Elbow Pipe Research Articles

Development of an empirical model to predict the burst pressure of corroded elbows of pipelines by finite element modelling

Burst capacity assessment at a corrosion defect of pipe elbows subjected to internal pressure is essential for oil/gas pipeline integrity management. In this study, a three-dimensional (3D) nonlinear finite element (FE) model validated by burst tests was developed to investigate the effect of corrosion defects on the burst capacity of X80 pipe elbows. Subsequently, the effects of corrosion geometry (i.e. depth, length, and width of the defect) on the pipe burst pressure were determined. Based on the Goodall model of intact pipe elbows, a reasonable mathematical expression for the failure pressure prediction formula for corroded pipelines under external loads was derived by introducing a defect geometry factor function. Then, combined with a series of FE cases, a new prediction model of burst pressure for corroded pipe elbows experiencing internal pressure was developed. Finally, the accuracy and reliability of the proposed model were verified using extensive parametric FE analysis. The results show that the average error of failure pressure between the proposed model and FEM was only 3.63% for 291 cases. Moreover, the prediction accuracy was better than other well-known models. Therefore, the proposed model can be widely used in the safety assessment of corroded elbows of oil/gas pipelines.

Micromechanical elastoplastic limit analysis of in-plane bending of Functionally Graded Pipe elbows

Pipe elbows, also known as pipe bends, are important components of a piping system. These curved elements are very flexible when compared to their straight counterparts, and are often responsible for reducing the reaction forces and moments within the piping system. However, due to large deformations, the elbows are more likely to exceed their stress limits. The effect of in-plane bending on plastic limit loads of Functionally Graded (FG) pipe bends is presented using three-dimensional non-linear finite element analysis and a micromechanical constitutive model. The effective properties of the material are estimated by the Mori–Tanaka homogenization scheme and the TTO plasticity model. The analysis was carried out for different loading cases, geometries and volume fraction distribution. The results showed that an FG elbow has a very distinct behavior comparatively to a similar homogeneous elbow made out of metal, specially in terms of limit moments and stress distribution. Finally, an analytical model to estimate the limit moment of FG elbows is presented.

Discussion On Failure Behavior of Piping Systems Under Extremely Large Seismic Loads in BDBE

Abstract To investigate the failure behavior of piping systems under severe seismic loads considering beyond design basis event (BDBE), an experimental approach to use pipes made of simulation materials was applied. "Simulation material" means the substitute material for steel to realize the structural experiment by the existing testing facilities. The simulation materials adopted in this study were pure lead (Pb) or lead-antimony (Pb-Sb) alloy. Using pipe elbows made of simulation materials, static loading tests on elbows and shaking table tests on simple piping system models composed of one or two elbows and an additional mass were conducted. From the static loading tests, the load-deflection relationship of an elbow under monotonic loading was obtained as well as the fatigue failure modes under cyclic loading depending on the several cyclic displacement levels. From the shaking table tests, several failure modes were obtained, namely, "Collapse by self-weight", "Collapse by a few cycles of input", "Ratchet and subsequent collapse", "Overall deformation", and "No failure". It was considered that the occurrence of these failure modes was affected by the ratio of the input frequency to the specimen's natural frequency, the ratio of additional mass weight to the limit mass weight, the configuration of the specimen, and the input acceleration level. The experimental results indicated that it was crucial to understand the structure's ultimate behavior when treating BDBE, and that the research approach using simulation material is effective to investigate the ultimate behavior of piping systems.

Evaluation of the Limit State of a Six-Inch Carbon Steel Pipe Elbow in Base-Isolated Nuclear Power Plants

The installation of base isolation systems in nuclear power plants can improve their safety from seismic loads. However, nuclear power plants with base isolation systems experience greater displacement as they handle seismic loads. The increase in relative displacement is caused by the installed base isolation systems, which increase the seismic risk of the interface piping system. It was found that the failure mode of the interface piping system was low-cycle fatigue failure accompanied by ratcheting, and the fittings (elbows and tees) failed due to the concentration of nonlinear behavior. Therefore, in this study, the limit state was defined as leakage, and an in-plane cyclic loading test was conducted in order to quantitatively express the failure criteria for the SCH40 6-inch carbon steel pipe elbow due to low-cycle fatigue failure. The leakage line and low-cycle fatigue curves of the SCH40 6-inch carbon steel pipe elbow were presented based on the test results. In addition, the limit state was quantitatively expressed using the damage index, based on the combination of ductility and energy dissipation. The average values of the damage index for the 6-inch pipe elbow calculated using the force−displacement (P–D) and moment−relative deformation angle (M–R) relationships were found to be 10.91 and 11.27, respectively.

