Electromagnetic testing (ET), as a form of
nondestructive testing
Nondestructive testing (NDT) is any of a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage.
The terms nondestructive examination (NDE), n ...
, is the process of inducing
electric current
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
s or
magnetic field
A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...
s or both inside a test object and observing the
electromagnetic
In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...
response. If the test is set up properly, a defect inside the test object creates a measurable response.
The term "electromagnetic testing" is often intended to mean simply
eddy-current testing
Eddy-current testing (also commonly seen as eddy current testing and ECT) is one of many electromagnetic testing methods used in nondestructive testing (NDT) making use of electromagnetic induction to detect and characterize surface and sub-surfac ...
(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. also useful for the testing of drill pipes.
Common methods
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Eddy-current testing
Eddy-current testing (also commonly seen as eddy current testing and ECT) is one of many electromagnetic testing methods used in nondestructive testing (NDT) making use of electromagnetic induction to detect and characterize surface and sub-surfac ...
(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 nonferromagnetic materials, since in
ferromagnetic
Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagne ...
materials the
depth of penetration is relatively small.
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Remote field testing Remote field testing (RFT) is a method of nondestructive testing using low-frequency AC. whose main application is finding defects in steel pipes and tubes. RFT is also referred to as remote field eddy current testing (RFEC or RFET). RFET is sometim ...
(RFT) is used for nondestructive testing (NDT) of steel tubes and pipes.
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Magnetic flux leakage testing (MFL) is also used for nondestructive 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.
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Wire rope testing
Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm
A wire is a flexible, round bar of metal. Wires a ...
is MFL applied to steel cables, to detect broken strands of wire.
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Magnetic particle inspection
file:Wet magnetic particle testing on a pipeline.jpg, A technician performs MPI on a pipeline transport, pipeline to check for stress corrosion cracking using what is known as the "black on white" method. No indications of cracking appear in this ...
(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.
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Alternating current field measurement Alternating current field measurement (ACFM) is an electromagnetic technique for non-destructive testing
Nondestructive testing (NDT) is any of a wide group of analysis techniques used in science and technology industry to evaluate the properties ...
(ACFM) is similar to eddy current applied to steel. Its most common application is to detect and size cracks in welds. from the company that developed it.
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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.
See also
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Electromagnetic compatibility
References
*Hugo L. Libby, ''Introduction to Electromagnetic Nondestructive Test Methods'', New York : Wiley-Interscience, 1971.
*The
American Society for Nondestructive Testing
The American Society for Nondestructive Testing, Inc. or ASNT is a technical society for nondestructive testing (NDT) professionals. ASNT evolved from ''The American Industrial Radium and X-ray Society'' which was founded in 1941. Its headquarters ...
,
NDT Handbook', 3rd ed., Vol. 5,
''
*William Lord,
Electromagnetic NDT Techniques — A 40 Year Retrospective or Retirement for Cause in ''Materials Evaluation'', June 2006, p. 547 to 550.
Nondestructive testing
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