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9 Condition-Based Maintenance Techniques
Published in Jesús R. Sifonte, James V. Reyes-Picknell, Reliability Centered Maintenance-Reengineered, 2017
Jesús R. Sifonte, James V. Reyes-Picknell
Guided wave UT. Guided wave testing uses very low ultrasonic frequencies, enabling the sound wave to travel along a pipe, providing 100% coverage of the pipe length. An array of low-frequency transducers is attached around the circumference of the pipe to generate a wave that propagates along the pipe in both directions from the transducer location. Evaluating the properties of the wave relies on heavy mathematical modeling, which is typically presented in graphical plots called dispersion curves.
Effects of the wire mesh on pulsed eddy current detection of corrosion under insulation
Published in Nondestructive Testing and Evaluation, 2023
Zhiyuan Xu, Zhen Zhou, Hanqing Chen, Zhongyi Qu, Jixiong Liu
Several NDT methods were reported to address CUI detection with the insulation still in place, which mainly includes guided waves, neutron backscatter, thermography, microwaves, fibreoptics, radiography, capacitive imaging and pulsed eddy current. Guided wave testing uses low-frequency guided ultrasonic waves that propagate along the pipe wall and can detect CUI over a range of 50 m (25 m in each direction) or more from the transducer position [2]. This method, however, requires a small length of insulation be removed to attach a ring of ultrasonic transducers onto the pipe. Therefore, it is often used to assess CUI of pipelines in hard-to-access locations, such as sleeved road crossings, wall penetrations, pipe racks, and buried piping. Neutron backscatter, thermography, microwaves and fibreoptics do not directly detect CUI but give an indication of moisture/water under insulation [3–6]. Since water intrusion is a necessary precursor to active corrosion, these methods are accurate for identifying potential areas where CUI could occur. Thus, further implementation of direct methods is required to ascertain whether corrosion is occurring. Radiography utilises x-rays or gamma rays to create images and profiles of the tested component [7]. It can be used to not only detect CUI but also provide intuitive and quantitative measurement of the corrosion. However, the use of radiography is restricted in practical application considering the health and safety issues. Capacitive imaging is also investigated for the detection of CUI in recent years. This method is claimed to be sensitive to not only CUI but also defects inside the insulation, although the presented result is still limited to the proof-to-concept stage [8,9].