Elbow Erosion Research Articles

Modeling sand fines erosion in elbows mounted in series

A comprehensive CFD-based erosion prediction procedure is applied to predict erosion in two elbows mounted in series. First, different CFD models are evaluated with sand fines (28 μm) erosion data from Kumar et al. [1] for two horizontal-horizontal 2 in. short radius elbows mounted in series. The effects of turbulence model and particle rebound model are examined to obtain the most appropriate model combination for running erosion simulation. A systematic grid refinement study is also conducted for the geometry with application to sand fines (28 μm) erosion prediction. In the process, it is found that erosion prediction for sand fines can be significantly affected by grid configuration due to current limitations of CFD codes. Finally, the paper proposes a meshing strategy that is capable of capturing sand fines dispersion and transport which is highly recommended for use to run erosion simulations especially for predicting small particle erosion using current commercial CFD codes.

전산유체역학 배관 곡면 침식 모사를 통한 배관 실패 주기 분석

전산유체역학 배관 곡면 침식 모사를 통한 배관 실패 주기 분석

Numerical Analysis of Solid Particle Erosion in Pipe Elbow

Erosion due to particulate impingement is the key factor responsible for damage of industrial pipeline. A CFD-CFX based simulation study of particle-liquid erosion of pipe elbow that considers the solid-liquid, solid-solid and solid-wall interaction is presented in this work. The simulation work has been performed by using the combination of CFD code ANSYS CFX along standard k-є turbulent model. Erosion rates for particles of different diameters and concentration are investigated at different slurry velocity. The model presented can be employed in industrial flow applications for the forecast of erosion wear caused by solid-liquid slurry flow

A new dimensionless number for solid particle erosion in natural gas elbows

A 2-D Computational Fluid Dynamics (CFD) model was used to investigate erosion in standard elbows (r/D = 1.5) under different flow and particle conditions. Afterwards, dimensional analysis was performed to first obtain the governing dimensionless groups and then extract self-similar behavior among them when plotted against the ratio of erosion rate/gas velocity. This resulted in the development of a new dimensionless group named penetration rate (Pnr) correlated to dimensionless erosion ratio as (ER/Vg)∝(Pnr)1.0612. This correlation was plotted for different experimental data; the same trend was found.

Innovative pipe wall design to mitigate elbow erosion: A CFD analysis

Pneumatically conveyed particles are commonly responsible for triggering the erosion process by impacts on the wall. Those impacts result from the fluid-particle interaction and understanding their mechanisms is the key to mitigate the erosion damage in engineering applications. In this paper, we propose a novel pipe wall design in order to reduce the erosion on a 90° elbow. This design consists of twisting a pipe wall along the flow streamwise direction. Basically, such configuration generates a swirling flow upstream of the elbow and consequently re-disperses the transported particles, preventing them from focusing on a single point at the elbow. An accurate CFD model based on the Euler-Lagrange approach is used for evaluating the erosion depth. Experimental data on a standard pipe elbow is employed for validating the numerical results. Further, simulations are run for the new pipe geometry. To elucidate the nature of the erosive process on the new pipe wall design, fundamental variables such as impact velocity, impact angle, impact frequency are assessed. In general, the changes in the two-phase flow brought about by the twisted pipe wall are effective for reducing elbow erosion. The simulations show that a reduction of erosion peak up to 33% can be achieved in a pipeline equipped with the twisted pipe wall in comparison to the baseline configuration.

Effects of particle shape and swirling intensity on elbow erosion in dilute-phase pneumatic conveying

Elbow erosion, which is mainly caused by collisions between particles and wall, is a prominent problem encountered in dilute-phase pneumatic conveying systems. The particle shape and air-flow regime markedly influence the particle-wall collision characteristics through the ambiguous impacts of both the geometric boundary and relative velocity. This paper numerically investigates the effects of particle shape and swirling intensity on elbow erosion in dilute-phase pneumatic conveying using the CFD-DEM method. Initially, the non-spherical particles are modelled based on polyhedrons and scanned real coal particles, and their morphologies are characterized according to sphericity. Subsequently, the calculation compatibility of attrition models based on CFD-DEM simulation is calibrated by comparing the erosion rates calculated on the basis of different classical models. In addition, the compatibility of the selected model for the coarse particle pneumatic conveying is verified via experimental measurements. Based on the two-way coupled Eulerian-Lagrangian method, simulations of the gas-solid flow that consider the elbow direction, particle shape, and swirling intensity are performed, and the correlation models with sphericity and swirling number for different elbow directions are assessed. In general, it is found that the elbow direction affects the magnitude, distribution, and position of the maximum of the erosion rate. The mean erosion rate generally varies with the particle sphericity in a nearly inclined “S” pattern in all elbow directions. The mean erosion rate evidently decreases with swirling number first quickly and then slowly. To develop a modified predictive model based on the classical erosion model, the polynomial and the Exp3p2 exponential function are adopted to fit the influences of particle shape and swirling intensity, respectively. The fitting deviations agree reasonably well with the calculation results.

