The Corrosion Mechanism Of 20# Steel In CO₂/H₂O Two Phase Bubble Flow And Its Forecast Model

The safety and the stabilization in producing the oil and gas are restrained and threatened seriously by the CO2 corrosion,which has become an international focus for a long time about the corrosion and protection.This paper,referring plenty of literatures,systematically elaborates CO2 corrosion mechanism.and expresses the influencing factors of CO2 corrosion,and establishes the forecasting model based on the influencing factors,and summaries the corrosion-resistant technology.It will offer the reference for the materials election and the corrosion-resistant the oil and gas field.The dynamic simulation test of CO2 corrosion of 20#steel was carried out in a self-designed experiment device in this paper,the corrosion mechanism of 20#steel in CO2/H2O gas liquid two phase bubble flow were studied by means of SEM,EDS and so on.The effects of time,CO2 partial pressure on corrosion were discussed respectively,and the corrosion rate,morphology and microstructure corrosion appearance,structure of the corrosion product film were mainly studied.The results show that the increase of time under different pressure conditions has a different effect on the corrosion rate,and the corrosion rate decreases with time at P=0.05MPa.At P=0.075MPa,the corrosion rate of the extended corrosion rate was decreased rapidly,then increased rapidly and then decreased significantly.At P= O.lmpa,the corrosion rate decreases gradually with time.At P=0.12MPa,the corrosion rate increases with time,then decreases slightly and then increases rapidly.At P= 0.15mpa,the corrosion rate increases with time and then decreases rapidly,then increases rapidly,then decreases and then increases.The corrosion due to the flow characteristic of bubble flow,under the condition of upper and lower wall surface corrosion morphology presents different characteristics,on the wall light yellow corrosion products more,and the wall yellow brown corrosion products,upper and lower wall appeared yellowish green products,and then disappear;On pipe wall corrosion products over time can form large relatively dense membrane layer,regularly arranged under the pipe wall corrosion products formed by flocculent products loose flocculent mass characteristics of single layer film and the pitting corrosion pit.Corrosion products is mainly composed of three elements,Fe,C,can be concluded that corrosion products is mainly composed of iron oxides,carbonates,cementite and oxides,just different time their respective levels.Different time under the condition of pressure effect on the corrosion rate are also different,as a whole,as the change of pressure,corrosion rate of change,and is within the range of pressure of 0.05 MPa to 0.15 MPa,corrosion rate fluctuates up and down with the increase of the CO2 partial pressure.At the time of T=60min,the change corrosion velocity of CO2 partial pressure was first reduced and then decreased,and the corrosion rate was the lowest at 0.075mpa,which was 0.013mm/a and 0.12mpa to reach the maximum corrosion rate of 0.052mm/a.In terms of the macroscopic morphology,the upper wall and lower wall surface are finally deposited with a layer of brown-yellow products.The larger the partial pressure of CO2,the more density the product membrane and the darker the color.Wall on microstructure,corrosion products are assembled in sheet form,and then into a homogeneous spherical particles,and the wall and the corrosion product film formed first,gradually with the increase of CO2 partial pressure product membrane peeling,eventually form individual pitting corrosion pit.Corrosion products mainly consists of three elements Fe.C,O,the element analysis on the Fe content in the wall were higher than the wall,and the C,O content were higher than in the wall on the wall,combined with the corrosion product film microstructure,can be concluded that the increase of Fe content can increase the density of membrane layer.Under the experimental conditions of this paper,the existing model is combined with the actual situation of this experiment,and a preventive model of corrosion protection suitable for this experiment is developed or developed:1gCR*=k(5.8-1710/T+0.671gPco2)+ △.In the formula,CR is indicates corrosion rate in mm/a;T is temperature in K;PCO2 is CO2 partial pressure in MPa;k is effective correction coefficient,k=2;△ is correction factor,PCO2≤0.075,△ =0.15,PCO2≥ 0.1,△=0.05.