Research On Corrosion Behavior Of Low Cr Corrosion-resistant Materials In Tarim Oilfield

Aautoclave tests and SEM, EDS, XRD technologies were used to study CO2 and H2S corrosion behavior of 3Cr110 steel tubing under the high temperature and pressure environment. Electrochemical method was used to analyz the effect of temperature and Cl-concentration on CO2 corrosion of 3Cr110.Hydrogen damage was also investigated.The results showed that in CO2 corrosion environment, with the CO2 partial pressure,temperature and Cl- concentration increased, uniform corrosion rate of 3Cr110 increased at first then decreased. Uniform corrosion rates were maximum when CO2 partial pressure was 1.5MPa, temperature was 90℃and Cl- concentration was 35g/L respectively. As the flow rate increased, uniform corrosion rate increased. In CO2 and H2S corrosion environment, with the H2S partial pressure increased, uniform corrosion rate decreased, With the CO2 partial pressure increased, uniform corrosion rate of 3Cr110 decreased at first then increased.Polarization curves showed that with the temperature increased, corrosion potential of 3Cr110 decreased and corrosion current density increased, so corrosion rate increased. As the Cl" concentration increased, corrosion potential of 3Cr110 increased at first then decreased, when Cl- concentration less than 35g/L, the slope of anodic polarization increased as the Cl-concentration increased, when Cl- concentration was more than 35g/L, the slope of anodic polarization decreased as the Cl- concentration increased. So as the Cl- concentration increased, corrosion rate of 3Cr110 increased at first then decreased and reached the peak at 35g/L. the EIS showed that the radius of high frequency capacitance at 30℃was larger than 50℃, the EIS consisted of high frequency, low frequency capacitance arc and low frequency inductive reactance arc at 70℃and 90℃, this result showed that as the increased of temperature, corrosion scale dissolved. So, the corrosion rate increased with the temperature increased. The radius of high frequency capacitance decreased at first then increased with the increased of concentration of Cl-, and reached the minimum at 35g/L, which means corrosion rate was maximum.The SSC (Stress Corrosion Cracking) text results showed that the property of SSC resistance of 3Cr110 was very bad. The tensile strength and the plasticity decreased after electrochemical hydrogen charging. When the hydrogen concentration reached a certain value, the fracture mode was changed from ductile fracture to brittle fracture.