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Summer 2005

composite tanks 

Each process for making fiberglass tanks provides different strengths for the finished tanks and the application in which the tanks are used. Fiberglass tanks are usually made by hand-lay-up/spray-up with chopped glass and resin; or chopped glass, resin, and helically wound glass; or by helically winding glass that is saturated with resin.

In a direct bury system, an adhoc deadman is installed to keep the tank from floating where high water tables exist.In the mid-1970s, Containment Solutions, Inc. (CSI), switched to a computer-aided manufacturing system. The computer controls the rotation and speed of a mandrel (a collapsible, steel, cylindrically shaped mold) plus the application and advance rate of a mechanical arm that applies the resin/glass matrix to the mandrel.

“We use steel mandrels and build our tanks from the inside out,” explains Bill Schneider, Director of Research and Development, CSI. “Steel molds provide firm and consistent surfaces upon which to apply materials. They also allow us to easily vary the location, types, and amounts of materials we apply to meet the needed strength requirements of the tank. As the mandrel rotates, resin, glass, and specially treated silica are precisely metered onto the mandrel from above. The final result is a closely controlled process and a tank wall consistent in composition and thickness.”

Schneider is careful to point out that after a chopped glass and resin liner is applied, the laminate composition is changed by adding silane-treated sand, and it is not a filler.

“Fiberglass has always been coated with silane to allow bonding between the resin and the fiberglass,” continues Schneider. “We used the same technology to coat sand and increased the bonding capabilities between the sand and resin. The resultant matrix of fiberglass, treated sand, and resin allows the laminate to perform well with modern alcohol fuels and blends without having to use more expensive resins.”

Don Hildreth of North American Composites (NAC) is the point man for CSI. “NAC supplies 90% of CSI’s raw materials, other than resin and silica,” says Hildreth. “CSI is a quality-conscious customer that has its customers’ best interests in mind. It is a pleasure to work with the entire staff.”

Putting the Spin on It

Wax coats the mandrel’s end cap, and Mylar film coats its cylindrical shape. As the resin, glass, and sand materials are applied to the mandrel’s cylindrical wall and the end cap, they are continuously rolled out to thoroughly wet-out the laminate and remove any entrapped air.

After curing, the shell wall and the end cap are checked with a device that measures thickness by sensing the steel mandrel under the laminate. This ensures the tank meets the minimum thickness requirements. Ribs made with chopped glass, resin, and sand are applied to the cylindrical structure to provide stiffness. Hoop glass or continuous strand glass is strategically placed on top of the shape to most efficiently maximize the stiffness of the ribs.

The amounts of materials applied are weighed and checked against required minimums for the shell wall and the end cap. Once the tank shell is finished, the mandrel is collapsed and the tank shell is pulled off the mandrel for a visual inspection.

In the assembly operation, tank shells are joined together and accessories are laminated to the finished tank. All the steel fittings are welded to plates and then laminated in place. “We continue to use steel fittings in petroleum applications because the industry uses steel pipes that connect directly to the tank,” says Schneider.

Depending on the type and size of the tank, typical manufacturing time is three to five days.

Unsurpassed Performance and Warranty

CSI’s tanks for petroleum applications are warranted for 30 years against internal and external corrosion and structural failure. “I don’t think there is anyone out there that will warrant a tank longer than we will,” says Ron Shaffer, Vice President of Marketing at CSI. “Many Owens Corning (OC)/CSI tanks (see “Pioneering Composite Tank Fabrication” sidebar) are still in service from the late 1960s. We have manufactured and sold more than 300,000 tanks since 1965. As EPA regulations have evolved, other pieces of underground equipment have been upgraded, but often, the tank is left in the ground because it’s still perfectly fine.”

In the mid-1990s, the EPA’s regulations became more restrictive and double-wall tanks were developed to further protect the environment against potential leaks. “The movement is toward doublewall tanks as the standard if a tank is installed anywhere near a water source,” relates Shaffer. “All double-wall (and triple-wall) tanks are required to have monitoring of the inner and outer walls. We introduced our continuous hydrostatic monitoring system in 1985 as a simple, convenient way to do this.”

At the factory, a calcium chloride solution that won’t freeze is added to fill the tank’s interstitial space. It is also colored green so it’s easily seen, providing the installing contractor and local regulator the ability to quickly assess the condition of the delivered tank with a visual inspection.

