An unusual “lost core” composite material adds double-wall protection to non-compliant storage tanks without excavation. #outofautoclave #weaving #adhesives

The GENESIS retrofit by Delta Composite Systems is a cost-effective alternative to this scenario: gas station operations are stopped for four weeks to remove and replace underground storage tanks to address corrosion, damage, and secondary sealing requirements, at a cost of US$150,000 to US$200,000. Source: Delta Composite Systems LLC

Unearthed underground oil storage tank. Source: Delta Composites LLC

ZPlex is a 3-D woven fabric with foam thread woven in the gap between two glass fiber faces. The foam keeps the dough at a certain distance and removes the resin in the voids during the lamination process. Source: 3TEX

Once the lamination of the glass fiber tank barrier is completed, the foam thread will melt, forming a secondary containment structure with hollow gaps, and any leaking fluid can flow into it. There, it is collected and monitored. Source: 3TEX

The image on the left shows the location of the tank where intrusive fluids (from the outside or inside of the tank) are collected and detected by the system, which warns that there is a breach in the storage integrity of the tank’s main storage tank. The picture above shows the process of velvet. Source: High Performance Computing

Step 1a: Open the existing storage tank and remove its contents, source: Delta Composite Systems LLC

Step 1b: Prepare a manhole at the opening of the storage tank to allow workers to enter. Source: Delta Composite Systems LLC

Step 2: After the inner surface is abrasive blasted to prepare for bonding, the outer barrier of the composite system consists of several layers of glass fiber mats, which are applied to the inside of the tank by hand laying. Source: Delta Composite Systems LLC

Step 3: Apply ZPlex material, then the last layer of several layers of glass fiber cushion. Source: Delta Composite Systems LLC

Step 4: The bottom of the sink is made of biaxial glass fabric and is connected to the gap so that the leaked fluid can be discharged downward and be collected, monitored and removed (see the sink diagram above). Source: Delta Composite Systems LLC

Step 5: Apply the last layer of gel coat to form the new inner surface of the water tank. Source: Delta Composite Systems LLC

Step 6: This proprietary heating system is used to melt the foam in the ZPlex fabric, leaving open voids. Source: Delta Composite Systems LLC

The U.S. Environmental Protection Agency (EPA, Washington, DC) estimates that as of March 2012, petroleum or other hazardous materials are stored in 587,000 underground storage tanks (UST) in the United States. Because 51% of the U.S. population relies to some extent on groundwater for drinking water, the EPA formulated an UST regulatory plan in 1984 to eliminate the risk of groundwater pollution caused by leaks from these water tanks. Federal UST regulations were revised in 1986 and 1988 and became stricter. By 2005, they included the requirements for a secondary containment. The result is a double-walled tank. Similar to the double-walled hull in an oil tanker, all new or replaced underground storage tanks must now have a secondary barrier and a gap between the two walls. The latter realizes gap monitoring, which uses sensors in the gap to detect the leakage of oil or contained chemical substances through the inner wall of the storage tank and the leakage of groundwater through the outer wall of the storage tank.

EPA designed the UST program implemented by each state. However, the regulatory environment is complex, and some states allow counties and municipalities to determine UST repair and replacement specifications. States report that UST emissions are indeed the most common source of groundwater pollution, while petroleum is the most common storage pollutant. Most oil is stored in retail gas stations in the form of gasoline and diesel.

State and municipal regulations may require the excavation and complete replacement of leaking single-walled storage tanks, or allow them to be repaired, inspected, certified, and modified for secondary containment. The latter type of leaking tanks and still-usable single-walled tanks include a large number of containers that require secondary containment. Therefore, various fiberglass composite systems have been developed to retrofit these existing storage tanks without excavation-using steel, polymer coatings or fiberglass composites-as the high cost and downtime for the complete replacement of the tank Alternatives to time. These systems range from installing pre-cured fiber reinforced plastic (FRP) inner tank sections to various methods of applying glass fibers and resin directly to the inside of the tank.

Delta Composite Systems LLC (Plymouth, New Hampshire) developed its new GENESIS internal secondary barrier system, using 3TEX (Cary, North Carolina) ZPlex glass laminated fabric, which not only ensures containment and gap monitoring, but also speeds up and improves stability Application process and provide a fast and cost-effective way to cover 700 to 800 square feet (65 to 74 square meters) of surface area in a typical storage tank. Importantly, when the GENESIS system is in place, it is a fully functional double-wall fiberglass structure, independent of the existing tank, and can maintain UST-compliant functions regardless of any corrosion issues with the original external tank material.

Tony Rieck of TR Consulting Inc. (Colorado Springs, Colorado), a long-term consultant in the field, stated that “of the 587,000 USTs cited by the EPA, about half are now double-tiered.” He explained, For a company, seeking to modify its storage tanks does not always have leakage or cleanup issues. "Tank owners can take the initiative to comply with secondary sealing requirements," he said. Rieck said that the benefits of retrofitting to achieve a secondary containment is that “it does not require shutting down gas stations for four weeks, nor does it need to spend $150,000 to 200,000 to install a secondary containment.” For example, for a typical 8,000 gallons to 10,000 gallons. For gallon (30,283 liters to 37,854 liters) fuel tanks, the average cost of Delta Composite Systems GENESIS is only $30,000. This type of system is a viable solution where the existing infrastructure cannot be removed and replaced with storage tanks.

