The bottom plates of petroleum aboveground storage tanks (ASTs) are especially susceptible to corrosion attack due to wear and tear from floating roof legs, floor flexing or changes in the materials being stored which may be incompatible with the tank’s protective coating system. Taking a tank out of service to replace its flooring is expensive and time consuming, which is why some petroleum facilities are initiating preventive maintenance programs that include the use of long-lasting, high-solids, thick film epoxy liners.

“Replacing a floor is about four times the cost of applying a protective liner,” according to Tnemec coating consultant Brandon Lomasney, who was brought in to Red River Terminals in the Port of Shreveport-Bossier after the bottom in one of its tanks was found pitted and in need of replacement. “The tank did not have enough steel thickness to get through its next inspection cycle,” Lomasney recalled.

After the new bottom was installed and the lining was applied, the decision was made to reline the facility’s remaining tanks under a preventive maintenance program designed to reduce their life cycle costs. “To lose a tank for two months because you have to replace the tank bottom is significant, whereas you can line the same tank in a week or two,” Lomasney noted. “The plan is to recoat these tanks over a four-year period, doing three tanks per year.”

Ranging in size from 15,000 barrels to 100,000 barrels, the tanks are being coated with Series 330 Bridgeport Glass Armor 300, a reinforced, self-priming epoxy lining. The liner is spray-applied at 30 mils dry film thickness (DFT), then tested for hardness and holidays. “With the Glass Armor lining there’s no priming, you just apply it and you’re done,” Lomasney explained. “The applicator was impressed with the product’s performance. After it was applied to a test panel and allowed to cure, they couldn’t beat it off with a hammer.”

Interior testing was performed in accordance with the American Petroleum Institute (API) 652 Linings of Aboveground Petroleum Storage Tank Bottoms, which describes the procedures for achieving effective corrosion control in existing and new ASTs in hydrocarbon service.

The exterior roofs and shells of each tank were also evaluated as part of the preventive maintenance program. “The roofs are exposed to direct sunlight, moisture and coastal conditions, so you have a very corrosive environment,” Lomasney observed. “We evaluated the existing coatings on the exterior shell of each tank for adhesion, film erosion and percentage of rusting to see if they were in good enough condition to be overcoated. Our recommendation was to overcoat tank walls and blast and coat the roofs.”

Tnemec’s advanced technology acrylic polymer, Series 30 Spra-Saf EN, is specified for use on the roofs and tank walls. Spra-Saf EN is a direct-to-metal, corrosion-inhibiting coating with early flash rust resistance, long-term corrosion protection and weathering properties.

Red River Terminals is a petroleum distribution complex that includes a liquid storage terminal with related dock, piping, tanks capable of 340,000 barrels of storage and four-bay automated truck racks. The company was the Port of Shreveport-Bossier’s first tenant and remains the port’s highest volume tenant.

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