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The importance of ultrasonics in nondestructive testing and evaluation
Nondestructive testing (NDT) has evolved from an empirical art into a highly scientiﬁc practice drawing on the latest developments in imaging processing, mathematical and computer modeling, robotics, materials science and metallurgy and many other ﬁelds. Where the quantitative aspects of inspection come to the fore, the term nondestructive testing and evaluation (NDE&E) is used. This present issue of Ultrasonics focuses on the ‘‘Application of Ultrasound to Quantitative and Non Destructive Evaluation’’, and is dedicated to the late Bernard Hosten, a long-time Editor of Ultrasonics. This provides an opportunity to reﬂect on the important role of ultrasonics in NDT&E, and mention some of the directions the ﬁeld has taken in recent years. Recently several of the Editors of Ultrasonics participated in the 14th Asia Paciﬁc Conference on Nondestructive Testing (14th APCNDT), which provided inspiration for this editorial. Although it could be said that 14th APCNDT projected somewhat of an Asian perspective on NDT&E, in reality there is little distinction to speak of between the technology being implemented and type of research and development being conducted in the East and in the West. If there are differences, they would lie in the relative maturity of the ﬁeld in the West, and in the more rapid growth of NDT in many Asian countries. 14th APCNDT took place in the Renaissance Convention Centre Hotel in Mumbai, India, 18–22 November 2013 (website: http://www.apcndt2013.com/), and was excellently run by Dr. B Venkatraman and his team. Although it was a regional conference, because of the large number of invited speakers drawn from all over the world, and the high caliber and diversity of the presentations, it had the attributes of a fully ﬂedged international conference. The conference was attended by 700 delegates from India and over 25 other countries, and catered for NDT professionals as well as researchers and engineers. Generous sponsorship for this conference was received from the major international NDT equipment suppliers and service providers, which was recognition of the importance attached to NDT in the national strategies of the Asia Paciﬁc nations. One reason for their attention given to NDT&E, is that Asian countries are keen to export their manufactured goods to the West, and in order to get these products accepted, have to prove their quality and reliability through careful inspection. Another apparent reason is that in emerging economies equipment and plant are expected to last past their design lifetime, and this requires careful inspection and proper maintenance. In countries such as Korea and India, with heavy investments in nuclear power and anxiety about safety issues, the focus of much of their research and development in NDT&E is on the nuclear industry. http://dx.doi.org/10.1016/j.ultras.2014.06.009 0041-624X/Ó 2014 Published by Elsevier B.V.
NDT&E is carried out using a wide range of techniques including X-ray, c-ray and neutron radiography, optical, infra-red and THz radiation imaging, eddy currents, magnetic ﬂux leakage and various modalities of ultrasound. Ultrasonics is the most important of these approaches, with more than half of all inspection done with one or other form of ultrasonic probe. Since this editorial is aimed at the ultrasonics community, this is the aspect it will focus on, and little will be said here of the other forms of inspection. It may come as a surprise to some of the readers of Ultrasonics how important and extensive the practice of NDT&E is Worldwide. Regular downtime is scheduled for power and petrochemical plants and aircraft to inspect for ﬂaws that could in time lead to catastrophic failure. When pipelines are laid, all welds are inspected for ﬂaws. Railway rolling stock and rail track are inspected, as increasingly are bridges and other civil structures. There is a growing trend to use mechanized NDT&E for quality assurance in production lines to continuously monitor output and thus preempt the need to scrap entire batches. While much of NDT&E of plant and structures is done after certain deﬁned time periods, there is growing reliance on continuous monitoring using implanted sensors and computerized logging. This practice goes by the name of condition monitoring or structural health monitoring. In the preservation of cultural heritage objects, use is made of [email protected]
