It is known to use various superalloy materials, such as cobalt or nickel-based superalloys, for making blades, vanes and other components for power generating turbines, propulsion equipment, etc. These turbines can operate at relatively high temperatures and are generally protected by a series of protective coatings. The coatings may comprise layers of metallic base coats, thermally grown oxide layers, as such layers grow in service-run components and a final ceramic thermal barrier coating (“TBC”). Long-term exposure of these ceramic coatings to the hostile, high temperature, abrasive environment in which such turbines typically operate can cause phase destabilization, sintering, microcracking, delamination and ultimately spallation within the coating layers, exposing the superalloy component and possibly resulting in rapid degradation or failure and potentially requiring costly and burdensome repairs.
U.S. patent application Ser. No. 10/610,214 titled “Method And Apparatus For Measuring On-Line Failure Of Turbine Thermal Barrier Coatings” describes an infrared (IR)-based system configured to non-destructively measure the radiance of a rotating turbine component (e.g., a blade) in a gas turbine in the context of monitoring the formation and progression of TBC defects where images of relative high spatial resolution are needed but where accurate absolute temperature information may not be needed. The foregoing patent application is a Continuation-In-Part of U.S. application Ser. No. 09/470,123, and each is commonly assigned to the assignee of the present invention and herein incorporated by reference in their entirety.
U.S. Pat. No. 7,422,365 describes a thermal imaging system that purportedly uses an in-field-of-view electronically controlled heat source having a known and fixed temperature for generating a calibrated temperature map of a scene. However, such an approach would not be a feasible approach in a high temperature combustion environment of a turbine, where operating temperatures change as a function of the load of the turbine. Moreover, the system described by U.S. Pat. No. 7,422,365 appears to be limited to thermally imaging non-moving objects. Accordingly, such a system would not be suitable for temperature mapping a rotating turbine component.
It would be desirable to acquire two-dimensional IR images of the rotating turbine component to consistently provide accurate absolute temperature measurements of the component. However, temperature measurement errors can be introduced due to various factors, which under prior techniques have not been appropriately accounted for. For example, the emissivity of the TBC can change as a function of wavelength, temperature, age, contamination, etc. Additionally, it would be desirable to account for thermal emissions that may be transmitted through the TBC from subsurface coatings and/or thermal gradients than can arise in a cooled turbine component. Accordingly, it is desirable to provide a system and techniques that overcome the foregoing issues.