Numerical investigation on ice slurry flow in horizontal elbow pipes

Ice slurry has been put into use as secondary refrigerant in many industrial fields due to its promising characteristics. But the complex flow properties of ice slurry flow have brought significant difficulties to transport processes. In this paper, a CFD-PBM coupled model has been employed to investigate the flow characteristics of the ice slurry flow in horizontal various elbow pipes. The ice kinetics processes (growth, aggregation, and breakage) are all taken into consideration. The results show that different elbow angles affect the pressure, velocity, ice size and uniformity of ice slurry when flowing across the elbow. Longer length and higher bending angle of elbow make boundary layer separation and secondary flow more obvious. For the elbow angle less than 90°, the redistribution of pressure and velocity enhance the aggregation process at pipe section center at elbow outlet sections, which results in the growth of ice particles. The inlet velocity, ice packing fraction (IPF) and elbow angle both influence the uniformity of ice slurry. Inlet velocity has positive correlation, while IPF and elbow angle have reverse effect. In order to improve the efficiency of ice slurry transport process and avoid the ice blockage, higher velocity, lower IPF and suitable elbow angle (less than 90°) are suggested.

Water Hammer and Harmonic Excitation Response With Fluid-Structure Interaction in Elbow Piping

Abstract This study focuses on the numerical analysis of a piping structure subjected to the water-hammer event caused by a rapid valve closure that is combined with external harmonic loading representing an idealized machine excitation. The fluid–structure interaction procedure applied to solutions involves the method of characteristic for the fluid equations with the finite element method for pipe structures, which are modeled as beams. Junction coupling at the pipe elbow governs the two-way coupled fluid–structure interaction, and both the friction and Poisson couplings are incorporated as well. There is an application on a piping structure that consists of a valve, tank, and elbow that are defined as boundary conditions. The solved result quantities include pressure and bending stress responses as well as dynamic displacement modes of the piping structure. Comparisons of the results show that water hammer loading combined with the mechanical excitation load induces significantly increased displacements and higher stress peaks when frequencies of the harmonic load and the acoustic natural mode of the piping system coincide. Additionally, the resulting mode of lateral structural vibration of the piping member closely resembles an analytically solved eigenmode of the beam. The conclusion is that dynamically changing flows due to a water hammer event can solely excite natural frequencies of the piping structure causing resonance in the system.

Numerical Simulation of Internal Flow Field in Turbo-Expander

As everyone pays more attention to energy consumption, it is very meaningful to use natural gas pressure energy for power generation and turbo-expander is an important part of power generation devices. In this paper, the turbo-expander model for pressure energy generation is meshed and numerically simulated based on fluent, and the pressure distribution and velocity distribution in the turbo-expander are obtained. The volute profile is Archimedes spiral, and the impeller is modeled by cfturbo. The main conclusions are as follows: when the number of grids is more than 2.2 million, the simulation results are less affected by the number of grids. The internal basin of the turbo-expander has obvious pressure gradient and velocity gradient. Due to the negative pressure at the elbow of the inlet pipe of the centrifugal effect, the existence of the blade leads to the change of the flow direction. Different watershed planes have different pressure and velocity distributions. The velocity and pressure of the watershed plane near the impeller outlet and the volute outlet are often smaller, but the flow vortex is more intense.

Reconstruction of primitive-shaped pipe elbows from a triangular mesh in ship outfitting model

Reconstruction of primitive-shaped pipe elbows from a triangular mesh in ship outfitting model

Numerical Simulation of Erosion Characteristics for Solid-Air Particles in Liquid Hydrogen Elbow Pipe

The crystalline solid-air in the liquid hydrogen will cause erosion or friction on the elbow, which is directly related to the safety of liquid hydrogen transportation. The CFD-DPM model was used to study the erosion characteristics of solid-air to liquid hydrogen pipelines. Results show that the outer wall of the cryogenic liquid hydrogen elbow has serious erosion in the range of 60–90°, which is different from the general elbow. The erosion rate is linearly positively correlated with the mass flow of solid-air particles, and the erosion rate has a power function relationship with the liquid hydrogen flow rate. The fitted relationship curve can be used to predict the characteristics and range of the elbow erosion. The structure of the liquid hydrogen elbow also has an important influence on the solid-cavity erosion characteristics. The increase of the radius of curvature is conducive to the reduction of the maximum erosion rate, while the average erosion rate undergoes a process of increasing and then decreasing. The radius of curvature is 60 mm, which is the inflection point of the average erosion rate of the 90° elbow. The research results are expected to provide a theoretical basis for the prevention of liquid hydrogen pipeline erosion.

