Elbow Pipe Research Articles

Effect of Interstage Pipeline on the Performance of Two-Stage Centrifugal Compressors for Automotive Hydrogen Fuel Cells

At present, two-stage centrifugal compressors based on air bearing and high-speed motor technology are widely used in automotive hydrogen fuel cells. The low-pressure stage and high-pressure stage of the compressor are directly connected through an interstage pipeline, thus the structure of the interstage pipeline has an important influence on the aerodynamic performance of the compressor. In this work, a two-stage compressor with three different interstage pipelines were investigated experimentally and numerically. Results show that affected by the interstage pipeline bend section, the flow distortion will be induced at the impeller inlet of the high-pressure stage, and the distortion intensity changes with the pipeline structure. Among the three models, the EPC (elbow pipe change) model induces the most intense total pressure distortion at the condition of 80 kr/min and 130% mass flow rate, resulting in an efficiency reduction of 2 and 1.5 percentage points compared with the SPC (straight pipe change) and the TPC (total pipe change) model, respectively. Further research indicates that the upstream distortion has obvious influence on the downstream rotor blades. As the blade height decreases, the load becomes more uniform on the main blades, while the load extremum migrates to the trailing edge on the splitter blades. Finally, three models are tested, and their performance is compared at three typical rotational speeds., It is recommended that interstage pipelines similar to SPC models should be chosen to improve the two-stage compressor efficiency in the design.

FEA based prediction of crack growth behavior of 304LN stainless steel cracked and healthy piping elbows

FEA based prediction of crack growth behavior of 304LN stainless steel cracked and healthy piping elbows

Novel assessment of in-operations mapped stainless steel elbow pipe internal wall for detection of corrosion and scale deposition

Novel assessment of in-operations mapped stainless steel elbow pipe internal wall for detection of corrosion and scale deposition

Validation and analysis of turbulence modeling in pipe elbow under secondary flow conditions

Validation and analysis of turbulence modeling in pipe elbow under secondary flow conditions

Gas-Solid Erosion Study of Elbow Pipe based on Erosion Dynamic Grid Technology

The dynamic erosion characteristics of pipe bends exposed to gas-solid two-phase flow are investigated by using an erosion-coupled dynamic meshing method to elucidate the erosion failure phenomenon that is common in pipe elbows, transporting coal fly ash and subjected to particle erosion. The static mesh is compared with the erosion-coupled dynamic mesh method by CFD. The dynamic erosion characteristics of bends with different r/D ratios, D and r are investigated before and after surface deformation under gas-solid two-phase flow. The results lead to the following conclusions: Improved performance of the erosion-coupled dynamic mesh by taking full consideration of the coupling between the erosion-induced surface deformation and the particle motion under prolonged erosion. The erosion rate at the elbow changes significantly upon surface deformation, and the sites with a high risk of erosion shift downstream. With increasing of deformation, the larger the r/D ratio, the more obvious the concentration of erosion location evolving downstream. As D decreases, the high-risk erosion areas become more concentrated. In particular, the emergence of the “bending increase” phenomenon leads to a different perception of how r/D ratio and the diameter affect erosion in static-grid simulations: a larger r/D ratio of the elbow makes it more sensitive to surface deformation and increases the erosion rate. This study leads us to consider the coupled deformation of erosion in the context of erosion problems, which has important implications for predicting the service life of overflow components.

Failure criteria evaluation of steel pipe elbows in nuclear power plant piping systems using cumulative damage models

A steel pipe elbow is an important component in the piping system of a nuclear power plant. Accordingly, its structural performance requires a piping system with high-structural integrity, especially when it is subjected to seismic loads. This component fails when subjected to cyclic loads, such as earthquakes, because of low-cycle fatigue in conjunction with ratcheting. Therefore, steel pipe elbows in piping systems should exhibit sufficient strength, ductility, and energy dissipation capacity characteristics to withstand seismic loads. In this study, various cumulative damage models were used to express quantitatively the failure criteria of the actual failure mode of an SCH40 steel pipe elbow. Experiments were performed until the point of leakage via fatigue cracking, which is the actual failure mode of steel pipe elbows, and in-plane cyclic bending was performed by using displacement control. Based on the experimental results, damage indices were calculated by using various cumulative damage models that considered ductility, energy dissipation, and their combination. Consequently, it was confirmed that the Banon index can express quantitatively the failure criteria for the leakage caused by fatigue cracking.

