| Several industries rely on the use of refractory furnaces, including iron and steel processing and glass manufacturing. The goal in each of these industries is to keep the furnaces in operation as much of the time as possible with minimum time off-line for repair or replacement. Currently, empirical techniques (visual inspection and measurement of external wall temperatures) are used to monitor the integrity of the walls. A more precise and reliable method for measuring wall thickness, which could be used while the furnace remains on-line and in operation, would aid in determining more accurately when maintenance or replacement of the refractory is required. The goal of this research project was to develop a method for monitoring the thickness of refractory furnace walls while the furnace remains in-service. The chosen method, impact-echo, is a nondestructive testing technique which uses transient stress waves and was originally developed for use on concrete structures. Three-dimensional dynamic finite element simulations were used to gain an understanding of the propagation of elastic stress waves in temperature gradients, at interfaces between solid and liquid materials and within the unique geometry of refractory blocks. Experimental instrumentation was developed that could withstand the high temperature environment that may be encountered surrounding refractory furnaces. Two refractory furnaces were then tested and the wall thickness measured: one off-line, cooled and ready for replacement and one at high temperature during its operation. The results showed that the impact-echo method could be used successfully to monitor the wall thickness of refractory furnaces. The effects of uncertainties in wave speed and material properties on the accuracy of the measured wall thickness are discussed. |
