Storage tank and Special features

A storage tank is a container that holds liquids, compressed gases (gas tanks; or "pressure vessels" as they are called in the United States and is not usually marked or regulated as a storage tank), or media used for short- or long-term storage of heat or cold.The term can be used for both reservoirs (artificial lakes and ponds) and man-made containers.The word tank is uncommon in American English, but it is common in British English. In other countries, the term tends to refer only to artificial containers.In the US, storage tanks operate with no (or very little) pressure to distinguish them from pressure vessels.Tanks are usually cylindrical, perpendicular to the ground, have a flat bottom, and have a fixed frangible or floating roof.There are generally a number of environmental regulations that apply to the design and operation of storage tanks, often depending on the nature of the fluids contained within them. Aboveground storage tanks (AST) differ from underground storage tanks (UST) in the type of regulations that apply.Aboveground storage tanks can be used to store materials such as petroleum, waste, water, chemicals and other hazardous materials while meeting stringent industry standards and regulations.Reservoirs can be covered, in which case they can be called covered or underground storage tanks or reservoirs.Covered tanks are common in urban areas.Storage tanks come in many shapes: vertical and horizontal cylindrical; open and closed top; flat bottom, conical bottom, inclined bottom, dish bottom.Larger tanks tend to be vertically cylindrical or have rounded transitions from the vertical sidewalls to the bottom profile in order to more easily withstand the hydraulic hydrostatic pressure of the contained liquid. Most tanks used to handle liquids during transport are designed to handle varying degrees of pressure. 

In order to use storage tanks for volume measurements, a capacity table should be created using the appropriate standard.Each row of the capacity table contains the fill level value and the corresponding volume value (and other relevant data).Large storage tanks are sometimes mounted on wagons (trucks) or articulated wagon trailers,later called tank wagons.In the United States, air emissions equate to losses of usable liquid commodities and/or marketable products, often requiring air quality permits under the federal Clean Air Act.Quantification of potential emissions for permitting purposes is usually accomplished by applying the emissions equations published in Chapter 7.1 of AP-42 of the US EPA: Compilation of Air Emission Factors.

Special features

Since most liquids can spill, evaporate or seep through even the smallest openings, special consideration must be given to their safe and secure handling.This usually involves building dikes or dikes around the tank to safely contain any spills.Some storage tanks require a floating roof in addition to or instead of a fixed roof and structure.This floating roof rises and falls with the liquid level in the tank, reducing the vapor space above the liquid level.Floating roofs are considered a safety requirement and pollution prevention measure in many industries including petroleum refining.In the United States, metal tanks that come into contact with soil and contain petroleum products must be protected from corrosion to prevent product leakage into the environment.The most effective and commonly used corrosion control technique for steel in contact with soil is cathodic protection.Outside the United States and in some locations in the United States,elevated tanks with a sand-asphalt mix finish are often used to support the foundation. These types of foundations keep the tank floor away from the water, thus preventing corrosion.