Experiments were done with two levels of electrode diameters. Average localized corrosion rates and maximum pit-depths were monitored over time. Coupons of 17-4PH and GTD450 stainless steels were placed in the same environment to compare the results with that of CMEAS probes.

Electrical Resistance (ER) based probes are widely used to monitor corrosion of the aboveground storage tank (AST) bottoms. Prevention of soil-side corrosion of the bottom plates of aboveground crude oil storage tanks is a major challenge in the oil and gas industry. Vapor corrosion inhibitors (VCIs) are increasingly being used to mitigate tank bottom corrosion. Therefore monitoring AST bottom corrosion and VCI effectiveness is an important factor in determining the bottom plate corrosion rate and in taking preventive action such as application of VCIs. ER probes are based on the bulk resistivity measurements. The change in resistivity data over a given period is converted to corrosion rates. Since the resistivity is the bulk measurement the ER-measured corrosion rate is an average value representing general pitting and microbiological induced corrosion. A study was conducted to rigorously compare the ER probe measurements with the corrosion observed on the mass-loss coupons. The ER probes were placed in a corrosive sand environment along with the mass-loss coupons which experienced both general and pitting corrosion. The coupons were removed after 6 months and ER probe data were continuously recorded over the test duration. The coupons were scanned using a laser profilometer which provided metal depth versus position data. The coupon data were analyzed to estimate the corrosion rate distribution. In parallel the ER probe data were also analyzed using the rolling average method. The two data sets were compared to identify similarities and delineate differences between the ER probes and mass-loss coupons. This analysis was used to determine suitability of using the ER probes for monitoring the tank bottom corrosion and VCIs’ effectiveness.

On-line real time corrosion monitoring in processes featuring low conductivity fluids akin to sulfolane aromatic extraction have represented a challenge for traditional electrochemical techniques. Sulfolane specific conductance that is typically about 5mS/cm enables proper determination of corrosion current with standard Linear Polarization Resistance (LPR) technology. Other electrochemical techniques such as Electrochemical Impedance Spectroscopy (EIS) or Zero Resistance Ammetry (ZRA) are useful mostly in laboratory practice but offer little or no utility for field-operational regime. Therefore corrosion processes in sulfolane units are mostly monitored by time-lagging techniques like electrical resistance (ER) and corrosion coupons or by purely qualitative approaches utilizing sulfolane color as the “corrosion indicator”.The authors’ earlier work on multi-electrochemical industrial corrosion monitoring technique integrating impedance measurement Electrochemical Noise (ECN) and Harmonic Distortion Analysis showed demonstrable efficacy in fast and accurate determination of instantaneous corrosion rate in low-conductivity sulfolane solutions. Initial data generated showed that properly adjusted surface area of the electrode facilitates attainment of stable corrosion trends in sulfolane solutions at conductance of about 2-5 mS/cm. Rapid response of the sensor to process changes (temperature oxygen water) in both general and localized modes was also observed.The current paper provides additional data and insights from the authors’ continuing research on sulfolane corrosivity utilizing industrial-type corrosion sensors. Results from comprehensive evaluation of properties of the aqueous phase as well as other relevant process parameters on general and localized corrosion of ferrous metallurgy in sulfolane applications are presented in this paper. Keywords: on-line corrosion monitoring electrochemical sulfolane aromatic extraction