Eddy Current Testing (ECT)
Electromagnetic Testing (ET)

Eddy Current

1. an electric current in a conducting material that results from induction by a moving or varying magnetic field.

“eddy current.” Dictionary.com. 2021. http://www.dictionary.com.

Eddy currents, as an electromagnetic phenomenon, has been observed as far back as 600B.C., with Thales of Miletus. Throughout the centuries, academics and researchers alike would study the curious actions and properties of eddy currents to ever increasing understanding of the forces at play.

By 1820, Hans Christian Orsted had begun detailing the behavior and properties of magnetism, noting that the lines of magnetic force move at right angles to current in a perpendicular and circular manner. The remainder of the 19th century saw significant development, codification, and advancements on electromagnetic theory through the substantial contributions of individuals like Michael Faraday, Heinrich Lenz, and James Clerk Maxwell. Without their contributions, the field of eddy current testing and non-destructive testing in general would look very, very different.

Although eddy current instrumentation was first developed in the 1920s it wasn’t until 1950 that Freidrich Forster developed the first impedance-plane signal display. By the 1970s, eddy current testing had reached a level of accuracy and maturity that scientific measurements could be taken in the field for the practical application of non-destructive testing.

Today, Eddy Current Testing (ECT) and Electromagnetic Testing (ET) are the terms most frequently used to refer to specific and general elements of the field as a whole.

Non-Destructive Testing (NDT)

Non-Destructive Testing, as a measure to test the reliability of materials, has been in practice as long as engineering and construction itself. Throughout time, independent innovations have always driven the methods used by non-destructive testing practitioners, and the state of the field today stands as a reflection of that.

Radiographic Testing (RT)

X-Ray Techniques were largely discovered in 1895, with the discovery of “an unknown kind of radiation” by Wilhelm Conrad Rontgen. Although not immediately appreciated for industrial application at the time, the technical advancements of x-ray application in the field of medicine quickly brought it to the fore. Today, Radiographic Testing (RT) is encompasses the use of x-rays, gamma-rays, and sub-atomic particles.

Magnetic Particle (MP)

This form of non-destructive crack detection was successfully executed earlier than X-Ray, having its concept successfully demonstrated in 1868 by William Hoke and S.M. Saxby. By the 1930s, the wide-spread industrial application of this technique was already underway.

Liquid Penetrant (LP)

The dominant method for the detection of cracks in material objects prior to Magnetic Particle (MP). Itself started in the last half of the 19th century, Liquid Penetrant was briefly displaced as a proper testing method until the aviation fields reliance on increasingly lighter nonmagnetic metals returned it to the cannon of non-destructive testing.

Ultrasonic Testing (UT)

The most recent of the NDT techniques, had been underway as a field of study by the early 19th century. Industrial application can be said to have began in 1912 when Lewis Fry Richardson proposed an ultrasonic application for the detection of icebergs, following the sinking of the Titanic. By WWI, the technology was already being researched for military application. Before the end of WWII, innovations independently and simultaneously from Floyd Firestone, Donald O. Sproule, and Adolf Trost had converged to usher in Ultrasonic Testing (UT) as an NDT technique with wide ranging and useful applications.

Today, the field of Non-Destructive Testing (NDT) stands as unified field of multiple techniques, all focused on understanding the natural world around us in order to increase the durability and longevity of materials.