Corrosion Inhibition Property of Oleic Imidazoline to Under‐Deposit Corrosion of X65 Steel in CO₂ Environment

ABSTRACT In this paper, the investigation was carried out for the inhibition property of oleic imidazoline quaternary ammonia salt (OIM) as corrosion inhibitor for under‐deposit corrosion (UDC) of X65 steel in CO 2 corrosion environment. Weight loss and In Situ electrochemical measurements were used in an autoclave to study the corrosion behavior of UDC by adding corrosion inhibitor after immersion for a period (pre‐corrosion). The results indicated that adding 50 mg/L of OIM corrosion inhibitor at the initial time (0 h) can achieve the best corrosion inhibition effect, with a corrosion inhibition efficiency of 90.3%. With the delay in OIM adding time, the corrosion inhibition effect gradually weakened. In Situ electrochemical results behaved similar to weight loss. The corrosion product layer displayed differently after 72 h corrosion, the condition of adding OIM at different moments. The surface roughness R a increased with the delay of OIM adding moment, indicating an increase in UDC and reduced protectiveness of layer to the substrate metal. At last, the inhibition mechanism of OIM in the presence of corrosion product layer was proposed.