Thank you for visiting Nature.com. The version of browser you are using has limited CSS support. For best results, we recommend using a newer version of your browser (or turning off compatibility mode in Internet Explorer). In the meantime, to ensure ongoing support, we are showing the site without styling or JavaScript.
This paper examines the causes and factors of failure due to mechanical wear (erosion) of the internal surfaces of elbows and pipes for transporting mild steel cement and finds ways to reduce this failure. Nanocoating technology is used to apply layers of tungsten carbide nanoparticles of varying thicknesses (30, 40, 50 μm) to the sample surface. These specimens were tested using a pin-on-disc test by placing them inside the elbow under the same operating conditions. The test results under the same operating conditions showed that the corrosion rate of the sample with a coating thickness of 50 μm was reduced by 71%, and the results of testing the disc pin showed that the corrosion rate of the sample with a coating thickness of 50 μm was reduced by 71%. µm has been reduced by 97% (50 µm) as the test is carried out under ideal conditions. Reducing the wear rate of elbows and pipes will extend their service life by at least twice and reduce maintenance costs by approximately 75%. Numerical modeling of the erosion profile inside the knee was also carried out; agreement with the experimental results reached 90%.
The term suspension is defined as “a heterogeneous mixture of solids and liquids, gases or air.” High-speed mixed flow of cement and air can cause mechanical wear on the internal surfaces of pipes and elbows, resulting in huge losses of money and time. Solids have particle sizes ranging from a few microns to several millimeters. The effect of high particle concentration is influenced by various factors such as the amount of density, size, mass fraction, density of solid particles and carrier, depending on the size of the solid particles, the solution can be classified as unstable; Solid particles have less ability to stabilize carrier gases1. Many fine powders, such as cement, have very low degassing rates and are suitable for dense phase transport. When these powders were transported in a dense phase, a flow pattern was observed in horizontal pipes and stratified flow was observed. A layer of highly concentrated fluidized material occupies the bottom of the pipe. At the top of the pipe, particles are suspended in the transport gas. A fluidized layer created at the top and bottom of the pipe keeps particles suspended in the transport air2. Pipelines are important for transporting gases, liquids and solid materials over long distances from their primary sources to warehouses or silos. The cement industry is one of the important industries in the world as it has many applications in the construction sector3. The erosion and corrosion rates of 30°, 60° and 90° carbon steel elbows in a multiphase flow containing sand particles were studied. Qualitative techniques such as multilayer coating modeling and microscopic surface imaging are used to thoroughly study the mechanisms of flow-accelerated erosion corrosion. The results show that the erosion rate of the 90° knee is higher than that of the low-angle knees (30° and 60°), and the highest erosion rate is observed in the upper part of the knee4. These conditions apply at high pressures up to 7 bar, where the flow is turbulent and, due to the high degree of turbulence, the cement particles are distributed directly across the cross-section of the pipe. Particulate matter has a greater impact on metal surfaces, causing surface damage and parts removal. This phenomenon is called mechanical wear (erosion). Erosion always occurs when solid particles directly impact a hard surface. Mechanical erosion (wear) inside pipelines plays a vital role in the design and operation of transportation systems5. Conduct wear research focused on areas of interest to various industries. Early work in corrosion research began in industrialized countries in the 1960s and demonstrated the complexity of wear phenomena6; Mild steel is used to study the wear of pipes mixed with compressed air and hard abrasive particles. Their results showed that reducing the bending curve resulted in reduced wear7. A numerical study on the erosion of slurry transport pipes was carried out using ANSYS software. The results showed that the erosion rate increased eightfold8; Nanoindentation needs to be simulated using powerful finite element software to extract a large number of mechanical properties such as hardness, elastic modulus, load endurance, as well as various parameters such as optimal thickness and optimal critical load, stress distribution and substrate-layer coupling. The contact pressure between them can be determined from the load displacement curve A9. The wear resistance and