Cooling performance of multi-nozzle spray with liquid nitrogen

Spray cooling with liquid nitrogen has great advantages to achieve a cryogenic environment simulation system. The nozzle number, the mass flow rate and the gas velocity have crucial impacts on the cooling efficiency and the high-precision temperature control in the system. To gain insight into the multi-nozzle spray cooling performance, the small wind tunnel prototype with liquid nitrogen spray cooling was built, and the transient and steady-state cooling performance was experimentally studied. The results show that during the transient cooling process, the temperature is lower when the region is closer to the spray field. The temperature on the test plane near the spray has the biggest difference. After flowing through two elbow pipes, the high uniformity of the temperature distribution is obtained. The research of the steady state cooling shows that the average temperature gradually increases along the flow direction from the spray region, while the temperature uniformity is in the reverse order. And the small deviation among the data on the later three planes means a good temperature uniformity within the wind tunnel except the spray region. In addition, a lower gas velocity, a larger nozzle number and a higher injection pressure can enhance the cooling performance. However, the temperature uniformity becomes worse as the nozzle number increases. The results could provide theoretical guidelines for the engineering application of the cryogenic spray cooling.

CFD investigation of internal elbow pipe flows in laminar regime

Elbow pipes are crucial parts of many fluid transport systems in the oil and gas industry. The curved shape of such pipes induces centrifugal forces on the internal flow, ultimately affecting the flow velocity and creating pressure differences within the elbow. The present study aims to investigate the effects of the curvature ratio of an elbow pipe on the internal pipe flow using three-dimensional numerical simulations. For laminar flows, the simulations are based on four Reynolds numbers ranging from 200 to 2000 and three curvature ratios of Ro=5.6, 11.2 and 22.4. A mesh convergence study is carried out for 3 meshes with increasing resolution. The results based on the optimal mesh is then compared with the published experimental and numerical results for validation. Once the validation is confirmed, further simulation and analysis are performed for each combination of curvature ratio and Reynolds number. The results reveal that there is flow separation due to the centrifugal forces induced by the curved shape. It is also shown that secondary flows consisting of symmetrical helical vortices called Dean vortices are generated. The intensity of this secondary flow is shown to increase with the increasing Dean number.

Experimental investigations of the critical values of J-integral and crack tip opening displacement (CTOD) of high-density poly-ethylene PE100 elbow

The present study aims to characterize the cracking behaviour of high-density poly-ethylene (HDPE) pipe elbow. Experimental studies were performed to determine the mechanical behaviour of HDPE and study the anisotropy of the material. Tension tests were performed on compact tension (CT) specimens to identify the toughness value, expressed by the critical value of the J-integral JIc. These tests were carried out on specimens cut from a PE100 plate with a different orientation angle with respect to the extrusion direction. The testing results have shown that HDPE can be considered as an isotropic material. The methods used to calculate the JIc value resulted in different value. Due to these uncertainties, a study of a failure criteria using crack tip opening displacement (CTOD) was proposed and conducted. The combination of the J-integral and “CTOD” method gave the possibility to determine for the critical value of the J-integral as a value of the fracture toughness of the HDPE. The obtained results suggest that the value of 8.4 kJ/m2 can be considered as the JIc fracture toughness required to initiate the crack for the HDPE.

Burst capacity analysis of thin-walled pipe elbows under combined internal pressure and bending moment

Structural integrity analysis of pipe elbows is of critical significance because they not only withstand the internal or external pressure but also absorb the bending moment in a pipeline system. While the burst capacity of pipe elbows under internal pressure only have been extensively investigated in the literature, the study on the burst capacity of pipe elbows under combined internal pressure and bending moment is still limited. In this paper, the effect of bending on the burst capacity of thin-walled defect-free and local wall-thinning (LWT) elbows subjected to combined internal pressure and bending moment is systematically investigated. A correction factor is defined to quantify the bending effect on the burst capacity; extensive parametric finite element analysis (FEA) is carried out to analyze the dependence of the correction factor on the bending mode and magnitude, elbow size and steel grade, and LWT size and location. The results indicate that as the magnitude of the bending increases, the burst capacity of both the defect-free and LWT elbows generally deceases. For the defect-free elbows, the elbow steel grade has a significant influence on the correction factor while the influence of the elbow geometry is marginal. For the LWT elbows, the correction factor depends markedly on the LWT location and bending mode.

