Estudo da susceptibilidade à corrossão eletroquímica e corrossão sob tensão de dois açõs perlíticos em solução de água do mar e presença de CO2

Abstract

Corrosion causes serious damage to metal structures, equipment, and materials, causing significant failures and losses. Understanding this process helps prevent damage, especially in the oil and gas industry, where a component failure can have serious consequences. When in the presence of seawater, corrosion becomes more aggravating due to the saline and corrosive conditions of the marine environment. This research analyzes the susceptibility to electrochemical corrosion and stress corrosion cracking of two types of carbon steels exposed to synthetic seawater with and without the presence of CO2 at room temperature. The steels used in this research have small variations in their chemical composition according to optical emission spectroscopy analysis. When evaluating the mechanical properties of pearlitic steels from hardness and microhardness analysis, it was possible to observe that the steel composed of a pearlite matrix with cementite spheres, demonstrated a lower strength and hardness compared to the steel that presented a fine perlite microstructure. This is due to the reinforcing effect of cementite on ferrite, in addition to the resistance to the movement of displacements promoted by the contours between ferrite and cementite. In the electrochemical tests, which included measurements of open circuit potential, polarization and impedance, both steels showed stability in the equilibrium potential around 0.65 V, regardless of the medium with or without CO2 saturation. In this potential, it was found that the steels studied in this research experience active corrosion, characterized by the continuous loss of material without the formation of a protective layer that can slow down or prevent this process. The impedance analysis showed that steels A, composed of a perlite matrix with a cementite sphere and B composed of a fine perlite matrix, have distinct corrosion resistance in saturated and unsaturated media. In the test carried out in an autoclave by the U-bend method, which investigated the combined effect of temperature (40 °C), pressure (10 bar) and a solution of synthetic seawater saturated with CO2, it was observed that the steel with a fine perlite microstructure showed greater resistance to crack formation and stress corrosion, better maintaining its physical integrity at the end of the test. The results obtained indicate that the studied steels present variations in corrosion resistance under different electrochemical conditions. The data from this research confirms the mechanisms of corrosion in pearlitic steels, helping in the development of more corrosion-resistant materials.