Degradação de revestimentos poliméricos aplicados em tubulações de esgoto

Abstract

Urban sewer pipelines operate under severe conditions, including chemical corrosion, microbiological degradation, and abrasive wear. Metallic materials such as ASTM A36 carbon steel are highly susceptible to corrosion, especially in acidic, sulfide-rich environments, leading to material loss and reduced infrastructure service life. To mitigate these effects, the use of polymeric coatings has been widely adopted, although their performance under combined corrosion-abrasion conditions is not yet fully understood. This research proposes an integrated experimental methodology to evaluate the degradation of polymeric coatings applied to ASTM A36 steel, using a synthetic medium representative of urban sewage from Uberlândia (MG). Coal tar-epoxy and Zebron® coatings were tested, with nominal thicknesses of approximately 0.25, 0.50, and 1.00 mm. Electrochemical characterization was performed through open circuit potential (OCP) measurements, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS). Uncoated steel exhibited corrosion potentials below −0.50 V, high corrosion current densities on the order of 10⁻⁴ A·cm⁻², and charge transfer resistances (Rct) below 10² Ω·cm², indicating a high degradation rate. In contrast, polymeric coatings exhibited coating resistance (Rcoating) values of 10⁴ Ω·cm² at higher thicknesses (0.5 mm and 1.0 mm), demonstrating effectiveness in protecting the steel. The Zebron® coating maintained Rcoating values between 10³ and 10⁴ Ω·cm² after 168 h of immersion, especially near 1.00 mm thickness. The coal tar-epoxy coating showed progressive degradation over time, particularly at thicknesses below 0.50 mm. Abrasive wear tests using a rubber wheel in a wet medium revealed greater thickness loss for coal tar-epoxy, reaching approximately 0.05 mm after 8 hours, while Zebron® showed losses below 0.015 mm under similar conditions. The analysis revealed that reduced coating thickness decreases corrosion resistance due to the interaction between abrasion and corrosion, affecting long-term coating durability.