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

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.

Product Number: 51319-13100-SG
Author: Pavan Shukla
Publication Date: 2019
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