Research On Anti-erosion Performance And Mechanism Of A Pipe Bend With The Bio-inspired Internal Surface

Pipeline is a fluid transport installation widely used in oil,chemical and metallurgical industries.The fluid in pipe contains lots of solid particles,which lead to serious pipe erosion wear and frequent accidents.As an indispensable part of the pipeline system,elbow was considered to be vulnerable,and the erosion rate of it is 50 times higher than that of straight pipe.Therefore,it becomes the most common location of thickness reduction.To ensure the safety of pipeline transportation,improving the elbow anti-erosion performance has been becoming the focus of researchers for a long time.In the evolutionary process,organisms have formed some characteristics which are suitable to their living environments.Learning and imitating these typical features,and then apply them to improve the functional characteristics of the mechanical components,has become a new method to solve the engineering technical problems.In this paper,bionic ideas are used to explore the means of improving the anti-erosion performance of the pipe elbow.The studies have been carried out as follows:In this work,the Argopecten irradias,a common specie found in sediment environment,was used as biological prototype.Based on reverse engineering method,3D scanner was exploited to capture the point cloud data of the ribbed shell and the smooth shell,and high-precision shell geometric models were established as well.Subsequently,the FLUENT-EDEM coupling method was employed to simulate the multiphase flow field of the shell surfaces.Particle trajectory and force condition of them were analyzed.Results suggest that the shell whose ribs are perpendicular to the flow velocity direction possesses a better stability,and the total force of it is 18% lower than that of the ribbed shell which is parallel to the flow direction,and the frequency of particle collision is correspondingly reduced by 11%.Further analysis demonstrates a low velocity vortex region formed between the ribs of shell changes the trajectory and impact velocity of the particles,which makes the ribbed shell better `anti-erosion performance.According to working conditions of oil pipeline,choosing flow rate and particle diameter as the investigation factors,the flow field and surface erosion rate of the standard elbow were simulated by FLUENT software.It is found that the velocity separation and the secondary flow phenomenon appear in the elbow,and the erosion wear area is mainly in the range of 10~90° elbow,and the erosion rate increases with the angle of the elbow.A special erosion wear test rig was designed,which was composed of pipeline system,information collection system and operation condition monitoring system.Three different colored latex paint mixed with gesso were applied on the inner surface of elbow and they were taken as the erosion rate visualization specimens.Under different velocities and particle diameters,erosion experiment was carried out.Compared with the numerical simulation erosion contour above,it is found that the strength and position of the erosion are extremely similar and the feasibility of the numerical simulation is proved.According to the anti-erosion principle of shell ribs and the erosion location of smooth elbow,a bionic elbow whose ribs direction are perpendicular to the flow velocity was designed.The experiment optimization design method was used to the rib parameters optimal,and we obtained the primary and secondary factors and optimal combination by range analysis.The results show that the factors which influence the relative erosion rate in sequence are the number of ribs(C),rib diameter(D),flow velocity(A),particle diameter(B).The optimum design parameters of bionic elbow are as follows: C is 10,D is 1.5 mm,A is 7 m/s,B is 0.5 mm.The regression equation between the relative erosion rate and the experimental factors was obtained by orthogonal polynomial regression analysis,the mechanism of erosion resistance of bionic samples was also preliminarily revealed via comparing the erosion of the smooth elbow and bionic elbow.Low speed vortex region generated between the ribs changes the particle trajectory and reduces the particle impact velocity.Simultaneously,the increasing flow rate of the mainstream area enhances the follow-ability of the particles.In addition,the change in the flow field reduces the outward offset degree of particles trajectory,the collision probability between the particles and the outer wall is also reduced.