In order to achieve the purpose of cold insulation, it is necessary to select the appropriate thickness and material of cold insulation. There are two important technical indicators for selecting cold insulation materials: first, the thermal conductivity, because the thermal conductivity is directly proportional to the heat loss of the pipeline. When there are multiple cold insulation materials to choose, the smaller the product of the thermal conductivity of the material and its unit volume price is, the more economical it is; second, the smaller the density of the material, the smaller the thermal conductivity. In addition, the mechanical strength, applicable temperature and flame retardancy of the materials are also the factors to be considered in the correct selection of cold insulation materials.

Attention should be paid to the following problems when using foam glass and polyurethane double layer cold insulation structure.

(l) Minimum thickness of cold insulation material. For foam glass, the minimum thickness is generally 60mm, otherwise the mechanical strength is difficult to guarantee.

(2) The temperature at the interface of the double-layer different material insulation layer shall be higher than 0.9 times of the safe use temperature of the outer insulation material, otherwise the thickness of the inner and outer layers shall be readjusted. When the outer layer is polyurethane, the temperature at the interface shall not be lower than - 58.5 ℃.

(3) The cooling loss shall not exceed the maximum value allowed by the standard. When the difference between the ambient temperature and the dew point temperature of the hottest month under the local meteorological conditions is less than or equal to 4.5 ℃, the maximum allowable cooling loss per unit area of the outer surface of the cold insulation layer is 23.6w/m2.

(4) The external surface temperature of the cold insulation layer shall be at least 1-3 ℃ higher than the local dew point temperature.