The electromagnetic test method includes several

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The electromagnetic test method includes several subsidiary methods, sometimes called submethods or techniques: eddy current testing, remote field testing, flux leakage testing, alternating current field measurement testing and microwave testing. Of these several submethods, conventional eddy current testing is the most widely used. Magnetic particle testing is an electromagnetic test that industry administers as a separate method. Applications of eddy current tests in industry are numerous and widespread. The total number of test measurements made annually by this nondestructive test method may exceed that of all other methods combined. Eddy current testing is used for the following: 1. noncontacting measurement of the thickness of metallic foils, sheets, plates, tube walls and machined parts from one side only; 2. measurement of the thickness of coatings over base materials where the coating and base material have significantly different electrical or magnetic properties; 3. identifying or separating materials by composition or structure; 4. detecting material discontinuities that lie in planes transverse to the eddy currents, such as cracks, seams, laps, score marks or plug cuts, drilled and other holes and laminations at cut edges of sheet or plate; 5. identifying and controlling heat treatment conditions and evaluation of fire damage to metallic structures; 6. determining depths of case hardening of steels and some ferrous alloys; 7. locating hidden metallic objects such as underground pipes, buried bombs or ore bodies, or metallic objects accidentally packaged in foodstuffs; 8. timing or locating the motions of hidden parts of mechanisms, counting metallic objects on conveyor lines or detecting metallic missiles in flight; and 9. precise dimensional measurement of symmetric, machined or ground and polished metallic parts, such as bearings and bearing races, small mechanism components and others. Advantages of Electromagnetic Testing Modern eddy current and electromagnetic test techniques offer low cost means for high speed, large scale testing of metallic materials such as those used in nuclear, aerospace, marine, high pressure, high temperature and high speed engineering systems where premature failures could represent economic disasters or the endangering of human life. The method’s special suitability for testing of automobiles, engines, machine parts and consumer products has long been recognized. Like other nondestructive methods, eddy current tests permit measurements of material properties and dimensions and detection of discontinuities. In general, electromagnetic tests provide nearly instantaneous measurements. The test speed and modern signal analysis permit such analysis to be performed in real time. Consequently, the method can be used in production lines to test swiftly moving bars, tubes, sheets, plates, welds and other symmetric parts. These parts either pass through test coils or are scanned by moving test probes. The automation of eddy current testing and
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  • Fall '19
  • The Land, Nondestructive testing, electromagnetic testing

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