CORROSION AND MECHANICAL FRACTURE OF STEELS FOR CASING PIPES UNDER THE INFLUENCE OF ELEVATED TEMPERATURES AND PRESSURE OF CARBON DIOXIDE

We study the influence of temperature and pressure of carbon dioxide on the corrosion and corrosion-mechanical fracture of two steels of strength grades Q-125 and P-110 in model stratal water (MSW). The electrochemical studies showed that, at the beginning of holding in MSW at t = 25 degrees C and P-CO2 = 0.1 MPa, corrosion proceeds under cathodic control with hydrogen depolarization. The data of gravimetric studies carried out in an autoclave demonstrate that, as temperature increases to t = 60 degrees C and pressure to P-CO2 = 6 MPa, the corrosion rate of these steels becomes higher than under the standard conditions. It was discovered that the difference between the yield and ultimate strengths of steels in air and in model stratal water at P-CO2 = 0.1 MPa is insignificant and that the decrease in relative elongations and narrowings is more pronounced for Q-125 steel. For P-110 steel, the corrosive medium weakly affects its plastic properties. The fractographic analysis of this steel showed that, in air, it is characterized by ductile fracture, whereas for Q-125 steel, we observe mixed (ductile-brittle) fracture. Under the influence of MSW with P-CO2 = 0.1 MPa, the content of the components of brittle fracture in the fracture surfaces becomes higher.