Study On Erosion-corrosion Of Tubing Collar In Solid-liquid Two-phase Flow Speciality:Chemical Process Engineering

The developing of process of fracturing which in the higher pump rates will cause moreand more severe for intense erosion,which lead to short service time of well tubing.Especially,the changing of solid velocities and impingement angles in the location of tubingcollar will enhance the material loss.It will lead to a serious loss of tubing collar wall thicknessand stress field intensity lower than before.The flow-accelerated corrosion(FAC) and solid particle erosion(SPE) of super13Crtubing steel was investigated in solid-liquid two-phase flow by electrochemical measurementsand computational fluid dynamic(CFD) simulation on an impingement jet system.Numericalsimulation of this paper was used to get particle impact parameters, combined with jetexperiments to find out the main factors of super13Cr mass loss.Finally,the equation whichwas fitted by experimental data was applying to predict erosion-corrosion rate of tubing collarinner wall.The main conclusion of this thesis are as follows:(1)Jet flow numerical simulation results showed that corrosion rate was lower thanerosion rate in the same condition.The highest erosion rates occurred on the surface whichimpact angle is65degree.In this area,the materials surface damaged by particles’ indentingand cutting.(2)Fluid flow and particles’ impingement made effects on the open-circuit behaviour ofsuper13Cr stainless steel in chloride solution.Under fluid velocity of9m/s in3.5wt%NaCl,theopen-circuit potential was distinguished for main three regions:the steady region,the impactingregion and the passivated region.It suggested that super13Cr stainless steel had a great abilityto resist pitting in chloride solution,and the most important factor of mass loss was particleimpingement on the specimen surface.The rate of repassivation was more lower than rate offilm damage.(3)Flow field was changed in API tubing collar,because it had specifical geometries-pipeannular cavity,resulting in accelerated erosion reaction.To predict the erosion of API tubingcollar,the semi-empirical equation which getting from impingement jet system was employedto calculate.Then flow characteristics in the connection of API tubing were simulated.It wassuggested that the most serious erosion area was forward-facing step(FWFS);As the time goes on,maximum erosion rate occurred in displacement of6m3/min and40%volume fraction ofsolid.Finally,some technical measures to reduce erosion in API round thread connection wereproposed.(4)The erosion of special tubing collar inner face is lower than API tubing collar becauseof it’s inner structure of a flat plane.However, the deformation of inner wall which caused byaxial tensile force and radial pressure will cause solid particle impingement angle and velocitydifferent from before.Finally,the inner structure changed by serious damage of erosion so thatlead to connection failure.