Effect of H₂S/CO₂ partial pressure ratio on uniform corrosion of N80 steel tubing

The corrosion mechanism of N80 steel tubing in an oilfield group of water injection wells in the coexistence of H₂S and CO₂ corrosive gases was studied by means of scanning electron microscopy and energy spectrum analysis, and X-ray diffraction analysis. The effects of different temperature, gas mass fraction and H₂S/CO₂ partial pressure ratio on the corrosion behavior of tubing were studied. The results show that the corrosion products on the surface of the tubing were mainly FeS. The partial pressure ratio of H₂S and CO₂ was the main reason affecting the uniform corrosion rate. When the mass fraction of H₂S was fixed, the uniform corrosion rate would not change greatly whether the mass fraction of CO₂ increased or decreased. Under the same temperature condition, the uniform corrosion rate was mainly controlled by H₂S partial pressure.