This document specifies the requirements for materials, design and installation of the insulation of refrigerated liquefied gas (RLG) storage tank systems. RLG storage tank systems store liquefied gas with a low boiling point, i.e. below normal ambient temperature. The concept of storing such products in liquid form and in non-pressurized tanks therefore depends on the combination of latent heat of vaporization and thermal insulation. Consequently, thermal insulation for RLG storage tank systems is not an ancillary part of the containment system (as for most ambient atmospheric hydrocarbon tanks) but it is an essential component and the storage tank system cannot operate without a properly designed, installed and maintained insulation system. The main functions of the insulation in RLG storage tank systems are: to maintain the boil off at or below the specified limits; to protect the outer tank components by maintaining them at or above their minimum design temperature; to prevent damage by frost heave of the foundation/soil beneath the tank base slab (in combination with the slab heating system for tanks resting at grade); to minimize condensation and icing on the outer surfaces of the tank. A wide range of insulation materials is available. However, the material properties differ greatly amongst the various generically different materials and also within the same generic group of materials. Therefore, within the scope of this document, only general guidance on selection of materials is given. NOTE For general guidance on selection of materials, see Annex A. This document deals with the design and manufacture of site built, vertical, cylindrical, flat-bottomed tank systems for the storage of refrigerated, liquefied gases with operating temperatures between 0 °C and -196 °C.