A weighted unification yield criterion and its application in analysis of burst pressure of pipe elbow

In order to solve the problem of insufficient accuracy in predicting the burst pressure of a pipe elbow based on the existing yield criteria, a new yield criterion is established firstly and then used to analyze the plastic failure of a pipe elbow. According to this idea, the mathematical characteristics of the Tresca criterion and the Mises criterion are revealed from the perspective of square shear stress, and a new yield criterion with generality is established by introducing a weighting coefficient δ. The yield criterion can be transformed to various yield criteria with different δ, including the existing yield criteria. On this basis, the plastic failure analysis of a pipe elbow is carried out, and the analytical formula of the burst pressure is derived, in which the strain hardening effect of the material is also considered. Besides, the main parameters that affect the burst pressure are analyzed. It is shown that the theoretical burst pressures calculated by the present yield criterion with different δ can coincide well with the experimental values for different materials, and the burst pressures decrease with the increase of the strain hardening exponent, while increase with the increase of the thickness-diameter ratio. The burst pressure formula established in this paper is of great significance to the structural design and safety assessment of a pipe elbow.

Vibration characteristics analysis and structural improvement of natural gas venting ignition pipeline

In order to study the flow-induced vibration characteristics of the natural gas vent pipeline under the internal flow field, taking the gas transmission station pipeline as an example, the ANSYS Workbench software was used to establish models under two working conditions, uncoupling and fluid-solid coupling, for modal analysis, and analyze and compare the calculation results and propose a structural improvement plan. The results show that the maximum amplitude of the first three modes under the two working conditions is concentrated on the riser mouth, and the amplitude under the fluid-solid coupling condition is slightly larger than that of no coupling; the inner diameter of the pipe elbow is large and the pressure is small, and the outside diameter is small and the pressure is small. Large, this instability will increase the air pulsation of the flow field. In the improved scheme, adding a restriction on the top to increase the rigidity of the pipeline can significantly reduce the maximum amplitude of the gas pipeline; adding an orifice to eliminate air flow pulsation has a certain effect on reducing the maximum amplitude and natural frequency, and the combination of the two can make the pipeline more stable. The research results of this paper can provide improved ideas for vibration reduction at the natural gas venting operation site.

Seismic performance limit of nuclear power plant piping system with seismic isolation system considering measurement points: Low-cycle fatigue life

This paper presents the first part of a two-part investigation on the seismic performance limits of nuclear power plant piping systems with seismic isolation systems considering the measurement points and proposes a scheme for low-cycle fatigue life. This part of the study focuses on pipe elbows, which are components vulnerable to seismic loads in crossover piping systems connecting structures with and without seismic isolation systems in nuclear power plants. The low-cycle fatigue life, which is the seismic performance limit of the pipe elbow, was determined by considering the cyclic loading of the low-frequency characteristics caused by the seismic isolation system. Three-inch test specimens of SCH40, which are typical standards for nuclear power plant piping systems, are fabricated herein consisting of a pipe elbow and straight pipes. In the test specimens, the pipe elbow where the load is concentrated and the lengths of the straight pipes that are connected to the elbow may differ from those in field conditions. Therefore, their effects on the seismic performance limit were analyzed using the relationship between the moment and deformation angle. Cyclic loadings were performed at varying amounts of a constant amplitude, and an imaging system was used to measure the moments and deformation angles. The deformed shapes of the test specimens caused by external forces were compared for each measurement point, and the leakage lines and low-cycle fatigue curves were presented using the relationship between the moment and relative deformation angle.

