Steel tanks are defined as vessels made of steel plates, utilized for storing various liquids such as water, petroleum, diesel, and kerosene oil. These tanks may be either placed on the ground or elevated on towers. When situated on the ground, they are supported either by cement concrete foundations or steel grillage foundations.
Tanks with a vertical cylindrical surface, flat bottom, and ground support are referred to as surface tanks. On the other hand, tanks elevated on towers to provide necessary pressure heads are known as elevated steel tanks, often used in conjunction with pumping stations.
Design of Steel Tanks
Steel tanks are designed by the code of practice for the use of steel in gravity water tanks, specified in IS: 805-1981. The minimum thickness of the steel plates used in tank construction is 6 mm, except for the roofs. In cases where the tank’s contents contain salts, the thickness of the steel plates should be increased by 1.5 mm to account for corrosion concerns.
Rectangular Steel Tanks
Rectangular steel tanks, depicted in Fig. X, are constructed from steel plates with flat bottoms. The widths of these plates typically range from 1.20 m to 1.30 m, depending on availability, with a minimum thickness requirement of 6 mm. Bottom plates are arranged transversely, turned up at the ends, and accompanied by tee sections on the inner side to form butt joints with the side plates of the tanks.
Elevated Circular Steel Tank
To ensure structural integrity, the plates used in the cylindrical shell are shaped to suit the tank’s curvature, with overlapping courses inside and outside. The minimum thickness of plates in the suspended bottom should match that of the lowest course of the cylindrical part of the tank. Additionally, the plates are sheared or planed to a suitable bevel along the edges to facilitate caulking.
Pressed Steel Tanks
Pressed steel tanks have gained popularity due to their ease of erection, transport, standard construction, dismantling, and re-erection capabilities.
Permissible Stresses
Permissible stresses, as outlined in IS 800-1984, serve as the fundamental guidelines for tank design and construction, ensuring structural reliability and safety.