The use of steel has grown rapidly over the past decades. However, corrosion under coating detection still presents challenges for nondestructive testing (NDT) techniques. One of such challenges is the lift-off introduced by complex structures. Inaccessibility due to structure leads corrosion to be undetected, which can lead to catastrophic failure. Furthermore, lift-off effects reduce the sensitivities. The limitations of existing NDT techniques heighten the need for novel approaches to the characterization of corrosion. This paper begins with a discussion of the challenges associated with corrosion detection of metal under coating. Secondly, reviews are given of the most NDT methods used for the detection of corrosion under coating. The different techniques based on nondestructive testing methods such as ultrasonic, acoustic, electromagnetic, radiographic, and thermographic have been detailed out. This review presents the significance and advantages provided by the emerging NDT techniques. In the end, the trends and identified problems are summarized.

中文翻译：

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涂层下金属腐蚀评估的无损检测

在过去的几十年中，钢铁的使用量迅速增长。然而，涂层下腐蚀检测仍然对无损检测 (NDT) 技术提出了挑战。其中一项挑战是复杂结构引入的升空。由于结构原因无法接近导致无法检测到腐蚀，从而导致灾难性故障。此外，剥离效应降低了灵敏度。现有无损检测技术的局限性增加了对腐蚀表征的新方法的需求。本文首先讨论与涂层下金属腐蚀检测相关的挑战。其次，回顾了用于检测涂层下腐蚀的大多数无损检测方法。基于无损检测方法的不同技术，如超声波、声学、电磁、射线照相和热成像已经详细说明。本综述介绍了新兴 NDT 技术的重要性和优势。最后，总结了趋势和发现的问题。