PR644-223604-R01 Monitoring Long-Term Compatibility of VCIs and CP

Several tank operators have been using vapor corrosion inhibitors (VCIs) as a corrosion control measure for the tank bottom for reasons including partial or complete failure of the existing cathodic protection (CP) system, presence of soil-side corrosion indications even with an active CP, in tanks with double bottoms where CP current distribution is insufficient due to the proximity of the anode to the second bottom, and when operators want to increase the inspection intervals to reduce the life-cycle maintenance cost. Objective of this research was to quantify the interactions between VCI and CP and associated components and evaluate validated technologies and processes to monitor the corrosion conditions under the bottoms of the breakout tanks.

This research comprised of field testing utilizing in-service VCI-treated ASTs, laboratory testing and evaluations, and analysis of large amount of monitoring data collected from the VCI-treated tanks. Various corrosion control monitoring methods were evaluated as part of the field testing in the VCI-treated tanks. The monitoring data from field testing was used to develop guidelines for VCI monitoring and to establish VCI reinjection requirements. Large-scale experiments with active CP were used to determine the VCI dispersion range in highly corrosive conditions, and to determine the effects of VCI on the anode current output. VCI dispersion range is several tens of feet, and VCIs do not affect anode current output. The CP rectifier data collected for tanks treated with VCIs indicated that the rectifier current output before- and after-VCI are not affected by the VCIs. A limited analysis of the VCI-treated tanks indicated that VCIs seem to be effective in mitigating soil-side corrosion, and the VCI-treated corrosion mitigation is equivalent to the tanks with effective CP. Experimental data also indicated that use of VCI in tanks with active CP could help improve the CP current distribution. The intended audiences of the work documented in this report include AST operators across multiple industries, such as midstream operators and crude oil refineries.