Study On The Influence Of Liquid-solid Swirling Flow On Erosion-corrosion In Pipeline

Swirling flow in pipeline has been widely used in industrial fields such as oil and gas exploration and transportation,solid-liquid separation,hydraulic sand transportation,and pneumatic transportation.Despite the apparent effect of the swirling flow on the erosion or erosion-corrosion behavior in pipeline,there is a lack of systematic research on the erosioncorrosion or erosion behavior of liquid-solid swirling flow in the research field of pipeline erosion-corrosion.Therefore,it is of theoretical significance and application value to carry out the research on the influence of liquid-solid swirling flow on pipeline erosion-corrosion for the prevention and control of pipeline erosion-corrosion and broadening the application of swirling flow in industry.In this paper,a circulating pipe flow device and a multi-point measurement experimental elbow without disassembly and with weight loss and electrochemical measurement functions were independently designed.By means of weight loss,electrochemical test and various surface analysis methods in combination with high-speed camera and computational fluid dynamics simulation,the influence of swirling flow on pipeline erosion-corrosion behavior and synergistic effect were systematically studied,and the corrosion reduction mechanism under the synergistic effect of swirling flow and inhibitor was discussed.The main research work includes:(1)A multifactorial experimental research on erosion-corrosion of straight pipe under liquid-solid swirling flow conditions was carried out by full factor analysis combined with a variety of test methods.The influence of the selected factors and their interactions on erosioncorrosion rate of pipeline under the condition of liquid-solid swirling flow was quantitatively characterized,and the key factors affecting the erosion-corrosion rate were determined.On this basis,a multifactorial prediction model for the erosion-corrosion rate of swirling flow was established.At the same time,the erosion-corrosion behaviors of straight pipe under the condition of liquid-solid swirling flow and non-swirling flow were compared and analyzed to study the influence of swirling flow on the erosion-corrosion behavior of liquid-solid twophase flow in pipeline.It is shown by the results that:①The analysis of statistical significance reveals that the variation of erosion-corrosion rate of straight pipe under liquid-solid swirling flow is explained by three main effects(velocity,sand size,and sand concentration)and two interactions(velocity/sand size and sand size/sand concentration).② An empirical linear regression equation was established through multiple linear regression to describe the correlation between erosion-corrosion rate of straight pipe and the test parameters and their interactions under the condition of liquid-solid swirling flow.The regression equation has reasonable accuracy to take into account all the variations of statistically significant parameters with minimal error,and the measured erosion-corrosion rate is correlated within 95%confidence interval.③The sand suspension effect and enhanced oxygen mass transfer effect produced by swirling flow have great influence on the erosion-corrosion behavior rn pipelines.The comparative analysis of erosion-corrosion between swirling flow and nonswirling flow shows that the net effect of swirling flow on erosion-corrosion varies with sand size.(2)An experimental research on the synergistic effect of erosion and corrosion of elbow under the condition of liquid-solid swirling flow was carried out by using a circulating pipe flow device in combination with numerical simulation.The numerical values of four components of erosion-corrosion rate of working electrode at different parts of elbow under the conditions of liquid-solid non-swirling flow and swirling flow were determined and compared.The influence of swirling flow on the synergistic effect of pipeline erosioncorrosion was studied.The results show that:①There are obvious differences between the synergistic effect of liquid-solid two-phase flow erosion-corrosion at elbow under swirling flow and non-swirling flow conditions.Under the swirling flow condition,the pure erosion rate and the erosion-enhanced corrosion rate and their percentage in total erosion-corrosion rate are generally lower than the results under the non-swirling flow condition.While,the pure corrosion rate and its percentage in total erosion-corrosion rate under the swirling flow condition are higher than the results under the non-swirling flow condition.②The sand suspension effect and mass transfer enhancement effect produced by swirling flow have different effects on the four components of erosion-corrosion of each working electrodes at the elbow,which makes the erosion-corrosion behavior of the elbow at different positions gradually change from erosion-electrochemical corrosion control to electrochemical corrosion-erosion control.The influence of erosion is weakened,and the influence of electrochemical corrosion is increased.