Electromagnetic testing uses electricity and magnetic fields to detect defects in objects. Different tests have varying applications and methodologies, with some using both electricity and magnetic fields. The tests can also determine material properties and thickness. Examples of electromagnetic testing include pulsed eddy current testing for pipes and magnetic flux leakage testing for metal containers. It is also used in medical applications and land surveying.
An electromagnetic test is a class of non-destructive tests used to find defects in an object. Each type of test has a different application and methodology. All tests use either electricity or magnetic fields, some use both. Depending on the specific type of test used, the amount of electrical current that is reflected, refracted, or otherwise conducted through the workpiece is measured. Changes in the current or magnetic field, as it moves through or around a test object, indicate possible flaws or defects.
In the past, the term “electromagnetic testing” typically referred to eddy current testing. The eddy current test finds defects near the surface of metal objects. Improvements in testing capabilities, however, have led to an ever-increasing number of electromagnetic testing options. Other tests such as remote field test, magnetic flux leakage test, wire rope test, and magnetic particle inspection allow users to test for defects in a variety of materials, shapes, and locations. Using electricity and magnetic fields, each type of electromagnetic test produces a response indicating cracks, heat damage, corrosion or other defects in a wide range of materials and environments.
In addition to detecting defects, the use of electricity in magnetic fields can also help determine the other unseen properties of metal, earth and soft tissue. The results indicate material thickness, electrical conductivity, the presence of foreign objects, and other information. The purpose of any electromagnetic testing is to provide the ability to gather information before undertaking costly or unnecessary excavation, disassembly, or surgery, or to ensure the safety of a manufactured component.
Examples of the many uses of various types of electromagnetic testing can be found in the commercial building and medical fields. For example, pulsed eddy current testing is used on pipes to determine metal loss without the need to expose the pipe itself. This type of electromagnetic test can be performed from a considerable distance when direct access to the pipe in question is impractical.
When applied to metal storage tanks, aircraft fuselages, and similar metal containers, an electromagnetic test such as the magnetic flux leakage test can locate internal damage to the metal. Such tests use a magnetic field that passes over the test object, producing different results on areas prone to corrosion or pitting. Tests of this type can be performed on a completed aircraft, on tanks that have already been put up for storage or during the manufacturing process.
While typically used on metal test objects, electromagnetic testing is also useful in medical applications, land surveying, and specific niche applications. Magnetic resonance imaging (MRI), for example, is a type of electromagnetic test used to view inside the human body. Ground penetrating radar is a similar electromagnetic testing method used to create a geophysical map of underground areas. Radar can detect buried objects and determine subsurface conditions. Similarly, Barkhausen noise analysis uses a magnetic field combined with noise signals to test ferromagnetic or naturally magnetic samples.
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