Elbow Erosion Research Articles

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.

Numerical study of elbow erosion due to sand particles under annular flow considering liquid entrainment

Sand particle erosion is always a challenge in natural gas production. In particular, the erosion in gas–liquid–solid annular flow is more complicated. In this study, a three-phase flow numerical model that couples the volume of fluid multiphase flow model and the discrete phase model was developed for prediction of erosion in annular flow. The ability of the numerical model to simulate the gas–liquid annular flow is validated through comparison with the experimental data. On the basis of the above numerical model, the phase distribution in the pipe was analyzed. The liquid entrainment behavior was reasonably simulated through the numerical model, which guaranteed the accuracy of predicting the particle erosion. Additionally, four erosion prediction models were used for the erosion calculation, among them, the Zhang et al. erosion model predicted the realistic results. Through the analysis of the particle trajectory and the particle impact behavior on the elbow, the cushion effect of the liquid film on the particles and the erosion morphology generation at the elbow were revealed.

A Novel Trajectory-Based Mechanistic Model for Predicting Solid Particle Erosion in Elbows

Abstract Solid particle erosion is a common and challenging phenomenon during the production and transport of particle-containing fluids and it is important to have models for predicting erosion rates accurately, especially for geometries such as elbows. Mechanistic models aim at predicting erosion accurately with low computational cost. In this study, a new particle trajectories-based mechanistic model is proposed to address the issues of liquid-dominated flows and the effect of particle size. Detailed flow and particle information for a standard elbow with water and air and different particle sizes are extracted from computational fluid dynamics (CFD) and analyzed to obtain a representative trajectory. The developed model includes various components that are sensitive to the particle size and flow conditions and accounts for the angle of impact and the turbulence in the flow. The proposed model is examined against CFD predictions for different pipe and particle sizes, and velocities with air, water, high-pressure air, and high-viscosity liquid. In comparison to an available mechanistic model, the new model provides relatively lower errors in predicting maximum erosion for many flow conditions. Moreover, the proposed model is found to be more consistent with CFD data for high-pressure air and higher-viscosity liquids. The model is further validated with experimental data for various conditions. Comparisons against numerical and experimental data suggest that the proposed model provides a significant improvement for liquid–solid flows and small particles.

Modeling erosion process in elbows of petroleum pipelines using large eddy simulation

Elbows are widely used in piping systems to change the direction of flow. However, it is also extremely susceptible to erosive damage, which may lead to the leakage of petroleum and gas pipelines. Therefore, revealing the erosion process and accurately predicting erosion rate are of great importance to pipeline safety. In this study, the unsteady slurry erosion process in the 90° elbow is investigated numerically using LES Eulerian-Lagrangian methodology. The Large eddy simulation (LES) is coupled with Lagrangian particle tracking to simulate slurry flow and erosion process in elbows. The erosion prediction model is validated using experimental data before investigating the unsteady erosion process in elbows with different radius. The results show that the unsteady secondary flow can be precisely captured using LES and thus the prediction accuracy of the fluid flow velocities and turbulent intensities are improved by this model comparing to RANS. The particles movement coupled with the unsteady secondary flow and boundary separation in elbows with different radius can be successfully revealed using this methodology. The LES Eulerian-Langragian erosion model presented is helpful to understand the flow and slurry erosion in elbows and improve the accuracy of the CFD-based prediction of slurry erosion rate.

Numerical study on the particle erosion of elbows mounted in series in the gas-solid flow

Solid particles in the fluid cause great damages to elbows. In particular, the erosion behavior of elbows mounted in series is more complicated than a single elbow. In the present study, the Eulerian-Lagrangian approach is applied to solve the gas-solid flow in the pipeline with four elbows mounted in series. Three erosion models are used for prediction and Zhang et al. model is finally selected for the development of the numerical model after comparison with the experimental data. Based on the numerical model, the effect of particle diameter, connection length between elbows, and curvature radius on the erosion behavior of four elbows are investigated through the particle trajectory analysis and particle impact characteristic at the elbows. Obtained results show that the erosion behavior of downstream elbows of the connecting pipe is considerably affected by the connection length. The sensitivity of four elbows to particle size is significantly different. Compared with small size particles, large size particles cause greater damage at the first elbow and less erosion at downstream elbows. Additionally, due to the secondary collision of particles, V-shaped erosion morphology appears at elbows and gradually evolves into the closed ring under a larger curvature radius.

