Abstract
The failure of a flange for seawater service in the top side of an oil platform was investigated in this work. The flange was made of superduplex stainless steel UNS S32760, and the chemical composition and the microstructure were found to be adequate, according to ASTM A-182 standard. Deleterious phases such as sigma and chi phases were not found by optical and scanning electron microscopy. The material's mechanical properties and corrosion resistance were also typical of superduplex steel without intermetallic phases. However, the flange has undergone severe crevice corrosion in the gasket region. In the microstructural scale, the ferrite phase was preferentially attacked. EDS analyzes revealed elements typically found in corrosion processes caused by microbiological bacteria. The work shows that the superduplex steel is susceptible to crevice microbiological induced corrosion (MIC), even when the microstructure and fabrication process used are correct.
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