scratch resistance of low-carbon steel St-37 coated with nickel-boron nanoparticles were studied. The electrodeposition and heat treatment method, time (1 hour) and temperature (400°C) were used. The results showed that wear rate decreased by approximately 50% and hardness increased by approximately 28%10; To determine the causes of erosion on pipelines, experimental studies were carried out using sandblasting machines with different flow speeds (20~80 m/s). The results show that at high speeds and over long periods of time, erosion is an abrasive mechanism, while at low speeds erosion is due to plastic deformation11. Numerical studies were carried out on mild steel to elucidate the wear behavior. Their study used steel pipes with a length of 1.5 m and a diameter of 50-250 mm. Mix sand and water to form a slurry and control the speed between 2-8 m/s. The results show that the larger the bending angle, the greater the wear. The maximum wear rate is observed at angles of 30°~60°12. The thermal spray process was used to coat the surface of high chromium cast iron with tungsten carbide nanocoating to study the improvement of wear resistance and microhardness. The results show that due to the good wear resistance of tungsten nanocarbide powder and its good adhesion to the steel surface at high temperatures, thermal spraying increased the microhardness by 34% and the wear resistance increased by 79%13,14. From the above literature review and to the best of the author’s knowledge, studies on mechanical wear caused by cement particles passing through 90° bent pipes indicate that a unique approach has been adopted to reduce this mechanical wear by coating the inner surface of the pipe. Elbows with tungsten carbide (WC) nanoparticle layers have not been well studied. The purpose of this work is to search for technologies that can reduce the wear rate of elbows and pipes, increase their service life, reduce maintenance costs, and reduce production downtime. Experimental and numerical studies will make a significant contribution to the open literature and will improve the wear resistance of coatings on the inner surface of elbows and pipes used in pneumatic cement conveyors.
Most cement plants use mild steel to make pipes and elbows. The chemical composition of mild steel is given in Table 1. The material is also used to prepare specimens for internal testing of disc knees, hardness testing, and SEM image analysis;
Nanometer-sized (55 nm) tungsten carbide (WC) nanoparticles were used as a coating material to coat mild steel samples. The nanoparticles have a true density of 15,500 kg/m3, a melting point of 2870°C and a boiling point of 6000°C. In Fig. Figure 1 shows tungsten carbide nanoparticles used as coating materials.
High-velocity flame spraying (HFFS) is used on the surface of metallic and non-metallic (ceramic) materials to form a coating in a semi-molten or molten state. Both fuel oxygen and acetylene were supplied to the chamber at a 3:1 oxygen to acetylene gas flow ratio and the applied pressure was 10 bar for oxygen and 5 bar for acetylene. Both gases and nanoparticles are controlled by special valves14, as shown in Figure 2. The feed rate of tungsten carbide nanoparticles is approximately (1.3*10–2 g/s).
The specimens used for testing inside the elbow are made of mild steel with a size of 70*30*5mm and an inner surface roughness of 0.9mm, and the position of the specimens inside the elbow is set to ensure that they are exposed to real impact. Wednesday. harsh operating conditions, and the liquid flows easily through the template, ensuring contact with every point on every surface of the sample. In addition, holes were drilled into the sample to facilitate installation inside the elbow with the best type of fastening, as shown in Figure 3. One side of each sample was cut at an angle of 10 degrees to the horizontal to avoid flow separation zones behind where the water flow begins flow through the sample. In addition, the surface curvature of the sample was precisely adjusted so that it could easily fit inside the knee.
Based on the preliminary simulation results, a cut-off angle of 10 degrees was formed with the X-axis at the front side of each sample (as shown in Figure 3) to prevent any expected flow separation zone beyond the initial flow position through the sample. and maintain full flow attached to the sample surface
The samples were prepared as follows: 1 sample without coating, 1 sample with a coating thickness of 30 μm, 1 sample with a coating thickness of 40 μm and 1 sample with a surface roughness (0.03-0.045 mm) coating thickness of 50 μm).
A location is selected on the inner surface of the elbow, which is expected to be subject to the worst conditions of cement particles and flow rate, and the sample is placed around the inner circumference of the elbow using steel bolts, as shown in Figure 4; .
