Cylindrical steel tanks



Types of steel tanks

Stiffening of membrane of single deck floating roof

Methods of erection

Typical damages of aboveground steel tanks

Inspection of steel tanks

Realized projects of tanks

Typical drawings of tanks


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Generally, the double bottoms of cylindrical steel tanks could be classified by following criteria:
a) according to used material for construction for the second (complementary) bottom:
- from steel;
- from polymer material.

b) according to the kind of the system which detects leaks:
- passive system - it means that there are pipes under internal (upper) bottom, by which the product felt among the two bottoms, comes out to the spot determined for this purpose and easily accessible. The liquid movement is due to its own weight. On this reason detecting of leakage has delay;
- continuously activated vacuum system - pressure between the bottoms is decreased. The system observes without interruption the increase of the pressure between the two bottoms. The discovery of the breakage on the bottom is immediate.

c) according to position of
the second (complementary) bottom:
- above the basic steel plates;
- under
the basic steel plates.

If it is necessary to change whole area of the bottom of tanks in service, or new tanks will be erected, it is recommended to mount leak detection systems. They ensure continuous control of entirety of the bottom and minimize likelihood of soil pollution.
The systems for leaks detection are obligatory for the tanks where ecologically dangerous products are stored. These systems must assure canal for outflow of the liquid toward to the spot where the liquid will be found easily and the result can be shown out of the tank.

In American standard API Std. 650 are shown various decisions of double bottoms :

First type of double bottom of aboveground steel tanks Second type of double bottom of aboveground steel tanks
Thirdth type of double bottom of aboveground steel tanks Fourth type of double bottom of aboveground steel tanks
Various types of double bottoms of aboveground steel tanks

Contemporary tendency in Europe leads to mounting of additional (second) steel bottom and active vacuum system. Level of pressure between steel bottoms is decreased with vacuum pump and it is continuously monitored. When pressure going to be height it is sign that one of the bottoms is punctured.

This kind of monitoring is one that guarantees uninterrupted control and immediate reaction if there are holes on the bottoms.

Joint between upper bottom and shell has been made with welding to them of angle section with low thickness . The thickness of angle section should be equal to thickness of the upper bottom. This guarantees comparatively easy little movements and bending of angle section.

It is recommended minimum thickness of upper bottom to be t = 6 mm.

Double bottom of aboveground steel tank with active vacuum system
Double steel bottom with active vacuum system

The sheets of two bottom are separated with wire net putted between them. Diameter of these rods is approximately 3 – 4 mm. The steel net prevents full contact between steel plates. On this reason is impossible creation of areas where movement of liquids and gases is not free.

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