Brenton S. McLaury

Modeling Solid Particle Erosion in Elbows and Plugged Tees

Predicted erosion patterns on the surface of a pipe fitting can now be obtained using a technique implemented into a computational fluid dynamics (CFD) code. This comprehensive erosion prediction procedure consists of 1) generation of a flow field simulation, 2) computation of a large number of particle trajectories inside the flow field, and 3) erosion model equations applied as particles impinge the walls of the geometry. Other quantities related to erosion, namely the particle deposition rate as well as local average impingement angle and velocity components, are also stored in the procedure. All predicted quantities (flow solution, particle trajectories, and erosion profiles) are analyzed using a three-dimensional visualization tool that was also developed. The current work focuses on two pipe fittings commonly used in the oil and gas production industry: elbows and plugged tees. First, the flow field and erosion predictions are evaluated through comparisons with experimental data. Erosion predictions yield trends and locations of maximum wear that are consistent with experimental observations. Next, two 90-deg pipe elbows with centerline curvature-to-diameter ratios of 1.5 and 5.0 are analyzed under prescribed erosive conditions. Predicted erosion results are presented in the form of surface contours. Finally, a simulated plugged tee geometry placed under erosive conditions is studied and erosion rates are compared to that of the two elbow test cases.

A Comprehensive Procedure to Estimate Erosion in Elbows for Gas/Liquid/Sand Multiphase Flow

A comprehensive procedure that combines mechanistic analysis and numerical simulation approaches is proposed to estimate the erosion in elbows for gas/liquid/sand particle multiphase flow systems. The erosion problem in multiphase flow is approximately transferred to one in single-phase flow by introducing the effective sand mass ratio and a representative single-phase flow to which a single-phase computational-fluid-dynamics-based erosion-prediction model can be applied. Erosion in elbows is calculated for various multiphase flow patterns and compared to experimental data in the literature. Reasonable agreement between the simulations and the literature data is observed. The proposed approach is an effective tool to estimate the erosion in multiphase flow.

An Alternate Method to API RP 14E for Predicting Solids Erosion in Multiphase Flow

One commonly used method for determining oil and gas production velocities is to limit production rates based on the American Petroleum Institute Recommended Practice 14E (API RP 14E). This guideline contains an equation to calculate an erosional or a threshold velocity, presumably a flow velocity that is safe to operate. The equation only considers one factor, the density of the medium, and does not consider many other factors that can contribute to erosion in multiphase flow pipelines. Thus, factors such as fluid properties, flow geometry, type of metal, sand production rate and size distribution, and flow composition are not accounted for. In the present paper, a method is presented that has been developed with the goal of improving the procedure by accounting for many of the physical variables including fluid properties, sand production rate and size, and flowstream composition that affect sand erosion. The results from the model are compared with several experimental results provided in the literature. Additionally, the method is applied to calculate threshold flowstream velocities for sand erosion and the results are compared with API RP 14E. The results indicate that the form of the equation that is provided by the API RP 14E is not suitable for predicting a production flowstream velocity when sand is present.

Improvements of Particle Near-Wall Velocity and Erosion Predictions Using a Commercial CFD Code

The determination of a representative particle impacting velocity is an important component in calculating solid particle erosion inside pipe geometry. Currently, most commercial computational fluid dynamics (CFD) codes allow the user to calculate particle trajectories using a Lagrangian approach. Additionally, the CFD codes calculate particle impact velocities with the pipe walls. However, these commercial CFD codes normally use a wall function to simulate the turbulent velocity field in the near-wall region. This wall-function velocity field near the wall can affect the small particle motion in the near-wall region. Furthermore, the CFD codes assume that particles have zero volume when particle impact information is being calculated. In this investigation, particle motions that are simulated using a commercially available CFD code are examined in the near-wall region. Calculated solid particle erosion patterns are compared with experimental data to investigate the accuracy of the models that are being used to calculate particle impacting velocities. While not considered in particle tracking routines in most CFD codes, the turbulent velocity profile in the near-wall region is taken into account in this investigation, and the effect on particle impact velocity is investigated. The simulation results show that the particle impact velocity is affected significantly when near-wall velocity profile is implemented. In addition, the effects of particle size are investigated in the near-wall region of a turbulent flow in a 90 deg sharp bend. A CFD code is modified to account for particle size effects in the near-wall region before and after the particle impact. It is found from the simulations that accounting for the rebound at the particle radius helps avoid nonphysical impacts and reduces the number of impacts by more than one order-of-magnitude for small particles (25 μm) due to turbulent velocity fluctuations. For large particles (256 μm), however, nonphysical impacts are not observed in the simulations. Solid particle erosion is predicted before and after introducing these modifications, and the results are compared with experimental data. It is shown that the near-wall modification and turbulent particle interactions significantly affect the simulation results. Modifications can significantly improve the current CFD-based solid particle erosion modeling.

