A Survey of Electromagnetic Methods of Nondestructive Testing: Fid-Bau Portal

A Survey of Electromagnetic Methods of Nondestructive Testing

Lord, W.

Summary Electromagnetic methods of nondestructive testing (NDT) can be classified according to their mode of specimen excitation: Direct current excitation results in active leakage fields around defects in ferromagnetic materials. Residual leakage fields around defects in ferromagnetic materials occur after removal of the dc excitation current. Alternating current excitation of conducting materials results in induced eddy currents which are sensitive to a wide variety of specimen properties. All of these techniques, when used in conjunction with an appropriate test probe, can be applied to the problems of testing metals nondestructively. Each technique has its own particular field of application and many are used on a daily basis in the energy, transportation and aerospace industries. The classification covers not only a broad frequency spectrum (from 0Hz into the MHz range) but also a large number of individual testing techniques associated with each sub group. Despite the longevity of the subject matter, industry’s demands for better performance and reliability from metal components have caused increased interest in improving the state of the NDT art. This has resulted in a growing number of studies into the modeling of basic electromagnetic field/defect interactions and into techniques for improving the evaluation of test signals. The major objective of this paper is to provide a survey of the topic by describing both practical and theoretical developments to-date and indicating current and future trends, thus characterizing the general philosophy of the field. An extensive bibliography is included with the paper which should enable the reader to obtain further in-depth information concerning most aspects of electromagnetic NDT techniques, and which also serves to indicate the general resurgence of interest in the field.