This paper presents results of an irnidazoline based (ECN) and Electrochemical Impedance Spectroscopy (EIS) inhibitor using the Electrochemical Noise techniques in a multiphase flow pipeline. ECN and EIS measurements were made simultaneously in a 101.6mm I.D., 15m long acrylic pipeline using saltwater and carbon dioxide mixtures. Full pipe flow was studied for liquid velocity of 1.25 mh and slug flow for Froude numbers 6 and 9. Experiments were carried out at a constant pressure of 136kPa and temperature of 40°C. The ECN signals and EIS spectra of blank and inhibition tests were obtained. The ECN technique is able to monitor the inhibitor film formation continuously. The current noise fluctuation is correlated to the corrosion rate for both blank test and inhibitor test. The higher current fluctuation indicates higher corrosion rates. Different EIS spectra were obtained for blank and inhibitor studies. The simple charge transfer process was seen to occur for blank tests while charge transfer and diffusion processes were taking place under inhibitor effects.
The corrosion inhibitor is the main tool used for preventing internal corrosion in carbon steel pipelines, which are used to transport multiphase mixtures from oil production. The successful selection of corrosion inhibitors depends on a clear understanding of the inhibition performance of the inhibitor under multiphase flow conditions. The Electrochemical Impedance Spectroscopy (EIS) technique is seen to be a powerful method for studying the inhibition performance of inhibitor in a multiphase flow system ?. However, the EIS is unable to monitor inhibitor film performance and corrosion process continuously. Electrochemical noise (ECN) has attracted a lot of research attention for the past twenty years. ECN is able to monitor stochastic processes that might be correlated to the overall kinetic and provide detailed information, which is not available through DC and AC methods. It is recognized that ECN provides scientific answers in corrosion research and solves practical problems in corrosion engineering 2. The noise resistance, which is calculated by standard deviation of voltage and current noise, might correlate to the polarization resistance for some systems 3-4.The ECN technique is able to monitor the inhibitor film formation and destruction processes 3.
The ECN is a practical technique in the continuous monitoring of corrosion processes at a fast sampling rate, which is suitable for monitoring corrosion and inhibition processes in multiphase flow systems. A multiphase flow can be classified into many different flow regimes according to the flow rate of gas and liquid for the multiphase flow system. At high production rates, the slug flow regime is prominent. The characteristics of slug flow have been discussed in a previous paper 5.Froude number is used to describe slug flow. The slug flow is known to significantly enhance internal corrosion in oil/water/gas pipelines. This is due to the high levels of shear and turbulence occurring in the mixing zone of the slug 7-9. The high turbulence system must be monitored using a technique with a fast sampling rate, which must be at least at a frequency of the order of the perturbing effect, otherwise a significant amount of detail is missed 10.Hence, the ECN at a higher sampling rate is very helpful for monitoring corrosion process in a turbulent multiphase flow system. The corrosion monitoring by ECN techniques under multiphase flow conditions have been studied extensively at the Corrosion Center of Ohio University. Voltage and current noise signals under fill pipe flow and slug flow at different water cuts were obtained 11.The noise fluctuation shows trends whi