Corrosion behavior of welded joints of copper pipe in artificial seawater
The corrosion behavior of the welded joints of copper pipe in artificial seawater was studied with anodic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM).Experiment results indicated that the anodic processes of copper, cupronickel-welded joint and brass-welded joint were similar in artificial seawater.At the same electrode potential, the corrosion current of cupronickel was the lowest and the corrosion resistance was the best,which is consistent with the EIS result.The current density peak of brass welded line appeared at -0.012 V, and a porous corrosion film was formed.The electrode was passivated subsequently.The passivation film was made up of Cu_2O,CuCl and ZnO.The passivation film dissolved with electrode potential, and displacement deposition took place between Cu and Zn.The copper redeposition on the electrode surface induced the increase of electrode activity and corrosion rate.At an electrode potential of +0.87 V, the electrode surface was rich of acicular Sn and stannum oxide.This film would prevent the electrode from dezincification, and the current density decreased and homeostasis was reached at the same time.The corrosion mechanism of brass welded line in artificial seawater was dissolution/redeposition.