Electrochemical Corrosion Behavior of Welded Joint of CT80 Grade Coiled Tubing in NaCl Solutions with Different Mass Fractions

Electrochemical corrosion behavior of base metal and weld from welded joint of CT80 grade coiled tubing in NaCl solutions with different mass fractions (3.5%, 5.0%, 7.0%) was investigated by potentiodynamic polarization technique and electrochemical impendence spectroscopy testing method. The results show that the polarization curves of the base metal and weld presented a typical anodic dissolution characteristic in NaCl solutions with different mass fractions. No passivation phenomenon was observed. With the increase of NaCl mass fraction (i.e., Cl^-1 concentration), the open circuit potential and the free corrosion potential of the base metal and weld showed negative shifts, the polarization resistance decreased and the free corrosion current density increased; the corrosion resistance decreased. The thermodynamic stability and corrosion resistance of the base metal were better than those of the weld.