Installation of VCIs within New and Existing AST Double Bottoms

The protection of an aboveground storage tank bottom against corrosion has primarily been limited to the application of Cathodic Protection (CP) either by the installation of a passive (galvanic) type system or an active (impressed current) type system. Corrosion is mitigated by the development of a potential difference between the anodes and the protected structure. CP systems are reliant on electrical principles in order to distribute current to any proximal conductive surfaces. Adequacy of the cathodic protection system has been historically determined by the use of permanently installed reference cells. Copper/Copper Sulfate cells would be installed within the interstitial space throughout the tank. Voltage measurements would be obtained between the tank and the reference cell to determine if the potential difference was sufficient to indicate the likelihood of protection.

As an alternative to Cathodic Protection, the use of Volatile Corrosion Inhibitors, or VCIs has become a standard practice. VCIs are a chemical substance that can be introduced into a variety of mediums, as well as utilized in powder form to mitigate corrosion. The substance will continuously form a vapor, known as volalitizing, until an equilibrium point is reached. Once in equilibrium, all exposed metallic surfaces are protected from corrosion by the vapor coating. Adequacy of the vapor coating has historically been determined using Electrical Resistance (ER), or corrosion monitoring, probes. ER probes are installed within the perimeter of the interstitial space through the tank tub. Resistance measurements are obtained from the probe which corresponds to a metal loss of the probe, indicating actual corrosion rates within the interstitial space.

PCA Engineering, Inc. offers VCI installation for both new aboveground storage tank double bottoms, as well as existing double bottoms. Contact us to learn more.

PCA Engineering, Inc.

NJ Office 57 Cannonball Road
Pompton Lakes, NJ 07442
MA Office 7 West End Way
Norwell, MA 02061

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