Design optimization of hemispherical protrusion for mitigating elbow erosion via CFD-DPM

Pneumatically conveyed particles are commonly responsible for triggering the erosion process by impacts on the wall. Elbows with hemispherical protrusions had been proposed to mitigate erosion. Numerical simulations were carried out using the experimentally verified CFD-DPM method. The continuous impact of particles and secondary flow made the erosion scar on the extrados surface appear as an ellipse with v. For a single row of protrusions, a small arrangement angle and a large protrusion radius is more effective in improving the erosion resistance of the elbow. When θ = 30° and r = D/6, the maximum erosion rate could be reduced by up to 36.59%. The multiple rows of protrusions further mitigated the erosion of the elbow and can reduce the maximum erosion rate by 39.09% at most, but it will cause greater flow resistance.

Study on reducing elbow erosion with swirling flow

Pipe erosion caused by solid particles is an important cause of pipeline damage, for example, parts such as elbows are particularly prone to erosion problems. In this work, the insertion of a twisted tape on different working conditions upstream of an elbow is investigated numerically in order to study the mechanism of the swirling flow reducing the erosion of the elbow. In order to ensure the reliability of numerical calculations, experimental data are used to verify the CFD simulation model of the standard elbow. The influence of the twist ratio of the twisted tape, the insertion position of the twisted tape and the gas velocity on the erosion of the elbow was studied. It was found that the swirling flow induced by the twisted tape make the solid particles suspended and more evenly distributed in the pipeline, which reduces the focusing effect and the impact frequency of particles on the same position of the elbow wall. The insertion of the twisted tape results in a reduction in the area of the maximum erosion zone of the elbow and a significant decrease in the erosion rate along the elbow curvature angle, indicating that the swirling flow can significantly reduce the erosion of the elbow. The smaller the twist ratio of the twisted tape, the closer to the elbow, the more obvious the erosion mitigation effect is. In addition, swirling flow can interfere and inhibits the Dean Vortex on the cross section of the elbow. Under the condition of swirling flow, as the gas velocity increases, the influence range of the Dean vortex increases, the kinetic energy of particle impact increases, and the type of collision changes from sliding collision to direct collision. The erosion rate of the elbow with a twisted tape insert also increases with the increase of the gas velocity, but the swirling flow reduces the velocity index of the erosion rate to a certain extent. • The swirling flow makes the particles distribute more evenly, reducing the focusing effect. • The swirling flow can interfere and inhibits the Dean Vortex. • The swirling flow reduces the velocity index of the erosion rate. • Erosion reduction efficiency of swirling flow depends on twist ratio and insertion position.

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.

The effect of excessive penetration of welding on sand erosion pattern due to high speed gas-solid flows in elbows and reducers

The aim of the current study is to investigate the effect of excessive penetration of welding and natural gas impurity particles on increasing erosion in elbows and reducers. To this end Euler–Lagrange model is used to simulate the two-phase solid–gas flow, the Discrete Phase Model (DPM), k-ε turbulent model and DNV erosion model are used to model the solid particles, natural gas flow and erosion rate, respectively. Erosion in elbows occurs downstream of vertical welding while in reducers is weaker and occurs at the inlet. The results show that erosion rate increases by increasing excessive penetration, particles size, particles flow rate and natural gas flow rate. The effect of excessive penetration becomes more important in high speed flows containing solid particles, in such a way that reducing excess penetration from h = 3 mm to h = 0 mm, causes 45% reduction in erosion rate in elbows containing 20 m/s natural gas flows. Therefore, for high velocity impure gas flows, it is recommended to reduce the allowable excessive penetration in welding standards.

Experimental study on collision characteristics of large coal particles (7–15 mm) in 90° elbows of pneumatic conveying systems

Pneumatic conveying of coal particles widely used for environmental friendliness and automation. In this study, orthogonal experiments were carried out in 90° elbows of large coal particles (7–15 mm) to study the effect of the elbow shape, particle size, airflow velocity, and gas supply pressure on elbow erosion. Elbows with double-layer wall structures were designed to present the erosion characteristics, particle breakage ratio, and pressure drop. Results indicate that the angle between the erosion center and the tangential direction of the elbow inlet is approximately 25°–30°. The elbow shape and airflow velocity have significant effects on all three evaluation indices, whereas the particle size and gas supply pressure have significant effects on the pressure drop. The optimal parameters of each factor were confirmed: the blind elbow with a plug, particle size of 9–11 mm, airflow velocity of 20 m/s, and gas supply pressure of 0.4 MPa.

