Owens Corning introduced the first glass fiber, fiberglass, in 1935. When fiberglass was combined with a plastic polymer, it created a lightweight structure of incredible strength. This was the beginning of the Fiber Reinforced Polymers (FRP) industry. Over time, these FRP laminates have evolved into our modern corrosion-resistant and abrasion-resistant fiberglass composite systems. Today, FRP liners lend new life and durability to aboveground metal storage tanks. In certain circumstances, tanks with FRP liners equal or surpass stainless steel vessels for containing corrosive liquids.
Ideally, an aboveground steel tank is expected to have a lifespan of 20-30 years. However, internal and external factors can shorten that span to as little as five years by attacking the tank’s bottom steel plates. Internally, water containing corrosives such as salt and chlorides may settle to the tank’s bottom, causing damage to the metal. Externally, the tank’s steel plates can suffer damage from salt and other corrosives in the soil, as well as from stray electrical currents.
A damaged, leaking tank can cause environmental harm with resultant legal penalties. When an above ground tank corrodes, it must either be replaced or repaired using an FRP lining. Fortunately, FRP linings have proven to be an effective option for combating corrosion in aboveground tanks and cost considerably less than a new tank or tank bottom. In addition, the linings are comparatively quick to install, minimize downtime, and are durable enough to last longer than 30 years.
Installation of an FRP lining has several steps. First, the tank must be dry and the surface properly prepared. Next, installers apply primer and putty. Finally, the surface is coated with catalyzed resin with a glass mat and sealcoat. The thickness of the applied lining depends on the condition of the tank bottom. A single FRP layer is capable of staunching minor leaks and withstanding 37 psi.
If the bottom has been perforated or if it is severely corroded, it is recommended that a double layer of the laminate be applied to achieve a thickness of 110 to 120 mils. The FRP lining bonds tightly enough to the storage tank that it effectively creates a new bottom. A double lining is capable of repairing holes up to 8” in diameter and withstanding 82 psi. Since the average internal tank pressure is about 20 psi, it stands to reason that FRP linings will hold even if hydraulic pressure is present. However, it’s important to note that the long-term ability of FRP linings to bridge large openings may be negatively affected by cyclic loading.
In terms of correct installation, preparation is key, and installers must be highly trained professionals. It is important to be aware that using pigmented gel coats will make it difficult to assess the condition of the storage tank bottom.
In summary, FRP linings have proven to be an excellent method of repairing steel tank bottoms and extending the life of the tank. They are more cost-effective than tank or tank bottom replacement and have a lifespan as long or longer than the actual tank. In addition, the linings are capable of bridging large holes at 80 psi with double laminate. Installation by experienced professionals is a relatively quick process, minimizing any downtime.