Sizing Subsurface Defects in Metallic Plates by Square Pulse Thermography Using an Oriented Gradient Map

Jing Xie,Xumei Gong,Guoming Chen,Weiping Huang,Changhang Xu

doi:10.3390/app6120389

Jing Xie, Xumei Gong + Show 3 more

Open Access

https://doi.org/10.3390/app6120389

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Abstract

We developed a new approach for sizing subsurface defects in the square pulse thermography of metallic plates by employing the oriented gradient of histograms. To size defects with high accuracies is still a challenge in infrared (IR) thermography today. Especially for blurry defects, accurate sizing of them is difficult with existing methods. The oriented gradient of histograms, which is used in the successful probability of boundary (Pb) contour detector in natural image processing literature, is employed in this work to improve the sizing accuracy in square pulse thermography. Experiments on a corroded steel plate with flat blind holes have verified the effectiveness of the proposed approach to size defects. Experimental results show that the proposed approach can size distinct and blurry defects with high accuracies. Comparison research is also implemented between the proposed approach and other sizing methods. The comparison results show that the proposed approach is superior to existing methods.

Highlights

Defects in components can severely reduce the strength of a structure and may even result in a serious failure of the structure
Decision-making in maintenance management of a metallic component usually depends on the size information of the detected defects, and many Non-destructive testing (NDT) techniques have been used for defect sizing [3,4]
The sizing of defects in IR thermography has been researched for decades, sizing a blurry defect accurately is still a challenge

Summary

Introduction

Defects in components can severely reduce the strength of a structure and may even result in a serious failure of the structure. Non-destructive testing (NDT) is an essential technique to detect defects on surface and subsurface defects in components. The objectives of NDT include detection of defects and their characterization. Characterization of defects is to determine dimensions of defects, including depth, thickness, and size. The size of a defect is a critical factor which should be considered when evaluating the remaining useful life and the capacity of a metallic component. Decision-making in maintenance management of a metallic component usually depends on the size information of the detected defects, and many NDT techniques have been used for defect sizing [3,4]. Accurate sizing of defects is of great importance in NDT of metallic components

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