Underground Fuel Tanks

UNDERGROUND FUEL TANKS
- Application of 100% Solids Polyurethane Coatings

Since 1975 there have been over 300,000 cathodically protected, underground steel fuel storage tanks installed in the United States and Canada. The tanks in Canada were designed according to the Underwriter Laboratories of Canada standard S603.1. The majority of the American tanks were built according to the STI-P3 standard of the Steel Tank Institute of Lake Zurich, IL or the Underwriters Laboratories UL1746.

Virtually all of these tanks have been coated with 100% solids polyurethane coating. The amount of steel coated is in excess of over 150,000 million square feet. The design of the system has been so effective that, to date, there have been zero failures reported as a result of external corrosion of the tanks. The simple design involves a dielectric coating (usually 100% solids polyurethane), nylon bushings (to electrically isolate the tank from the piping) and sacrificial anodes.

The fabricators of the STI-P3 tanks continue to use 100% solids polyurethane coatings and offer a 30 year warranty against external corrosion.

A most recent development in underground fuel storage tank coatings is the use of 100% solids polyurethane coatings in replacing the existing FRP (fiber-glass reinforced polyester) technology. Thick (100 mils or 2500 microns) FRP coatings have been for a long time the only technology used for the external protection of fuel steel tanks when there are no anodes attached. However, both the Steel Tank Institute and the Underwriters Laboratories have recently tested and approved that a 70 mils (1750 microns) thick "special designed" 100% solids polyurethane coating can outperform in every aspect a 100 mils (2500 microns) thick FRP coating.

The FRP technology deals with Hazardous solvents, styrene, glass fibers, and very long curing time, therefore having significant disadvantages over the 100% solids polyurethane coating technology. The use of the 100% solids polyurethane coating gives out a better and also more economic solution in protecting underground fuel storage tanks while cathodic protection is not being used.

Because FRP coatings are also used in many other industries, the STI and UL experience may as well lead these industries to use 100% solids polyurethane coatings for replacing the FRP technology.

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