A New System for Defects Inspection of Boiler Water Wall Tubes Using a Combination of EMAT and MFL

As the main part of the boiler, the water wall tube which runs on hazardous environment may lead to serious boiler accidents, causing of the tubes’ failure. For this reason, inspecting the defects on the water wall tube comprehensively is extremely required. However, single traditional NDT inspection method is limited in terms of the ability of identifying different kinds of defects. In order to meet the requirement of full-scale inspection, in this paper, a new system is designed using a combination of the electromagnetic acoustic transducer (EMAT) and the magnetic flux leakage (MFL) technology. In this new system, EMAT takes advantage of the horizontal magnetic field that is used for MFL detection to excite the ultrasound. Under this circumstance, the excitation mechanism of the EMAT is different from the general mechanism that is mainly based on the Lorentz-force. After experiment, the new system can effectively measure the remaining wall thickness and identify different kinds of defects including pinholes and circumferential cracks with the sensor being moved outside the tubes.