Desempenho das ligas ASTM A179, AISI 316 e SAF 2205 em sistema de água de refrigeração sujeito a corrosão sob depósito: um estudo aplicado a trocadores de calor com feixe helicoidal

Abstract

Corrosion in industrial equipment is one of the main challenges to reliability and operational safety in process plants. In heat‑exchange systems, the combination of severe operating conditions, process‑fluid characteristics, and metallic materials can promote localized degradation mechanisms. In this context, under‑deposit corrosion stands out due to its silent and accelerated nature, requiring special attention in monitoring, inspection, and mitigation strategies. Accordingly, this study addresses under‑deposit corrosion in helical‑coil heat exchangers installed in a petrochemical plant located in the Camaçari Complex. The equipment, manufactured from ASTM A179 carbon steel and integrated into the thermal safety system of the recirculation pumps of a recovery boiler, has shown a recurring history of perforation failures at intervals of less than three years—significantly below the regulatory inspection period (72 months). These failures, responsible for unplanned boiler shutdowns, were attributed to localized corrosion beneath scale deposits formed by the cooling water. The methodology involved the characterization of the operational environment, physicochemical analysis of the cooling water, and under‑deposit corrosion tests under static potential using a three‑electrode cell and artificial deposits. Electrochemical techniques were applied, such as Open Circuit Potential (OCP), potentiodynamic polarization with Tafel extrapolation, static immersion tests, and surface characterization by scanning electron microscopy (SEM). The results confirmed that ASTM A179 carbon steel exhibited higher susceptibility and corrosion rates in the presence of deposits (0.4241 mm/year). AISI 316 stainless steel showed intermediate behavior, with localized attack and partial loss of passivity. Duplex stainless steel SAF 2205 demonstrated superior performance, with a minimal corrosion rate (0.0062 mm/year), low surface degradation, and high passive stability. Based on the significantly extended expected service life (219.9 years for SAF 2205 versus 1.6 years for ASTM A179) and a cost–benefit analysis favoring operational reliability, duplex stainless steel SAF 2205 was identified as the most suitable and economically viable alloy for replacing the evaluated heat exchangers.