Mineral insulated heating cable sheath temperature test methods and design optimization techniques

Abstract

Methods to measure and predict maximum sheath temperatures of mineral insulated (MI) heating cable vary by testing agency, standards writing body and manufacturer. This has resulted in confusion in the industry about the best approach to predict sheath temperatures of MI heat tracing cables. This paper presents an analysis of two different test methods for sheath temperature prediction. The test methods studied are commonly known in the industry as the ‘pipe test’ and the ‘plate test’. The paper demonstrates that the pipe test has significant variation in the measured sheath temperatures in successive test runs while the plate test produces a much more repeatable and accurate result. The paper proposes the use of the plate test as a preferred method to measure and predict maximum sheath temperature. As a related topic, the paper also presents general considerations for optimizing designs that will reduce costs and improve constructability of electrical heat tracing designs using MI heat tracing cables. A case study is presented to demonstrate application of these design optimization techniques.