Generalization of the API RP 14E Guideline for Erosive Services

The commonly used practice for controlling sand erosion in gas and oil producing wells is to limit production velocities following the provisions of American Petroleum Inst. (API) RP14E. This guideline contains a procedure to calculate a threshold velocity, the flow velocity below which an allowable amount of erosion occurs. While providing the advantage of computational ease, the approach has some disadvantages. One is that, while many factors influence the erosion rate, APE RP14E includes only one factor, the density of the medium. Thus, such factors as flow geometry, type of metal, sand size, and Reynolds number are not accounted for. In this paper, the method is applied to calculate threshold velocities. The computational procedure allows an allowable amount of erosion to be specified in mils per year for elbows, tees, and direct impingement geometries. Threshold flow-stream velocities are calculated for carrier fluids of crude oil, water, and methane at elevated pressure. Resulting threshold velocities are presented for a range of sand sizes, pipe diameters, sand production rates, and methane pressures. Results show that threshold velocities for single-phase gas flows are much lower than those for single-phase liquid flows.

Experimental Investigation of Horizontal Gas–Liquid Stratified and Annular Flow Using Wire-Mesh Sensor

Stratified and annular gas–liquid flow patterns are commonly encountered in many industrial applications, such as oil and gas transportation pipelines, heat exchangers, and process equipment. The measurement and visualization of two-phase flow characteristics are of great importance as two-phase flows persist in many fluids engineering applications. A wire-mesh sensor (WMS) technique based on conductance measurements has been applied to investigate two-phase horizontal pipe flow. The horizontal flow test section consisting of a 76.2mm ID pipe, 18m long was employed to generate stratified and annular flow conditions. Two 16 16 wire configuration sensors, installed 17 m from the inlet of the test section, are used to determine the void fraction within the cross section of the pipe and determine interface velocities between the gas and liquid. These physical flow parameters were extracted using signal processing and cross-correlation techniques. In this work, the principle of WMS and the methodology of flow parameter extraction are described. From the obtained raw data time series of void fraction, cross-sectional mean void fraction, time averaged void fraction profiles, interfacial structures, and velocities of the periodic structures are determined for different liquid and gas superficial velocities that ranged from 0.03m/s to 0.2m/s and from 9m/s to 34m/s, respectively. The effects of liquid viscosity on the measured parameters have also been investigated using three different viscosities. [DOI: 10.1115/1.4027799]

Experimental Investigation of the Location of Maximum Erosive Wear Damage in Elbows

Erosive wear damage of elbows due to solid particle impact has been recognized as a significant problem in several fluid handling industries. Solid particle erosion is a complex phenomenon due to different parameters causing material removal from the metal surface. The particle density, size, shape, velocity, concentration, impact angle, and impacting surface material properties are some of the major parameters. Among the various factors, the particle impact velocity has the greatest influence in erosion. The particle impact velocity and impact angles depend on the fluid velocity and fluid properties. The particle to particle, particle to fluid, and particle to wall interactions increase the complexity of the erosive wear behavior. In multiphase flow, the presence of different fluids and their corresponding spatial distribution of the phases, adds another dimension to the problem. Most of the previous investigations were focused on determination of erosion in terms of mass loss of the eroding surfaces without identifying the specific location of the maximum erosive wear. During this investigation, magnitude of erosion at different location of an elbow specimen was measured to determine the location of maximum erosion. Experimental investigation of erosion in single-phase and multiphase flows was conducted at different fluid velocities. Both mass loss and thickness loss measurements were taken to characterize erosion behavior and erosion patterns in an elbow. Experimental results showed different erosion behavior and location of maximum erosion damage in single-phase and multiphase flows. The locations of maximum wear due to erosion were also different for horizontal flow compared to vertical flow.

