Api tanks

ESDEP WG 15
STRUCTURAL SYSTEMS: MISCELLANEOUS - Lecture 15C.1:
OBJECTIVE/SCOPE:
The lecture describes the basic principles used in the design of tanks for the storage of oil or water. It covers the design of vertical cylindrical tanks, and reference is made to the British Standard BS 2654 [1] and to the American Petroleum Industry Standard API650 [2].
PREREQUISITES
None.
RELATED LECTURES
Lecture 8.6: Introduction to Shell Structures
Lecture 8.8: Design of Unstiffened Cylinders
SUMMARY
Welded cylindrical tanks are commonly used to store oil products or water.
The principal structural element of these tanks is a vertical steel cylinder, or shell, which is made by welding together a series of rectangular plates and which restrains the hydrostatic pressures by hoop tension forces. The tank is normally provided with a flat steel plated bottom which sits on a prepared foundation, and with a fixed roof attached to the top of the shell wall.
This lecture explains the design basis for the structural elements of cylindrical tanks and illustrates the arrangements and the key details involved.
1. DESIGN OF WELDED CYLINDRICAL TANKS
1.1 General
Oil and oil products are most commonly stored in cylindrical steel tanks at atmospheric pressure or at low pressure. The tanks are flat bottomed and are provided with a roof which is of conical or domed shape.
Water is also sometimes stored in cylindrical steel tanks. When used to store potable water they are of a size suitable to act as a service reservoir for a local community; they have a roof to prevent contamination of the water. Cylindrical tanks are also used in sewage treatment works for settlement and holding tanks; they are usually without a roof.
The sizes of cylindrical tanks range from a modest 3m diameter up to about 100m diameter, and up to 25m in height. They consist of three principal structural elements - bottom, shell and roof.
For petroleum storage, the bottom is formed of steel sheets,