ET01.pdf

The following section briefly describes several other

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The following section briefly describes several other methods and the applications associated with them. 7 Introduction to Electromagnetic Testing F IGURE 3. Electromagnetic testing: (a) representative setup for eddy current test; (b) in-service detection of discontinuities. Coil in eddy current probe Primary electromagnetic field Direction of primary current Eddy current strength decreases with increasing depth Direction of eddy currents Conducting specimen Induced field (a) (b)
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Visual Testing Principles. Visual testing (Fig. 4) is the observation of a test object, either directly with the eyes or indirectly using optical instruments, by an inspector to evaluate the presence of surface anomalies and the object’s conformance to specification. Visual testing should be the first nondestructive testing method applied to an item. The test procedure is to clean the surface, provide adequate illumination and observe. A prerequisite necessary for competent visual testing of an object is knowledge of the manufacturing processes by which it was made, of its service history and of its potential failure modes, as well as related industry experience. Applications. Visual testing provides a means of detecting and examining a variety of surface discontinuities. It is the most widely used method for detecting and examining for surface discontinuities associated with various structural failure mechanisms. Even when other nondestructive tests are performed, visual tests often provide a useful supplement. When the eddy current testing of process tubing is performed, for example, visual testing is often performed to verify and more closely examine the surface condition. The following discontinuities may be detected by a simple visual test: surface discontinuities, cracks, misalignment, warping, corrosion, wear and physical damage. Liquid Penetrant Testing Principles. Liquid penetrant testing (Fig. 5) reveals discontinuities open to the surfaces of solid and nonporous materials. Indications of a wide variety of discontinuity sizes can be found regardless of the configuration of the work piece and regardless of discontinuity orientations. Liquid penetrants seep into various types of minute surface openings by capillary action. The cavities of interest can be very small, often invisible to the unaided eye. 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 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, maintenance and overhaul in the transportation industries, in-plant and machinery maintenance and in testing of large components. The following are some of the typically detected discontinuities: surface discontinuities , s
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  • Fall '19
  • The Land, Nondestructive testing, electromagnetic testing

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