NONDESTRUCTIVE EVALUATION OF CERAMIC CANDLE FILTERS
Nondestructive evaluation (NDE) techniques have been used to reduce the potential mechanical failures and to improve the reliability of a structure. Failure of a structure is usually initiated at some type of flaw in the material. NDE techniques have been developed to determine the presence of flaws larger than an acceptable size and to estimate the remaining stiffness of a damaged structure (Chen, et. al, 1995). Ceramic candle filters have been tested for use in coal-fueled gas turbine systems. They protect gas turbine components from damage due to erosion. A total of one hundred and one candle filters were nondestructively evaluated in this study. Ninety-eight ceramic candle filters and three ceramic composite filters have been nondestructively inspected using dynamic characterization technique. These ceramic filters include twelve unused Coors alumina/mullite, twenty-four unused and fifteen used Schumacher-Dia-Schumalith TF-20, twenty-five unused and nine used Refractron 326, eight unused and three used Refractron 442T, one new Schumacher-T 10-20, and one used Schumacher-Dia-Schumalith F-40. All filters were subjected to a small excitation and the dynamic response was picked up by a piezoelectric accelerometer. The evaluation of experimental results was processed using digital signal analysis technique including various forms of data transformation. The modal parameters for damage assessment for the unexposed (unused) vs. exposed (used) specimen were based on two vibration parameters: natural frequencies and mode shapes. Finite Element models were built for each specimen type to understand its dynamic response. Linear elastic modal analysis was performed using eight nodes, three-dimensional isotropic solid elements. Conclusions based on our study indicate that dynamic characterization is a feasible NDE technique in studying structural properties of ceramic candle filters. It has been shown that the degradation of the filters due to long working hours (or excessive back pulsing conditions and high temperature transient) could be reflected from the shift of vibration frequencies. These shifts are due to changes in structural properties such as stiffness, which are directly related to the Young's modulus of the candle filters. Further studies are necessary in implementing and verifying the applicability of dynamic NDE characterization methods for actual in-situ conditions, and in establishing a systematic testing procedure for field applications. Also investigations on the filter's natural frequency due to the effect of dust cake or due to the change of boundary conditions may provide insight as to how the filter will perform in the field.
- Research Organization:
- Federal Energy Technology Center Morgantown (FETC-MGN), Morgantown, WV (United States); Federal Energy Technology Center Pittsburgh (FETC-PGH), Pittsburgh, PA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- FG21-97MC34160
- OSTI ID:
- 780456
- Report Number(s):
- DE-FG21-97MC34160-01; TRN: AH200120%%110
- Resource Relation:
- Other Information: PBD: 1 Sep 1999
- Country of Publication:
- United States
- Language:
- English
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