Numerical Simulation and Analytical Prediction of Residual Strength for Elbow Pipes with Erosion Defects.

It is well known that the safety and reliability of pipeline transportation are crucial. We are aiming at the problem that the residual life and residual strength of the defective elbow pipes are difficult to predict and usually need to be obtained through experiments. Consequently, a combined method of numerical simulation technology combined with a genetic algorithm to optimize neural network extreme learning machine (GA-ELM) is proposed. Firstly, the erosion characteristics of elbow pipes with different defects under the conditions of different impurity particle flow rates, particle sizes, and mass flow rates are analyzed by numerical simulation. At the same time, the effects of erosion defects of different sizes on the equivalent stress and residual strength of elbow pipes are also studied. Based on numerical simulation data, the extreme learning machine prediction model optimized by a genetic algorithm is used to predict the erosion rate, residual life, and residual strength and compared with the traditional ELM network model. The results show that residual strength of the elbow pipes with the increase of the depth and length of the defect, and increases with the increase of the width of the defect; the GA-ELM model can not only effectively predict the erosion rate, residual life and residual strength of defective elbow pipes, moreover its prediction accuracy is better than the traditional ELM model.

Numerical Investigation on Particle Erosion Characteristics of the Elbow Pipe in Gas-Steam Ejection Power System

In gas-steam ejection power systems, the Al2O3 particles in combustion products can cause severe erosion on the downstream elbow pipe. To calculate the particle erosion, a modelling approach is developed by combining a discrete phase model with a flow-thermal coupling model and introducing wall temperature parameters into the erosion model. Furthermore, the influence of particle size, total temperature and pressure, and particle mass flow rate was investigated. The results show that high temperature erosion depth can be expressed as the product of the time integral of temperature factor and the erosion rate at room temperature and is 1.63–3.57 times that at room temperature under different particle sizes. With the increase of particle size, the maximum erosion position tends to the inlet of the bend, and its value increases first and then decreases with the peak value 0.418 mm at particle diameter of 100 µm. The decrease in total temperature and total pressure reduces the erosion rate by reducing the particle velocity. The particle mass flow rate affects the gas-particle flow which, may cause the erosion to change greatly, especially when particle diameter is below 40 µm.

Corroded pipe elbow blamed for 2019 explosion

Corroded pipe elbow blamed for 2019 explosion

A Tensegrity-Based Inchworm-Like Robot for Crawling in Pipes With Varying Diameters

Most current in-pipe robots are usually designed for pipes of a specific size. In this letter, we propose a novel inchworm-like in-pipe robot based on the concept of tensegrity for moving in pipes with varying diameters. Firstly, a tensegrity-based robotic module capable of two kinds of shape change is designed. One kind is extension in the axial direction accompanied by contraction in the radial direction, which is the basis for the wave-like crawling movement of the in-pipe robot. The other kind is expansion in the radial direction while keeping changeless in the axial direction, enabling the module adaptable to pipes with different diameters. Then, the geometrical equilibrium configuration of the tensegrity module is determined, followed by kinematic analysis using force density method. By cascading three modules, the in-pipe crawling robot is developed. Finally, a series of experiments are performed to test the shape changeability and friction force of the tensegrity module, and the mobility, load capacity, and adaptability of the in-pipe robot. The results validate that the robot can crawl in horizontal pipes, vertical pipes, and elbow pipes under the control of a simple actuation sequence. Furthermore, the robot has the abilities to adapt to pipes with different diameters varying from 100 mm to 180 mm. It is suggested that the usage of tensegrity structures brings about higher adaptability, flexibility, and mobility to the in-pipe crawling robot.