Just how widespread the practice of NDT&E is, can be judged by the following illustrative ﬁgures. The American Society for Nondestructive Testing has 52,000 members, which is just a subset of all individual engaged in inspection in the USA. There are in excess of 180,000 NDT technicians working in China, and a similar number in Japan. In its most common basic form, ultrasonic NDT involves a technician sending ultrasonic pulses into an object using say a piezoelectric transducer, and looking for echoes from cracks and other ﬂaws, and attempting to locate and size these imperfections. Operators in the ﬁeld and in industry will adhere to certain standardized codes of practice based on well established knowledge. Researchers in NDT&E are constantly striving to extend this knowledge base, increase the sensitivity and accuracy of measuring techniques and their ease of application, make more reliable the interpretation of recorded data through the use of artiﬁcial intelligence and computer modeling results, and so on. Point by point inspection of pipelines, railway track and other extended or partially inaccessible objects would be extremely laborious and expensive, and much effort has gone into developing and implementing methods using guided ultrasonic waves that explore extended lengths of these objects. Inspection of layered solids
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and ﬁber composites presents another set of challenges, on which much progress has been made. Some applications call for noncontact inspection, which is provided by air-coupled ultrasound and laser ultrasonics. Stressing an object, as for instance by increasing the pressure inside a closed vessel, can lead to acoustic emission (AE) from micro-fracture events, and monitoring AE yields information about incipient weakness in the structure. The 14th APCNDT provided an excellent overview of the current status of and recent developments in NDT&E in general, and ultrasonic NDT&E in particular. The striking feature of this conference was the very large number of invited talks, some plenary and the rest presented in the parallel sessions, which provided a broad coverage of topical subjects. Some of the talks took a holistic approach to [email protected]
, dealing with issues like the broad-based use of NDT&E in the nuclear, petrochemical and aerospace industries, signal and image processing and probability of detection (POD), while others focused on techniques. The plenary and invited talks that dealt speciﬁcally with ultrasonic topics were as follows: Guided wave inspection was covered by Krishnan Balasubramaniam, who discussed some recent approaches to ultrasonic guided waves and their application, Philip Loveday, who dealt with long range guided wave monitoring of rail track, and Younho Cho, who discussed ultrasonic nonlinear guided wave NDE. Ultrasonic modeling was covered in talks by Michael Lowe, who discussed array imaging of austenitic welds by measuring weld material map, and Sohichi Hirose, who discussed the application of ultrasonic wave theory and simulation to ﬂaw imaging. The pitfalls and opportunities for acoustic nonlinearity in structural health monitoring were discussed in a plenary talk by Sridhar Krishnaswamy.
Laser ultrasound was covered in a plenary talk by Arthur Every on laser based investigations of surface acoustic waves, and in an invited talk on process monitoring applications of laser ultrasonics by Marvin B Klein. Yoon Young Kim, in a plenary talk, discussed advances in magnetostrictive patch transducers for ultrasonic guided wave inspection, and how, for example, they allow inspection with non-dispersive shear-horizontal waves, while Sivaram Nishal Ramadas gave an invited talk on ﬂexural and robust piezoelectric transducers for air coupled ultrasound. Martin Spies discussed ultrasonic inspection, defect reconstruction and POD issues for complex materials and components such as ship propellers, and Chunguang Xu discussed ultrasonic ﬁelds and inspection of huge complex composites. Jennifer Michaels discussed measurement and signal processing of ultrasonic angle-beam wave ﬁelds. Mitsuharu Shiwa discussed acoustic emission from stress corrosion cracking in stainless steels. Philippe Benoist discussed advanced phased array techniques for industrial applications. Sarmishtha Palit Sagar discussed ultrasonic imaging: a tool to evaluate quality of continuously cast high carbon billets. Other ultrasonics topics covered in contributed papers included time of ﬂight diffraction (TOFD), nonlinear testing for corrosion, inspection of concrete, Rayleigh, Lamb and interfacial waves, laser Doppler vibrometry, wavelet analysis applied to C-scans, magnetoacoustic emission, and underwater ultrasonic imaging. A.G. Every Available online xxxx