Liquid storage tanks are a requirement in many industries; they are used for liquid raw materials, in process liquids and waste. In many cases the tanks are huge, easily 2 million gallons and more, in other cases they may only hold 500 or 600 gallons. These tanks can be open top or fully enclosed complete with specific piping for filling and draining.
Although there are many applications where underground storage tanks are used, in most industrial applications the tanks are above ground. The tanks sit on a prepared surface, it can be any level ground but frequently the surface is a poured concrete slab.
There is a considerable difference between a storage tank and a pressure vessel. A storage tank operates under no pressure at all, it simply contains a liquid. The shape of a storage tank is normally round or square with straight vertical sides. A pressure vessel on the other hand is usually spherical. Both tanks of tanks are manufactured under different rules and regulations, not only based on whether they are pressurized or not, but also based on the liquid which is stored within.
Most liquid storage tanks for containment of non-hazardous materials are open top; however, when these tanks are used to store potable water they have a fitted top. There are certain designs where the top floats on the surface of the liquid; this is common when the liquid gives of noxious fumes as the floating top greatly reduces any air that is above the liquid. These types of floating top tanks are usually seen inpetroleum storage tank farms.
As above ground tanks have no fill around them such as is the case if they are buried, the corners are rounded which offsets the pressure put on the tank walls by the liquid. If the corners are not rounded, the tank walls are reinforced with buttresses.
Many tanks are surrounded by a secondary containment system. In the event of a tank rupture or any form of a leak, the material is captured in the secondary system. Depending on the material and the arrangement of the tank this containment arrangement can be another tank, an earthen dike with a liner made from material which is resistant to the tank contents or a moat.