이기종 CAD 시스템에서 설계된 엘보우 파이프 모델의 통합을 위한 부분 토러스 재건

For constructing various geometric shapes of ship components, computer-aided design (CAD) models need to be integrated into shipbuilding CAD systems. As package models provided by CAD solution vendors are designed using mechanical CAD systems, complex triangular meshes have a serious impact on the modeling performance. In particular, reconstructing the elbow pipe represented by triangular meshes in a shipbuilding model is a difficult problem. We present a method to reconstruct elbow primitives for the Plant Design Management System (PDMS) from triangular meshes using mesh segmentation and elbow parameter extraction methods. The mesh segmentation method divides the mesh of irregular and minimal 3D points into segments for elbow parameter extraction based on curvature and face normal vector. The proposed method could also enable to extract parameters for the elbow pipe by using the geometrical features of the partial torus. As a result of the experiment, the average reconstruction difference is 2.278㎜, which showed that the proposed method can be applied to integration of elbow pipe models designed in heterogeneous cad systems.

The water hammer in the long-distance steam supply pipeline: a computational fluid dynamics simulation

In this paper, a computational fluid dynamics (CFD) simulation based on FLUENT software was performed to analyze the flow and heat transfer of the accident pipeline network in the water hammer burst accident of a thermal power plant in Jiangsu Province, China. Furthermore, the CFD simulation is also performed on the modified pipeline network to verify the effect of pipe network modification. The simulation results from the original accident pipeline show that in the accident pipeline, the steam velocity can reach up to 50 m/s due to the aggregation of liquid water. And when the high-velocity steam strikes the pipe elbow, it will lead to a sharp pressure change and cause the burst accident finally. Then it can be concluded that in the modified pipeline network, the distribution of temperature, pressure, and velocity at the pipe burst place is more uniform and reasonable. In addition, the simulation is also used to analyze the variable working conditions, which ensures that the new design of the pipe network can be used in more complex conditions. The paper is expected to guide the design of other similar pipelines and ensure the safe production and operation of thermal power plants.

The Relationship between the Flow Velocity of Freshwater and the Corrosion Performance of Steel Pipe Elbow Sections in Water Resource Allocation Engineering

The Relationship between the Flow Velocity of Freshwater and the Corrosion Performance of Steel Pipe Elbow Sections in Water Resource Allocation Engineering

Study on erosion wear mechanism of natural gas elbow pipe with uneven corrosion defects

Due to erosion and corrosion, natural gas pipelines can be easily damaged, causing uneven corrosion defects on the inner surface of the elbow. The existence of uneven corrosion defects will affect the surface structure of the inner arch of the elbow. In this paper, the influence of uneven corrosion defects on the further corrosion of elbow was studied by computational fluid dynamics (CFD). The results show that the particles are distributed in a regular V-shape after hitting the outer arch of the non-defect elbow. However, part of the particles bounced irregularly after hitting the defect elbow, forming an irregular particle trajectory region. The uneven corrosion defects that have been created can affect the particle trajectory distribution. When the axial angle α is 45°–55° and the hoop angle φ is between 60° and 120°, the erosion of defect elbow is easily affected by corrosion pits. In addition, the maximum erosion rate of non-defect elbow can be increased with the increase of particle diameter. However, in terms of the impact of particle diameter on erosion, there are two inflection points in the maximum erosion rate of the defect elbow, showing the trend of “increase,”“decrease” and “increase.” The research can provide a theoretical support for subsequent engineering applications.