Erosion of natural gas elbows due to rotating particles in turbulent gas-solid flow

This work investigates the erosion of an elbow pipe due to the gas-solids turbulent pipe flow using computational fluid dynamics (CFD) with special attention to the effect of particle rotational motion on erosion. The gas-solid flow is solved by employing two-way coupled Eulerian-Lagrangian approach while enhanced wall treatment is used for modeling the flow behavior close to the walls and in boundary layer. Effects of key erosion parameters such as gas velocity, particle diameter and particle mass flow rate on the erosion rate was evaluated and discussed. Simulation results are verified with experimental data with concept of percent bias. Results show that the erosion rate is strongly affected by the particle rotation. The particles rotation has a considerable effect on the particle motion path and consequently the erosion pattern of the elbow. Particle trajectories show that particles have reverse motion due to rotation which plays a significant role on erosion pattern due to the more collision to the elbow wall.

Numerical investigation of the erosion behavior in elbows of petroleum pipelines

Oil spill caused by the erosion in elbows is widely encountered in long-distance crude oil transmission pipelines and will lead to a considerable economic loss and potential safety hazards. In order to prevent the equipment failure and evaluate the campaign life of piping systems, there exists an urgent need to identify the positions suffering severe erosion damage and predict the erosion rate in pipelines for multiphase flow. In this study, a mathematical model is established to predict the solid particle erosion in the elbows of petroleum pipelines, in which the particle-fluid interaction is taken into account. The effects of bend orientation and particle properties on the erosion process are investigated in details. In order to understand the erosion mechanism related with the dynamic behavior of flow fluid and entrained particles, the relationship between the secondary flows and the particle trajectories is analyzed emphatically. The results indicate that erosion mainly occurs in the regions near the elbow exit, especially the side walls of the downstream straight pipe and extrados of the bend section. However, erosion on the side walls could not always happen when the effect of the secondary flows is not remarkable. It is also found that the erosion behavior depends upon both the centrifugal effect of pipe flow and the forces acting on particles. Finally, an erosion pattern based on Stokes number is developed to quantify the complex coupled effects of the flow field and particle properties.

The role of inter-particle collisions on elbow erosion

Erosion due to particle impingement, which can occur in a variety of practical cases, is often the key factor in pipeline failure. Parts such as elbows, for instance, are particularly prone to erosion issues. In this work, the Unsteady Reynolds Averaged Navier–Stokes (URANS) equations are combined with a stochastic Lagrangian particle tracking scheme considering all relevant elementary processes (drag and lift forces, particle rotation, inter-particle collisions, particle-wall interactions, coupling between phases) to numerically predict the erosion phenomenon on a 90° elbow pipe. After a detailed validation of the erosion model based on the experimental data of Solnordal et al. (2015), several cases regarding the wall roughness and static and dynamic coefficients of friction are analysed to elucidate the nature of the erosive process. For such analysis, more fundamental variables related to particle-wall interactions (impact velocity, impact angle, impact frequency) were used to scrutinize the basic erosion mechanisms. Finally, to prove the importance of inter-particle collision on elbow erosion, different mass loadings are additionally simulated. Especially for the high mass loading cases, interesting results about the role of the inter-particle collisions on elbow erosion are enlightened.

