Monitoring outer surface temperature to assess thermal fatigue at T-junctions

Mixing fluids at different temperatures in T-junctions can lead to the formation of cracks from thermal fatigue. In this study, mock-up tests and analyses were conducted to develop a monitoring procedure for the temperature fluctuation on the pipe inner surface using temperature measurements of the outer surface at a T-junction. In the tests, the temperatures on the inner and outer surfaces at the T-junction were measured with thermocouples and thermography, respectively. Both the distributions of the time- averaged temperature and the temperature fluctuation range on the outer surface measured by thermography were similar to those on the inner surface measured with the thermocouples. The temperature fluctuation range and accumulated fatigue damage on the inner surface were estimated using the developed inverse analysis. Since the measured temperature on the outer surface includes noise for the high frequency component, the cut-off frequency should be determined prior to making the inverse analysis. The prediction accuracy, however, can be improved for high temperature conditions such as actual plants.