As is the case in many countries, liquid storage in Brazil is a critical infrastructure element. Although the need for storage tanks is great, composite tanks have had a hard time competing against those made of more conventional concrete and glass-lined steel, says Giocondo Rossi, director of large fiber-reinforced polymer (FRP) tank builder Tecniplas (Cabreúva, Brazil). Rossi, who spoke in August at the National Exhibition on Sanitation and Environment (Fenasan), held in São Paulo, says the traditional tank materials have some severe limitations.
“Concrete is porous, and requires an internal rubber seal,” he contends. “In addition to raising tank cost, the elastomeric coating has a limited lifetime. Then, after three or four years, the water begins to attack the steel reinforcement in the concrete, requiring heavy investments in maintenance or even the replacement of the tank.” Large, glass-lined steel tanks require assembly of thousands of steel plates, each seam offering a potential leak point. But large FRP often lost out because finished FRP tanks were too big to transport on the roads to installation sites. To address this difficulty, Tecniplas began several years ago to use “oblate” technology, in which the tank’s filament-wound hoop sections, or “rings,” are compressed after fabrication into an oval shape and then compressed further in the middle, forming a shape like a lazy number eight (8), with care taken not to overstress the laminate. Rossi says a 15m diameter tank can thus be reduced in one dimension to about 5m. Although it actually grows larger in the other dimension, the 5m width falls within the Brazilian standard for wide-load transport.
Ring sections are uncompressed at the installation site, then they and tank tops, also are made in sections, are wet-laminated together to form the finished tank structure.
Tecniplas has manufactured dozens of tanks using this method. Advantages of oblate technology include reduced transportation time and costs and better logistics. These join composites advantages that include leak resistance, corrosion resistance, high mechanical strength and the ability to use resins compatible with drinking water.