Conventionally in waste incineration facilities, the integrity of refractory walls of the boiler furnace is checked visually and/or by tapping. Tap inspection is widely applied because of its simplicity involving only hammer tapping and listening to the sound that is made. However, tap inspection also has problems in the case of the inspection area being of a great height and/or covering a large area, such as temporary scaffolding being expensive and criteria of inspection and interpretation of the results depending on individual inspectors. These issues are expected to be solved by Non-Contact Acoustic Inspection (NCAI). So, Mitsubishi Heavy Industries, Ltd., together with Toin University of Yokohama, trialed the use of NCAI for refractory wall inspections and assessed its performance in terms of identification of internal defects in test pieces into which simulated defects had been added. The results show that a 200-mm-square defect, which is the identifiable minimum defect size by the conventional tap inspection method, can be visualized and identified by the NCAI method from a distance of 10 m.
