Monitoring Effectiveness of Vapor Corrosion Inhibitors for Tank Bottom Corrosion Using Electrical Resistance Probes and Coupons

摘要

Electrical Resistance (ER) based probes are sometimes used to monitor corrosion of the aboveground storage tanks (AST) bottoms' underside. 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. Monitoring an 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 vapor corrosion inhibitors (VCIs). ER probes are based on the bulk resistance measurements; change in element resistance data over a given period is converted to corrosion rates. ER-measured corrosion rate is an average value representing the combined effects of general, pitting, and microbiological induced corrosion. A study was conducted to rigorously compare the ER probe measurements with the corrosion observed on mass-loss coupons. 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 several months, and ER probe data were continuously recorded over the test duration. The coupons were scanned to measure metal depth versus position data which were analyzed to estimate the corrosion rate distribution. In parallel, the ER probe data were also analyzed to estimate corrosion rates. 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.