An analysis of detectable leakage rate for oil pipelines based on acoustic wave method

Oil pipeline leakage will not only cause economic losses, but also pollute the environment, so the leakage detection of pipelines is very important. The acoustic wave method is widely used in pipeline leak detection, and the leak acoustic signal collected by the acoustic wave sensor often contains a lot of noise, which makes it impossible to accurately determine the inflection point of the signal curve and reduces the accuracy of pipeline leak detection. This paper proposes a denoising algorithm based on mutual information optimization complete ensemble empirical mode decomposition with adaptive noise combined with cross-spectral analysis. Compared with other methods, this method can accurately select the effective intrinsic modal function for signal reconstruction, the denoising effect is more obvious, and the original information is preserved to a greater extent. Acoustic waves are attenuated during the propagation process, and will be affected by factors such as pipe connection ports and elbows, making it impossible to accurately determine the amplitude of acoustic waves around the pipeline. According to the propagation characteristics of acoustic waves and various factors that affect the propagation of acoustic waves, this paper establishes a model for calculating the amplitude of acoustic waves, which can accurately determine the amplitude of acoustic waves everywhere in the pipeline. Finally, according to the model, the relationship between pipeline characteristics and detectable leakage rate is analysed. Field experiments show that the proposed model is accurate and the denoising algorithm is efficient. The minimum detectable leakage rate of the oil pipeline can reach 0.43% when the acoustic wave method is used for leak detection.

Modeling interconnections of safety and financial performance of nuclear power plants, part 3: Spatiotemporal probabilistic physics-of-failure analysis and its connection to safety and financial performance

This paper is a byproduct of a line of research by the authors to analyze interrelationships of safety and financial performance of nuclear power plants (NPPs). The result of this line of research is summarized in three parts: Part 1 covers a categorical review of relevant literature and the theoretical bases that support the methodological developments in Part 2. Part 2 introduces an Integrated Enterprise Risk Management (I-ERM) methodological framework to quantify the interconnections of safety and financial performance with a focus on operation and maintenance (O&M) of NPPs. Part 2 has also demonstrated the applicability and values of the I-ERM methodology through an NPP case study. This paper is Part 3, where detailed development and implementation of one of the I-ERM modules, i.e., probabilistic physics-of-failure (PPoF) analysis, and its connection with safety and financial performance is reported. In this article, the physical failure modeling for hardware components is advanced by incorporating finite element analysis (FEA) into PPoF analysis and coupling the FEA-based PPoF with the maintenance performance through a renewal process model. This article covers two scientific contributions: (i) first-of-its-kind incorporation of FEA into the PPoF model of thermal fatigue for NPP components; and (ii) advancing the interface between the PPoF analysis and the renewal process model in order to deal with spatiotemporal FEA outputs and to efficiently estimate the physical transition rates even when the PPoF outputs are dominated by success data. Through the incorporation of FEA, the resolution of the PPoF analysis is enhanced as spatiotemporal conditions such as stress and temperature can be considered explicitly instead of relying on simplified assumptions or analytical models with reduced spatiotemporal dimensions. To demonstrate an application of the FEA-based PPoF analysis and its coupling with maintenance through the renewal process model, a case study is conducted using excess letdown elbow piping in the chemical and volume control system of a Pressurized Water Reactor.

Numerical Simulation of Viscosity Effects on Carbon Steel 90° Elbow Erosion due to Sand-Liquid Flow

Elbow pipes are important pipeline components in hydrocarbon transportation systems, and they were prone to erosive wear by the impact of abrasive particles. A discrete phase modeling (DPM) and numerical simulation of the liquid-sand transportation process was carried out focused on the investigation into the influence of carrier fluid viscosity on erosion distribution of carbon steel 90° elbows. The accuracy of the predicted results was validated by comparison with experimental data. CFD simulations have been carried out by combining DPM to predict the erosion rate and particle impaction regions in carbon steel 90° elbow with a diameter of 50.8 mm. The fluid viscosity is set for 1cP, 5cP, and 15 cP with an inlet velocity of 8 m/s, and the size of sand particles is 200 μm. While the maximum erosion rates enhance with an increase in fluid viscosity, the location of maximum particle impaction has been specified to be adjacent to the outlet for 1 cP and 5 cP carrier fluid viscosity. It is also found that increasing the viscosity does not considerably alter the average erosion rate. Moreover, the increase in carrier fluid viscosity with the same flow velocity influences maximum erosion rate and yields 1.45 times higher erosion rates at 15 cP compared to 5cP and 1cP. This is mainly due to severe sand impaction at the side of the elbow wall.