The wear test specimens (pin on disc) were made of mild steel with diameter (40 mm) and thickness (10 mm) according to standard specification (ASTM G-99-17)16. The surface of the samples was smoothed in the laboratory of the Faculty of Engineering, University of Kufa, Iraq. The rotation diameter of the pin shaft is selected according to the standard rotation speed setting (400, 500 rpm). The load applied to the pin shaft is 20 N. Abrasive wear (deformation and cutting) occurs on the surface of the test sample. ) Due to the high rotation speed, hard metals and abrasive particles will be continuously removed, as shown in Figures 1 and 2. 5 and 6.
The first step in predicting erosion is modeling the flow field. Fluid flow is modeled using time-averaged Navier-Stokes equations to calculate the represented flow field. Turbulence is modeled using the RANS method. The gas flow is assumed to be an incompressible Newtonian fluid with constant properties, three-dimensional, unstable and in a turbulent regime. Consequently, there are 17 continuity, momentum and turbulence equations for an incompressible fluid, three-dimensional and time-varying:
To find the turbulent eddy viscosity (\({{\varvec{\mu}}}_{{\varvec{t}}}\)), Menter k–\({\varvec{\omega}}\ ) In this study The following SST18 turbulence model is used:
份位: \({{\varvec{P}}}_{{\varvec{k}}}=2{{{\varvec{\mu}}}_{{\varvec{t}}}{\varvec { \delta}}}_{{\varvec{i}}{\varvec{j}}}。{{\varvec{\delta}}}_{{\varvec{i}}{\varvec{j}} } -\frac{2}{3}{\varvec{\rho}}{\varvec{k}}{\nabla .\overrightarrow{{\varvec{U}}}{\varvec{\delta}}}_ { {\varvec{i}}{\varvec{j}}}\) 和 \({{\varvec{\delta}}}_{{\varvec{i}}{\varvec{j}}}=\ frac {1}{2}\left(\frac{\partial {{\varvec{u}}}_{{\varvec{i}}}}{\partial {{\varvec{x}}}_{{ \varvec{j}}}}+\frac{\partial {{\varvec{u}}}_{{\varvec{j}}}}{\partial {{\varvec{x}}}_{{\ varvek {i}}}}\右)\)
Therefore, the turbulent eddy viscosity can be defined as \varvek{\omega}}\)
\({{\varvec{\sigma}}}_{{\varvec{k}}}=1.0\), \({{\varvec{\sigma}}}_{{\varvec{\omega}}1 }=2.0\), \({{\varvec{\sigma}}}_{{\varvec{\omega}}2}=1.17\), \({\varvec{\gamma}}= 0.44\), \({{\varvec{\beta}}}_{1}=0.09\), \({{\varvec{\beta}}}_{2}=0.083\), \({{\varvec{P }}{\varvec{r}}}_{{\varvec{t}}}=0.9\)
Once the flow field simulation is complete, particle tracking technology can be applied. In this STAR CCM+ method, CFD models the motion of particles as discrete phases (solid particles) in a Lagrangian frame and calculates the motion of these particles at a single scale using Newton’s second law of motion (particle equation of motion). . The momentum of a particle can be expressed as 18;
Among them: \({{\varvec{m}}}_{{\varvec{p}}}\), \({{\varvec{u}}}_{{\varvec{p}}}\) and t are the particle mass (kg), particle speed (m/s) and time (seconds), respectively. \({{\varvec{F}}}_{{\varvec{D}}}\) represents the resistance acting on the particle, the unit of measurement is N, \({{\varvec{F}}}_{{ \varvec{G}}}\) represents gravity in N. Any other external forces are included in F.
Where\({{\varvec{\tau}}}_{{\varvec{p}}}\) is the particle velocity response time, u is the instantaneous flow velocity, which can be expressed as\({\varvec {u} } ={\varvec{U}}+\bar{u^\prime}\) where U is the time-averaged velocity calculated directly from the equation. (4) A \(\bar{u^\prime}\) is the speed of turbulent pulsation, defined as;
Where: \({\rho }_{p}\) is the density of the particle, ρ is the density of the liquid, and g is the direction of gravity.
