Influence of Temperature and Carbon-Dioxide Pressure on the Corrosion and Stress-Corrosion Fracture of Pipe Steels in Model Stratal Water

We study the influence of temperature (20–120°C) on the corrosion and stress-corrosion fracture of JFE-13CR-80 (I), JFE-13CR-95 (II), JFE-HP1-13CR-110 (III), and JFE-HP2-13CR-110 (IV) martensitic steels in a model stratal water (MSW) under a CO₂ pressure of 1 and 6 atm. It is shown that the corrosion rates of steels I and II in MSW under ${P}_{{\mathrm{CO}}_2}$= 6 atm are 4–40 times higher than the corrosion rates of steels III and IV (depending on temperature). The highest corrosion rate in steels I and II, namely, 0.11–0.16 g/(m² ⋅ h) was observed at 60°C. The electrochemical investigations carried out in MSW at 20°C under ${P}_{{\mathrm{CO}}_2}$= 1 atm showed that steels III and IV are more resistant to pitting corrosion than steels I and II. Under static stresses σ = 0.6σ_0.2, local corrosion of steels in MSW was not observed for ${P}_{{\mathrm{CO}}_2}$= 6 atm at a temperature of 20°С. At higher temperatures, we observe the formation of pits on the surfaces of deformed steels I and II, which may lead to the initiation of cracks propagation. The local corrosion of steels III and IV was not discovered under the action of static stresses at higher temperatures. The mechanical properties of steels II, III, and IV undergo insignificant changes in the case of slow tension (at a rate of 10^–6sec^–1) in MSW under ${P}_{{\mathrm{CO}}_2}$= 1 atm. We revealed a significant influence of corrosive media on the mechanical properties of steels caused by the high concentration of corrosion-active nonmetallic inclusions, which exceeds the permissible limits. It is shown that steels I and II are characterized by a lower resistance to low-cycle corrosion fatigue. Under cyclic stresses σ = ± 500 МРа, the service life of steels III and IV becomes shorter by 8–9%.