Pipe Insulation Testers

Abstract

The steady-state temperature distribution of two pipe insulation testers was modeled using the HEATING5 computer code available in the computers at Oak Ridge National Laboratory. One pipe tester, which conformed to the ASTM Test for Thermal Conductivity of Pipe Insulation (C 335-69) specification, had the core heater mounted inside a pipe around which the test insulation was placed. Guard heaters were employed to reduce unwanted axial heat conduction. Computer modeling showed that adjustment of the guard heaters was critical for short testers but not for long ones. A second tester, called an ideal tester, had no guard heaters, and only a simple, resistively heated core heater. The modeling results showed that there is a minimum length-to-thickness (L/S) ratio that will lead to a correct value of thermal conductivity calculated at the midplane of the tester. A peripheral heater with backup insulation can be added to the ideal tester to permit selection of the mean temperature of the test insulation. The ideal tester has the advantage over the ASTM design in that no balancing of heater power is required. A mock-up of the ideal tester was constructed and tested with calcium silicate pipe insulation. The core heater was a stainless steel screen, whose low thermal conductivity reduces end losses and permits use of a short tester (~0.9m). Measured values on asbestos-free calcium silicate show reasonable agreement with the data of others that contain asbestos.