Erosion modeling predicts the erosion rate of particles impacting solid boundaries. When calculating erosion rates, STAR-CCM+ adds up the damage caused by each particle impact. The calculation is made by choosing the ratio of the erosion coefficient, i.e. mass washed out of the wall per unit mass of impacting particles. The erosion rate is calculated by summing the surface damage caused by each impact of a solid particle on the contact interface:
where \({A}_{f}\) is the area of each face, \({\dot{m}}_{\pi }\) is the mass flow rate of particles in the packet \(\pi \), \ ({e }_{r}\) — erosion rate. Various correlations for modeling erosion rates are presented in the open literature. In this study, the erosion rate \({e}_{r}\) is calculated using the following Oka correlation.
•\({\mathrm{v}}_{\mathrm{rel}}\) — the relative velocity of solid particles relative to the contact boundary, \(\left|{\mathrm{v}}_{\mathrm {rel} }\ right|, \left({\mathrm{v}}_{\mathrm{rel}}={\mathrm{v}}_{\mathrm{particle}}-{\mathrm{v} } _{\mathrm{ стена}}\справа)\).
\({\mathrm{e}}_{90}={{\mathrm{e}}_{\mathrm{r},\mathrm{DNV}@90({\mathrm{D}}_{\mathrm { ref}}/{\mathrm{D}}_{\mathrm{p}})}}^{{\mathrm{k}}_{3}}\)
In Fig. Figure 7 shows a simulated geometry in which a standard elbow was used as one of the cement conveying devices, for example, in the Najaf cement plant. The knee diameter is D = 19 cm, and the curvature ratio (R/D) is 2.78. The boundary condition of constant pressure is set at the outlet section; the pressure is equal to atmospheric pressure (101325 Pa). The initial flow and boundary conditions are given in Table 2.
Three-dimensional, multiblock, hexagonal, and polyhedral meshes were generated using the mesh generation portion of the STAR CCM+ code to generate the entire computational knee domain. The mesh formation structure is shown in Fig. 8a, b. The mesh independence study is performed using a four-grid study to ensure that the simulation obtained using the selected mesh is independent of its size. The overall erosion rate is used as a convergence indicator, and the results of the network independence test are shown in Table 3. Therefore, the current simulation is an independent study using the number of grids (4157524) based on the overall erosion rate results obtained from the grids. The model solution takes into account the knee surface roughness for the coated model (0.038 mm) and the uncoated model (0.9 mm).
Eulerian-Lagrange simulations performed within STAR CCM+ first solve the system’s governing equations discretized using finite volume methods and using the SIMPLE algorithm approach. In combination with this, the Menter k-SST RANS turbulence model is used to predict the effect of turbulence on the airflow field17. Apply the relaxed Gauss-Seidel scheme to iteratively solve the resulting system of linear algebraic equations to calculate values for velocity, pressure, etc. The time step is approximately 1 × 10–4 s. used in all calculations. Airflow field simulations were run for 24 cycles to obtain stable flowfield results and turbulence statistics. The solution process continues until the error criterion of each component is reached and the convergence criterion of the solution is satisfied. In Fig. Figure 9 shows a block diagram of the numerical simulation.
The test samples are 4 samples, 1 of which is uncoated and 3 samples with a thickness of 30, 40 and 50 μm respectively, which were obtained at different coating times of 10, 20 and 30 s, and coating times longer. more than 30 s (more than 50 µm) create unstable coatings (cracking, missing and destruction) due to the lack of adhesion between the surface of the sample and the coating, as shown in Figure 10, due to the rate of delivery of nanoparticles, occurs due to the flame. Control and personal ability to control the coating process. The operating conditions of pipelines and elbows for transporting cement are 30 tons/hour, the total working time is 170 hours, the pipeline capacity is about 5100 tons. The graph shown in Figure 11 shows the relationship between coating thickness and weight loss rate. It can be seen that when the coating thickness increases to 50 μm, the percentage of weight loss reaches a minimum value of 3.62%, which indicates the uniformity of the coating and decreases. thickness of the coating layer. Defects, high strength and hardness of the coating, as well as uniform (WC) distribution and high strength make elbow and pipe surfaces more resistant to wear and ablation. At a maximum coating thickness of 50 µm, the improvement rate in wear resistance of the coated specimen reaches 71%, as shown in Figure 12. The coating acts as a protective barrier on the inner surface of the knee against high-speed cement particles that can cause erosion of the knee surface, since the coating has good adhesive properties to the inner surface of the knee, and tungsten carbide nanoparticles have good mechanical properties. properties, especially hardness and wear resistance.
