Fly ash erosion is leading cause of boiler tube failure in a PC boiler. The Pri. RH and Economizer, especially, are plagued with fly ash erosion problem, so shields or baffle plates, mitigating fly ash erosion, are installed on the areas to prevent a boiler tube failure. However, the tube failure problems caused by fly ash erosion cannot be eliminated only by the solution, because each PC boilers are different in flue gas flow pattern to one another and erosion can be severe at the unsuspected zone. The problem is caused by asymmetric internal flow velocity and local growth of flue gas velocity. For these reasons, clearly defining the flow pattern in PC boiler is important to solve the tube failure caused by fly ash erosion, so, CAVT is needed to apply to the fly ash erosion problem. This study carries out CAVT on the Hadong #2 PC boiler and validates probability of applying CAVT to the conventional PC Boiler