Pg. 1,  2,  3

Polyurethanes are different from most plastic materials in that they can be tailored to meet the requirements of varying applications. Soft elastomers in flexible foams with low density are used in cushions and bedding. Tougher elastomers with higher densities are used for soles of shoes and boots. Rigid foams are used in construction, automobiles, furniture, boating, and many other applications.

History
The commercial potential of polyurethane chemistry was first recognized in the late 1930’s. I.G. Farben (Germany), ICI (U.K.), and du Pont (U.S.A.) developed a variety of applications. ICI introduced rigid foams in 1957. Production line insulation for refrigerators was introduced in 1963. In 1968 General Motors started making polyurethane bumpers for the Pontiac G.T.O. The combination of strength to support loads and thermal insulation made rigid polyurethane foam an attractive material for the cryogenic pipe supports required for major LNG facilities constructed in the 1970’s.

Pipe Support Design
The primary design parameter for the polyurethane component of a pipe support is density because this determines the compressive strength. As shown in Figure 1, on a log-log scale the relation between compressive strength and density is linear. Tensile strength also has a linear log-log relation to density. Because the loads on supports for larger diameter pipes are larger than those on polyurethane components in many other industrial applications, we require higher density materials. For components used in pipe supports with densities from 10 to 40 pounds/cubic foot (160 to 640 kg/cubic meter), particularly those produced in molds, the compressive strength is essentially the same in all directions. Thermal conductivity is another design parameter of concern for the pipe support designer. For rigid foam polyurethanes, thermal conductivity increases with density. Fortunately, the 10 to 40 pound-density materials are less sensitive to the choice of blowing agent and aging, two concerns for industries which use low density foams to achieve very low thermal conductivity.

(click here for a larger image)

Pg. 1,  2,  3