Galvanic Corrosion Behavior of the Welded Joint of Ni-Based Alloy and X60 Steel in CO{sub}2 Saturated Solution

摘要

Ni-based alloy C4 （N06455） and pipeline steel X60 were welded by TIG welding method with Ni-based alloy welding-wire ENiCrMo-3, Corrosion experiments of the welded joint were carried out by a high temperature and pressure autoclave in a CO{sub}2 saturated solution. The cross-section corrosion morphologies of the welded joint were observed by Scanning Electron Microscopy (SEM). The cyclic volt-ampere method (CV), the galvanic couple current, polarization curves and electrochemical impedance spectroscopy (EIS) of the X60 steel/weld metal couple and X60 steel matrix were measured, respectively. The results show that FeCO{sub}3 corrosion scale mainly deposited in the fine grain area of heat-affected zone (FGHAZ) of X60 steel during corrosion for 96h, and gradually extended into fusion zone (FZ) with an increase in corrosion time. The double electricity layer capacitance and polarization resistance of X60 steel/weld metal couple are lower than X60 steel matrix due to the acceleration effect on ion diffusion caused by the high potential difference between the X60 steel and weld metal, by which the forming mechanism of corrosion scale was obviously affected.