基于CFD数值模拟的异面三通管冲蚀磨损规律研究*

针对管道在输送过程中,由流体中固态颗粒产生的冲蚀磨损导致的失效问题,通过CFD-DPM模型开展关于不同流速、颗粒直径、含砂体积比和异面管夹角对异面三通冲蚀磨损性能影响的分析。结果表明：三管交汇处的弯面是管道主要发生冲蚀磨损的位置,水平两管弯头上侧管壁处是受损最为严重的部位;在流速2~10 m/s、含砂体积比1%~9%、异面管夹角90°~150°、颗粒直径0.1~0.5 mm时,管道的最大冲蚀率随着流速增大呈指数型增长,冲蚀面积明显扩张;低流速下,含砂体积比对最大冲蚀率影响较弱,高流速下,最大冲蚀率与含砂体积比呈线性正相关;异面管夹角的增大降低了管道对固体颗粒的流动约束性,其冲蚀率呈线性减小;最大冲蚀率随颗粒直径的增大整体呈现平缓上升的趋势,大颗粒产生的冲蚀破坏相比小颗粒更为集中一些。     

颗粒流撞击壁面的离散元模拟

为了解决催化裂化装置中催化剂颗粒的磨损、撞碎等问题,首要解决催化剂颗粒的运动特性问题,为此将离散元数值模拟的技术应用到催化剂颗粒撞击壁面的模型中,简化了催化剂颗粒撞击壁面的模型为颗粒流撞击壁面模型,开展了颗粒流撞击壁面的离散元分析;建立了颗粒流中随机标记颗粒的速度与时间、位移与时间的关系,及整个颗粒流的动能与时间的关系;追踪了标记颗粒的运动轨迹,解释了颗粒流撞击壁面产生不规则分布的原因;提出了分段区间随机取样求得壁面平均应力的方法,在不同入射速度下对壁面产生的平均应力大小进行了对比分析。研究结果表明,入射颗粒流的速度对壁面应力的影响呈不稳定性,不同的入射速度影响壁面的平均应力大小,且在一定范围内入射速度越大,壁面的应力越大。     

Slurry erosion resistance of boride-based overlays containing boride crystals oriented perpendicularly to the wearing surface

Components exposed to the flow of liquid solutions containing hard particles experience significant material loss. For defined slurry conditions, the extent of damage to the components depends upon their microstructure and the slurry particle impingement angles. This paper presents the research work carried on to develop a gas metal arc welding (GMAW) clad overlay that resists slurry erosion at both low and high particle angles. GMAW overlays containing hard primary Fe₂B crystals in a supporting matrix enriched in molybdenum, carbon and silicon have been considered. Cored wires of specific compositions deposited with adapted welding parameters produce weld overlays presenting a peculiar microstructure. These iron boride-based overlays contain fine elongated boride crystals aligned mainly perpendicularly to the wearing surface. This peculiar microstructure is responsible for the outstanding slurry erosion resistance observed at both impinging angles of 30° and 90°. These iron boride-based overlays present a slurry erosion resistance at low and high impinging angles far beyond that observed with known materials including chromium carbide overlays.     

Sand-water slurry erosion of carburized AISI 8620 steel

The erosion behavior of carburized AISI 8620 steel for sand slurry service was investigated. The jet impingement type of test was used where sand slurry is directed at flat specimens to determine the erosion rates and mechanism of erosion. The effects of steel heat treatments, slurry velocities and particle concentrations on erosion rates were investigated.     

螺旋槽小孔节流动静压空气轴承颗粒冲蚀研究

为研究空气轴承在运转过程中细小颗粒对壁面冲蚀情况，借助三维建模工具建立动静压空气轴承模型，从连续方程、可压缩流体润滑方程、气体状态方程出发，推导出等温条件下稳态气体润滑Reynolds方程；结合离散相模型(DPM)颗粒平衡方程，分析颗粒运动轨迹和颗粒对壁面的最大冲蚀速率。借助Fluent仿真软件分析气源压力、主轴转速、粒径参数对气体轴承壁面冲蚀的影响。结果表明：随着粒径尺寸的增加，相同运行工况下，壁面冲蚀磨损速率呈现先增加后降低趋势；随着主轴转速的增加，壁面冲蚀磨损的面积在增加，但最大壁面冲蚀磨损速率在下降，同时壁面磨损面积向主轴正向旋转的方向延伸。     

