Caracterização eletroquímica de risers flexíveis em água do mar sintética: influência do CO2

Abstract

The oil and gas sector is responsible for supplying the main sources of energy used worldwide, driving industries, transportation, energy production, infrastructure and technology investments, and generating millions of direct and indirect jobs. It is currently one of the most important sectors for the global economy and the development of many countries. In deepwater oil and gas exploration, carbon steels are widely used in components such as flexible risers, multilayer pipelines that connect production platforms to subsea wells. The high cost associated with the corrosion of these materials significantly impacts the industry, where CO₂ is one of the main causes of degradation. This study evaluated the corrosion resistance of AISI 1070 and 1075 carbon steels, applied in the tensile armor of risers, in synthetic seawater (ASTM D1141), in the absence and presence of CO₂. The investigation sought to understand the effects of CO₂ on the integrity of these materials. The methodology involved electrochemical tests such as Open Circuit Potential (OCP), Electrochemical Impedance Spectroscopy (EIS), and Linear Polarization Spectroscopy (LPR), in addition to microstructural analyses by optical microscopy (OM) and scanning electron microscopy (SEM). The samples were subjected to environments with and without CO₂ saturation under controlled temperature and pH conditions, using a three-electrode electrochemical cell. The results demonstrated that the presence of CO₂ significantly aggravated the corrosive processes, with a sharp drop in polarization resistance (Rp) values and an increase in corrosion rates. AISI 1075 steel showed better performance in all tests, suggesting greater stability of its protective films. The OM and SEM images are consistent with these results, revealing greater oxide formation and surface attack in the samples exposed to CO₂. An increase in corrosion resistance over time was also observed, associated with the formation of surface layers that limit load transfer.