Eddy current thermography imaging for condition-based maintenance of overlay welded components under multi-degradation

This paper presents a new multi-wave imaging method for the condition-based maintenance of offshore hydraulic systems containing overlay welded components under multi-degradation. These components suffer from combined tribocorrosion interacting with static and cyclic loading, for which effective mathematical models have not yet been established. In this paper, we propose eddy current thermography imaging for real-time structural health monitoring to enable condition-based maintenance of these critical components. The main challenge for the structural health monitoring of these components is that defects are often embedded at the substrate-coating interfacial regions that have irregular shapes in anisotropic and heterogeneous material as a result of the welding process. The eddy current thermography imaging method utilizes coupled electromagnetic-thermal fields and diffusion waves for robust detection of these hidden defects. A mathematical algorithm and software based on the discrete Fourier transform of thermal videos registered by an infrared detector was developed to characterize and visualize defects. The detectability of this method was investigated using a real cobalt superalloy overlay welded onto a carbon steel piston rod, in which an artificial volumetric defect was made at the interfacial region. The probability of detection and condition-based maintenance using the detected defect data is discussed based on the P-F curve and the probability of failure graphs.