This brine is monitored electronically for any leaks after the tank is installed and provides incredibly sensitive leak monitoring of all the surfaces of the inner and outer walls of a double-wall tank for the life of the tank, with little maintenance.

Shaffer says their larger customers, who are more liability conscious, want to do more than meet the basic intent of the EPA standards. “Today, there is only one major oil marketer in the United States still specifying steel tanks, and even those have an FRP jacket,” he says. “There is still a market out there for steel tanks despite the popularity of FRP. Many times, the decision is cost driven.”

Shaffer tries to get potential customers to think long term. “Obviously, we talk about our 30-year warranty,” he says. “The CSI warranty covers structural integrity as well as corrosion resistance. Some steel-tank manufacturers only offer an internal corrosion warranty — provided regular maintenance is conducted. They require removal of water bottoms (contaminated fuel), which is what actually starts the corrosion process. That is cumbersome and expensive over time.

“Furthermore, we encourage customers to think about secondary containment and continuous pressure monitoring of the tank’s interstitial space,” Shaffer continues. “Other methods of monitoring the space utilize probes and mechanical systems that can mask small leaks, and they require regular maintenance. The hydrostatic system is much more cost effective and easier to operate over the life of an underground storage tank.”

Perfecting Design

Along with their corporate offices in Conroe, Texas, CSI has facilities dedicated to research and development for product design, development, and testing. “We are able to conduct almost all of our own tests in-house,” says Schneider. “Physical properties, Barcol hardness, Izod impact, dynamic mechanical analysis for degree of cure, post-curing ovens resin gel/cure characteristics, and long-term testing at elevated temperatures are all conducted here. We also have a concretewalled, underground pit to test completed tanks and new installation procedures. We’re the only undergroundtank manufacturer to have this inground testing.”

Notably, not a single tank that the OC Tank Division or CSI has built ever leaked due to internal or external corrosion. As they say in their literature, Fiberglass tanks simply will not rust — inside or out. And that’s what you need to know when comparing fiberglass underground storage tanks to underground tanks made from steel.


Meeting Evolving Needs

Pioneering Composites Tank Fabrication

Containment Solutions, Inc., was formed in 1995 when Denali, Inc., bought Owens Corning Underground Tank Division’s assets and technology. Many of OC’s engineering and management staff joined CSI at that time.

OC pioneered composite underground storage tanks beginning in 1965, when a major U.S. oil company approached OC Fiberglass to design and build composite storage tanks to replace steel tanks that were corroding and leaking. The costs for cleanup and the potential for future lawsuits were too great to ignore even then. A tank division was created at OC, and the first single-wall composites tank was built that year.

OC worked extensively with Underwriters Laboratories to assist in the development of the First Edition of UL 1316, which was published in 1983. UL 1316 is a performance-based standard that outlines the requirements for fiberglass-reinforced plastic tanks for the underground storage of petroleum-based flammable and combustible liquids, alcohols, and alcohol-blended fuels. It qualifies the resin and raw materials that can be used and includes performance testing of finished tanks to prove their structural integrity. UL 1316 is accepted in the United States and some other countries as the governing standard for underground petroleum tanks.

When other tank fabricators got into the business and pressure from California to improve the single-wall tank didn’t let up, OC built a double-wall tank and first sold it in California in 1984.

CSI also makes an extensive line of tanks that have separate compartments inside the vessel. Over the last 10 years, compartment tanks have become popular with petroleum marketers who prefer to blend two grades of gasoline at the pump in order to offer mid-grade octanes. Consequently, fewer tanks are manufactured, but the tank sizes have dramatically increased.


CSI also continues to offer new accessories like tank sumps. The enclosure holds the gravel back and provides access to the manway and critical equipment.

“Our newest product is a multipiece, double-walled sump, which can be field-assembled and hydrostatically monitored,” says Schneider. “We were awarded a patent on that design, which provides maximum environmental protection for containing potential leaks. We strive to offer our customers a complete system solution, not just the tank.”

Shaffer says they are investing significantly in new water/wastewater handling opportunities. CSI manufactures tanks for septic, potable water, and nonpotable water applications. Tanks in these markets were traditionally made of concrete, which degrades over time and often leaks due to poorly installed joints.