“FRP duct with antimony is going to have a flame-spread index of less than 25 but a smoke-developed index of more than 50 which will not pass UL 181,” Naugle says. “So we made a product with a fluoropolymer liner that uses a phenolic resin to achieve a flame-spread index of less than 5 and smoke-developed index of less than 10.” With an added Halar® liner, the DualGuard 2000™ ductwork also is resistant to corrosion from a variety of the chemicals – from hydrochloric acid to sulfuric acid – that are used in cleanrooms or chemical processing plants, with no sprinklers required.
With FRP products able to achieve a powerful combination of corrosion and heat resistance, new possibilities open up. For example, Naugle points out that wastewater treatment plants also often call for UL 181 ratings, as do some industrial paint booths. Composites USA has supplied its DualGuard 2000 product to Boeing for buried ductwork in paint booths at its plants. “There’s high heat and highly corrosive chemicals in their paint, and they use DualGuard 2000 to keep the ductwork from catching fire or corroding,” says Naugle. “And it doesn’t rust so you can put it underground.”
One of the biggest challenges, of course, is that new applications mean a fresh learning curve for end users who still believe that FRP products are more limited than steel in high heat environments. Geoff Clarkson, president and CEO of UTComp, an FRP engineering and testing firm with global operations based in Cambridge, Ontario, recalls a recent project for which the company designed and supported fabrication of a liner for a basin used in extraction of titanium dioxide at a mineral processing facility. The process involves applying hydrochloric acid during several high heat cycles to extract the desired concentration of titanium dioxide. “The liquid that gets dumped in could be as hot as 419 degrees Fahrenheit, and this liner had to be able to survive temperature changes from room temperature to that temperature in probably a minute or less,” Clarkson says.
Creating a liner that meets these demands is a balancing act at which UTComp has become adept. “The first thing you have to do is use the right resin material. There are some commercially available resins that can work to those temperatures without running into the structural problems that tend to develop,” Clarkson says. The structural failures of concern are related to glass transition of the resin. “Above a certain temperature, the resins used go through a change where they become like rubber and would deform under the stresses applied,” he says.