In addition to material choice, storage tanks differ in size and capacity, ranging from small tanks holding a few gallons to tanks exceeding 35 feet in length, with a storage capacity of 50,000 gallons or more.
Storage tanks encompass a very broad category, and more specific types of storage tanks include water tanks, septic tanks, chemical tanks, fuel tanks, oil tanks and double wall tanks. Due to the wide range of capabilities, storage tanks are utilized in numerous industries including: agricultural, in the storage of water for irrigation as well as herbicides and fertilizer; oil/gas, for the storage of various fuels and oils for automotive and aerospace applications; wastewater treatment, for use in municipal waste water treatment plants and other water treatment facilities; medical, for use in pharmaceutical industries for the storage of liquid and powder medications or even gases such as hydrogen, ammonia, nitrous oxide, carbon dioxide or boron hydride.
Storage tanks are formed using either a molding or a welding process. Plastic tank molding involves using a model shape to form the tank, while plastic tank welding is a process in which two pieces of heat-softened plastic are joined through the application of pressure. Examples of this welding process are hot air and extrusion welding.
In hot air welding, also known as hot gas welding, a specially designed heat gun is used to produce a jet of hot air that functions to soften both the parts that are to be joined and a plastic filler rod, which must all be a similar plastic material. In extrusion welding, a welding rod is drawn into a miniature plastic extruder and then plasticized. After it is plasticized, it is forced out of the extruder and pressed against the parts being joined, which have been softened by means of a hot air jet in order to allow bonding to occur.
Storage tanks are formed from a wide variety of plastic materials. Of all the plastics, polyethylene is the most commonly used to fabricate storage tanks. Polyethylene, a light, chemical-resistant thermoplastic, is advantageous as a material for storage tanks because it offers high chemical inertness as well as being a very light-weight material.