Turbine Blade Health Management
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The turbine blades in this IPA application were designed for an operational life of 40,000 hours. Implementing a life extension program through a combination of repair and IPA testing could double the useful lives of the blades. The benefit to the operating utility was significant because the majority of turbine blades tested were reused. This provided a significant cost savings through deferred replacement and a positive environmental impact due to reuse and reduction.
- IPA Results Correlate to Predictive Modeling
- IPA Able to Resolve the Material Refurbishment Process
- IPA Able to Resolve Material Change With Operating Hours
- Empirical Behavior Model can be Developed
- Characterization of Internal Cracking cannot be detected without Internal Probes
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Key Observations and Conclusions.
IPA Results Correlate to Predictive Modeling
IPA-S measurements showed trends in varied blade material condition that generally agree with expectations based on predictive thermal and structural model data. The blade leading edge and trailing edge at its mid-length showed S parameter response consistent with long term exposure to high temperature, the concave surface at mid-length measured relatively unchanged, and the blade root and trailing edge near the root showed long-term trends consistent with mechanically induced stress. Because the data represent only a snap-shot in the overall lifetime of each blade, these observed trends must be interpreted as hypothesized and un-validated behavior. However, the results are significant because they represent valuable correlation data on material condition, obtained prior to the presence of detectable defects. No other non-destructive technique can provide the same insight.
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IPA Able to Resolve the Material Refurbishment Process
The IPA-S measurements were sensitive to material condition differentiated by the refurbishment process. The blade refurbishment response may be indicative of material microstructure repair. To quantify the extent of this rejuvenation, destructive material analyses could be conducted and compared to the IPA measurements.
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IPA Able to Resolve Material Change With Operating Hours
General S parameter trends with operating hours were evident, with their direction and magnitude depending upon the material degradation mechanism which predominates. For example, the IPA data are consistent with the leading edge degradation being dominated by thermal degradation and the root and trailing edge near the root predominantly mechanical stress. Competing effects are likely occurring and data interpretation requires additional knowledge made available through destructive analyses, prior testing, or design analyses.
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Empirical Behavior Model can be Developed
An approximate empirical model was presented that demonstrates how a specific blade location can be characterized over its lifetime using IPA measurements. The figure also revealed that to begin building a reliable predictive model, additional data is required. Through development and design of a specific application, blade components could be monitored with IPA measurements on an ongoing basis throughout their life cycle. The results would in turn be evaluated with the customer to validate that the IPA measurements correlate to data obtained via destructive analyses as well as predicted behavior from design modeling. After the application is in place on an ongoing basis, its' use as a decision-making tool will become increasingly reliable as additional blades are characterized.
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Characterization of Internal Cracking cannot be detected without Internal Probes
The presence of cracking in two blades could not be resolved using IPA-S at external locations where internal cracks are present. Instead, internal surface probe techniques are likely to be required in this case. The development of an appropriate internal probe technique was beyond the scope of this project.
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