Seismic performance limit of nuclear power plant piping system with seismic isolation system considering measurement points: Damage index

This paper presents the second part of a two-part investigation on the seismic performance limits of nuclear power plant piping systems with seismic isolation systems considering the measurement points and aims to quantitatively express these limits using a damage index based on the dissipated energy. This part of the study focuses on a method to quantitatively express the seismic performance limits needed for seismic fragility evaluations of crossover piping systems connecting structures with and without seismic isolation systems in nuclear power plants. Test specimens for this study were manufactured by welding straight pipes to both ends of a 90° long pipe elbow. The dissipated energy was calculated using the relationship between the moment measured at the center of the pipe elbow and relative deformation angle at each of the straight pipe’s measurement points using an imaging system; this was compared to the dissipated energy calculated from the relationship between force and displacement, and a suitable length of the straight pipe for low-cycle fatigue tests was found. Further, a method of applying a weighting factor to the yield points, which are needed to calculate the damage index, are examined; thus, it was confirmed that the damage index can be used to quantitatively express the seismic performance limits of thin-walled steel pipe elbows.

Effects of the Nasal Cavity Complexity on the Pharyngeal Airway Fluid Mechanics: A Computational Study.

The impact of the human nasal airway complexity on the pharyngeal airway fluid mechanics is investigated at inspiration. It is the aim to find a suitable degree of geometrical reduction that allows for an efficient segmentation of the human airways from cone-beam computed tomography images. The flow physics is simulated by a lattice Boltzmann method on high-performance computers. For two patients, the flow field through the complete upper airway is compared to results obtained from three surface variants with continuously decreasing complexity. The most complex reduced airway model includes the middle and inferior turbinates, while the moderate model only features the inferior turbinates. In the simplest model, a pipe-like artificial structure is attached to the airway. For each model, the averaged pressure is computed at different cross sections. Furthermore, the flow fields are investigated by means of averaged velocity magnitudes, in-plane velocity vectors, and streamlines. By analyzing the averaged pressure loss from the nostrils to each cross section, it is found that only the most complex reduced models are capable of approximating the pressure distribution from the original geometries. In the moderate models, the geometry reductions lead to overpredictions of the pressure loss in the pharynx. Attaching a pipe-like structure leads to a higher deceleration of the incoming flow and underpredicted pressure losses and velocities, especially in the upper part of the pharynx. Dean-like vortices are observed in the moderate and pipe-like models, since their shape comes close to a [Formula: see text]-bend elbow pipe.

Shakedown and Limit Analysis of Kinematic Hardening Piping Elbows Under Internal Pressure and Bending Moments

Abstract In this paper, the stress compensation method (SCM) adopting an elastic-perfectly plastic (EPP) material is further extended to account for limited kinematic hardening (KH) material model based on the extended Melan's static shakedown theorem using a two-surface model defined by two hardening parameters, namely, the initial yield strength and the ultimate yield strength. Numerical analysis of a cylindrical pipe is performed to validate the outcomes of the extended SCM. The results agree well with ones from literature. Then the extended SCM is applied to the shakedown and limit analysis of KH piping elbows subjected to internal pressure and cyclic bending moments. Various loading combinations are investigated to generate the shakedown limit and the plastic limit load interaction curves. The effects of material hardening, elbow angle, and loading conditions on the shakedown limit and the plastic limit load interaction curves are presented and analyzed. The present method is incorporated in a commercial finite element simulation software and can be considered as a general computational tool for shakedown analysis of KH engineering structures. The obtained results provide a useful information for the structural design and integrity assessment of piping elbows.

MODELING OF STEEL ELBOW MANUFACTURING PROCESSES VIA FINITE ELEMENT METHOD AND OPTIMIZATION OF PRODUCTION PARAMETERS

With the advancement of today's technologies, parts of pipe and elbow elements, natural gas pipelines, petrochemicals, machinery manufacturing industry, water distribution and flow systems, sewage systems, foundation piles, shipbuilding industry, nurse containers, aviation, space and defense industry, pipe networks, refineries , steel structures, tube and pipe engineering, etc. widely used in areas. In this study, extrusion method, which is one of the cold forming methods of elbow pipes, has been investigated. When the literature is examined, the production conditions of steel pipes and the problems that occur in production have been examined by different people and suggestions have been made. In this study, the production process of AISI 316L (EN 1.4404) quality stainless steel elbow pipes has been investigated. The mold design model created with the Solidworks program was transferred to the non-linear finite element analysis software ANSYS program for simulations. The process was modeled and simulated in the transient structural analysis section of the ANSYS program. In the process of transforming the pipe into an elbow product, we have learned about the stress distributions and obtaining the total deformation changes on the elbow. The parameters of the production process have been optimized by comparing the work done in the simulation and experimental data. In this way, cost-effective production is aimed by minimizing production costs. The data was extracted by simulating the production environment and conditions.