Several ASTM material standards for pipe insulations require thermal performance data for systems in which pipe surface temperatures are below room temperature. ASTM Test Method for Steady-State Heat Transfer Properties of Horizontal Pipe Insulation (C 335) and ASTM Test Method for Steady-State Heat Transfer Properties of Pipe Insulation Installed Vertically (C 1033) are the only ASTM pipe insulation test methods, but these are used above room temperature. This paper describes proof-of-concept tests near room temperature on a new pipe insulation tester for evaluating pipe systems operating below room temperature.
The pipe insulation test specimen is inside an electrically heated cylindrical screen which is guarded by a fluid-cooled copper shell with intervening insulation. The main heat flow is radially inward through the test specimen to a central fluid-cooled tube. By matching the temperature of the heater to that of the guard, unwanted radial heat flow to or from the screen heater is minimized. Assuming only inward radial heat flow, a preliminary combined uncertainty was estimated at about ±0.8%.
The new tester has yielded results on three types of pipe insulation: fiberglass, polyisocyanurate foam, and elastomeric foam. Results on the latter two types were compared with results on board specimens of similar materials using ASTM Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus (C 518).
Finite difference thermal modeling using the HEATING7 program was performed to assess the potential for systematic errors due to deviation from purely radial heat flow. The modeling results showed this type of error to be less than 0.5% for the prototype tester. Modeling was also used to identify design parameters for future testers that would accommodate different pipe sizes and insulation thicknesses and would operate at other temperatures. Designs are in progress to allow use of the tester to pipe surface temperatures as low as -190 °C (-310 °F).