An experimental and numerical study of slurry erosion behavior in a horizontal elbow and elbows in series

Erosion in elbows is one of the most important issues in pipeline flow assurance for the oil and gas and mining industries. In this study, slurry erosion in a horizontal elbow and elbows in series are numerically and experimentally investigated. The maximum erosion location of horizontal elbow is revealed by conducting slurry erosion painting experiment. The erosion process is then modeled by using computational fluid dynamics (CFD) techniques. The accuracy and stability of the CFD-based erosion model are carefully examined using experimental results. Using the validated numerical methods, the effects of particle concentration, geometry parameter, inlet conditions are investigated. The erosion processes under these different conditions are further analyzed by examining fluid flow development, particle trajectories and impact information. The results of this CFD study present some cautious guidelines for conducting erosion studies of liquid-solid flows and pipeline system designs.

Numerical simulation of air-solid erosion in elbow with novel arc-shaped diversion erosion-inhibiting plate structure

The erosion-induced failure of elbows commonly occurs in the pipeline transport industry. In this study, a computational fluid dynamics (CFD) method was adopted to study the erosion of air-solid elbows. The results show that when the working conditions in the air-solid elbow are changed, there are three types of erosion morphologies: the concentrated-exit type, transition type, and “V” type; the erosion morphology is mainly related to the trajectory of the particles. An arc-shaped diversion erosion-inhibiting plate structure (ASDEIPS) is proposed to reduce the erosion rate for elbows with transition type or “V” type erosion morphologies by up to 41%. Another advantage of the ASDEIPS is its ability to improve the flow field of the elbow under any working condition and to reduce the pressure drop, turbulent kinetic energy, and turbulence dissipation rate of the elbow.

Numerical investigation of elbow erosion in the conveying of dry and wet particles

Liquid bridges between wet particles affect pneumatic elbow erosion, but the associated mechanism remains unclear. This paper presents a numerical study of elbow erosion using a combined approach of computational fluid dynamics and discrete element method facilitated with erosion and capillary force models. Particle dynamics and the elbow erosion location, depth and ratio are analysed in detail. The results show that wet particles tend to adhere to the inner wall of the elbow during transport under the effect of liquid bridges. This phenomenon forms a particle layer that covers the impact area, thereby substantially decreasing both the erosion depth and ratio of the elbow. A U-shaped erosion scar is observed in the extrados of the elbow when conveying wet particles. Additionally, the effects of gas velocity and moisture content on particle flow and elbow erosion are revealed to clarify the differences between dry and wet particles.

Numerical Simulation of Elbow Erosion in Shale Gas Fields under Gas-Solid Two-Phase Flow

Erosion is one of the most common forms of material failure and equipment damage in gas transmission pipelines. Shale gas fields use hydraulic fracturing whereby solid particles are often carried in the gas flow, and the pipeline is in a high-pressure state, which is more likely to cause erosion. The prediction of particle erosion regulation in gas-solid two-phase flow is an effective means to ensure the safe operation of shale gas fields. In this paper, an integrated CFD-DPM model is established to investigate the erosion of 90° elbow in a shale gas field under gas-solid two-phase flow, employing the realizable k-ε turbulence model, discrete phase model, and erosion rate prediction model. The reliability of the proposed numerical models is verified by comparing the predicted data with the experimental data. Moreover, the effects of six important factors on maximum erosion rate are analyzed, including gas velocity, mass flow rate of sand particles, particle diameter, shape coefficient of sand particles, pipeline diameter, elbow radius of curvature. Specifically, the results indicate that the gas velocity, mass flow rate and shape coefficient of sand particles are positively correlated with the maximum erosion rate, while the pipe diameter and the elbow radius of curvature are negatively correlated with the maximum erosion rate. A new correlation was developed, which included four dimensionless groups, namely Reynolds number, diameter ratio, density ratio and particle number. The correlation can be used to predict maximum corrosion rate of elbows. This work can provide data reference and theoretical basis for mitigating the erosion rate of pipelines and managing the integrity of gas pipelines.

Design optimization of guide vane for mitigating elbow erosion using computational fluid dynamics and response surface methodology

A 90° elbow equipped with guide vanes was developed with the intent of reducing elbow erosion. Numerical models were formed to predict the maximum erosion rate of elbow and Face-1, and the response surface methodology was used to study the relationship between the erosion rate and structural parameters of guide vane. A second-order response surface model was established to determine the relationship between R1 and variables, and a reduced cubic (RC) polynomial model was obtained to reveal the relationship between R2 and the three factors. The numerical results show that the low-speed region is expended and the maximum discrete particle matter (DPM) concentration is reduced after installing the guide vane. This internal component provides a shelter for the elbow from the direct impact of high-speed solids.

