Implementation and application of NDE on ceramic candle filters

A nondestructive evaluation (NDE) technique has been developed to determine the deterioration and remaining life of full-size ceramic candle filters used at the Power System Development Facility (PSDF) in Alabama. Ceramic candle filters are hollow cylindrical structures made of porous ceramic materials used in advanced coal-fired power generation systems. They protect power plant\u27s gas turbine components from damage due to erosion. In general, advanced coal-fired power systems operational conditions include extreme thermal/pressure environment and vibration-induced stresses over a great period of time. The knowledge of the dynamic behavior of ceramic candle filters is essential and can be used to measure changes in the mechanical properties of the filters, nondestructively. The NDE technique developed can help ensure the efficiency and safe performance of the ceramic candle filters and the power plant systems. More than 140 candle filters have been nondestructively evaluated and the results are presented in this study. Fifty-two of these filters having various in-service exposure times were used at the PSDF and the rest were new filters. The candle filters are tested using a laser/accelerometer setup with various boundary conditions. The evaluation of experimental results is processed using digital signal analysis techniques including various forms of data transformation. Finite element models are built to calculate the filter\u27s dynamic response. A general Timoshenko beam equation that includes different boundary restraints is derived to simulate the dynamic behavior of the candle filters. Results from this study indicate that dynamic characterization is a feasible NDE technique for studying structural properties of ceramic candle filters. It has been shown that the vibration signature could be used as a tool to evaluate both the material properties of the ceramic candle filters and the boundary restraints. The degradation of the filters due to long working hours is reflected in the shift of natural vibration frequencies. These shifts are due to changes in structural properties such as stiffness, which are directly related to the Young\u27s modulus of the candle filters. A relationship between the stiffness reduction and the reliability of the ceramic candle filters due to exposure hours is presented. Fatigue results from the present study show the importance of considering the operational vibration as well as the temperature gradient due to back-pulse as the factors that may cause failure of the ceramic candle filters