When considering secondary containment systems for your API 650 above ground storage tanks, there is a range of options. To meet state requirements, most systems are designed to catch the liquid after it leaks from the tank, such as with dikes or double walled tanks. Polyvinyl Chloride (PVC) Secondary Containment Liners, on the other hand, wind up being the primary containment of the liquid and the walls of the tank become the secondary containment. Most states allow such a system as long as a leak detection system is in place.
In order to use a PVC liner system, care must be taken to ensure that the PVC is compatible with the liquid being contained. For storing liquid fertilizer in a steel walled tank, a PVC liner should fit the bill. However, cleaning the liner and filling the liquid fertilizer tank must be done in a way that will not puncture the liner. PVC is a strong material, but will puncture when subjected to sharp objects.
There is more to installing a PVC liner than simply dropping the liner into the tank and filling it up with liquid. The PVC liners are usually suspended from the top of the tank to secure it in place. The liner then needs to be integrated into the tank system with openings for hoses, valves, and the leak detection equipment, as well as having provisions for manways and nozzles.
There are several advantages to using PVC liners over dikes or double walled tanks. Dikes require extra real estate around the circumference of the tank, which is an added expense as well as takes up more space. Additionally, there are operational costs associated with keeping rainwater out of the dikes. Many states require that the water pumped out of the dikes be used in agriculture, further increasing the operational costs. And although potentially more durable, double walled tanks are obviously more expensive as they require twice as much steel as a single tank. Flexible PVC liners avoid the pitfalls of dikes and double walled tanks, and are far more economical.
An added benefit to using PVC liners as secondary containment that is often overlooked is the potentially longer life span of the tank itself. Over time, a steel tank will degrade and lose strength along its welds due to exposure to the corrosive properties of the liquid being stored. Because the liner in effect acts as the primary containment, the stored liquid does not come into contact with the walls of the tank, thereby protecting it from possible corrosion and extending its life.
And finally, a PVC secondary containment liner is far easier to implement than it is to build a double walled tank or erect a lined dike. Most PVC liners can be installed in one day.
Given the significant cost savings of using a flexible PVC liner as a secondary containment system, coupled with the added benefits of longer tank life and reduced operational costs, a PVC tank liner is a system that is worth considering for your above ground storage tanks.