Abstract

Thermal History Paint (THP) is a new technique used to measure temperature in the harsh operating conditions inside gas turbines or other machinery. It is applied to the surface of a test component and upon heating, changes permanently according to the maximum temperature of exposure. After operation, the THP is read-out at many locations across the surface. Through calibration, the measurements are translated to temperature to deliver high-resolution thermal maps.

The technique has been recently demonstrated in short-term development tests for the validation of thermal models in the design phase. It has been shown that the THP has several advantages compared to traditional temperature measurement techniques. In comparison to thermocouples and thermal crystals the paint can acquire measurements at many locations without the challenging installation limitations. THP has been shown to have greater durability than thermochromic paints and can be applied to measure the temperature non-destructively.

The increased durability opens the possibility that the THP could be applied to an operational component and operated through its lifetime and measured at maintenance intervals to monitor the maximum temperature of the component. This would improve run, repair and replace decisions, reducing life cycle costs. For example, rotor discs in industrial gas turbines are critical components that are expensive and time-consuming to replace and experience creep when exposed to excessive temperatures.

This paper provides the first investigation into the behaviour of the THP for extended operational exposures, with rotor discs as an example application. The objective was to understand whether the THP could be used for temperature measurements after such long exposures and, if so, how it would be calibrated. The results show that the THP exhibits good durability, enabling measurements up to 450°C after 7200 hours of exposure, covering the useful range for rotor disc applications. In addition, the behaviour of the THP allows the effect of time to be neglected for such long exposures, simplifying the calibration procedure and enabling practical use in this application. The results indicate the viability of this new technique to capture temperature information that is not currently possible to acquire.

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