Experimental Study of Electrochemical Corrosion Behavior of Coiled Tubing Welding Seam in CO₂ Environment

CO₂ electrochemical corrosion is one of the main reasons for the failure of coiled tubing（CT） in gas field exploitation. In order to obtain the corrosion law of CT weld and base material in CO₂ environment, the electrochemical corrosion of CT110 base material and weld samples in CO₂ simulated gas field environment was studied by electrochemical workstation and electrothermal thermostatic water bath by electrodynamic polarization curve and electrochemical impedance spectroscopy tests. The results show that the polarization curves of the CT base material and the weld samples show typical characteristics of anode dissolution, and the corrosion process is controlled by the cathode. The corrosion resistance of base material and weld in saturated CO₂ solution is weaker than that without CO₂. Under the condition of saturated CO₂, with the increase of temperature, the corrosion potential of base metal and weld decreases, the corrosion current density increases, the polarization resistance decreases and the corrosion resistance weakens. Compared with those of the base metal, the corrosion potential and polarization resistance of the weld are lower and the corrosion current density is higher, indicating that the corrosion resistance is lower than that of the base metal.