Experimental and numerical analysis of ratcheting behavior of A234 WPB steel elbow joints including corrosion defects

In this paper, ratcheting behavior of intact and corroded 90o elbow pipe specimens of A234 WPB steel is investigated at intrados, crown, and extrados positions. A special fixture was designed and constructed to carry out the fatigue experiments. Then, the effects of fatigue loading parameters (mean and amplitude) and defect depth were examined on ratcheting responses of intact and corroded specimens at intrados, crown, and extrados positions. To simulate the ratcheting behavior of specimens, a finite element analysis was performed based on the combined nonlinear isotropic/kinematic hardening model. As a reasonable agreement was found between the finite element (FE) simulation results and experimental data, the influence of constant internal pressure during the cyclic loading was examined on ratcheting responses through FE simulation. Results indicated that decreasing the load amplitude was more effective on decreasing the ratcheting strain than that of the mean fatigue load. Moreover, the most critical ratcheting response was associated with the intrados location of the pipe. For defective specimens, decreasing fatigue loading parameters resulted in a shakedown behavior for a defect placed at extrados, while, for the defects at intrados and crown, an increasing behavior was observed for the ratcheting strain. It was revealed that, at extrados position, the ratcheting behavior was arrested up to 1 mm defect depth. The ratcheting strains were increased at intrados and crown by increasing the internal pressure, while they were decreased at extrados.

Investigation of the effects of pipe diameter of internal multiphase flow on pipe elbow vibration and resonance

Computational fluid dynamics modelling of internal two-phase flow induced transient forces at 90° elbows have been carried out to evaluate the effect of pipe diameter on the characteristics of multiphase flow induced vibration. Simulations of two-phase flows of slug, cap bubbly and churn induced vibration at a pipe elbow were carried out using the volume of fluid model for the two-phase flows and the k – ε model for turbulence. Modal analysis has been carried out to evaluate the risk of resonance. Results were compared across three geometrically similar pipes of different diameters. Simulation results showed that the behaviours of the flow induced forces at the pipe elbow as a function of gas velocity for internal diameters of 0.0525 and 0.2032 m are similar. However, the multiphase flow induced force characteristics are different in the 0.1016 m diameter (intermediate) pipe. It can be attributed to the transition behaviour of gas–liquid two-phase flows caused by Taylor instability in an intermediate sized pipe. The predicted root-mean-square flow induced forces as a function of Weber number were correlated with an existing empirical correlation for a wider range of pipe sizes and gas volume fractions between 40% and 80%. Furthermore, the pipe natural frequencies increase with the increase of gas volume fraction in smaller pipes and the resonance risk increases with the increase of pipe diameter.

Shakedown limit of elbow pipe under coupled cyclic thermal-mechanical loading based on the LMM

In this paper, the linear matching method (LMM) is used to study the shakedown limit of elbow pipes under coupled cyclic mechanical-thermal load. Firstly, the thermal stress analyses of elbow pipes under constant internal pressure and cyclic temperature load are investigated. Further, the shakedown limits of the elbow pipes are calculated using the LMM. For the verification purposes, step-by-step inelastic analyses are performed, showing different structure responses under different loading conditions. All the obtained results indicate that the LMM is able to simulate large range of coupled cyclic mechanical-thermal loading conditions with high computational efficiency, and provide shakedown limit with high accuracy. In addition, the effects of bend angles, mean radius to wall thickness ratio (r/t) and five load conditions on the shakedown behavior are also presented.