The article presents the data on how different microstructures affect the CO2 corrosion rate of tubing made of low-carbon manganese steels. Corrosion protection under such conditions requires inhibitors or replacing items with those made of corrosion-resistant materials. The chemical composition and microstructure type of carbon steels can affect the resistance to СО2 corrosion. To prove this statement, tubing metal specimens were examined according to the current standards. It was found that the ferritic-pearlitic microstructure is formed during heat treatment of steels and results from equilibrium austenite decomposition at slow cooling. Such microstructure significantly reduces the carbon dioxide corrosion rate compared with the secondary sorbite microstructure due to dissolution of the ferrite and retaining of the laminated pearlite. Thus, the corrosion rate of steel with ferritic-pearlitic microstructure was 5.3 times lower than that of the secondary sorbite microstructure steel. However, the latter has better strength properties than the ferritic-pearlitic steel. Secondary sorbite has an acicular structure that gives high tensile strength results in mechanical testing. The trade-off between corrosion resistance and strength properties should be resolved to use manganese steels as a high-tensile tubing material in СО2 environments.
Keywords: TUBING, CARBON DIOXIDE CORROSION, СО2 PARTIAL PRESSURE, FERRITIC-PEARLITIC MICROSTRUCTURE, SECONDARY SORBITE, AUSTENITE, CORROSION RATE.