BS EN 14620-1:2006 pdf download – Design and manufacture of site built, vertical, cylindrical, flat-bottomed steel tanks for the storage of refrigerated, liquefied gases with operating temperatures between 0 °C and p165 °C — Part 1: General
4 Concept selection
4.1 Types of tank
4.1.1 Single containment
A single containment tank shall consist of only one container to store the liquid product (primary liquid container). This primary liquid container shall be a self-supporting, steel, cylindrical tank.
The product vapours shall be contained by:
either the steel dome roof of the container;
or, when the primary liquid container is an open top cup, by a gas-tight metallic outer tank
encompassing the primary liquid container, but being only designed to contain the product
vapours and to hold and protect the thermal insulation.
NOTE 1 Depending on the options taken for vapour containment and thermal insulation; several types of single containment tanks exist.
A single containment tank shall be surrounded by a bund wall to contain possible product leakage.
NOTE 2 For examples of single containment tanks, see Figure 1.
4.1.2 Double containment
A double containment tank shall consist of a liquid and vapour tight primary container, which itself is a single containment tank, built inside a liquid-tight secondary container.
The secondary container shall be designed to hold all the liquid contents of the primary container in case it leaks. The annular space, between the primary and secondary containers, shall not be more than 6,0 m.
NOTE 1 The secondary container is open at the top and therefore cannot prevent the escape of product vapours. The space between primary and secondary container can be covered by a “rain shield” to prevent the entry of rain, snow, dirt etc.
NOTE 2 For examples of double containment tanks, see Figure 2.
4.1.3 Full containment
A full containment tank shall consist of a primary container and a secondary container, which together form an integrated storage tank. The primary container shall be a self-standing steel, single shell tank,holding the liquid product.
The primary container shall:
either be open at the top, in which case it does not contain the product vapours
 or equipped with a dome roof so that the product vapours are contained.
The secondary container shall be a self-supporting steel or concrete tank equipped with a dome roof and designed to combine the following functions:
 in normal tank service: to provide the primary vapour containment of the tank (this in case of open top primary container) and to hold the thermal insulation of the primary container;
 in case of leakage of the primary container: to contain all liquid product and to remain structurally vapour tight. Venting release is acceptable but shall be controlled (pressure relief system).
The annular space between the primary and secondary containers shall not be more than 2,0 m.
NOTE 1 Full containment tanks with thermal insulation placed external to the secondary container are also covered by these requirements.
NOTE 2 For examples of full containment tanks, see Figure 3.
4.1.4 Membrane containment
A membrane tank shall consist of a thin steel primary container (membrane) together with thermal insulation and a concrete tank jointly forming an integrated, composite structure. This composite structure shall provide the liquid containment.
All hydrostatic loads and other loadings on the membrane shall be transferred via the load-bearing insulation onto the concrete tank.
The vapours shall be contained by the tank roof, which can be either a similar composite structure or with a gas-tight dome roof and insulation on a suspended roof.
NOTE For an example of a membrane tank, see Figure 4.
In case of leakage of the membrane, the concrete tank, in combination with the insulation system,shall be designed such that it can contain the liquid.