Inspection of Delamination Defect in First Wall Panel of Tokamak Device by Using Laser Infrared Thermography Technique

Abstract

First wall panels (FWPs), which adjoin the inner wall of the blanket modules in the vacuum vessel (VV) of a Tokamak device, are in structures of multilayer bounded together with a solid welding technique in order to perform its heat exchange, VV protection, and neutron breeding functions. The quality of the welding joint between layers is the key factor for FWP integrity. In order to conduct online inspection of the delamination defect in the FWPs, a nondestructive testing (NDT) method capable to detect delamination defect without accessing into the VV is required. In this paper, the feasibility of the laser infrared thermography (LIRT) testing NDT method was investigated experimentally for this purpose. To clarify its detectability under practical VV environment, inspections of several inspection modes were conducted based on the practical structure of FWP and VV of the EAST Tokamak device, i.e., modes of different distances and angles of FWPs toward the LIRT transducers. In practice, an LIRT testing system was established and several double-layered plate specimens with different artificial delamination defects were inspected under the selected testing conditions. Through thermography signal reconstruction, an image processing algorithm was proposed and adopted to enhance the defect detectability. From the results of different inspection modes, it was found that the angle factor may worsen the inspection precision and reduce the detectability for delamination defects in case of big defect depth-to-width ratio, even though the LIRT method is still applicable for inspection of relative large defects in FWP. Finally, the detectability in different inspection modes was clarified, which proved the feasibility of LIRT for FWP online inspection.

Inversion Technique for Quantitative Infrared Thermography Evaluation of Delamination Defects in Multilayered Structures

“…In this paper, the difference between the 1 st derivative signal from the defective target and the non-defective target, respectively, is selected as the characteristic signal. In pulse thermography, the 1 st derivative image provides abundant defect profile information and can be easily obtained by the thermographic signal reconstruction (TSR) method [16].…”

“…Fig.11 presents the extracted characteristic signal images of the biggest delamination in each specimen. The experimental details, extraction method and data have been carefully discussed [16].…”

“…Hence, laser thermography, as shown in Fig. 1, and its varied forms has been applied in many NDE scenarios such as, welds [16] and surface evaluation [17], mechanical equipment [18], composites structures etc. [19,20].…”

Studies on the infrared thermography technique for quantitative nondestructive evaluation of surface crack and delamination of multilayer structures

“…Recently, laser infrared thermography (LIT) with homogenous heat energy in a large region is proposed and validated by authors for inspection of delamination in layered structures. An inspection system is also developed based on the homogenous LIT technique for the in-situ inspection of the multi-layered first wall panels in the vacuum vessel (VV) of a Tokamak device [7][8][9] . Moreover, we have developed a laser array spots thermography (LAST) technique for the efficient inspection and evaluation of the surface cracks [10][11][12][13][14][15][16] .…”

Detectability evaluation of attributes anomaly for electronic components using pulsed thermography

“…IRT can be divided into two modes: active and passive. Active thermography encompasses different approaches according to the choice of heat source, including flash [18], laser [19], eddy current [20] and ultrasonic vibration. The heating mode differs between pulse, lock-in and modulated patterns, selected according to the appropriate type of defect.…”