Electrochemical corrosion behavior of X80 pipeline steel welded joints fabricated by ultrasound-assisted submerged arc welding in CO2-saturated solution

Abstract

In this study we investigated the electrochemical corrosion behaviors of X80 pipeline steel welded joints fabricated by ultrasound-assisted submerged arc welded (UASAW) joints in CO2-saturated solution. The microstructures of the UASAW joints were analyzed by using metallographic microscopy. Corrosion behavior of UASAW joints was investigated using immersion test, electrochemical polarization, and electrochemical impedance spectroscopy (EIS). The corrosion morphologies and products were characterized by scanning electron microscopy (SEM), energy dispersive spectroscope (EDS) and X-ray diffraction. Metallographic and the corrosion mechanism of UASAW was systematically studied. The investigation results showed that the microstructure of the UASAW weld zone is mainly composed of acicular ferrite and a little granular bainite. The minimum microhardness is obtained in fusion zone (FZ) because of many alloying elements dominated in the final precipitate distribution. Pitting corrosion resistance of the strong vibration region in FZ is attributed to the decline in active sites of the bainite, the UASAW had beneficial effect on the improvement of pitting corrosion resistance of X80 pipeline steel weldment.