③Due to the structure of the elbow and the complexity of the flow of the swirling flow through the elbow,a certain swirl intensity is required as a precondition for the erosion corrosion inhibition of the swirling flow on the elbow.The swirling flow with strong swirl strength induced by the twist tape with a twist ratio of 6.2 has obvious inhibitory effect on the erosion-corrosion.(3)A series of comparative experiments of using inhibitor to inhibit pipeline erosioncorrosion under the conditions of liquid-solid non swirling flow and swirling flow were conducted by a circulating pipe flow device in combination with a variety of test methods.The potential for the synergistic use of swirling flow and inhibitors was evaluated,and the erosioncorrosion reduction mechanism of the synergistic action of swirling flow and inhibitor was discussed.The results show that:①Imidazoline inhibitor can inhibit the erosion-corrosion of working electrode in liquid-solid two-phase non swirling flow and swirling flow,and the higher the inhibitor concentration,the higher the inhibition efficiency.Under the same inhibitor concentration,the inhibition effect of the synergistic action of swirling flow and inhibitor on the erosion-corrosion is more significant than that of inhibitor acting alone,which indicates that the synergistic action of swirling flow and inhibitor has potential advantages in reducing pipeline erosion-corrosion.However,swirling flow and inhibitor working synergistically must be ensured by strong swirl intensity under the condition of higher solid particle concentration.②In the complicated elbow section,under non-swirling flow and swirling flow conditions,the inhibitor has an effective inhibitory effect on the four components of erosion-corrosion of each working electrode.In general,the synergistic inhibition efficiencies of swirling flow and inhibitor on the four components of erosion-corrosion are higher than those of inhibitor on the four components alone.The maximum comprehensive inhibition efficiencies of the synergistic action of swirling flow and inhibitor on pure corrosion,pure erosion,erosion-enhanced corrosion,and corrosion-enhanced erosion are 88.49%,96.53%,95.65%and 89.54%,respectively.Under the synergistic effect of swirling flow and inhibitor,the erosion-corrosion of liquid-solid two-phase flow at the elbow is more effectively inhibited.At the same time,the inhibitor is more easily adsorbed on the electrode surface of the outer arch of the elbow under the condition of swirling flow,and the inhibition efficiency at the outer arch of the elbow is higher than that at the inner arch.③The swirling flow produces the sand suspension effect and mass transfer enhancement effect which facilitate the adsorption of inhibitor on the working electrode surface and acts in conjunction with the oxide film to form a more complete and dense corrosion product layer.This further promotes the inhibition of inhibitor on the four components of erosion-corrosion rate,and gives full play to the inhibition effect of inhibitor.(4)The erosion behavior of elbow under liquid-solid swirling flow was studied by numerical simulation.The influence law of different factors on the erosion of elbow was obtained,the influence degree of each factor on the erosion rate was determined,and the multifactorial erosion rate prediction model of liquid-solid swirling flow was established.At the same time,the calculation results of the prediction model were compared with the experimental results to verify the validity of the model.The results show that:①The swirling flow suspension effect generated by the twisted tape makes the distribution of particles more uniform in the elbow,reduces the focusing effect and impact frequency of particles on the same position of the elbow wall,and significantly reduces the maximum erosion rate of the elbow.Moreover,the smaller the twist ratio of the twisted tape,the closer the insertion position is to the optimal insertion position of 4D,and the more obvious the erosion reduction effect is.The swirl motion produced by the swirling flow can interfere and inhibits the Dean Vortex on the cross section of the elbow,and the instability and change of the Dean vortex affects the erosion behavior of the elbow to some extent.②Under the condition of liquid-solid swirling flow,due to the inhibitory effect of swirling flow on Dean vortex,there is no secondary flow driven collision in the elbow,and there are only direct collision and sliding collision between solid particles and elbow wall,among which sliding collision is the most common.The combined effect of direct collision and sliding collision makes the erosion morphology of the elbow under the condition of liquid-solid swirling flow dominated by banded erosion morphology.③The most significant factor affecting the erosion of elbow under the condition of liquid-solid swirling flow is the fluid viscosity,and the least influential factor is the twist ratio.A prediction model for the maximum erosion rate of elbow based on grey relational analysis is established,and the average error between the predicted value and the experimental value is-37.89%.