钻井液固液分离旋流器壁面磨损特性

针对石油钻井过程中,由于钻井液中泥沙等固体颗粒产生的冲蚀磨损导致的旋流器失效问题,采用CFD-DPM模型开展以非牛顿流体为钻井液时旋流器冲蚀磨损研究,探讨不同流速、稠度系数、流动性指数、含砂体积比和入口倾角对旋流器内壁冲蚀磨损的影响。结果表明：旋流器内壁磨损呈螺旋状,锥段处磨损率随着半径的减小而增大,底流口处是受损最为严重的部位;在流速5～15 m/s、含砂体积比1%～9%时旋流器的最大冲蚀率随着流速增大呈指数型增长,冲蚀面积明显扩张;低流速下含砂体积比对最大冲蚀率影响较弱,而高流速下最大冲蚀率与含砂体积比呈正相关;入口倾角的增大同时增大了向下的轴向速度,使得颗粒能更快地到达底流口减小了与壁面的接触,其冲蚀率呈线性减小;最大冲蚀率随稠度系数的增大整体呈现平缓下降的趋势,随着流动性指数的增大而急速下降,流动性指数对冲蚀破坏的影响相比稠度系数更剧烈一些。     

Slurry erosion of polyphenylene sulfide-glass fiber composites

The erosive wear of glass-fiber-reinforced polyphenylene sulfide in a sand slurry has been investigated as a function of sand particle velocity and sand particle size. The morphology of slurry erosion failure has been examined by scanning electron microscopy and a possible equation for slurry erosion has been derived.     

Particle size effects in bend erosion

From work on the erosion of flat plates in test rigs of the sand blast type published in recent years it has generally been concluded that there is a critical particle size above which erosion is not influenced by size. Recent work on the erosion of pipe bends by sand in a pneumatic conveying line tends to confirm this theory. For pipe bends, however, it was observed that particle size has two additional effects of major significance: the appearances of the eroded surfaces are totally different and the depth of penetration by erosion is much greater for smaller particles; this means that pipe bends will fail much earlier if smaller particles are conveyed.     

Erosion damage of polymeric material by slurry

An attempt was made to reveal the erosion mechanism of a plastic material in slurry containing glass beads of approximately 176 μm in diameter. The experimental observations were interpreted in terms of parameters such as the impact velocity V_p, the impact angle α of the beads and the striking efficiency η. A theoretical flow analysis for a solid-liquid two-phase flow was made and it was found that the trajectories of the particles curved as they approached the specimen, indicating that the actual surface onto which the particles were impinging was much narrower than that which would be expected for sand erosion in an air stream. In the slurry erosion the impact velocity and impact angle differed greatly at different positions of the specimen. This is possibly due to the differences in the density and viscosity of liquid and air. Two distinctly different types of erosion were observed: a typical brittle behaviour occurred near a stagnant point, after an initial incubation period, whereas at a distance from the stagnant point only a slight surface roughness was produced. These two different types of erosion produced a clear boundary. Erosion rates depended on the positions of the specimen and were found to be proportional to (V_p sin α)^2.6. This suggested that the normal component of the impact velocity of the particle determined the erosion rate of the plastic material due to slurry.     

气枪喷嘴除尘除水效率的实验研究

利用图像处理的方法对小尺度气枪喷嘴冲击射流的除尘除水效率进行研究,实现了对喷嘴除尘除水效率的定量测量。利用该方法对影响气枪喷除尘除水效率的各种因素进行研究,并将实验结果与用热线风速仪测量的结果进行了比较,得到了关于喷嘴工作最佳工况的一些结论。这些结论可对了解喷嘴的除尘除水工作原理及对气枪喷嘴进一步改进和优化提供帮助。     

The influence of high shear and sand impingement on preferential weld corrosion of carbon steel pipework in CO2-saturated environments

Preferential weld corrosion (PWC) has proved problematic for the oil and gas industry for a number of years. Although the effect of high flow rates on PWC in inhibited CO₂-saturated solutions has been studied by authors, the consideration of a higher, localised turbulence over the weld material and the implications this has on PWC appears minimal. This work considers this very effect, along with developing an understanding of the threats posed to weld integrity by sand particle presence in the process fluid using a submerged impinging jet (SIJ) apparatus.Experiments were conducted using a commercially available film-forming oilfield corrosion inhibitor which was evaluated in both flow-induced corrosion and erosion–corrosion environments in its ability to control PWC. The SIJ setup allowed control over the individual flow velocities at each nozzle, meaning shear stress could be intensified over the 1% Ni–0.25% Mo weld material to simulate localised turbulence at the sample surface. Galvanic current and mixed potential measurements were performed to ascertain changes in galvanic interactions between the two materials. The work demonstrates that localised turbulence over internal weld beads and the presence of sand within oil and gas systems can influence PWC in certain environments.     

