Abstract
Vapor Corrosion Inhibitors (VCIs) are increasingly being used as a corrosion control measure for soil-side corrosion of Aboveground Storage Tanks (ASTs). VCIs are primarily applied to the tank bottoms using one of the following two delivery methods: (i) through-the-sandpad, and (ii) through-the-floor. Through-the-sandpad delivery is employed for tanks that are in-service, while through-the-floor delivery is used for out-of-service tanks. Access to the tank bottom is relatively uninhibited for the out-of-service tanks, and therefore, VCIs applied using the through-the-floor delivery method are expected to provide coverage to the entire bottom plate. However, for in-service tanks using the through-the-sandpad delivery method, VCIs are discharged through the multiple injection ports that are at discrete locations along the ring-wall (single bottom) or dead-shell (double bottom). After VCIs are injected, it is expected that VCIs would migrate via various mechanisms such as molecular diffusion, volatilization, convection, etc., and provide corrosion mitigation coverage throughout the bottom plate. A Pipeline Research Council International (PRCI) sponsored study was conducted to quantify VCI migration for the through-the-sandpad delivery method. Laboratory-scale experiments were conducted to determine VCI migration; two tubular-shaped sand-filled glass vessels were used. VCIs were injected at one end, and electrical-resistance data pre- and post-VCI injection were collected and analyzed to determine the VCI migration rates. The experimental data and associated analysis showed that VCIs migrated quickly from the injection port.