Based on weight loss tests, the wear resistance of the samples was compared in the laboratory, comparing the wear resistance of coated and uncoated samples, simulating the experimental test results and their consistency. This test used (24) samples by comparing uncoated samples, (6) samples with 30 µm coating thickness, (6) samples with 40 µm coating thickness and finally (6) coated samples. The layer thickness is 50 microns. Before testing, samples are weighed on a precision digital scale (4 digits). The test time for each sample is (10 minutes). The results in Figure 13 show the wear resistance of the uncoated sample under load (20 N) and angular speed (400, 500 rpm). Weight loss increases with increasing speed of rotation and friction, and the optimal rate of weight loss is. speed (500 rpm) is (0.3905%).
In Fig. Figure 14 shows the results of wear tests (pin-disk) of samples with coating thicknesses of 30, 40 and 50 μm under a load (20 N) and angular speeds of 400 and 500 rpm. Mass loss increases with increase. Rotation speed and friction. The 50 µm thick coating sample has the lowest weight loss rate at 500 rpm of 0.0117%. Figure 15 shows that the improvement rate of wear resistance of the 50 μm thick coating sample reaches 97%. hardness and good adhesion of tungsten carbide nano coating. Uniform and therefore more resistant to erosion and solid particle penetration.
The coating thickness of the samples at different plating times was calculated using SEM images, and the coating thickness was measured using image J software. It was found that when the plating time was 10, 20 and 30 seconds respectively, the layer thickness reached 30, 40 and 50 µm respectively, as shown in Figure 16.
SEM images also show that coating times greater than 30 seconds (layer thickness greater than 50 μm) result in unstable coatings with cracks, peeling, and failure due to lack of adhesion between the sample surface and the coating, as shown in the figure. Figure 17. Comparison. with stable coatings of 30, 40 and 50 microns thickness.
(a) 30 µm, (b) 40 µm, (c) 50 µm, (d) thickness more than 50 µm (coating cracking, peeling and destruction of the coating, coating application time exceeds 30 seconds).
Figure 18 shows the predicted distribution of the erosion profile of the inner surface of the elbow with different coating thicknesses as a result of simulating actual performance tests. In this simulation, the erosion rate is modeled using the Oka correlation. It has been found that the erosion rate can be reduced by increasing the thickness of the coating of tungsten carbide nanoparticles, since the coating protects the inner surface of the knee from friction of high-speed cement particles. The coating protects the inner surface of the knee from erosion by high-velocity cement particles. The coating has good adhesive properties to the inner surface of the knee, and WC nanoparticles have good mechanical properties. Especially hardness and wear resistance.
Distribution of knee erosion rate profile for different coating thicknesses.
Figure 19 illustrates the confirmation of the predicted erosion rates with those measured during the experimental work. The erosion rate is calculated in g/hour per wall surface area (7 * 5 cm). The figure shows good agreement with the experimental results, although there are minor discrepancies. This discrepancy is due to the numerical accuracy and inlet boundary conditions, especially the inlet velocity, which cannot be accurately measured in a cement plant due to measurement difficulties. The figure shows the correspondence of erosion rates between numerical results and experimental results for test specimens inside the elbow under the same operating conditions.