Numerical prediction of erosion in elbow based on CFD-DEM simulation

A new erosion model, which is referred to as SIEM (shear impact energy model), is used to investigate elbow erosion under different working conditions using numerical simulations. The fluid motions are predicted by CFD (computational fluid dynamics), and the particle movements are calculated using DEM (discrete element method) in the simulations. Both a one-way coupling method and a two-way coupling method in CFD-DEM are adopted to calculate the gas-solid interaction. The prediction results of elbow erosion subject to a condition of dilute gas-particle flow are validated against corresponding experimental data. Because DEM and SIEM can be easily applied to dense gas-particle flows, the effect of the particle concentration on the erosion is also investigated. The simulation results show that the coupling methods have little influence on the erosion prediction when the particle concentration is low, whereas erosion in the elbow is significantly sensitive to the particle concentration. Finally, the effects of the friction coefficient, restitution coefficient and spring stiffness coefficient on elbow erosion are also investigated using simulations, and the effects were not as remarkable as the concentration.

Reducing bend erosion with a twisted tape insert

Due to the ongoing problem related to erosion caused by the impingement of solid particles in many engineering fields, parts such elbows, for instance, are particularly prone to erosion issues. In this work, the insertion of a twisted tape at different positions upstream of a bend is investigated numerically with the intent of reducing the elbow erosion. To ensure the reliability of the numerical calculations, experimental data were used to validate the CFD model for the standard elbow. Subsequently, simulations considering one, two and four-way coupling were evaluated for both the standard and the twisted tape-equipped elbows. Simulations were run to evaluate the average particle impact angle, impact frequency and impact velocity and the penetration ratio for each geometry. It was found that the swirling motion imparted to the particles by the twisted tape reduces the maximum penetration ratio in the bend. Another important finding is that the farther the insert is placed upstream of the elbow, the lower the erosion in the elbow, although the tape itself becomes more prone to erosion. In general, it was noticed that the fluid-particle and particle-particle interactions are very important and cannot be neglected. Consequently, depending on the mass loading and geometry configuration, elbow erosion can be dramatically reduced.

Similarity criteria of the solid particle erosion in elbows between model experiments and engineering for dry gas and gas–mist flows

Solid particle erosion in elbows is a prominent problem encountered in hydrocarbon transportation pipelines, especially for dry gas and gas–mist flows. There is great difference in flow conditions between model experiments and engineering. A set of similarity criteria is proposed to analyze the corresponding relationship between engineering conditions and that in laboratory tests. The similarity criteria aim at building a procedure that can predict the maximum penetration rate and its position in engineering conditions through the corresponding experimental design, reducing the heavy monitoring work in field circumstances. Principal dimensionless numbers on the flow field and particle response behaviors are presented to make up the similarity relationship between engineering cases and laboratory tests, respectively for dry gas and gas–mist flows. For several typical lab tests from the literature, each of them is extrapolated to a series of similar engineering cases which vary in pipe diameter and operating pressure. Then the typical laboratory tests and the corresponding engineering cases are calculated by the validated CFD method and four classic empirical or semi-empirical models to get the dimensionless penetration rates and maximum erosion positions, which are the two dimensionless similarity judgment numbers. The judgment numbers show good equivalence trends for the same series of laboratory test and its corresponding engineering cases. The similarity criteria developed in this study are verified and prove to be rational and efficient in predicting erosion in engineering through model experimental design.

Experimental and computational study of erosion in elbows due to sand particles in air flow

Severe equipment degradation in production piping can occur for gas–solid flows. Advances in modeling and solid particle erosion simulations are gained through matching computer generated predictions to real-world experimental results. This paper presents a comprehensive approach in modeling and computational study to determine erosion in elbows due to sand particles entrained in air. Firstly, utilizing a particle image velocimetry (PIV) technique, the slip velocity between the gas and sand particles in a direct impact geometry has been measured. Secondly, an erosion equation has been generated based on PIV results and erosion testing of stainless steel in air. Thirdly, erosion patterns are measured in a 76.2mm ID standard elbow for air-sand flows using a state-of-the-art non-invasive Ultrasonic Technology (UT) device. The metal loss is measured at 16 different locations in the elbow using dual element ultrasonic transducers. Erosion experiments in the vertical to horizontal elbow are performed with gas velocities ranging from 11m/s to 27m/s at nearly atmospheric pressure. Two different sand sizes (150 and 300μm sand) were used for performing tests. The shapes of the sand are also different with the 300μm sand being sharper than the 150μm sand. Finally, the new erosion equation has been implemented into a commercially available Computational Fluid Dynamics (CFD) code to predict erosion ratios in elbows for a variety of flow conditions and particle sizes. The predicted CFD erosion magnitudes are compared with present and previous UT erosion data in elbows. The comparisons show that CFD predictions are within a factor of two of present and previous UT single-phase erosion data. Four correlations for erosion from literature are also studied and validated in simulations. The correlation developed and validated in this work can be used to predict the bend lifetime for particular operating conditions.

