-Sh intended for thermal power plant steam lines. Material from various bending zones is studied in order to evaluate the effect of bending on the quality of electroslag metal: a straight section, stretched, and compressed areas. Analysis of research results with the assessment of pipe bend operating life characteristics is conducted. [ABSTRACT FROM AUTHOR]

This study investigates the solid particle erosion in an elbow of a slurry conveying circuit by using a commercial computational fluid dynamics (CFD) code FLUENT. Erosion wear was predicted by using the Euler-Lagrange model applied with a turbulence scheme of standard k-ε. In the present study, the effect of various design parameters, namely radius of bend-to-pipe diameter (r/D) ratio, pipe diameter (D), bend curvature angle, and bend radius angle, was studied. The radius of the r/D ratio varied from 1.4 to 1.7. The flow velocity varied between 2 and 5 m/s and the solid concentration was kept constant, i.e., 10 vol.%. The mean size fraction of bottom ash varied from 102 to 300 μm. Numerical simulation results show that erosion rate increases with velocity, particle size, and pipe diameter. The optimum value of the r/D ratio was between 1.5 and 1.6. Lower erosion wear occurred near the entrance of the elbow and reached the maximum near 60° of the bend curvature. The particle size range of 162–230 μm was found critical for high erosion wear. [ABSTRACT FROM AUTHOR]

The present study investigates head loss for flow of coal–water slurry inside 90° pipe bend. The experiments were conducted with slurries of different solid concentrations, varying from 31.4 to 60.8% (by weight). Pulverized coal samples with particle sizes of less than 53 µm were used to prepare the slurry. During experimentation, average flow velocity was kept in the range of 2–5 m/s. Extensive rheological experimentation was performed to analyze the flow characteristics of coal–water slurry with and without the addition of additive namely sulfonic acid. Sulfonic acid was mixed with coal–water slurry in proportions of 1–4% (by weight) at higher concentrations (i.e., 60.8%). Coal–water slurry showed Newtonian behavior at low concentrations of 30%; above, it shows pseudoplastic behavior. The head loss across the pipe bend increases as the solid concentration of slurry increases and decreases as the proportion of an additive increases. Losses occurring in bend curves were given in terms of bend loss coefficient. The bend loss coefficient decreased as flow velocity increased and increased as solid concentration increased. The present study also highlights the role that solid concentration plays with regard to settling velocity of coal–water slurry. A trend of decreasing settling velocity was observed while the solid concentration (by weight) of the slurry was increased. [ABSTRACT FROM AUTHOR]

Pipe bends are inevitable in industrial piping systems, turbomachinery, heat exchangers, etc. Computational fluid dynamics (CFD), which is commonly employed to understand the flow behavior in such systems has very accurate estimation but is computationally cost intensive. Thus, in this paper, an efficient computational approach for such computationally expensive problems is presented. Using genetic programming (GP), metamodels are built using a small number of samples points from the CFD data. These GP metamodels are then shown to be able to replace the actual CFD models with considerable accuracy. The applicability and suitability of the GP metamodels are validated using a variety of statistical metrics on the training as well as independent test data. It is shown that the use of metamodels leads to significant savings in computational cost. [ABSTRACT FROM AUTHOR]

In the flow of fluid in pipeline, the pressure drop in a curved pipe is generally greater than that in a straight pipe. Several studies have been conducted on the quantitative prediction of concrete pumping using the rheological properties of concrete and lubricating layer. However, there have not been many studies to quantitatively investigate the pressure loss in a pipe bend. In this study, the effects of pressure loss by the pipe bends were investigated through realscale concrete pumping tests. The real-scale pumping tests were performed for horizontal pipelines of 133, 369, and 560 m (145, 404, and 612 yd), and a total of four concrete mixtures were used for tests. In addition, the data obtained from previous pumping tests with 350 and 548 m (383 and 599 yd) horizontal pipelines were also analyzed. From the tests and analysis, it was found that the pressure loss in pipe bends is greater than the straight pipeline by approximately two times. [ABSTRACT FROM AUTHOR]

