Performance evaluation of corrosion inhibitors for L245N pipeline steel under CO2-O2 mixed conditions

Purpose This study aims to evaluate the performance of selected corrosion inhibitors for L245N pipeline steel under mixed CO2-O2 conditions representative of oilfield production environments, and to provide a practical basis for inhibitor selection under oxygen-contaminated CO2 corrosion systems. Design/methodology/approach Ten commercial corrosion inhibitors were investigated using electrochemical measurements, weight-loss tests and surface morphology observations. Potentiodynamic polarization and electrochemical impedance spectroscopy were conducted to assess corrosion behavior. Gravimetric measurements were used to determine inhibition efficiency, and scanning electron microscopy was used to examine surface damage characteristics. Adsorption behavior was analyzed using isotherm fitting to interpret inhibitor–steel interactions. A multiparameter comparison approach was applied to integrate the experimental results for performance ranking. Findings Among the tested inhibitors, T4 exhibited the best overall performance, achieving a weight-loss inhibition efficiency of 73.74% at an optimal concentration of 150 mg/L. Electrochemical measurements revealed a significant increase in charge-transfer resistance and a reduction in corrosion current density compared with the uninhibited condition. The CII successfully integrated short-term electrochemical responses with long-term corrosion performance and identified T4 as the most effective inhibitor. The proposed CII framework successfully distinguished inhibitors exhibiting strong short-term electrochemical behavior but inferior long-term corrosion protection, thereby reducing the risk of misleading evaluations based on single-parameter testing. The results demonstrate that the proposed framework provides a more reliable basis for inhibitor selection in oxygen-contaminated CO2 corrosion environments. Originality/value This study provides an experimentally based comparative evaluation of corrosion inhibitors under mixed CO2-O2 conditions that simulate practical oilfield environments. The integrated analysis of electrochemical, gravimetric and surface characterization data offers a practical framework for inhibitor screening and selection in field applications.