The ability of a given liquid to flow over a surface

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The ability of a given liquid to flow over a surface and enter surface cavities depends principally on the following: cleanliness of the surface, surface tension of the liquid, configuration of the cavity, contact angle of the liquid, ability of the liquid to wet the surface, cleanliness of the cavity and size of the surface opening of the cavity. Applications. The principal industrial uses of liquid penetrant testing include postfabrication testing, receiving testing, in-process testing and quality control, testing for maintenance and overhaul in the transportation industries, in-plant and machinery maintenance testing and testing of large components. The following are some of the typically detected discontinuities: surface discontinuities , s eams, cracks, laps, porosity and leak paths. Magnetic Particle Testing Principles. Magnetic particle testing (Fig. 6) is a method of locating surface and near-surface discontinuities in ferromagnetic materials. It depends on the fact that when the test object is magnetized, discontinuities that lie in a direction generally transverse to the direction of the magnetic field will cause a magnetic flux leakage field to be formed at and above the surface of the test object. The presence of this leakage field and therefore the presence of the discontinuity is detected with fine ferromagnetic particles applied over the surface, with some of the particles being gathered and held to form an outline of the discontinuity. This generally indicates its location, size, shape and extent. Magnetic particles are applied over a surface as dry particles or as wet particles in a liquid carrier such as water or oil. Applications. The principal industrial uses of magnetic particle testing include final, receiving and in-process testing; testing for quality control; testing for maintenance and overhaul in the transportation industries; testing for plant and machinery maintenance; and testing of large components. Some of the 8 Acoustic Emission Testing F IGURE 5. Liquid penetrant indication of cracking. F IGURE 6. In magnetic particle testing, particles gather where lines of magnetic flux leak from a discontinuity. Magnetic particles N S N S Crack Legend N=north pole S=south pole
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typically detected discontinuities are surface discontinuities, seams, cracks and laps. Eddy Current Testing Principles. Based on electromagnetic induction, eddy current testing (Fig. 7) is perhaps the best known of the techniques in the electromagnetic test method. Eddy current testing is used to identify or differentiate among a wide variety of physical, structural and metallurgical conditions in electrically conductive ferromagnetic and nonferromagnetic metals and metal parts. The method is based on indirect measurement and on correlation between the instrument reading and the structural characteristics and serviceability of the test objects.
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  • Fall '19
  • Nondestructive testing, Acoustic Emission

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