Introduction to nondestructive testing

Introduction to nondestructive testing

-Book Reviews Introduction to nondestructive testing P.E. M i x John Wiley and Sons Ltd, 1987 (406 pp, £50.45) The need for training text books in no...

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-Book Reviews Introduction to nondestructive testing P.E. M i x

John Wiley and Sons Ltd, 1987 (406 pp, £50.45) The need for training text books in nondestructive testing methods for operators and technicians is increasing annually and therefore it was with much satisfaction that I agreed to review this new book from America. This volume is said to contain basic information for students and personnel qualifying to Levels I, II and I!1, and to be ideal for N D T employers who want to set up onsite training and certification programmes. It is also claimed to be an excellent training guide for anyone who wants to get started in the growing field of NDT. The wide range of N D T topics covered includes radiation physics and techniques, isotope applications, magnetic particle, ultrasonic, liquid penetrant, electromagnetic and leak testing, neutron radiography, acoustic emission, visual inspection and holography. Appendices give lists of manufacturers and suppliers as well as a series of questions and answers relating to the text. These questions and answers are a valuable addition to any text book which is to be used for training. Each chapter is refreshing in its approach to the subjects listed above and I found two comments of particular value: 'Technicians who are about to embark on a career in nondestructive testing should seek out the best possible training and never take routine test results for granted. Inexperienced technicians should always be teamed up with experienced technicians and professional help should be enlisted when the interpretation of test results are in doubt." 'Journal articles have also advocated a 'get tough' policy regarding the certification of Level III technicians, and taking away the responsibilities of

NDT International June 1988

certification from the employers. ! think that as a society, we have the right to expect technicians to be competent in the fields for which they are certified as Level III. However, it should be pointed out that employers have the most to lose by not having competent technicians; in most cases they would be the ones facing potential lawsuits due to incompetence.' The book covers a wide range of N D T and I have a number of criticisms to make. The following is not an exhaustive list: • it is not true to say that 'inherent unsharpness results because we do not have point sources, infinite distances between the source and test object, infinitesimal distances between the test object and film, single plane test objects, and uniform perpendicular energy rays'. Inherent unsharpness is a film screen radiation phenomenon which increases with an increase in radiation energy. Geometric unsharpness is related to geometric factors of image production, eg focal spot size, and film object and source object distance • X-ray fluorescence analysis is a method for obtaining the chemical analysis of a specimen; it may be confusing to discuss this in the same paragraph as real-time radiography (fluoroscopy) • while it is true to say that 'gamma ray energy is derived from natural sources and X-ray energy is man made', it is difficult to relate this statement to a later phrase, 'naturally occurring Xrays.' A simple explanation of how X-rays are produced from a gamma source would have been of value • the use of a variety of units is confusing since the book refers to both the imperial and metric systems; it is unfortunate that within international circles two

methods of measurement are still being used • Formula (7.1) in the chapter on Neutron radiography states: p = Noat

where N = number of nuclei per cubic centimetre, a, = total cross section in square centimetres and a, = the sum of the absorption and scattering across sections. Obviously there is an error in notation • there is an error in Figure 8.5 of the chapter on Leak testing: methods 2 and 3 should be reversed A complete chapter is devoted to magnetic particle testing, whereas eddy current and flux leakage methods are incorporated into the chapter on electro-magnetic testing. As I have always considered eddy current and flux leakage methods to be different, I was confused to find them discussed in the same chapter. This chapter states 'flux leakage testing involves the use of a permanent magnet or DC electromagnetic fields...' However, high frequency AC magnetizing fields may also be used for magnetization. The author distinguishes between eddy current and flux leakage systems and points out that flux leakage systems are only applicable to ferro-magnetic materials. However, more emphasis should have been placed on this and on the subtle difference between the examination of ferrous (magnetic) as opposed to non ferrous (non magnetic) materials when using eddy currents. It would have been more logical and less confusing to separate eddy current from magnetic/electrical techniques. If a training guide is to be written for nondestructive testing then it might have been better to.have concentrated on the basic physics of the techniques together with an

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-Book Reviews explanation of how they are used within the production environment. Certain aspects discussed were rather confusing.

may be useful to Level II and III personnel, although care must be taken to assimilate the facts presented.

The book presents an interesting approach to N D T training and

The book should be considered not as a comprehensive training guide

but as an addition to existing training methods. The publication costs £50, which is expensive taking into account the points raised.

J.D. Lavender

Effective nondestructive examination for structural integrity Edited by R.W. Nichols, G.J. Daw and S. Crutzen

Elsevier Appfied Science, UK, 1987 (xiv + 373 pp, £75.00) Papers presented at the 4th International Seminar on Nondestructive Examination in Relation to Structural Integrity, held at Ispra, Italy, in August 1985, form the basis of this book. The 373 pages include 19 papers from the seminar together with a record of discussions and an index. This seminar set out to cover a broad field of nondestructive inspection for structural integrity. The ultrasonic techniques are considered on a country to country basis, and the other techniques are generally covered by papers describing European or US experience. In a seminar at this time the dominant technique was inevitably ultrasonics: many of the papers on this technique refer to the recently published PISC II data and the contents of the book clearly reflect this. Nevertheless, in addition to the ultrasonic approaches described, a strong section discusses other N D T techniques so that the majority of workers in N D T will find some material relevant to their interests. A drawback is that it is now about two and a half years since the seminar and much of the material presented has since appeared in other formats. Technically the seminar seems to have attracted a high standard of contribution from around the world and this is reflected in the generally high quality of the articles. Splitting most of the subject matter into articles depicting national or European progress is not a bonus,

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as I feel that reviews of this kind do not highlight the immediacy of the work, which would be the case with individual papers. Moreover it was impossible that the period just prior to 1985 was one of major progress in all the countries invited. On the other hand, this layout means that a lot of information is available in o n e cover for reference, together with references to more detailed papers. This apart, the book represents a good picture of the state of knowledge at the time of the seminar and also illustrates the global position in ultrasonics immediately after publication of the PISC II results. For once alternatives to ultrasonics for this kind of inspection are not forgotten and good articles on radiography, eddy current inspection and on theoretical support are found in the book. A small section considers the efficacy of N D T and both articles in this section deserve study. There are two final papers: one summarizes the PISC II data and the other considers proposals for the PISC III initiative. One value of the book is it reminds us that inspection of other systems is important in defining safety. This is true of all types of plant, but the concentration of N D T development on the reactor pressure vessel, as with the PISC and D D T trials, has tended to overshadow the importance of steam generators and primary pipework. Ultrasonics seems to be ideal for most inspections associated with the

pressure vessel but in other areas other N D T techniques have a role to play, as the authors of these reviews are quick to remind us. While we would like to use ultrasonics to inspect austenitic pipes, welds and castings, the problems in achieving this are also reviewed. Some questions remain unanswered were the defects in the PISC I1 trials missed due to inadequacy of the techniques or misinterpretation or failure to detect by the operators? It appears that quite large defects well above the resolution limits of the techniques used remain undetected. If this is due to the operator missing or misinterpreting the data it seems that reliability must be sought by improvements in data recognition as well as in technique resolution. The answers to such questions could be valuable to technique development because the luxury of using several techniques and teams of operators will only be possible on very specialized inspection tasks. For other inspections it will normally be necessary to select a single technique, selection being based only upon the adequacy of the candidate techniques. Operator performance in a particular trial is only important if the technique itself makes defect detection by the operator uncertain.

M. G. Silk

NDT International June 1988