Nondestructive Testing Handbook Third Edition ______ The Aims of a Handbook The volume you are holding in your hand is the second in the third edition of the Nondestructive Testing Handbook. Now is a good time to reflect on the purposes and nature of a handbook. Handbooks exist in many disciplines of science and technology, and certain features set them apart from other reference works. A handbook should ideally give the basic knowledge necessary for an understanding of the technology, including both scientific principles and means of application. The typical reader may be assumed to have completed three years of college toward a degree in mechanical engineering or materials science and hence has the background of an elementary physics or mechanics course. Occasionally an engineer may be frustrated by the difficulty of the discussion in a handbook. That happens because the assumptions about the reader vary according to the subject in any given chapter. Computer science requires a sort of background different from nuclear physics, for example, and it is not possible for the handbook to give all the background knowledge ancillary to nondestructive testing. A handbook offers a view of its subject at a certain period in time. Even before it is published, it starts to get obsolete. The authors and editors do their best to be current but the technology will continue to change even as the book goes to press. Standards, specifications, recommended practices and inspection procedures may be discussed in a handbook for instructional purposes, but at a level of generalization that is illustrative rather than comprehensive. Standards writing bodies take great pains to ensure that their documents are definitive in wording and technical accuracy. People writing contracts or procedures should consult real standards when appropriate. Those who design qualifying examinations or study for them draw on handbooks as a quick and convenient way of approximating the body of knowledge. Committees and individuals who write or anticipate questions are selective in what they draw from any source. The parts of a handbook that give scientific background ,for instance, may have little bearing on a practical examination. Other parts of a handbook are specific to a certain industry. Although a handbook does not pretend to offer a complete treatment of its subject, its value and convenience are not to be denied. The present volume is a worthy addition to the third edition. The editors, technical editors and many contributors and reviewers worked together to bring the project to completion. For their scholarship and dedication I thank them all. Gary L. Workman Handbook Development Director