This paper presents a critical review of the main sensing techniques considered for online monitoring of the integrity of alloys steel-made equipment used in process industry. This includes pipelines, tanks, electrical transformers and other metallic structures used in construction of buildings and bridges. Radio frequency (RF), Magnetic flux leak (MFL), ultrasonic-acoustic, fiber brag grating (FBG), thin layer strips, and photoacoustic sensors remain the main sensing techniques used or suggested for this purpose. However, despite lot of research works to improve their sensitivity and accuracy, further efforts are required to have them readily operational in the field especially for covering large volumes. This can be facilitated by the significant development carried out in various areas related to information technology (IT) and instrumentation, such as optical fiber sensors and self-powered wireless sensors under I4.0 paradigm. While optical fiber sensors, particularly FBG sensors, have the advantage to be scalable to cover wide areas with a few number of wires, they encounter the challenge of being not highly sensitive, especially for detecting degradations e.g. corrosion and erosion occurring at the opposite side of the steel structure. In addition, for such types of degradations, the fiber needs to be permanently and tightly connected to the structure, which is difficult to sustain. In addition, their proportional cost to the target sensitivity and resolution remains expensive. Wireless sensors equipped with ultrasonic sensors remain another tangible potential alternative for detecting internal corrosion and erosion of the structures if some pending issues relevant to power supply, using for instance energy harvesting, are sorted out. Overall, the existing technologies still suffer from a lack of sensitivity, accuracy, universality and/or cost effectiveness which justifies that more development efforts need to be done.

本文对用于在线监测过程工业中使用的合金钢制设备完整性的主要传感技术进行了严格的综述。这包括用于建筑物和桥梁建造的管道，储罐，电力变压器和其他金属结构。射频（RF），磁通量泄漏（MFL），超声声，光纤布拉格光栅（FBG），薄带和光声传感器仍然是为此目的使用或建议使用的主要传感技术。然而，尽管进行了大量的研究以提高其灵敏度和准确性，但仍需要进一步的努力使其易于在现场运行，尤其是在覆盖大量产品时。在与信息技术（IT）和仪器仪表相关的各个领域中进行的重大发展可以促进这一点，例如I4.0范式下的光纤传感器和自供电无线传感器。尽管光纤传感器（尤其是FBG传感器）具有可扩展的优势，可以用几根电线覆盖很宽的区域，但它们面临的挑战是灵敏度不高，尤其是对于检测退化（例如在导体的相对侧发生的腐蚀和腐蚀）钢结构。另外，对于这种类型的降解，光纤需要永久且紧密地连接到结构上，这难以维持。另外，它们与目标灵敏度和分辨率成比例的成本仍然很高。如果某些与电源相关的未决问题，则配备有超声波传感器的无线传感器仍然是检测结构内部腐蚀和腐蚀的另一种有形潜力。使用例如能量收集，进行整理。总体而言，现有技术仍然缺乏敏感性，准确性，通用性和/或成本效益，这证明需要做更多的开发工作。