Corrosion Protection of Soil Side Bottoms of Aboveground Storage Tanks

摘要

In Aboveground Storage Tanks (ASTs), corrosion of soil side bottoms and double bottoms is unpredictable and can be up to 5 mm/year. There are multiple tank bottom and foundation designs that address some of the corrosion problems, but can cause other, new, corrosion issues. The soil side of tank bottom plates, especially for larger ASTs, cannot be effectively coated, inspected or retroactively protected while the AST is in service. The typical corrosion protection method - cathodic protection systems (CPS) are not universally effective and a viable alternative is needed. This paper focuses on case studies of soil side bottom corrosion protection using corrosion inhibitors. Once introduced under the AST, volatile corrosion inhibitors (VCIs) by their nature will diffuse into the void spaces under tank bottoms - including the free space between sand/soil particles, and protect the exposed steel bottom plates. The systems can also be retrofitted under tanks in service. This paper will describe test results for a number of VCIs and Soluble Corrosion Inhibitors (SCI) that demonstrate efficiencies as high as 70-90% and also exclude pitting corrosion. Field trial and application experience has shown that inhibitor use can increase the anticipated tank service life from approximately 8-10 years to 25-30 years, resulting in greatly reduced maintenance and replacement costs. This paper will also present synergistic systems (SS) that combine VCIs, SCIs and CPS for double bottom corrosion protection.