Performance of Vapor Corrosion Inhibitors for Localized Corrosion Mitigation of Double Shell Storage Tanks at Hanford

摘要

Hanford stores millions of gallons of high-level waste storage site in 27 carbon-steel double shell, underground tanks (DSTs). A secondary shell surrounds the primary shell, where the bottom plate of the secondary shell rests on a channeled concrete pad. There have been instances of metal loss on the secondary shell bottom plates in contact with the concrete basemat where accumulation of the groundwater solution in the channels may have caused corrosion. In addition, uneven contact between the basemat and shell could create occluded areas where localized corrosion in form of crevice corrosion is possible. In previous studies, several commercially available vapor corrosion inhibitors (VCIs) were tested for their ability to mitigate concrete-basemat side corrosion of the secondary liner bottom. The previous studies involved use of disk coupons either immersed or placed in vapor space of the groundwater solution dosed with VCIs. Even though, VCIs have been found to be effective in mitigating corrosion on the disk coupons, it is not clear if VCIs can be sufficiently effective in mitigating the crevice corrosion. A study was conducted with disk coupons where each coupon's disk surface was partially occluded using a crevice former. Several sets of the disk coupons were exposed to the groundwater solution for several months in three separate corrosion tests. Approximately half of the coupons were extracted after several months of exposure and analyzed for metal loss. The remaining sets of coupons were exposed for additional time to the commercially available VCIs by adding the VCIs to the ground water solutions in the tests. The remaining coupons were extracted after completion of the tests and analyzed for metal loss. Corrosion rate data of the pre- and post-VCI exposed coupons were compared to evaluate effectiveness of the VCIs for mitigating the crevice corrosion. The paper will present experimental data and results on effectiveness of VCIs in mitigating crevice corrosion on the bottom plates of the secondary shells.