Effect of Particle Size and Liquid Viscosity on Erosion in Annular and Slug Flow

Erosion measurements in multiphase slug and annular flow regimes have been made in a horizontal 76.2 mm (3-in.) diameter pipe. These flow regimes are selected since they produce higher metal losses than other flow regimes, and they also occur for a wide variety of operating conditions. Experiments are performed with superficial gas velocities ranging from 15.2 m/s (50 ft/s) to 45.7 m/s (150 ft/s) and superficial liquid velocities ranging from 0.46 m/s (1.5 ft/s) to 0.76 m/s (2.5 ft/s), for liquid viscosities of 1 cP and 10 cP. Three different sand sizes (20, 150, and 300 μm sand) were used for performing tests. The shapes of the sand are also different with the 20 and 300 μm sand being sharper than the 150 μm sand. Erosion measurements are obtained using electrical resistance (ER) probes which relate the change in electrical resistance to the change in the thickness of an exposed element resulting from erosion. Two probes are placed in a bend and another probe is placed in a straight section of pipe. The probes in the bend are flat-head probes, and they are placed flush with the outer wall in the 45 deg and 90 deg positions. The probe in the straight pipe is an angle-head probe which protrudes into the flow with the face placed in the center of the pipe.

Experimental and Numerical Investigation of the Effect of Viscosity and Particle Size on the Erosion Damage Caused by Solid Particles

Oil and gas produced from wells usually contain impurities such as sand particles transported by fluid flowing through pipelines. The particles impinge on the pipe walls and fittings removing material from the wall and causes erosion damage. The effect of viscosity and particle size on the local thickness loss and total erosion ratio was investigated by conducting a comprehensive experimental study on the erosion of stainless steel 316 specimens caused by sand entrained in a submerged liquid jet. Two types of sand with sizes of 150 µm and 300 µm were used and added to liquids with 1, 14 and 55 cP viscosities. The tests were carried out for three different nozzle angles: 90

Effect of Entrance Shape on Erosion in the Throat of Chokes

Erosion is a complex phenomenon that depends on many factors such as fluid properties, solid particle properties, flow stream velocity, flow geometry, and type of metal. Flow modeling and particle tracking are important tools for predicting erosion. In erosion modeling, it is important to account not only for the factors that influence erosion, but also for changes in some of these factors that occur as the erosion process continues. For example, the change in the geometry resulting can have a significant impact on the erosion results. Geometry changes result when corners, found in couplings and chokes, are eroded with time. This change in geometry due to erosion can drastically change the flow field, especially the turbulent kinetic energy and dissipation rate. Recognizing this change is imperative, since the prediction of particle behavior is heavily dependent on the turbulent kinetic energy. Furthermore, more particle impingements occur in regions with higher turbulent kinetic energy. This paper shows that neglecting the change in the flow field solution resulting from the change in geometry can cause erroneous erosion predictions. A computational study was performed on a choke geometry to demonstrate the importance of incorporating the change in geometry resulting from erosion. Predicted turbulent kinetic energy contours are presented as a function of the changing choke geometry The predicted erosion rates along the choke are also examined for the various scenarios, and these results are compared to experimental results. Additionally, experimental results obtained from laser doppler velocimeter (LDV) measurements also demonstrate the change in fluctuating velocity (turbulent kinetic energy) as a result of rounding of the entrance of the choke, Results from this study show that it is necessary to update the flow geometry and flow model based on the changing geometry due to erosion.