Fluid dynamic mechanisms of particle flow causing ductile and brittle erosion

Traditional prediction of erosion focuses on the use of velocity and impact angle of particles as independent variables in analytically derived models. This approach is most suitable for numerical predictions of erosion in disperse flow fields where particle trajectories may easily be followed prior to impact. For dense particle flows, the prediction of individual particle or particle cluster movement is nearly never attempted by following trajectories. Instead, two-fluid Eulerian–Eulerian approaches are used in which a continuous particle fluid phase is considered.The present study shows that the impact velocity and angle of attack of particles at the eroding surface are difficult to obtain for dense flows, thus being difficult to consider as parameters for predicting erosion. Instead, it is proposed that the normal and the shearing components of the viscous dissipation of the particulate phase are more suitable as independent flow variables governing the erosion process. These variables describe deformation and cutting wear processes, respectively, and are readily derived from the flow field.Eulerian erosion models are proposed, based on these independent variables. It is possible to implement previous results and theories concerning the material–mechanical interaction between the abrasive and an eroding surface to achieve model improvements. In this work, only a simple model taking into account a threshold elastic strain limit is proposed, to more correctly model the deformation wear.The particle-flow boundary condition — a partial-slip condition — significantly influences the erosion process, particularly the cutting erosion. The boundary condition depends on parameters such as the local particle phase flow, the mean diameter and the sharpness of the abrasive as well as the surface roughness.A simple 2D test application — a jet stream of particles impinging a tilted plate — is presented, and the qualitative angular behaviour of ductile and brittle erosion is reproduced at the target position. A scheme is presented for determination of material constants and suitable boundary conditions to be used in the proposed erosion models.     

Prediction of particle degradation during impact on a flat surface

A critical review of the available literature on wear rate studies in an impactor system indicated that the particle size and shape both play an important role in erosion. A simple apparatus, normally used for the study of wear rate, was used to determine experimentally the particle size degradation for various impinging velocities at various numbers of impacts. A comminution model used in ball mill grinding systems was used with slight modifications. It was found that the model representation is adequate for the prediction of the attrited product size distribution.     

Design and performance of a high velocity air–sand jet impingement erosion facility

This paper describes the design, construction and capabilities of a high velocity air–sand erosion rig. It has been designed with the aid of computational fluid dynamics to approximately simulate the erosion conditions often experienced by subsea choke valves used in the offshore oil industry. It has also been designed to evaluate the erosion performance of CVD diamond coatings at sonic velocity. The rig is of the gas-blast design in which solid particles, typically sand 60–660 μm in size, are injected into a high velocity air stream and accelerated down a 16-mm-diameter tube, 1 m in length, before striking the sample under test. Tests can be carried out with particle velocities of up to 340 m/s under a wide range of sand fluxes, impact angles and standoff distances. The results of pressure, velocity and sand flux calibration work are described. In addition, preliminary experimental data on tests carried out on mild steel, bulk and sprayed tungsten carbide are also presented. The flexibility of the air–sand rig allows the erosion behaviour of materials to be studied under a wide range of conditions.     

缩径管内两相流砂粒碰撞和冲蚀特性研究

针对目前建模方法在描述两相流中砂粒碰撞行为方面存在的不足,运用计算流体力学和离散单元耦合方法建立了压裂工况下的缩径管两相流模型,实验验证了仿真模型的准确性。分析了缩径管内砂粒间碰撞及缩径斜面受力规律,研究发现,缩径斜面冲蚀深度随砂比增大而增大,砂比大于40%时,相同时间的冲蚀深度增量减小,并趋于最大值;缩径斜面冲蚀深度随黏度增大而减小,流体黏度对缩径斜面外缘比对内缘的冲蚀深度影响大。     

The erosion of aluminum by solid particle impingement at normal incidence

A rotating arm apparatus was used to study the erosion of polycrystalline aluminum by 1.58 mm diameter WC-6% Co spheres impinging at normal incidence. Dynamic hardness values were obtained from measurements of the impact craters and compared with corresponding quasi-static values. In addition, material removal was monitored gravimetrically, and quantitative information was obtained on threshold and incubation phenomena and steady state erosion behavior. The variation of the velocity dependence of erosion with the number of particle impacts was derived from these data. Supporting scanning electron microscope studies suggest that the mechanism of material removal responsible for ductile erosion at near normal incidence is somewhat different from that which operates at shallower angles. The similarities and differences between these mechanisms are discussed, and it is suggested that together they account for the characteristic variation of ductile erosion with angle of impingement.     

