ET01.pdf

ET01.pdf - C 1 H A P T E R Introduction to Electromagnetic...

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Marvin W. Trimm, Westinghouse Savannah River Company, Aiken, South Carolina (Parts 1 and 2) Holger H. Streckert, General Atomics, San Diego, California (Part 3) Andrew P. Washabaugh, Jentek Sensors, Waltham, Massachusetts (Part 2) 1 C H A P T E R Introduction to Electromagnetic Testing
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Definition Nondestructive testing (NDT) has been defined as comprising those methods used to test a part or material or system without impairing its future usefulness. 1 The term is generally applied to nonmedical investigations of material integrity. Strictly speaking, this definition of nondestructive testing includes noninvasive medical diagnostics. Ultrasound, X-rays and endoscopes are used by both medical and industrial nondestructive testing. Medical nondestructive testing, however, has come to be treated by a body of learning so separate from industrial nondestructive testing that today most physicians do not use the word nondestructive . Nondestructive testing is used to investigate specifically the material integrity or properties of the test object. A number of other technologies — for instance, radio astronomy, voltage and amperage measurement and rheometry (flow measurement) — are nondestructive but are not used specifically to evaluate material properties. Radar and sonar are classified as nondestructive testing when used to inspect dams, for instance, but not when they are used to chart a river bottom. Nondestructive testing asks “Is there something wrong with this material?” In contrast, performance and proof tests ask “Does this component work?” It is not considered nondestructive testing when an inspector checks a circuit by running electric current through it. Hydrostatic pressure testing is another form of proof testing, one that sometimes destroys the test object. Another gray area that invites various interpretations in defining nondestructive testing is future usefulness . Some material investigations involve taking a sample of the tested part for a test that is inherently destructive. A noncritical part of a pressure vessel may be scraped or shaved to get a sample for electron microscopy, for example. Although future usefulness of the vessel is not impaired by the loss of material, the procedure is inherently destructive and the shaving itself — in one sense the true test object — has been removed from service permanently. The idea of future usefulness is relevant to the quality control practice of sampling. Sampling (that is, less than 100 percent testing to draw inferences about the unsampled lots) is nondestructive testing if the tested sample is returned to service. If the steel is tested to verify the alloy in some bolts that can then be returned to service, then the test is nondestructive. In contrast, even if spectroscopy used in the chemical testing of many fluids is inherently nondestructive, the testing is destructive if the samples are poured down the drain after testing.
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  • Fall '19
  • The Land, Nondestructive testing, electromagnetic testing

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