Analysis of sand-containing media on the reducer erosion and wear
To investigate the sand-containing media on the reducer erosion and wear laws, the establishment of a physical model of the reducer, the use of Fluent software for numerical simulation, respectively, with the media inlet velocity, the media sand mass flow, pipe diameter ratio (the ratio of the diameter of the small mouth and the diameter of the large mouth) and the transition section inclination angle of the variables for simulation analysis. The analysis results show that the erosion rate of the reducer with the increase of the inlet velocity increases, and its growth rate also increases with the increase of the inlet velocity; reducer erosion rate and the fluid medium sand mass flow are positively correlated with the increase of the pipe diameter ratio, the medium on the reducer erosion rate gradually decreases; erosion site in the pipe diameter ratio changes will also change, when the pipe diameter ratio is small, the erosion site is distributed in the transition section near the transition section, and the transition section inclination angle as variables. Erosion site distribution in the transition section near the small end of the side, the pipe diameter ratio increases, the erosion site offset, and in the pipe diameter ratio of 0.7, became close to the large end of the side; transition section inclination increases, the sand-containing media on the reducer erosion rate gradually increased, and its growth rate with the increase in the transition section inclination increases. The study’s results can guide the reducer’s design and use.
0. Introduction
Table of Contents
In the petroleum industry, the erosion and abrasion of sand-containing media on pipelines is a common factor causing pipeline failure, especially in special pipelines such as bends, tees, and reducers. The degree of erosion and abrasion of the media on the pipe wall is much more serious than that of the straight pipe, and the hazards are also more serious. A reducer is a pipe configuration in the pipeline connectors, commonly used to regulate the flow rate of media, change the direction of the pipeline, and increase the overall flexibility of the pipeline to reduce pipeline stress. In practice, due to the change of fluid velocity at the reducer, the solid particles in the medium will cause serious erosion and abrasion on the pipe wall, resulting in thinning of the wall, which will lead to rupture or perforation of the pipeline under the action of internal pressure.
In order to reduce the failure of the reducer and extend the service life of the reducer, many scholars have carried out related research. Wang Kun et al. used numerical simulation to study the distribution of erosion and cavitation under different working conditions. They obtained the relationship between the distribution of erosion and cavitation and the velocity of the reducer at different temperatures and carried out experimental verification. Tao Chunda established a mechanical model of the reducer, discussed the change of stress characteristics of the reducer in different directions under the action of internal pressure, and determined the dangerous parts of the reducer and its stress change rule. Chen Chenxi in the former test results based on the use of finite element software on the reducer and straight pipe connection structure of the structural stress strength and ultimate load analysis, given the reducer and straight pipe connection structure in the pressure and bending moment under the action of the ultimate load estimation, and to verify its feasibility and accuracy.
Currently, most of the studies on the erosion of reducers are to investigate the erosion and wear law of reducers with different working conditions as variables. There needs to be more studies on the erosion caused by the change in pipeline structure. To further study the rules of reducer erosion, this paper combines the actual use of reducer from the reducer conditions and pipe structure of two considerations: the study of the medium inlet velocity, media containing sand mass flow rate, pipe diameter ratio, and the transition section inclination angle and other factors on the reducer erosion rate and erosion parts of the impact. The study’s results can guide the reducer’s design and use.
1. Calculation modeling
1.1 Mathematical model of the flow field
The liquid-phase medium used in this study is water. The fluid velocity in the reducer varies greatly. To better simulate the real situation of the fluid in the pipe, the standard k-ε model is used in the calculation; the specific equations are as follows.
In the formula:
- k is the turbulent kinetic energy, J;
- G_{k} represents the turbulent kinetic energy generated by the laminar velocity gradient, J;
- G_{b} represents the turbulent kinetic energy generated by the buoyancy force, J; ε is the turbulent dissipation rate, J/s;
- Y_{k} represents the compressible turbulent flow velocity gradient, J;
- G_{b} represents the turbulent kinetic energy generated by the buoyancy force, J;
- ε is the turbulent dissipation rate, J/s;
- Y_{k} is the fluctuating kinetic energy generated by transition diffusion in compressible turbulence, J; c_{ε1}, c_{ε2}, c_{ε3}, σ_{k}, σ_{ε} are constants, and their values are taken as 1.44, 1.9, 0.09, 1.0, and 1.2, respectively;
- S_{k} and S_{ε} are customized coefficients.
