Electrochemical Evaluation And Mechanism Exploration Of Several Oil Field Corrosion Inhibitors

CO₂ internal corrosion of carbon steel pipeline brings serious problems to oilfield production,and corrosion inhibitor is one of the most common and effective methods for that.In this paper,after discussing the factors influencing the performance of 3 new corrosion inhibitors using weight-loss method,electrochemical techniques such as OCP,LPR,PP and EIS are employed to investigate their inhibition behavior with filling process or pre-filmed process in simulated oilfield condition.Beyond that,accurate evaluation under different hydrodynamic conditions is also imposed to them for more information.In the weight-loss test,the adsorption processes of 3 corrosion inhibitors are in line with Langmiur isothermal behavior and the linear fitting results of one variable are good.All the 3 corrosion inhibitors at different concentrations?5,20,35,50 ppm?,different temperatures?30,45,60,75??,different velocities?0,0.8,1.5,2.3 m/s?,different Cl^-concentrations?6.1,12.2,18.3 g/L?and different CO₂ partial pressures?0.21,0.61,0.81MPa?have good inhibition efficiency,more than 90%respectively.In the adsorption test,inhibitor?reaches 5100 ohm.cm² which is the highest corrosion resistance of the three.and equivalent circuit fits the EIS data well,which is reflected in that the majority of fitting chi-square values are less than 0.001 and n values are greater than 0.6.R_ab2 which reflects inner adsorption species is the key of strong inhibition ability for inhibitor?.In the desorption test,3 prefilms strip gradually to the steady state over time and the maximum resistance retention are 72.55%,26.51%and 24.37%respectively.Only inhibitor?stays above 90%all the time and the equivalent circuit analysis shows adsorption species corresponding to R_ab2 is the reason why inhibitor?has better performance.In the reforming test,the electrochemical images are similar to the adsorption,but they spend less time reaching the stable values.Because of the pre-film existence,it's easier for the inhibition substance adsorbing to the metal surface.The polarization curves of Inhibitor?and?move to the positive direction,which means they work by inhibiting the anodic reaction.Inhibitor?comes into play by influencing the cathodic reaction.In the hydrodynamic test,inhibitor?performs bad with the inhibition efficiency less than 65.47%.Inhibitor?works well and has stable high corrosion resistance from 250 to500 rpm pump speed?It can achieve 1393.86 ohm.cm² at 500rpm,800min?.The inhibition performance of inhibitor?is good but far less than inhibitor II.At 500 rpm,the highest R_p value is only186.37 ohm.cm²??=89.83%?.At high shear stress,all inhibitors lost their corrosion inhibition quickly.