Mitigating elbow erosion with a vortex chamber

Wear due to particles is often the key factor for pipeline failure. Parts such as elbows, for instance, are particularly prone to erosion issues. In this work, the erosion in a bend equipped with a vortex chamber is investigated numerically. Initially, experimental data are used to validate the CFD model for the standard elbow. Subsequently, a vortex chamber is added to the original geometry, preserving its geometric characteristics (e.g., diameter and curvature radius) as well as the simulation parameters (e.g., boundary conditions, density, viscosity). Based on four-way coupled simulations of the gas–solid flow in both geometries, the comparison between the standard and vortex-chamber elbow results is performed and a detailed analysis of the mass loading influence on the flow and on the penetration rate is carried out. In general, it is found that even at low mass loadings, inter-particle collisions play an important role in the overall flow behavior. The maximum penetration ratio gradually diminishes as the mass loading increases for both geometries. This phenomenon has actually been observed in experiments and is named cushioning effect. Another important finding is that the vortex chamber significantly improves the efficiency of the cushioning effect, reducing the peak of penetration ratio up to 93% when compared to the standard elbow. In both standard and vortex chamber elbows, a layer of particles builds up adjacent to the elbow wall, protecting it from direct particle collisions. By virtue of the vortex motion in the vortex chamber, the shielding effect of the inter-particle collisions is potentialized, mitigating the erosion rate as the mass loading is increased.

CFD simulation of sand particle erosion in gas-dominant multiphase flow

A method for exploration of erosion in multiphase flow can be Computational Fluid Dynamics (CFD). A key advantage of utilizing CFD is that it can deliver a great deal of information such as the effects of different parameters on erosion, maximum erosion rate, and areas susceptible to erosion damage.The current work used a computational fluid dynamics (CFD) approach to study sand particle erosion in elbows, while the carrier fluid was multiphase flow of low, medium, and high gas flow rates. First, ANSYS MultiFluid VOF model was employed to simulate air–water multiphase flow with superficial gas velocities of 10.1, 18.3, and 27.1 m/s, while superficial liquid velocity was 0.3 m/s in all cases examined. The CFD data were validated against some experimental data previously obtained by a wire-mesh sensor.In the next step, particle tracking and erosion modeling were performed. Specifically, erosion in air–water flow with sand particles of two different sizes (150 and 300 μm) in a 76.2 mm elbow was simulated and compared with experimental data formerly obtained by an ultrasonic technique. Six different erosion equations were employed to discover which equation provides the best predictions. A good agreement was found between CFD results and the experimental data.

Numerical analyses of the solid particle erosion in elbows for annular flow

Solid particle erosion in pipelines is a severe problem involved in hydrocarbon transportation and hence an important topic in flow assurance. A simplified CFD-based procedure is proposed to calculate the penetration rates in elbows for annular flow. This new method overcomes the disadvantages of current empirical or semi-empirical models. The procedure consists of three main sections: flow modeling, particle tracking, and penetration calculation. The k–ε model is employed to analyze the flow field in the core area of the pipe based on the assumption that the gas–liquid interface is regarded as an actual pipe wall. Then a Lagrangian method is adopted to track trajectories of the entrained droplets and sand particles in the core area, and the velocity decay of sand particles across the liquid film is calculated combined with the film thickness correlation. Based on the knowledge of the flow field and the particle motion, penetration rates are calculated by introducing the solid particle erosion equation. By comparing with experimental data available from the literature, the new method is proved to be reasonable in simplifying the simulation of annular flow field and shows good accuracy in erosion prediction. A better agreement between predicted erosion rates and experimental data can be made when applied to larger curvature radius elbows.

