reza Labbaf - Department of Materials Science and Engineering, Tarbiat Mndares University, Tehran, Iran
Taghi Shahrabi - Department of Materials Science and Engineering, Tarbiat Mndares University, Tehran, Iran

C02 corrosion of carbon steels has been one of the most common corrosion problems in oil and gas industry. Low-alloy stee~ from economy and fabrication points of view. is the best option for pipeline manufucturers; but it is poor in corrosion resistance. For C02 corrosion contro~ several works have been done, tmst of them focusing on environmental and physical parameters such as p~ temperature. and C~ partial pressure. The new trend is to refine pipe steels with no deterioration in mechanical properties and cost production while CCh corrosion resistance is improved. In the present work, the influence of microstructure of low alloy steel is scrutinized. API 5L X70 steel was heat-treated to obtain di1feren.t morphologies of Fe3C. For this purpose, specific heat-treatments were introduced. The corrosive media was a deoxygenated 3% NaCI solution, saturated with CO2 at 60°C with a 2.5 mls flow at pecimen surface using RCE. CO2 corrosion behavior of X70 steels with different microstructure was studied by electrochemical impedance spectroscopy (EIS). The morphology of the surface scale was studied by scanning electron microscopy (SEM) and phases were analyzed with X-ray diffra.ctometery (XRD). Results show that the microstructure of steel influences the properties and tmrphologies of corrosion layers and consequently affects the corrosion rate.

CO2 Corrosion, Steel Microstructure, Iron Carbide, Rotating Cylinder Electrode