Failure of superduplex stainless steel flange due to inadequate microstructure and fabrication process

Flanges made of alloy steels used in the oil and gas platforms must be produced by hot forming (usually forging) in order to obtain a wrought product with refined microstructure and good toughness. In the present study, a flange of superduplex stainless steel, supposedly produced by forging (ASTM A-182 F53), has prematurely failed by pitting corrosion and cracking. The investigation was conducted to analyze the manufacturing processes, microstructures and properties of the failed flange. The analyses revealed that the flange has been produced by casting, and the chemical composition and microstructure were inadequate for the application in seawater conduction at room temperature. The failed flange was also analyzed by in situ double loop electrochemical potentiodynamic test (DL-EPR) and ferritoscope analysis. These two complementary non-destructive tests were able to detect the inadequate microstructure and corrosion resistance of the flange.