TABLE OF CONTENTS Eddy current testing is one of the oldest nondestructive testing (NDT) methods. However, it wasn t until the last few decades of the twentieth century that the eddy current method started to reach its true potential in the marketplace. One reason for this is that general purpose, user-friendly eddy current instruments are a relatively recent phenomenon. Whereas portable ultrasonic instruments offering considerable versatility have been available since the 1960s, comparable eddy current portables only became available in the 1980s. In addition, it is only recently that eddy current theory became widely understood by NDT professionals. The early 1980s, in particular, produced excellent explanatory material that made eddy current theory understandable to persons without advanced technical backgrounds. Modern microprocessor-based instruments, plus the availability of high-quality operator training, ensure the continued growth of this versatile, high-performance NDT method.
Development of the eddy current method was based on certain discoveries made during the early nineteenth century about the relationship between electricity and magnetism. In fact, the relevant electromagnetic principles were discovered in the same sequence in which they occur during an eddy current test.
In 1820, Hans Christian Oersted, a Dane, discovered electromagnetism the fact that an electrical current flowing through a conductor causes a magnetic field to develop around that conductor. Oerstead discovered electromagnetism accidentally. While demonstrating that heat is developed when an electric current passes through a wire, Oerstead observed that the needle of a magnetic compass deflected perpendicular to the wire while the...
