Study Of Erosion-corrosion Evolution Behavior Of Horizontal Elbow In Liquid-solid Two Phase Flow

In the process of oil-gas gathering and transferring,erosion-corrosion is one of the commonest failure modes of pipelines,which directly endangered safe production and operation of oil and gas transportation system.The elbow is the weak point of gathering and transporting system because of erosion-corrosion.The evolution of the erosion-corrosion process and its service life are of significance to the safety of the gathering and transportation system.At present,however,there is a limited understanding of erosion-corrosion of elbow,especially the erosion-corrosion evolution of elbow,so further research is needed.In this paper,the evolution of erosion-corrosion of elbow in liquid-solid two-phase flow is studied.The change of macroscopic morphology in the erosion-corrosion evolution process of elbow was observed by self-designed elbow image acquisition device.Combined with weight loss method,electrochemical test,micro-corrosion morphology and structure analysis,the erosion-corrosion characteristics of elbow for different time in the evolution process was defined,the erosion-corrosion behavior of different parts of elbow over time is confirmed,the mechanism of erosion-corrosion evolution is analyzed.The evolution process of erosion-corrosion behavior of elbow was researched.The results showed that the change trend of erosion-corrosion rate of elbow over time was rapidly increasing,slowly increasing,reducting and keeping stable.So the process of erosion-corrosion is divided into four periods: pre-acceleration,post-acceleration,deceleration and stabilization.Electrochemical properties of elbow changed over time: charge transfer for acceleration and diffusion for deceleration and stabilization.Tocal corrosion rate increased with time,which contraried to change trend of erosion-corrosion rate.Erosion plays a leading role in the erosion-corrosion evolution process of elbow.The function of micro-cutting wearing is dominant at acceleration period,while at decleration and stablilization periods,the function of extruding-slice wearing is dominant.From acceleration to stabilization,the corrosion product film growed,shedand regrowed.Corrosion product film regrowed slowly and new formed corrosion product film was denser than before.The erosion-corrosion behavior at different locations of elbow with different time was researched.The result was showed that the most serious location of erosion-corrosion was at the bottom of the immer and outer part of elbow in all periods.The difference of erosion-corrosion characteristics at different locations of the elbow gradually decreased with time increase and reduction between circular angles were slower than anxial angle.Since facters,like flow rate and sand concertration,were different at different location of elbow,different locations of elbow entred into different periods of erosion-corrosion evolution process at different time points.From upper part to lower part of elbow,different locations entred into acceleration period,but the time of deceleration and stabilization of top areas were shorter than bottom areas,so the evolution of erosion-erosion of the upper part of the gradually surpassed the middle and lower part of the elbow.