Thermocouple Degradation data in Corrosive environments

Thermocouples are widely used in industrial applications due to their robustness, low cost, reliability and ability to survive in harsh environments. However, these thermocouples are prone to failure in a highly acidic medium such as nuclear fuel reprocessing plants. This paper investigates the degradation phenomenon and its effect on measurement accuracy when a thermocouple with mechanical damage to the protective sheath is placed in a corrosive media. This work takes a novel approach of micro-machining a small hole in the thermocouple to mimic sheath damage, which enables the corrosive medium to directly interact with the sensing material, i.e., Chromel and Alumel. The thermocouples with artificially induced sheath defects are then subjected to ageing in different concentrations of acidic media at a constant temperature, while degradation data i.e. temperature is read and logged. The time-to-failure data of thermocouples at each concentration is analyzed using the Weibull distribution. Inverse Power Law is then used to model the life-stress relationship under a ruptured sheath condition. The study also explores the correlation between the residual life and the position of simulated ruptures. ANOVA is employed to test the hypotheses regarding the influence of rupture position on thermocouple performance. The analysis results show that the location of damage is statistically significant in determining the thermocouple’s residual life under damaged sheath condition.