The thermal performance of candidate pipe insulation systems for the sodium piping at the Fast Flux Test Facility (FFTF) in Richland, Wash., has been tested at pipe temperatures up to 838.7 K (1050°F) using a 40.64-cm (16 in.) pipe test rig. Where applicable, procedures outlined in the ASTM Test for Thermal Conductivity of Pipe Insulation (C 335-69) were followed. These tests have demonstrated the feasibility of measuring thermal performance using large-diameter, guarded pipe test systems. To compare and evaluate the large-diameter pipe test results, the thermal performance of these insulations was also measured by an independent testing laboratory on a 7.62-cm (3 in.) pipe test apparatus.

Mineral wool, calcium-silicate, and aluminum-silica refractory fiber blanket-type insulations were evaluated on both the 40.64-cm (16 in.) and 7.62-cm (3 in.) pipe test apparatus. A contractor-installed calcium silicate and a duplex calcium-silicate-mineral wool system were also tested on the 40.64-cm (16 in.) pipe test apparatus to investigate thermal performance resulting from different installation procedures.

These measurements of the thermal performance of insulations assembled on large-diameter testing apparatus have been shown to be both feasible and informative. In cases where the insulation can be installed in a seam-free manner, that is, few cracks and gaps, the thermal properties are in excellent agreement with those measured on the standard 7.62-cm (3 in.) pipe test system.

In cases where installation is difficult and seam cracks and gaps occur, the additional heat losses can be evaluated on the large-diameter pipe test apparatus.