Electrochemical Correlation Study Of On-line Corrosion Monitoring Probes

Corrosion probes have been widely used for online monitoring corrosion rate in the petrochemical industry, pipeline transmission industry. The most ex-tensive used probes are:electrical resistance (ER) probe, electrochemical linear polarization resistance (LPR) probe. Electrochemical monitoring method has high measurement speed, which reflects the instantaneous corrosion rate. Be-sides LPR technology of electrochemical techniques, weak polarization (WP), electrochemical impedance spectroscopy (EIS) has been widely used to monitor the corrosion rate in the laboratory, but it is rarely for the industrial applications. The probe setups includes:two electrode probes and three-electrode probes. By far, few systematic studies had been done for various electrochemical techniques on different probe setups. Therefore, this project studyed the correlation of var-ious electrochemical techniques in different electrochemical probes, in order to offer some guidance for industrial applications. The main subject of the study the following aspects:Firstly, corrosion coupons were set as baseline for corrosion rate meas-urement as a function of immersion time. Corrosion products were explored as well. Four different electrode system setups were chosen for the following elec-trochemical studies:Classical three electrodes system (CTES), Two identical electrodes system (Two IES), Three identical electrodes system (Three IES), Three electrodes systems of stainless steel as reference (Three ES (SS-RE)).Secondly, weak polarization (WP) behaviors were characterized for differ-ent immersion time. Corrosion parameters of ba, bc, and B values are obtained as a function of time. B values were used further for LPR technique calculation.Thirdly, polarization resistances from both LPR and EIS techniques were calculated. With the B values from WP, corrosion rates were calculated for comparison.Then the effects of different electrode setups and electrochemical tech-niques are summarized. For LPR method, three-IES are not suitable for long-term online monitoring, especially the environment with serious corrosion issues; Three ES (SS-RE) can be used for long-term applications in chloride containing environment; two electrodes of the same material can be used in the system of any corrosion of the electrolyte solution, just need other auxiliary method to measure corrosion kinetic parameters. With the immersion time, ac-curate measurement of the corrosion rate of the electrode surface adsorption layer has a larger impact, so corrosion is more serious corrosion system should be changed regularly probe.