Failures due to mechanical wear on pipes and elbows can cost the industrial base significant amounts of money and time. Such failures occur due to erosion, which involves the removal of material from component surfaces due to high-velocity impact. A stream of solid particles carried by a liquid or fluid stream. The mechanism of erosion occurs when a stream of solid particles impacts a surface. This may be intentional, as in shot blasting, or it may occur accidentally, such as in pipes and associated components that transport slurries or sandy crude oil, the same pipes and elbows that transport cement powder. The goal of this work is to find a unique method to reduce this defect using a coating of tungsten carbide (WC) nanoparticles. This coating technology improved the abrasion resistance of samples with a coating thickness of 50 microns by 71%. Tests were conducted on the inside of the knee under the same real-life operating conditions to understand the difference between the inside of the knee and the knee. Behavior of coated samples. Faced with a high-speed flow of cement particles. After removal, the coating can be reapplied several times. In addition, samples with a 50 µm coating thickness, tested using a special standard wear test (pin on disk), were found to be 97% more wear resistant than uncoated samples. Pin-on-disk test results show that nanocoatings can prevent steel surface degradation and increase the life of pipes and elbows. If the coating thickness exceeds 50 microns, cracking, peeling, failure, etc. will occur due to insufficient adhesion to the steel surface. A comparison of numerical simulations and internal knee tests shows that the experimental results are in good agreement with the numerical ones, and the convergence reaches 90%.
Wahid J, David P, Veli-Tapani K. Slurry attack on steel – a review of testing, mechanisms and materials. Department of Materials Science and Manufacturing Engineering, University of Oulu, Wear, 408–409, 248–273, (2018).
Levy, A. and Mason, D.D. Two-layer model of gas and solids flow in pipes without suspended particles. Powder technology. 112, 256–262 (2018).
Muhammad M.M., Elansezhyan R. and Anjali D. Surface coatings of steel pipes for the oil and gas industry – a review. Yes. Chemical. the science. 13(1), 1-23(2016).
Han, R., Ya, H.H., Pao, W., and Han, A. Erosion corrosion of 30°, 60°, and 90° carbon steel elbows in multiphase flow containing sand particles. Materials (MDPI) 12(23), 3898-3912 (2019).
Shimizu, K., Noguchi, T., Seito, H. and Muranaka, E. Finite element analysis of impact angle dependence during erosive wear. Clothing 233–235, 157–159 (2009).
Patnaik A., Satapathi A., Naveen Chand N.M. and Barkula S.B. Erosive wear characteristics of particulate-filled fiber and polymer composites: a review. Table of contents available. the science. Straight, Wear 268, 249–263 (2010).
Sukhane A. and Agarwal V.K. Effect of bending geometry on erosion and product degradation in pneumatic conveying piping systems. internationality. J. Engineering. resource. application. (IJERA) 2(4), 129–136 (2012).
Vikas K, Satish K, Mani K, Mohapatra SK. Modeling erosive wear in slurry pipelines using CFD. application. Fur. Matt. ISSN: 1662–7482 852, pp. 459–465 (2016).
Bagheri P., Farzam M., Mousavi A.B. and Hosseini M. Ni-TiO2 nanocomposite coatings are highly resistant to corrosion and wear. surf. coat. technologies. 204, 3804–3810 (2010).
Véronique, V., Abdul-Fatah, K. and Fabien, D. Mechanical and wear-resistant properties of chemically produced nickel-boron coatings. surf. coat. technologies. 206, 1879–1885 (2011).
Okonkwo, P. S., Shakur, R. A., Ahmed, E., and A. M. A. Mohamed. API X42 Pipeline Erosion and Wear Engineer. failure. anus. 60, 86–95 (2016).
Vikas, K. Computer simulation of erosive wear due to cuttings flow through a standard elbow: effects of bending angle, direction, diameter and cutting velocity. Assistant Professor, SGT University, Gurgaon, India (2018).
Ali, S.A. and Odai, K.M. Nano-coating technology is used to improve the wear resistance of horizontal cement mill balls in cement plants. J. Mechanical. engineer. resource. development. 44(1), 17–27 (2021).
Hannah
Post time: Apr-28-2024