NDT: an integral part of engineering

Editorial NDT: an integral part of engineering You may be asking the question; 'Why has a special issue of the IEE Proceedings been prepared on nondestructive testing?' Modern nondestructive testing (NDT) is increasingly involving electrical engineers through the use of advanced instrumentation and its range of application in fields as diverse as silicon-chip fabrication and its application to power generation equipment. The IEE has members active in many aspects of NDT and it has had a long involvement with the materials science and testing fields. There is now an IEE professional group (S6) for nondestructive testing, which grew from aspects of the work of the materials science and technology professional group (S2), and it is seeking to act as a focus for this previously extensive but diffuse IEE activity. There is at present a working party involving a number of institutions that has been organised by the IEE to produce 'Guidelines on design for testability' for application to the whole range of engineering products. The IEE has long had links with the British National Committee for NDT which represents 28 institutions and societies in the UK with interests in this field. The IEE has been asked by the British Institute of NDT to be associated with the organisation of a session at the 4th European NDT Conference which is to be held in London in September 1987. If you have any remaining doubts that NDT is of importance to all engineers, it is hoped that this special issue and the European Conference will show the full scope and importance of this expanding field of activity. The benefits of technology are all around us, and in so many ways technology can be seen to be capable of greatly improving our lives. However nothing is perfectly safe, and the consequences of major failures in high technology industries have recently been made all too real with the recent loss of the United States space shuttle Challenger and the accident at the Russian nuclear plant at Chernobyl. To seek to ensure safety in operation, at least as far as possible for whatever technology is in a system, there is a need to provide the best designs, to evaluate the state of components and systems and then to estimate the useful service life of a system, be it an integrated circuit, an aircraft engine or a nuclear power plant. Nondestructive testing and more recently quantitative nondestructive evaluation (NDE) form part of the process of condition monitoring and life estimation. It is not, however, through the public face of technology that NDT makes its most significant impact but through the economics associated with the total life costs of a product. A recent study of the UK Department of Trade and Industry has concluded that British industry could cut its costs by 15% through the introduction of better quality control procedures. For many systems the possibility of extending the life of a system is economically attractive, but it is necessary to ensure the system's safety for an extended period. The economic consequences of failure in service and unplanned maintenance can also be significant. Quality and reliability together with price and delivery hold the keys to the success or failure of 'your' version of a particular product in the market place. NDT and its use are fundamentally a question of economics, that includes a range of 'costs' that combine special, human and political factors as well as just normal IEE PROCEEDINGS, Vol. 134, Pt. A, No. 3, MARCH 1987

economics. The risk of failure is a factor in the economics of a design; in any system there is the need to ensure that all aspects are adequately considered at the design stage. When it comes to considering life extension it may simply be cheaper to scrap and replace parts; but the evaluation is needed to determine if it is more economical to consider its reuse and nondestructively test a part. NDT, which for the last decade in high technology industries has been called on to develop its scientific base and become much more quantitative, is now an integral part of quality control at all stages in the manufacturing process as well as in the in-service monitoring of critical components, such as in aircraft engines. Traditional materials are being asked to perform and meet ever more demanding specifications, and a wide range of new materials, ceramics and composites as well as new alloys and powder metals are being introduced to meet the everchanging engineering needs and the demands of the market place. To meet these changes it has been shown that there is a need to improve design and, in the design phase, to consider how a part is to be inspected, both in manufacture and in service. The philosophy of 'Design for testability' is increasingly considered as a significant design parameter, and this is combined with the need for a move to quantitative NDE, which combines NDT with life evaluation for both parts and systems. A wider concept of 'unified life cycle engineering' is now being developed in the USA to combine and balance the often conflicting requirements of the design, manufacturing and service performance, using CAD/CAM and artificial intelligence systems. Quantitative NDT can be combined with fracture mechanics and stress analysis in life and failure models. Technology is placing new demands on materials, and NDT seeks to demonstrate that a part is free from defects which may damage its performance and cause it to fail. It is also now accepted that nothing is perfect; all materials contain defects, even if they are only small dislocations in the basic crystal structure. There is an increasing need to both detect and size defects in a reliable inspection that gives quantitative results, including as a parameter the probability of detection, for particular populations of defects. It is the significance of particular defects that is crucial, and NDT is being called on to provide the data necessary to determine their location, type and characteristics. The last decade has seen NDT enter a period of rapid evolution into a science-based field of engineering that has an impact on the activity of professional engineers from the design office to the production line and through into service. This special issue presents eight papers which consider various aspects of recent developments in NDT. Applications to components as diverse as integrated circuits and nuclear power plants are presented. The paper by Martin and Smith reviews various aspects of the development of ultrasonic testing that have been made possible by the use of computers. A paper by Johnson presents the CEGB's approach to the efficient acquisition of data in automated inspections. A paper by Chaloner and Bond presents the 1-dimensional Born inversion technique which is just one of a growing range of signal processing techniques that can be employed for defect sizing. 237

