Study On Electrochemical Corrosion Behavior And Protection Technology Of Q345R Steel In Flue Gas Flooding Surface Reinjection System

Flue gas injection has become one of the most important methods to enhance heavy oil recovery due to its advantages of wide sources,low cost,lower CO2 emissions and environmental protection.However,the pressure equipments such as compressor dewatering devices and separators in the compressor station of reinjection system are confronted with serious and complicated corrosion due to O2,CO2 and tensil stress.In this work,the electrochemical corrosion behavior of Q345R steel under O2 environment,O2-CO2 environment and O2-CO2-stress environment is sequentially studied according to the site conditions.It is investigated by electrochemical methods,scanning electron microscope(SEM),energy dispersion spectrum(EDS),X-ray electron energy spectrum(XPS)and Raman spectrum.Corrosion inhibitors suitable for the flue gas environment are also screened and the corresponding corrosion inhibition mechanisms are explored.This work mainly involves the following contents:(1)A numerical model based on mixed potential theory is proposed,it works well when dissolved oxygen concentration ranges from 0.08 to 4.16 mg/L,tempreture ranges from 30 to 80℃ and pH ranges from 9.0 to 5.0.Using the proposed model,not only the corrosion rate of Q345R can be predicted,but also the oxygen reduction reaction,H+reduction reaction and H2O reduction reaction can be quantitatively analysed.Combining with electrodynamic polarization and electrochemical impedence spectra,the effects of dissolved oxygen concentration,temperature and pH on corrosion behavior of Q345R in O2-containing environment are revealed.The corrosion rate increases significantly with the increase of dissolved oxygen concentration and temperature,but decreases with the increase of pH.When the concentration of dissolved oxygen is higher than 0.5mg/L,the corrosion rate will be greater than 0.076mm/a,reaching at severe corrosion degree.(2)Electrochemical techniques,SEM,EDS,XPS and Raman are used to investigate the corrosion behavior of Q345R steel under O2-CO2 environment.The effects of dissolved oxygen concentration,CO2 particial pressure,pH and temperature on corrosion are discussed.The corrosion rate increases significantly with the increase of dissolved oxygen concentration,CO2 particial pressure and temperature,but decreases with the increase of pH.Moreover,the corrosion rate of Q345R steel under O2-CO2 environment is quite higher than 0.076mm/a.(3)Electrochemical techniques,SEM,EDS,XRD,Raman and finite element methods are employed to analyse the effects of stress and time on the corrosion behavior of Q345R steel under O2-CO2-stress environment.Tensil stress can enhance the surface activation of Q345R steel,and lower H+,H2CO3 and HCO3-chemical potential.Thus,cathodic reaction accelerates and corrosion rate increases with stress.The effect of stress on corrosion is more obvious with time.At 120h,the corrosion rate is as high as 0.731mm/a,reaching at severe corrosion degree.(4)The inhibition behavior of bis(2-ehylhexyl)phosphate(BEP)for the corrosion of Q345R steel under flue gas in flue gas flooding reinjection condition are analysed using using weight loss method,electrochemical techniques,surface characterization and quantum chemical study.The effects of oxygen concentration,stress,BEP concentration and time on the inhibition behaviors are discussed.The results show that BEP,as a both adsorption and precipitation inhibitor,can effectively inhibit the corrosion of Q345R steel in flue gas injection.When the BEP concentration reaches at 500ppm,the inhibition efficiency can go up to 94.76%.The results in this work can provide a reference to the corrosion behavior of the pressure equipments such as compressor dewatering devices and separators in the compressor station of reinjection system,and have a theoretical and practical value of inhibiting corrosion issues.