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The term "Electromagnetic Testing" is often intended to mean simply Eddy-Current
Testing (ECT). However with an expanding number of electromagnetic and magnetic test
methods, "Electromagnetic Testing" is more often used to mean the whole class of
electromagnetic test methods, of which Eddy-Current Testing is just one.
Common Methods of Electromagnetic Testing:
Eddy-Current Testing (ECT) is used to detect near-surface cracks and corrosion in metallic
objects such as tubes and aircraft fuselage and structures. ECT is more commonly applied to
no ferromagnetic materials, since in ferromagnetic materials the depth of penetration is
relatively small.
Remote field testing (RFT) is used for non-destructive testing (NDT) of steel tubes and pipes.
Magnetic flux leakage testing (MFL) is also used for non-destructive testing (NDT) of steel
tubes and pipes. At present RFT is more commonly used in small diameter tubes and MFL in
larger diameter pipes over long travel distances.
Wire rope testing is MFL applied to steel cables, to detect broken strands of wire. Magnetic
particle inspection (MT or MPI) is a form of MFL where small magnetic particles in the form
of a powder or liquid are sprayed on the magnetized steel test object and gather at surface-
breaking cracks.
Alternating Current Field Measurement (ACFM) is similar to eddy current applied to steel. Its
most common application is to detect and size cracks in welds. Pulsed eddy current enables
the detection of large-volume metal loss in steel objects from a considerable stand-off,
allowing steel pipes to be tested without removing insulation.
Radiographic Testing (RT), or industrial radiography, is a non-destructive testing (NDT)
method of inspecting materials for hidden flaws by using the ability of short wavelength
electromagnetic radiation (high energy photons) to penetrate various materials.
Either an X-ray machine or a radioactive source (Ir-192, Co-60, or in rarer cases Cs-137)
can be used as a source of photons. Neutron radiographic testing (NR) is a variant of
radiographic testing which uses neutrons instead of photons to penetrate materials. This can
see very different things from X-rays, because neutrons can pass with ease through lead and
steel but are stopped by plastics, water and oils.
Since the amount of radiation emerging from the opposite side of the material can be
detected and measured, variations in this amount (or intensity) of radiation are used to
determine thickness or composition of material. Penetrating radiations are those restricted to
that part of the electromagnetic spectrum of wavelength less than about 10 nanometres.
Weld radiograph with a burn-through defect
The beam of radiation must be directed to the middle of the section under examination
and must be normal to the material surface at that point, except in special techniques where
known defects are best revealed by a different alignment of the beam. The length of weld
under examination for each exposure shall be such that the thickness of the material at the
diagnostic extremities, measured in the direction of the incident beam, does not exceed the
actual thickness at that point by more than 6%. The specimen to be inspected is placed
between the source of radiation and the detecting device, usually the film in a light tight
holder or cassette, and the radiation is allowed to penetrate the part for the required length of
time to be adequately recorded.
The result is a two-dimensional projection of the part onto the film, producing a latent
image of varying densities according to the amount of radiation reaching each area. It is
known as a radiograph, as distinct from a photograph produced by light. Because film is
cumulative in its response (the exposure increasing as it absorbs more radiation), relatively
weak radiation can be detected by prolonging the exposure until the film can record an image
that will be visible after development. The radiograph is examined as a negative, without

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