Rob Pearlman, senior enclosure system engineer at Delta Composite Systems, explained: “Delta’s people have been developing processes since the early 1990s, but we eventually integrated all the different components into a retrofit system.” Pearlman added: “ Twenty years ago, a system like ours was only suitable for special applications, for example, the existing corroded or damaged storage tanks could not be removed and replaced without disturbing the building. Now, it will be used for excavating and replacing tanks. Mainstream alternative because it makes economic sense."

The Delta Composite Systems transformation uses not only the inner lining, but also a composite sandwich structure, which consists of two skins separated by a hollow gap, allowing any intrusive fluid to flow down the tank bottom or the centerline of the sump, where it is detected , And then removed by pump or other means. The first step is to open the water tank and pull out the contents. Rieck commented: “Sometimes you have to install a manhole to get in.” Next, sandblast the inside of the water tank to remove chemical residues, rust and scale in preparation for bonding. The multi-layer fiberglass mat was then manually laminated to the water tank to form the outer glass shell of the GENESIS retrofit barrier. After this, ZPlex fabric is applied. In order to manufacture ZPlex, 3TEX started with the traditional process used to manufacture velvet cloth. This method uses a special loom that can weave fabrics of two thicknesses at the same time, but they are tied together with a z-direction thread. Then, during the weaving process, the cutting knife separates the two sides to form two separate fabrics. The cut z-fiber produces a soft fluff effect, giving the velvet a plush feel (see picture on the left). In the production of ZPlex, glass is used to make velvet, but 3TEX will not separate the faces. This results in fiberglass laminates with built-in voids. The difference in ZPlex is that the foam is inserted into the space between the two fabrics during the weaving process. It is worth noting that the foam is sacrificial, that is, it will melt after the tank barrier lamination process is complete and keep the void open.

Rieck describes ZPlex as "the woven roving on both sides of the foam core that disappears when heated, leaving a cavity."

The ZPlex process starts with spools of glass fiber and olefin foam extruded into continuous strands. These are fed into a machine that produces 3D woven fabrics. In one step, the foam thread is woven into the gap between the two glass fiber surfaces. The foam thread maintains a uniform set distance between the woven skins (especially important because the installer must be able to stand and walk on the placed material). In the resin hand lay-up or resin infusion process, closed-cell foam can prevent resin from intruding into the void.

ZPlex is usually woven with skins up to 0.5 inches/12.7 mm thick and interstitial columns up to 0.1 inches/2.54 mm thick (formed by resin-impregnated Z-direction fibers between the fabric surfaces).

After the ZPlex fabric is manually laminated along the surface of the tank, a two-way glass tape layer is used to construct a groove along the center line of the tank bottom. This slot is connected to the gap space formed by ZPlex (see the left side of the figure above). The wet/dry battery enters the interstitial space through the pipe. It detects any water or fuel entering the space, triggering an alarm and inspection by the tank owner.

Finally, apply two to three layers of glass mats on the ZPlex fabric to prevent the pores on the surface of the woven roving from causing leakage, and then apply a gel coat to form the new inner surface of the water tank. Allow the glass fibers to solidify in the environment, and then use a proprietary system to heat the inside of the tank to melt the foam. Since the solids content of the foam is less than 5%, the molten foam will shrink into a tiny residue and open up the voids.

Many different resins can be used in this process to ensure compatibility with petroleum, acetone or other storage chemicals. Polyester, vinyl ester and epoxy resin are all optional, but no matter which one you choose, the resin used will be tested to ensure adequate chemical resistance. The composite tank retrofit system has flexibility in terms of the specifications and suppliers of fiberglass mats, and has successfully used a range of materials.

After the installation is complete, the final quality check is performed by pressurizing the gap with air and testing the tank for bubbles with soap under pressure. If the gap maintains pressure during the specified test, the modification process is certified by the installation technician. For a typical 8,000 gallon to 10,000 gallon (30,283 to 37,854 liter) fuel tank, the entire conversion process can be completed by an experienced crew in three days. When asked about the potential loss of tank volume and expected service life in the GENESIS system, Pearlman replied: "A 10,000 gallon tank will only lose a few hundred gallons of capacity, and the system is designed to provide 30 years of service life. ."

GENESIS has been tested in an approved testing facility and meets all EPA requirements for UST secondary containment modification. Now, Delta Composite Systems will seek the Underwriters Laboratories (UL, Northbrook, Illinois) UL 1316 standard ("Glass fiber reinforced plastic underground storage tanks for petroleum products, alcohol and alcohol-gasoline mixtures." ) Certification. “The next step allows consideration of our system for use in cases where there are problems with existing tank walls, so the retrofit may have to provide a self-supporting structure,” Pearlman said. He sees GENESIS as a cost-effective and reliable containment solution with a bright future. “Due to environmental issues and changing fuel product formulations, underground storage tanks have witnessed many changes in regulations and containment challenges,” he concluded. "GENESIS is a great example of how we use the latest materials to provide new solutions to the industry."

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