Effect of the gas–solid two-phase flow velocity on elbow erosion

Because of the rapid development of oil and gas pipelines and the increasing number of pipeline accidents, pipeline safety has garnered more attention around the world. Erosion on the inner diameter of pipes is one of the main factors in pipeline failure. Since experimental methods for wall thickness inspection of pipelines are expensive, an accurate model for predicting erosion rate of pipelines under working conditions is needed. A new erosion prediction model is proposed in this research which combines the theoretical and Lagrange discrete phase models for erosion. The model considers effects of gas–solid multiphase velocity and gas pressure. It is applied to elbows under the working conditions of a gas station of the Daqing Oil and Gas Company in China. The results are considerably closer to measured erosion of elbows than the results calculated using existing models. The comparison between erosion under high and low gas pressures shows that the effect of gas-phase velocity on erosion rate is more significant in elbows under high-pressure conditions.

Numerical investigation of mass loading effects on elbow erosion

Wear due to particles is often the key factor for pipeline failure. In this work, the effects of different sand particle concentrations on the erosion of an elbow pipe are investigated numerically. In order to assess the quality of the numerical predictions of the erosion rate, experimental data were first used to validate the erosion and restitution models at low concentration. The input parameters for the empirical erosion correlation were obtained from accurate CFD models for the gas–solid flow within the bend. One, two and four-way couplings were evaluated at different mass loadings. In general, it was found that even at low to moderate mass loadings, the effects of inter-particle collisions on the penetration ratio cannot be neglected. Another important finding is that the maximum penetration ratio gradually diminishes as the mass loading increases. As counterintuitive as it may appear, this phenomenon has actually been observed in experiments and is named cushioning effect. Based on the analysis of the simulation results, it can be concluded that a layer of particles builds up adjacent to the elbow wall, protecting it from direct particle collisions. Conversely, the inter-particle collisions damp the particle impact to the surface, therefore reducing the penetration peak.

An experimental and numerical analysis of erosion caused by sand pneumatically conveyed through a standard pipe elbow

Erosion of surfaces is an on-going industrial problem wherever solid particles are conveyed. The literature reveals very limited data reported for elbow erosion. Almost all data that is available only relates to the elbow extrados, or else provides an overall mass loss of surface material with no information on erosion distribution. A detailed surface map of erosion depth in a standard elbow (90° bend, with bend radius to pipe diameter ratio equal to 1.5) is presented using measurements taken with a surface profiler. The full erosion data map is reported on a 40×20 point grid for erosion caused by the passage of 200kg and 300kg of sand through the elbow. The sand had a median diameter of 184μm, and was conveyed by room temperature air travelling at 80ms−1.Numerical modelling of the erosion distribution is then performed using the conventional Euler–Lagrange approach to erosion prediction. It is found that the use of this approach, in combination with a smooth wall assumption for particle–wall collisions, leads to inaccurate prediction of maximum erosion depth together with a characteristic “vee”-shaped erosion scar that is not present in the experimental data. By adopting a suitable rough wall collision model the erosion depth and distribution are much more accurately predicted. However, particle shape, surface profile development and surface roughness development are all factors that may also affect the erosion pattern.The numerical modelling demonstrates the importance of accurately incorporating particle–wall collisions, as well as other more complex flow behaviour, into the simulation if a true prediction of the erosion distribution is to be captured.

Ultrasonic measurements of sand particle erosion in gas dominant multiphase churn flow in vertical pipes

Solid particle erosion can result in major pipeline failures, economic losses and more importantly safety and environmental issues. Erosion in multiphase flow is not widely understood and previous work has mostly focused on cases where the carrier fluid is single phase. There are different multiphase flow regimes, and amid them, churn flow appears frequently in piping systems such as risers, jumpers and flow spools. Furthermore, elbows have broad applications in the oil and gas industry, and they are subject to sand particle erosion damage. Therefore, the study of erosion in elbows, while the superficial velocities of the carrier fluids are in the range so that the flow pattern is churn flow, is of utmost importance. Experimental tests were carried out in order to investigate sand particle erosion in a 76.2mm ID standard vertical–horizontal (V–H) elbow. A novel non-intrusive ultrasonic device was implemented to attain erosion patterns under different flow conditions. The effects of superficial gas and liquid velocities, particle size and liquid viscosity on erosion rate were investigated. The results are compared to the available data of erosion rates in a horizontal–horizontal (H–H) elbow with the same size of the elbow employed here. The most striking outcome to emerge from the comparisons is that erosion rates in the V–H elbow are significantly higher than those in the H–H elbow.