Electrochemical investigation of erosion-corrosion using a slurry pot erosion tester

The aim of this paper is to use a modified slurry pot erosion tester to perform in-situ electrochemical measurements during solid particle impingement to investigate the effects of velocity, sand size and sand concentration on a passive metal (UNS S31603). Samples are subjected to a set of erosion-corrosion experiments. The electrochemical response of UNS S31603 to the test parameters is plotted and compared to develop an understanding of the erosion-corrosion process. The current trend with variation of test parameters has been explained by an erosion enhanced corrosion synergistic effect. The current transients associated with depassivation and repassivation during solid particle impingement are observed through electrochemical noise measurements. It was observed that the increase in velocity and sand concentration increased the current levels during erosion-corrosion. However, the increase in sand size had a more complex response. Single particle impact experiments conducted revealed that the peak corrosion current and the repassivation time increased with increase in velocity. A linear trend was seen between the peak current and the kinetic energy. A second-order exponential decay was fitted to the repassivation kinetics of the single particle impact. SEM has been used to develop a mechanistic understanding of erosion-corrosion. The surface scars reveal that the depth of the craters and the length of the lips increase with increase in velocity. Micro-cracks also appear on these lips, believed to be due to corrosive action attacking the roots of these lips.     

Solid particle erosion behaviour of hardfacing deposits on cast iron—Influence of deposit microstructure and erodent particles

Solid particle erosion (SPE) behaviour of different hardfacing electrodes deposited on gray cast iron (ASTM 2500) was studied using quartz sand and iron ore as erodent particles. Erosion test was carried out as per ASTM G76 test method. Considerable differences in erosion rates were found among different hardfacing electrodes at normal impact. Both volume fraction of carbides and type of carbides played an important role in the erosion behaviour of the deposits when quartz sand was used as erodent particles. On the other hand, only volume fraction of carbides irrespective of carbide type mainly controlled the erosion rate of the same deposits when iron ore was used as erodent particles. Such difference is attributed due to difference in metal removal mechanisms by the two erodent particles used. Hard quartz sand particles were capable of causing damage to most of the carbides while relatively softer iron ore particles were unable to fracture any carbides present in the microstructures. Furthermore, relatively brittle matrix led to high erosion rate which is significant in case of quartz sand as erodent, but not in case of iron ore particles. Like abrasion resistance, hardness is not a true index of erosion resistance of hardfacing deposits.     

Assessment of Erosion Resistance of Coated Polymer Matrix Composites for Propulsion Applications

The erosion behavior of tungsten carbide-cobalt (WC-Co) coated and uncoated polymer matrix composites (PMCs) was examined with solid particle impingement using air jets. Erosion tests were conducted with Arizona Road Dust impinging at 20°, 60°, and 90° angles at a velocity of 229 m s^–1 at both 294 and 366 K. Noncontact optical profilometry was used to measure the wear volume loss. Results indicate that the WC-Co coating enhanced erosion resistance and reduced erosion wear volume loss by a factor of nearly 2. This should contribute to longer wear lives, reduced related breakdowns, decreased maintenance costs, and increased product reliability.     

Solid particle erosion of diamond coatings under non-normal impact angles

This paper describes an erosion study, which examines the effect of impact angle on the erosion behaviour of diamond coatings deposited on tungsten substrates by chemical vapour deposition (CVD). The coatings were 37–60 μm in thickness and were erosion tested using angular silica sand with a mean diameter of 194 μm at a particle velocity of 268 m s⁻¹. The impact angles used were 30, 45, 60 and 90°. The results show that the damage features, termed “pin-holes” are generated at all angles, though the number of impacts required for pin-hole initiation is significantly increased at lower angles. This work provides useful information in attempting to explain the mechanism by which damage is generated during the high velocity sand erosion of CVD diamond.