Increasingly there is the need to automate the placing and control of transducers in inspections. A paper by Wray describes a computer-controlled manipulator system. A practical application of EMATs used in gas pipeline inspection is presented by Holler et al. The scale of application is then changed with two papers on the scanning acoustic microscope. The first, by Burton, is a review which shows the current state of application. The second, by Somekh, considers specific aspects of the contrast mechanism. The final paper by Rodger and King considers 3-dimensional finite-element models for eddy-current NDT. It is hoped that many more papers on NDT will be published in future issues of the IEE Proceedings. Other NDT technologies clearly require attention; eddy-current NDT, optical inspection technology, radiography in all its forms, as well as developments with magnetic particle and penetrants, acoustic-emission and thermal-wave NDT and the other new NDT technologies in allfieldsof application. We wish to thank the authors for their papers which have made this issue possible, and we also thank the referees for their comments and suggestions. L.J. BOND W.N. REYNOLDS Dr. L.J. Bond has been active in research into fundamental aspects of elastic- and acoustic-wave phenomena for NDT and seismology since 1974. His work has more recently expanded to also consider fundamental aspects of eddy-current phenomena. He graduated from a sandwich ^ course in applied physics at the City UniI versity and was awarded a PhD in I physics in 1978 for work on Rayleigh • waves, initially with the support of SEGAS and then of the British Gas Corporation. He then

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became a Research fellow supported by the UK Ministry of Defence. Since 1979 he has been at University College London, for five years in the Electronic and Electrical Engineering Department and now in the Mechanical Engineering Department in an 'academic initiative' post in NDE. His research interests cover forward models and inversion applied to ultrasonic and eddy-current NDT, acoustic emission and seismology. The core of much of the work involves the use of numerical modelling to study otherwise analytically intractable problems and the work is combined with experiments using digital NDT equipment. Dr. Bond is a Member of both the IEE and the Institute of Physics. He is currently a member of the British National Committee for NDT, representing the IOP; he is Chairman of the IEE Professional group for NDT (S6), Secretary of the IOP/IOA joint Physical Acoustics Group, Vice Chairman of the IOP Materials and Testing Group, and a member of the IEE working group on 'Design for testability'.

Dr. W.N. Reynolds graduated in physics from the University of London and was later awarded a PhD in atomic physics and a DSc in the physics of materials. After earlier experience in university, industrial and Government laboratories he joined AERE Harwell in 1958. For some time he was exclusively concerned with irradiation effects in the graphite moderator of Magnox and AGR power systems, but later moved into the carbon fibre development programme with a special interest in testing. This led to more general involvement in NDT, and he is now concerned with the development of special techniques for a wide range of materials and structures. Dr. Reynolds is a Fellow of the Institute of Physics and of the British Institute of NDT. He is also a present member of the British National Committee for NDT working party on the needs of industry and of the British Standards Institution working party on the revision of NDT tests for concrete.

IEE PROCEEDINGS, Vol. 134, Pt. A, No. 3, MARCH 1987