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Aboveground Storage Tank CP System Anodes Performance in the Presence of VCIs

Aboveground storage tanks (AST) soil-side corrosion protection is commonly implemented using cathodic protection (CP) technology. U.S. Department of Transportation mandate use of CP system for the tanks falling under federal regulations purview. In case of a double bottom tank i.e. a tank where original (old) bottom has been rendered useless and a second (new) bottom has been installed couple of inches above the original bottom the anodes are laid in the sand bed just above the old bottom. An impressed current cathodic protection (ICCP) system with an MMO anode is a preferred for this application however there are instances where a galvanic anode (GCP) system is also used for tank bottom protection. For effective operation of the CP system the current generated by the anode is a determining factor which mainly depends on the interface resistance between the anode and sand bed. In an ICCP system the current output can be driven to counter the circuit resistance of CP system whereas for a GCP system the potential difference between the anode and cathodeis the key driving factor. In other words the GCP system cannot function in a high resistivity sand bed system. Vapor Corrosion Inhibitors (VCI) are being used in combination with CP systems for the tank bottom soil side applications. VCIs tend to change the interface resistance by contact with the metal (anode and cathode) surfaces.In this paper investigations are carried out to understand the effect of VCIs on impressed current (MMO) and galvanic anodes and their ability to function in a VCI saturated electrolyte system. The passivation behavior of the anode is analyzed using electrochemical tests and the performance is evaluated. The paper also reports the simulated long-term performance of the ICCP and GCP system in the presence of VCIs.

Product Number: 51319-12787-SG
Author: Sujay Math
Publication Date: 2019
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Product Number: 51300-00829-SG
ISBN: 00829 2000 CP
Author: Tim Whited
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