The cost of the insulation of low-temperature pipe is usually of the same order of magnitude as that of the pipe itself. Also, since the diameter of the insulated pipe may be twice or three times that of the pipe itself, the designer must provide sufficient space for the complete assembly.
Vapor barriers are essential for low-temperature pipes. In contrast to the water vapor path through the insulation of a refrigerated building which enters the insulation from the warm outdoors and eventually is extracted by the coils
in the refrigerated space, there is no outlet for the water vapor that enters pipe insulation. For this reason, the water vapor retardation should be as effective as possible for prolonging the life of the insulation. Some specifications for insulation on low-temperature pipe include.
• Cover the insulation with vapor-retarding jackets with a perm rating of 0.02 or less.
• The supports must not be in contact with the piping.
• The thickness of insulation must be sufficient to maintain the insulation surface temperature above the dewpoint. Isocyanurate or Styrofoam are recommended.
• Since the cladding, insulation, and the pipe all have different coefficients of thermal expansion, double-layer application is suggested for extremely low temperature insulation with staggered joint construction.
• Pack contraction joints with flexible insulation material.