Study On The Corrosion Behavior And Speciality Of Corrosion Product Film Of Anti-sulfur Carbon Steel In 3%NaCl Solution Containing CO₂/H₂S

The corrosion behavior and speciality of corrosion product film of anti-sulfur carbon steels and alloy steels in 3% NaCl solution with CO2/H2S immersed were investigated by weight loss test,electrode matched,potentiodynamic polarization curves,electrochemical impedance spectrum,ESEM and EDS. The results showed that More quickly sulfuration film dissolved, more less was there sediment on the exterior of electrode with pH reduced at 30℃; In addition, reduction of pH makes product film turn into rich-sulfur from rich-iron, and content of Cr(OH)3,Cr2O3 reduce ,all which weaken protection of product film, So cathode process was controlled by pervasion when pH was 4, however, cathode process was controlled by electrochemistry reaction when pH was 2, and then corrosion rate that pH was 2 was more rapid than that when pH was 4. The corrosion of TJ steel has a sensitive section when pH was certain, corrosion rate expedited with H2S concentration increasing on the sensitive section; H2S couldn't accelerate to anode process of TJ steel when pH was 4 and H2S concentration was bigger than 100ppm, moreover, electrode reactions still were that acid catalyzed personally.The corrosion rate of TN steel increased with temperature increasing in 3%NaCl solution with CO2/H2S saturated, while that of TJ steel decreased; But 0.5% acetic acid was reentered, corrosion rate of carbon steels all increased firstly and then decreased, the corrosion rate of TJ steel was more rapid than that of TN steel. The component of film of TN steel was mostly composed of FeS under the condition of 3%NaCl+H2S +0.45MPa CO2,while the film of FeO attenuated ,the transference of ion was astricted from the film; The corrosion rate was 1.55mm/a at the condition of CO2/H2S, which lied between the rates in 3%NaCl+0.45MpaCO2 and 3%NaCl+H2S.; corrosion rate enhanced again at the condition of CO2/H2S which accelerated ;When 0.5% acetic acid was went into, the corrosion rate quickened , the film showed that composition of FeS reduced , however composition of Cr,Mo enhanced , Which made framework of corrosion product film much more tight, whereas, the diffluence of film was quicken up with pH reducing, this made corrosion rate more soon than that of 3%NaCl+H2S+0.45MPaCO2; structure,character and composition of the corrosion product film are important with corrosion rate.The electrodes matched of TJ steel and alloy steel NO. 4 were more sensitive to temperature than others, while the corrosion rate was quite lower,ion was prevented effectively from corrosion product film formed at high temperature, the corrosion rate of the electrodes matched of TN steel and alloy steel NO. 4 were least at the simulating condition at 120℃, whereas, which was higher than that of electrodes matched of TJ steel and alloy steel NO. 4. TJ steel can be used under high temperature and high pressure(HPHT)with CO2/H2S immersed conditions if it cooperates with rich sulfur oil-gas field inhibito because it contains 0.6% Mo and 0.25% Ni , and TN steel comprises of 1.50%Cr and 0.12% Mn, at the same time its corrosion rate was lower at the simulating condition; Alloy steel NO.4 is preferable CRAs, which can be matched at high temperature due to steady effect of chemical component to corrosion product.