Corrosion Protection of Soil Side Bottoms of Aboveground Storage TanksAbstractIn 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 then 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 system (CPS) is not universally effective and a viable alternative is needed. This paper focuses on case studies of bottom side floor corrosion protection using corrosion inhibitors. Once introduced under the AST by nature volatile corrosion inhibitors (VCIs) diffuse into all void spaces under tank bottoms – including the free space between sand/soil particles and protect the exposed metal plates. Soluble corrosion inhibitors (SCIs) mitigate corrosion when there is water under the tank bottoms. The systems are effective where a CPS is not and can be retrofitted under tanks in service. We will describe test results for a number of VCIs and SCIs that demonstrate their effectiveness in addressing corrosion problems. It is now possible to select a range of VCIs and SCIs based on the corrosive environmental conditions and the design of the tank bottoms to provide optimal protection. Initial testing in different aggressive corrosion environments has identified VCI and SCI compositions that can achieve efficiencies of 70-90% and 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. We will also present synergistic systems (SS) that combine VCIs SCIs and CPS for double bottom corrosion protection.Keywords: Tanks AST bottom plate soil side inhibitor VCI SCI oil gas environment corrosion retrofit design efficiency service life.