The coupling between sand and liquid-phase medium was calculated using the DPM model, and the erosion model was used for numerical calculation. The sand particles are discrete phases; the density is 1500 kg/m^{3}, and the diameter is 200 μm. The model is solved by steady-state coupling.
1.2 Geometric model
The structural dimensions of the reducer are shown in Fig. 1. In Fig. 1, the diameter of pipe section A is D_{1} with a value of 100mm, and the diameter of pipe section B is D_{2} with a value of 100mm. To ensure the full development of fluid in the pipe, the lengths of straight sections L_{1} and L_{2} are larger than 5 times the diameter of the pipe. Reduced section of the pipe angle of θ, to avoid large wall separation phenomenon of the fluid in the reducer area, that is, will not produce a large vortex, the inclination angle should be less than 15 °.
Figure.1 Reducer structure sketch
1.3 Grid division and boundary conditions
To ensure the accuracy of the calculation results, the reducer flow channel model is a structured mesh. The inlet and outlet boundary conditions are set as velocity inlet and pressure outlet, respectively, and the outlet pressure is set as 30MPa.
2. Simulation results analysis
2.1 Different working conditions of the reducer erosion law
2.1.1 Medium inlet velocity on the impact of reducer erosion
The medium inlet velocity is an important factor affecting the erosion rate. In the analysis, the choice of transition section inclination angle θ for 10 °, pipe diameter ratio of 0.5 as the object of study, and the media inlet velocity were taken as 4, 6, 8, 10, and 12m/s, solid particles mass flow rate was taken as 1.5kg/s, using the standard wall function. Fig. 2, Fig. 3, and Fig. 4 show the velocity vector, velocity cloud, and pipe erosion cloud of the internal flow field of the reducer when the inlet velocity is 10m/s, respectively.
Comprehensive analysis of Figure 2, Figure 3, and Figure 4 of the calculation shows the outer medium flow to the transition section; by the influence of the pipe wall, the velocity direction has changed, the sand particles in the medium due to inertia and the pipe wall collision, resulting in pipe wall erosion. Hence, the reducer erosion’s main region occurs for the reducer’s transition section.
Figure.2 Inlet velocity of 10m/s when the velocity vector map
Figure.3 Inlet speed of 10m/s when the velocity cloud diagram
Fig.4 Erosion cloud diagram when the inlet velocity is 10m/s
Figure 5 shows the relationship between the pipe erosion rate and the inlet velocity curve. Figure 5 can be seen: in other conditions are the same, sand media on the reducer erosion rate will increase with the increase in inlet velocity; when the inlet velocity increases, the medium of sand particles in the velocity increases, kinetic energy increases, sand particles and the wall of the reducer collision intensity increases, at the same time, the inertia of sand particles with the increase in velocity increases, the sand particles of the fluid to follow people with low incomes, which makes more sand particles collision with the wall, the number of collisions also increases, therefore, the sand particles with the wall collision. The number of collisions also increased, so the erosion rate with the media inlet velocity increases, and the growth rate is also accelerated with the increase in inlet velocity.
Figure.5 Inlet velocity and erosion rate of the relationship between the curve
2.1.2 Media containing sand mass flow on the impact of reducer erosion
With the transition section inclination angle θ for 10 °, pipe diameter ratio of 0.5 for the calculation model of the reducer, the inlet velocity is set to 10m/s; the sand mass flow was taken as 0.50, 0.75, 1.00, 1.25, 1.50, 1.75 and 2.00kg/s for calculation, the results of the calculations are shown in Figure 6.
Figure.6 Relationship between mass flow rate of sand and erosion rate of medium
Figure 6 shows that the inlet velocity is unchanged, the media sand mass flow rate gradually increases, and sand and pipe wall collision intensity is unchanged. Still, with the frequency of collision with the increase of sand particles and increase, the erosion rate of the reducer is also gradually increased. The media sand mass flow rate shows a primary function of the relationship’s growth.
2.2 Influence of pipe structure on reducer erosion
Different pipe structures directly lead to different flow fields inside the reducer. In this study, two pipeline structure variables are considered: the pipe caliber ratio of the reducer and the inclination angle of the transition section of the reducer θ. The single-variable method studies the influence of these two factors on reducer erosion.