Erosion evaluation of elbows in series with different configurations

Erosion of elbows in series has received more attention recently as many facilities have elbows in series with various orientations and installations. It has been observed from experiments that, for liquid-dominated flows when two elbows are placed in series and with a small distance between them, the maximum erosion takes place in the second elbow. However, it is also necessary to study the effect of the orientation of the elbows because in the oil and gas industry, for example, there are all types of combinations of elbows in series in the field. In this work, experiments were conducted in a 50.8 mm diameter experimental facility considering liquid-solid and liquid-gas-solid flows and one configuration of elbows in series: where the first elbow for both configurations is upward vertical-horizontal and the second elbow orientation is horizontal-vertical downward. Also, the distance between elbows was kept constant (being three diameters). Additionally, Computational Fluid Dynamics (CFD) studies were performed and compared with experiments. After validation and sensitivity studies concerning numerical solutions, a comprehensive numerical study was conducted, taking into account different scenarios regarding the orientation of elbows using three configurations of two elbows in series. The results show that the normal and the 180° configuration of two elbows in series are less sensitive to the gravity orientation for liquid-solid flows than the other two configurations investigated. On the other hand, for liquid-gas-solid flows, erosion changes with gravity orientation. The worst-case scenario for liquid-solid flow is suggested to be the 180° configuration, while for the liquid-gas-solid flow, the 90° configuration. Thus, it is important to understand the erosion behavior with the orientation of the elbows, because erosion can be reduced by changing the orientation or the configuration of elbows in series.

Impact of inter-particle collision on elbow erosion based on DSMC-CFD method

In this work, computational fluid dynamics (CFD) is used to study elbow erosion due to a gas–solid two-phase flow. In particular, the direct simulation Monte Carlo (DSMC) method is used to study the impact of inter-particle collision on the erosion behavior. The two-way coupled Euler–Lagrange method is used to solve the gas–solid flow, and the DSMC method is used to consider the collision behavior between particles. The effects of key factors, such as the particle concentration distribution and inter-particle collision, on the erosion ratio are evaluated and discussed. The effectiveness of the method is verified from experimental data. The results show that the inter-particle collision significantly influences the particle movement path and erosion ratio. When the inter-particle collision is considered, the maximum erosion position is offset. The erosion model proposed by Oka et al., who used the DSMC method, agrees best with the experimental data, and the average percentage error decreases from 39.2 to 27.4%.

Performance prediction of erosion in elbows for slurry flow under high internal pressure

Slurry erosion is an important cause of material failure in the oil and gas industry. Particularly, during hydraulic fracturing, the fracturing pipelines under high internal pressure inevitably suffer from erosion wear. In this study, the erosion tests involving tensile stress were carried out and a new stress-erosion model suitable for high internal pressure was developed based on the experimental data. Then the established erosion model was applied to conduct the numerical simulation to investigate the erosion behaviour in elbows of fracturing pipeline under different conditions. Finally, an intelligent method of erosion prediction was explored using machine learning technology, providing a potential solution in predicting the erosion severity of elbows under high internal pressure.

A novel approach for solid particle erosion prediction based on Gaussian Process Regression

Based on Gaussian Process Regression (GPR) method, a novel non-linear approach is adopted to predict solid particle erosion in standard elbows. Several data sets extracted from Computational Fluid Dynamics (CFD) results and experimental tests are used to evaluate the effectiveness of the approach for gas-solid as well as gas-liquid-solid flows. Elbow diameter, particle size and density, fluid density and viscosity, and flow velocity are considered as input parameters. By combining input parameters into dimensionless groups, dimensionality reduction is performed. This is conducted to understand the dimensionless numbers governing the erosion phenomenon and effect of dimensionality reduction on erosion prediction. Results and error analysis show that for gas-solid flow, over 80% of the predictions have relative error less than 20% compared to the experimental data. In gas-liquid-solid flow conditions, effect of mixture Reynolds number and ratio of the superficial velocities on erosion rate for both churn and annular flows are investigated. A GPR-based framework is demonstrated to predict erosion distributions over the elbow and results are compared with experimental measurements. Results demonstrate that the GPR approach can accurately and reliably predict solid particle erosion.

Numerical Analysis on Solid Particle Erosion in Elbow of a Slurry Conveying Circuit

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.