Johnathan Hernandez, Quentin Fouliard, Khanh Vo, Seetha Raghavan,
Detection of corrosion under insulation on aerospace structures via pulsed eddy current thermography,
Aerospace Science and Technology,
Volume 121,
2022,
107317,
ISSN 1270-9638,
https://doi.org/10.1016/j.ast.2021.107317.
(https://www.sciencedirect.com/science/article/pii/S1270963821008270)
Abstract: Corrosion degradation mechanics play a significant role in the safe operability and availability of aircraft components. To defend against corrosion, coating systems and insulation are used on aircraft structures to protect them from corrosion promoters. Due to this layer of protection, corrosion under insulation (CUI) and early onset corrosion remain difficult to characterize on exterior aircraft structures in a timely manner. Pulsed eddy current thermography (PECT) shows promise in enabling the detection of corrosion on aircraft while rapidly scanning large areas. However, the limitations of this technique and appropriate measurement parameters have yet to be explored on painted aluminum aircraft structures. In this work, pulsed phase thermography using electromagnetic coil excitation was performed on painted corroded aluminum samples to capture thermal transient localized responses for defect characterization. Defects ranging from 0.4 mm to 5 mm in a painted corroded aluminum sample were identified using PECT through the capture and analysis of changes in phase and amplitude. The results show that saturation of thermal response from larger defects overshadows smaller outlying defects, suggesting the need for an alternative approach to characterizing defects smaller than 1 mm in diameter. Despite inherently longer measurement times, phase measurements during the cooling period result in higher sensitivity thus enabling detection of smaller defects. This study helps to define a range of operation and measurement parameters for PECT to be effective as a means for corrosion detection on aluminum painted panels. The outcomes pave the way to further extend PECT as a non-destructive, non-contact method for detection of CUI.
Keywords: Corrosion under insulation; Aircraft panel; Pulsed eddy current; Phase analysis; Non-destructive evaluation