Investigation On Erosion-corrosion Characteristics Of 90° Elbow Based On The Water Wetting Of Wall In Gas-liquid Two-phase Flow

In this paper,the corrosion failure of pipelines caused by erosion-corrosion mechanism of multiphase flow in petrochemical industry,oil and gas transportation industry as the background was to carry out the basic theory research.In view of the scholars at home and abroad on gas-liquid two-phase wall water wetting involved with less corrosion research.Thus,the water wetting of the static and dynamic experiments and numerical simulations was conducted to establish the relationship between the corrosion and the regularity of the wall water wetting.Firstly,in terms of static wetting experiment,the corrosion characteristics under different media concentrations,materials and intermittent times were mainly investigated,and the corrosion rate was calculated and analyzed via weight loss method combined with macro-morphology and micro-structure comparative analysis of different factors,which revealed the corrosion mechanism under the condition of static water wetting and intermittent wetting in the gas-liquid two phase flow;In addition,taking the typical 90°elbow as the research object in this work,the relationship between the wall water wetting and the corrosion was investigated via self-designed gas-liquid two phase dynamic experiment platform and electrochemical corrosion test system.The second electrode electrochemical test method was utilized to measure resistant signal arranged at elbow wall,and the locations of the water wetting in the elbow wall were specified based on the monitored signals.On this basis,the corrosion current density and the corrosion rate of the wetted wall locations are calculated via three electrode electrochemical potential method;At the same time,the local flow characteristic of the elbow was simulated via computational fluid dynamics,and the numerical results predicted were compared with the experimental result of the gas-liquid two phase flow to verify the accuracy of the numerical method.Based on the accurate numerical method,the time distribution and spatial distribution of the water wetting with the elbow under variable working conditions were studied,and the relationship between wall water wettability and erosion-corrosion was revealed by combining with the corrosion rate calculated in actual experiment.The main work is as follows:(1)In this paper,the different materials(10#carbon steel,20#carbon steel Q235 and 316L),different HCl concentrations and intermittent frequency factors under the static condition such as the water wetting and intermittent was conducted to investigate the degree of corrosion on the surface of the material,the results show that under the same other conditions,the corrosion rate of the materials including 10#,20#,Q235 and 316L under the condition of water wetting is higher than intermittent wetting,and the trend of the corrosion rate with the four kinds of materials was basically consistent.With respect to the same condition of the material of 20#and intermittent times,with the increase of HCl concentration,the corrosion rate is positively correlated with it,and the corrosion rate of water wetting is higher than that of intermittent wetting.In addition,the corrosion rate shows a negative correlation trend with the increase of intermittent times.Combined with the macroscopic and microscopic morphology of the material surface,it reveals that the corrosion product film under water wetting was more loose and blocky than that under intermittent wetting.(2)The wall water wetting research for the actual elbow system was investigated in this work through self-designed gas-liquid two-phase dynamic corrosion experiment platform.The resistance signal arranged on the wall of elbow was monitored based on the two electrode electrochemical method,and specified the location of the wall water wetting under different flow conditions.The corrosion current density was calculated through three electrode electrochemical method based on the wetted wall location.Based on the actual experiment condition,the Euler-two fluid model in conjunction with the SST k-w wall shear turbulence model was utilized to carry out the numerical simulation research.The predicted flow pattern in the pipeline was compared with the actual flow pattern captured from the high-speed camera,the results indicate that the numerical method is verified with the experimental results(3)In this paper,the wall water wettability of the elbow under the different conditions was carried out based on the accurate numerical method.The results present that the flow pattern is mainly in the form of stratified flow existing in the pipeline when the mixture velocity is 0.5 m/s and 1 m/s,and the water phase thoroughly contacts with the internal wall of the elbow.With the increase of the alpha angle of the elbow,the corrosion rate decreases.In addition,the water phase is accumulated at the bottom of the pipeline due to the dominated gravity under the form of stratified flow,with the improvement of the velocity in the pipeline,the corrosion rate at the intrados of the elbow gradually rises,with a greater risk of corrosion.The outer wall of the elbow,the left side of the elbow and the right side of the elbow don't contact with water,and the corrosion risk is basically zero.(4)Based on the form of the stratified flow,when the velocity in the pipeline is increased from 2 m/s to 4 m/s,it is pronounced that the flow pattern gradually shifts from the stratified flow to the wave flow with the increase of the flow velocity from the view of the time and spatial evolution law of the wall water wetting of the elbow.The greater the flow velocity,the greater the wave of water phase,and part of the liquid in the form of discrete phase is gradually entrained into the gas phase as continuous phase.The corrosion rate at the intrados of the elbow gradually reduces with the increase of flow velocity under the form of the wave flow,and the trend of corrosion rate along the alpha angle of the elbow is similar to the stratified flow.(5)When the flow velocity reaches 2m/s,the liquid phase gradually shifts from the inter wall of the elbow to the outer wall of the elbow and thoroughly contacts with water under wave flow,and with the increase of the flow velocity,the position of the outer wall of with the elbow gradually diffuses from the original position(a=90°,0=90°)to(?=60°,?=90°).Simultaneously,as the flow velocity ascends,the corrosion rate at the outer wall of the elbow increases with the increasing alpha angle of the elbow.