Local wall-thinning of pipe is a common volume defect in application, which would cause pipeline leakage or rupture under complicated pipeline loads. The finite element analysis method was used to analyze the limit load of Pipe Bend with Local Wall-Thinning defect (PB LWT) under internal pressure, bending moment, torsion moment, axial force, and their combinations. The limit load empirical equations of PB LWT under single load and complex loads were fitted. According to the allowable pipeline load on equipment nozzles, the influences of torsion moment and axial force on the load bearing capacity of PB LWT were quantitatively analyzed. It is found that the load bearing capacity is reduced by an average of 1 % for medium and low-pressure equipment. For high-pressure equipment, the load bearing capacity is reduced by 10.07 %∼20.90 % under the influence of torsion moment. Under the effect of axial force, the load bearing capacity is reduced by 2.01 %∼12.40 %. • The limit loads of bends with extrados local wall-thinning defect are analyzed under internal pressure, bending moment, torsion moment, axial force, and their combinations. • Empirical equations for limit load of bend with defects are worked out for complex loads. • Torsion and tension can decrease the load-bearing capacity of bends by up to 10 %∼20 %. [ABSTRACT FROM AUTHOR]

The sections of pipe bends are hot spots for wall thinning due to accelerated corrosion by fluid flow. Conventionally, the thickness of a bend wall is evaluated by local point-by-point ultrasonic measurement, which is slow and costly. Guided wave tomography is an attractive method that enables the monitoring of a whole bend area by processing the waves excited and received by transducer arrays. The main challenge associated with the tomography of the bend is the development of an appropriate forward model, which should simply and efficiently handle the wave propagation in a complex bend model. In this study, we developed a two-dimensional (2D) acoustic forward model to replace the complex three-dimensional (3D) bend domain with a rectangular domain that is made artificially anisotropic by using Thomsen parameters. Thomsen parameters allow the consideration of the directional dependence of the velocity of the wave in the model. Good agreement was found between predictions and experiments performed on a 220 mm diameter (d) pipe with 1.5d bend radius, including the wave-field focusing effect and the steering effect of scattered wave-fields from defects.

Bending of pipes is a major problem facing the engineers during the construction of a long pipeline for transporting coal–water slurry. However, the use of 90° bends in slurry transportation is restricted because it causes high head loss, and so very high pumping power is required to overcome this resistance. In this context, the present study is carried out to reduce the head loss for the flow of coal–water suspension across 90° pipe bends by varying bend geometry. Rheological experiments were performed to study flow characteristics of coal–water suspension with/without the additive. Coal–water slurry exhibits Newtonian behavior at a solid concentration of 30 wt% and pseudoplastic flow nature at concentration above 30%. Head loss experiments were carried out on a pilot plant test loop for a solid concentration of 30.27–61.56% with flow velocity ranging from 2 to 5 m/s. The r / D ratio for the pipe bend varied within the range of 1.5–2.5. The present study reveals that the head loss across pipe bends increased as solid concentration and flow velocity was increased. The optimum r / D ratio value for a minimum head loss was found to be 2.0. Also, significant decreases in apparent viscosity and head loss were perceived with the addition of a small amount of sulfonic acid. Power required to pump coal–water slurry was decreased by 15.93% with the use of an additive. A correlation for the head loss in terms of solid concentration, flow velocity, and r / D ratio was also developed. [ABSTRACT FROM AUTHOR]

