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Chemistry
Rigid polyurethane foams have a relatively large amount of cross-linking as the foam expands. Suppliers of the chemicals control the degree of cross-linking by functionality (higher functionality produces more cross-links) and molecular weight of the components in the blend. Figure 2 shows a photomicrograph image of a cut piece of rigid foam. The closed cells formed during cross-linking can be seen. These rigid cells provide the strength and the interior space provides low thermal conductivity. Water can be used as the blowing agent for foam in this 10 to 40 pound-density range. This avoids the need to use chlorofluorocarbons which were so important in the production of 1 to 2 pound-density insulation prior to modern environmental regulation.

Permeability
The water vapor permeability of rigid polyurethane foam is low but pipe support applications often have a very large temperature differential between the cryogenic fluid inside the pipe and the climate outside the insulating system. For this reason, pipe support designers use impermeable facings (galvanized, rolled shields), with low-permeable coatings and linings to separate the moisture-laden air outside from the polyurethane component which is in contact with the cold pipe. An effective moisture barrier on the warm side is particularly important for this type of application.

Facilities
Piping Technology and Products has a complete manufacturing facility for production of polyurethane components required for pipe supports. We invite our customers to visit our facility and observe the fabrication of insulated pipe supports of all types. Our engineers will be happy to discuss the use of rigid foam polyurethane for cryogenic supports.

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