Storage tank

A storage tank is a container, usually for holding liquids, sometimes for compressed gases (gas tank). The term can be used for both reservoirs (artificial lakes and ponds), and for manufactured containers. The usage of the word tank for reservoirs is common or universal in Indian English, and moderately common in British English. In other countries, the term tends to refer only to artificial containers such as ponds or small lakes.

Storage tanks may often operate under no pressure (or very little), distinguishing them from "pressure vessels". Storage tanks are often vertical cylindrical in shape, perpendicular to the ground with flat bottoms and fixed domed roofs, hinged or floating roofs. There are many Environmental considerations and regulations applicable to the design and operation of storage tanks, often depending on nature the fluid contained within. Above ground storage tanks (AST) differ from underground (UST) varieties in the kinds of regulations that are applied.

Reservoirs open or covered, if covered they would be referred to as underground storage tanks or reservoirs. Covered water tanks are common in urban areas.

Storage tanks are available in many shapes, (vertical and horizontal cylindrical) (open top and closed top ) (flat bottom, cone bottom, slope bottom and dish bottom)but large tanks tend to be vertical cylindrical, or to have rounded corners (transition from vertical side wall to bottom profile, to easier withstand hydraulic hydrostatically induced pressure of contained liquid. Most "container tanks" for handling liquids during transportation are designed to handle varing degrees of pressure.

A large tank is sometimes mounted on a lorry, truck or on an articulated lorry trailer, are referred to as tankers.

pecial features

Since most liquids can spill, evaporate, or seep through even the smallest opening, special consideration must made for their safe and secure handling. This usually involves building a bunding, or secondary containment dike, around the tank, so that any leakage may be safely contained.

Some storage tanks need a floating roof in addition to or in lieu of the fixed roof and structure. This floating roof rises and falls with the liquid level inside the tank, thereby decreasing the vapor space above the liquid level. Floating roofs are considered a safety requirement as well as a pollution prevention measure for many industries including petroleum refining.

Types of tank

High pressure

Cylinders are not storage tanks at all, but "pressure vessels". In the case of a liquefied gas such as hydrogen or chlorine, or a compressed gas such as compressed natural gas or MAPP, the storage tank must be made to withstand the sometimes immense pressures exerted by the contents. These tanks may be called "cylinders"

Milk tank

In dairy farming a bulk milk cooling tank is a large storage tank for cooling and holding milk at a cold temperature until it can be picked up by a milk hauler. The bulk milk cooling tank is an important milk farm equipment. It is usually made of stainless steel and used every day to store the raw milk on the farm in good condition. It must be cleaned after each milk collection. The milk cooling tank can be the property of the farmer or being rented to the farmer by the dairy plant.

eptic tank

A septic tank is part of a small scale sewage treatment system often referred to as a septic system,. It consists of the tank and a septic drain field. Wastewater enters the tank where solids can settle and scum floats. Anaerobic digestion occurs on the settled solids, reducing the volume of solids. The water released by the system is normally absorbed by the drain field without needing any further treatment.

Mobile "storage" tanks

While not strictly a "storage" tank, mobile tanks share many of the same features of storage tanks. Also, they must be designed to deal with a heavy sloshing load and the risk of collision or other accident. Some of these include ocean-going oil tankers and LNG carriers; railroad tank cars; and the road and highway traveling tankers. Also included are the holding tanks which are the tanks that store toilet waste on RVs and boats.

Materials of construction

While steel remains one of the most popular choices for tanks, GRP and thermoplastic tanks are increasing in popularity. They offer lower build costs and greater chemical resistance, especially for storage of speciality chemicals. There are several relevant standards, such as British Standard 4994 (1989) and DVS (German Welding Institute) 2205 which give advice on wall thickness and quality of final product.

Tank failures

There have been numerous catastrophic failures of storage tanks, one of the most notorious being that which occurred at Boston Massachusetts USA on January 14th, 1919. The large tank had only been filled eight times when it failed, and resulting wave of molasses killed 21 people in the vicinity. The Boston molasses disaster was caused by poor design and construction, with a wall too thin to bear repeated loads from the contents. The tank had not been tested before use by filling with water, and was also poorly riveted. The owner of the tank, US Industrial Alcohol, paid out $300,000 in compensation to the victims or their relatives.

There have been many other accidents caused by tanks since then, often caused by faulty welding or by sub-standard steel. However, storage tanks also present another problem, surprisingly, when empty. If they have been used to hold oil or oil products such as gasoline, the atmosphere in the tanks may be highly explosive as the space fills with hydrocarbons. If new welding operations are started, then sparks can easily ignite the contents, with disastrous results for the welders. The problem is similar to that of empty bunkers on cargo ships, which are now required to use an inert gas blanket to prevent explosive atmospheres building up from residues.

ee also

*Ballast tank
*BS 4994: British Standard 4994:1987 specification for design and construction of vessels and storage tanks in reinforced plastics
*Bunding
*Cascade storage system
*Forensic engineering
*Forensic polymer engineering
*Fuel tank
*Gasometer
*Inerting system
*Irrigation tank
*Johad
*Oil depot
*Pressure vessel
*Rainwater tank
*Structural failure
*Tank blanketing
*Underground storage tank
*Vacuum flask
*Water heating
*Water tank

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Etymology

The word "tank" originally meant "artificial lake" and came from India, perhaps via Portuguese "tanque". It may have some connection with:
*Some Indian language words similar to "tak" or "tank" and meaning "reservoir for water". In Sanskrit a holding pond or reservoir is called a "tadaka". Gujarati "talao" means "man-made lake". These uses of the word were incorporated into the English language.cite web
url=http://www.indoarch.org/arch_glossary.php
title=Architecture on the Indian Subcontinent - glossary
publisher=
accessdate=2006-12-18 ]
*The Arabic verb "istanqa`a" اِسْتَنْقَعَ = "it [i.e. some liquid] collected and became stagnant".

External links

* [http://www.cfsan.fda.gov/~lrd/FCF129.html Code of Federal Register - CFR Title 21 Part 129 This information is excerpted from the Code of Federal Register, a US Government document, it is published as part of the Federal Register, these are both government rules and guidelines of water tank design and suggestions for installations. This data is found incrementally in the CFR.]
* [http://openlearn.open.ac.uk/mod/resource/view.php?id=211605 Plastic tank failures]

* [http://www.amprotec.net/FDA-CFR%20Best%20Practice.htm} Storage tanks for food grade applications suggestions FDA Best Practice for Handling Tanks.

References