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What are API Tanks?

API tanks are heavily used in the petroleum industry to hold and store oil and any other liquids. This article will detail what an API tank is, their construction, the different types, and the maintenance associated with the tanks.

Courtesy : https://advancetank.com/api_650/

What is an API tank?

An API tank, which stands for American Petroleum Institute- is a tank typically constructed of steel or carbon that has met the standards of construction and design of the American Petroleum Institute. They are typically used for the storage of oil, gasoline, and chemicals but may be used for the storage of any other type of liquid such as water. Internally, they may be aligned to accommodate whatever liquid is being stored. API tanks also have pumps that allow for the stored liquid to be accessed

API Tank Construction

An API tank may also be referred to as an AST, which stands for the above ground storage tank. Due to the large nature of an API tank, they are typically constructed in the location at which they will be used. Initially, a foundation is set in a place where the tank will be set, API tank foundations are usually made of concrete, crushed aggregate, or slab foundations. The tanks are typically field welded which means that the individual steel plates used to make the tank are constructed and welded on site. Once the construction of the major portions of the tank is complete, inner liners are completed depending on the fluid held by the tank as well as pumps and stairs as necessary.

API Tank Types

For their generalized uses, there are two main types of API tanks: API 620, API 650. Their usage is detailed below. API tanks may also be categorized by the roofing used in their construction.

API 620 tanks have large welds and are used mostly for high internal pressure fluids like natural gas that can be stored at relatively lower temperatures. They are required to be on either an elevated or flat bottom, with a tank minimum thickness of 3/16 of an inch. Typically the 620 is made of steel and must be properly inspected as directed by the API.

The other tank type is the API 650 which is heavily used in the oil and gas industry. They are required by the API to be above ground and are also required to have a minimum thickness of 3/16 of an inch. They are ideal for high temperature and low-pressure storage as opposed to that of the API 620.

API Tank Roofing

API tanks may have different roof types for which there are fixed-roof tanks, external floating roof tanks, internal floating roof tanks, and domed external floating roof tanks.

Fixed roof tanks are the most common tank type. They feature a roof that is completely closed off and welded shut. They are usually cone or dome-shaped roofs that seal off the tank. Usually, these tanks will also have a valve used to control and maintain the internal pressure of the tank.

External floating roof tanks feature a cylinder with an open-top while the roof floats on the surface of the stored liquid. They often protect from the discharge of the stored fluid and are considered cost-effective. They are equipped with a rim seal system to create a secure seal with the walls of the tank.

Internal floating roof tanks combine the mechanisms of a fixed and external floating roof. It is essentially a closed top cylinder with an internal floating roof.

The domed external floating roof combines an external floating roof with a domed fixed roof. The dome aids in blocking wind on the internal components of the tank.

Tank Maintenance



Maintenance of an API tank is crucial to ensuring proper functioning, personnel safety, and environmental safety. Ensuring that the welds are intact and not damaged is crucial and should be inspected often. Usually, visual inspection is appropriate, but other methods of NDE may be used. Similarly, depending on the inner lining of the tank, any damages should be noted and fixed before leaks occur. Leaks can be harmful to the environment and to personnel around the tank especially if the tank holds any harmful chemicals. Proper monitoring of the internal pressure and temperature of the tanks are also an essential part of maintaining the integrity and safety of an API tank.

By Michael Nasser of Punchlist Zero

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