2.2.1 Influence of pipe diameter ratio on reducer erosion
On the large end of the pipe diameter of 100mm, the transition angle θ is 10 °, and the pipe diameter ratio of 0.3, 0.4, 0.5, 0.6, and 0.7 reducer model for analysis. Media inlet velocity is taken as 10m/s, sand mass flow rate of 1.5kg/s, and the calculation of the relationship between the pipe diameter ratio and the erosion rate of the curve, as shown in Figure 7.
Figure.7 Relationship curve between pipe diameter ratio and erosion rate
Figure 7 shows that, in other conditions that are the same, the pipe diameter ratio increases, and sand-containing media on the wall of the reducer pipe erosion rate gradually decreases. This is because the pipe diameter ratio increases, the exit pipe diameter increases, the transition section of the media flow rate becomes smaller, the sand particles and the pipe wall surface collision strength are reduced, and the frequency becomes smaller. In addition, the erosion angle of the sand particles on the pipe wall surface will also be reduced with the increase in pipe diameter ratio. Hence, the erosion rate with the increase in pipe diameter ratio decreases, and the relationship between the curve gradually tends to flatten.
As the pipe caliber ratio gradually increases, the distribution of the erosion parts of the reducer is also changing. The reducer erosion cloud diagram is shown in Figure 8. Figure 8 shows that in the pipe caliber ratio of 0.3, the main distribution of reducer erosion parts near the small end of the width of 0.1D_{1} range, and in the pipeline, a circle of the wall is uniformly distributed; in the pipe caliber ratio gradually increased, the erosion parts gradually offset, gradually biased by the small end of the mouth to the large end of the mouth, the erosion range is also gradually expanding, such as in the pipe caliber than 0.5, the main part of the expansion of erosion to a width of 0.3D_{1}, the main part of the pipe caliber than 0.3D_{1} width of 0.3D_{1} width of the wall. For example, when the tube diameter ratio is 0.5, the main part of erosion extends to the range of width 0.3D_{1}; when the tube diameter ratio increases to 0.7, the erosion part is distributed near the small end, and the big end on both sides, the width of the side near the small end is 0.3D_{1}, the width of the side near the big end is 0.2D_{1}, and the most serious erosion part is transformed from the side near the small end to the side near the big end.
Figure.8 Reducer erosion cloud map
2.2.2 Influence of transition section inclination on reducer erosion
With the large end of the pipe diameter of 100mm, pipe diameter ratio of 0.5, the transition section inclination angle of 5.0 °, 7.5 °, 10.0 °, 12.5 ° and 15.0 ° of the reducer as a calculation model, other conditions are the same, the calculation of the transition section inclination angle and the erosion rate of the relationship between the curves, as shown in Figure 9.
Figure.9 The relationship between the transition section inclination angle and the erosion rate of the curve
Figure 9 shows the reducer erosion rate with the increase of the transition section angle, and the increase in other conditions is the same. This is because in the transition section inclination angle increases, the medium flow rate changes faster, the turbulence increases, and the medium on the wall surface of the pipe erosion accelerates. In addition, according to the literature, the transition section angle of inclination in the range of 0 ° – 30 °, sand on the pipe wall surface of the erosion angle increases, before and after the collision of sand particles, the direction of the change in the velocity is greater, sand and pipe wall surface of the collision intensity increases. Therefore, the erosion rate of the reducer increases with the increase of the inclination angle of the transition section, and the growth rate is also accelerated with the increase of the inclination angle of the transition section.
3. Conclusion
- (1) The erosion effect of sand-containing medium on the reducer mainly occurs in the transition section of the reducer.
- (2) The erosion rate of the sand-containing medium on the reducer will increase with the increase of inlet velocity, and the growth rate is also accelerated with the increase of inlet velocity.
- (3) Media containing sand mass flow rate gradually increased, the erosion rate of the reducer also gradually increased, and the media containing sand mass flow rate shows a primary function of the relationship’s growth.
- (4) The erosion rate with increased pipe caliber ratio reduces, and the relationship curve gradually tends to flatten. The pipe diameter is relatively small, and reducer erosion parts are mainly distributed in the transition section near the small end of the side. When the pipe caliber ratio gradually increased, the erosion site gradually offset, from the small end of the mouth gradually biased to the large end; in the pipe caliber ratio of 0.7, the erosion site from the small end of the side near the large end of the side of the change.
- (5) The erosion rate of the reducer increases with the increase of the inclination angle of the transition section, and the growth rate is also accelerated with the increase of the inclination angle of the transition section.
Author: Lv Zhipeng