The pipe bends are common elements in pipeline network of mechanical systems. The losses in pipes and bend are generally considered as insignificant and unavoidable. The recent trends in achieving a higher order of performance in machines led to optimization by reduction in minor energy losses. The usage of components with the higher surface finish is the main methodology adopted for minimizing frictional loss. In bends, especially in the case of turbulent flows, the losses are significant when comparing the frictional pipe losses. The viscous interaction between fluid layers is more in bends due to the presence of flow separation secondary swirling motion. The reduction in these interactions can be achieved by installing turning vane (guide vanes) inside the pipe bend. The current literature available lacks detailing of many included flow physics in bends and vaned bends. The present work focuses on flow characteristics on a 90° curved bend. Incompressible isothermal RANS solutions were performed using turbulence treatment with the k − ω SST model. The initial validation study is carried out with available experimental results. The bend downstream velocity distribution and bend wall pressure distribution are carried out. Further, the computational methodology is extended to bend with different vane configurations and for different Reynolds numbers. The velocity, wall pressure, swirl strength, turbulent kinetic energy, etc. are reported for downstream locations. The comparison of pressure loss through different cases and improvements in flow through bend due to the inclusion of vanes are discussed in this work. [ABSTRACT FROM AUTHOR]

In the present study, erosion wear of a 90o pipe bend has been investigated using the Computational fluid dynamics code FLUENT. Solid particles were tracked to evaluate the erosion rate along with k-ɛ turbulent model for continuous/fluid phase flow field. Spherical shaped sand particles of size 183 µm and 277 µm of density 2631 kg/m3 are injected from the inlet surface at velocity ranging from 0.5 to 8 ms-1 at two different concentrations. By considering the interaction between solid-liquid, effect of velocity, particle size and concentration were studied. Erosion wear was increased exponential with velocity, particles size and concentrations. Predicted results with CFD have revealed well in agreement with experimental results. The magnitude and location of maximum erosion wear were more severe in bend rather than the straight pipe. [ABSTRACT FROM AUTHOR]

Throughwall circumferential cracks (TWC) in elbows can considerably minimize its collapse load when subjected to in-plane bending moment. The existing closed-form collapse moment equations do not adequately quantify critical crack angles for structurally distorted cracked pipe bends subjected to external loading. Therefore, the present study has been conducted to examine utilizing elastic-plastic finite element analysis, the influence of structural distortions on the variation of critical TWC of 90° pipe bends under in-plane closing bending moment without and with internal pressure. With a mean radius (r) of 50 mm, cracked pipe bends were modeled for three different wall thickness, t (for pipe ratios of r / t = 5,10,20), each with two different bend radius, R (for bend ratios of R/r = 2,3) and with varying degrees of ovality and thinning (0 to 20% with increments of 5%). Finite element analyses were performed for two loading cases namely pure in-plane closing moment and in-plane closing bending with internal pressure. Normalized internal pressures of 0.2, 0.4, and 0.6 were applied. Results indicate the modification in the critical crack angle due to the pronounced effect of ovality compared to thinning on the plastic loads of pipe bends. From the finite element results, improved closed-form equations are proposed to evaluate plastic collapse moment of throughwall circumferential cracked pipe bends under the two loading conditions. [ABSTRACT FROM AUTHOR]

In the present study, erosion wear behavior of slurry pipeline due to solid–liquid suspension in the pipeline has been investigated using commercial computational fluid dynamics (CFD) code FLUENT. A multiphase Euler–Lagrange model was adopted to predict the solid particle erosion wear in a 90° pipe bend for the flow of bottom ash–water suspension. A standard k–ε turbulence modeling scheme was used to simulate the flow through the pipeline. Water and bottom ash were taken as liquid and as a dispersed phase of solid–liquid mixture, respectively. A simulation study for erosion wear in a pipe bend was carried out to investigate the influence of various parameters including velocity, solid concentration, and particle size. The velocity of the bottom ash–water suspension varied from 0.5 to 2.5 m/s for solid concentrations with a range of 2.5 to 10.0% (by volume). The particle diameters of the bottom ash were 162 and 300 µm. The simulation results agree with the results of previous studies. [ABSTRACT FROM AUTHOR]

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