ET01.pdf

Infrared and thermal testing principles conduction

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Infrared and Thermal Testing Principles. Conduction and convection are the primary mechanisms of heat transfer in an object or system. However, electromagnetic radiation is emitted from a heated body when electrons in that body change to a lower energy state. Thermal testing involves the measurement or mapping of surface temperatures when heat flows from, to or through a test object. Temperature differentials on a surface, or changes in surface temperature with time, are related to heat flow patterns and can be used to detect discontinuities or to determine the heat transfer characteristics of an object. For example, during the operation of an electrical breaker, a hot spot detected at an electrical termination may be caused by a loose or corroded connection (Fig. 11). The resistance to electrical flow 11 Introduction to Electromagnetic Testing F IGURE 10. Acoustic emission testing setup in which eight sensors permit computer to calculate location of crack propagation. Computer Preamplifier Test object Acoustic event Sensor Preamplifier F IGURE 11. Infrared thermography of automatic transfer switches of emergency diesel generator. Hot spots appear bright in thermogram (inset).
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through the connection produces an increase in surface temperature of the connection. Applications. There are two basic categories of infrared and thermal test applications: electrical and mechanical. The specific applications within these two categories are numerous. Electrical applications include transmission and distribution lines, transformers, disconnects, switches, fuses, relays, breakers, motor windings, capacitor banks, cable trays, bus taps and other components and subsystems. Mechanical applications include insulation (in boilers, furnaces, kilns, piping, ducts, vessels, refrigerated trucks and systems, tank cars and elsewhere), friction in rotating equipment (bearings, couplings, gears, gearboxes, conveyor belts, pumps, compressors and other components) and fluid flow (steam lines; heat exchangers; tank fluid levels; exothermic reactions; heating, ventilation and air conditioning systems; leaks above and below ground; cooling and heating; tube blockages; environmental assessment of thermal discharge; boiler or furnace air leakage; condenser or turbine system leakage; pumps; compressors; and other system applications). Other Methods There are many other methods of nondestructive testing, including optical methods such as holography, shearography and moiré imaging; material identification methods such as chemical spot testing, spark testing and spectroscopy; strain gaging; and acoustic methods such as vibration analysis and tapping. 12 Electromagnetic Testing
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Selection of Electromagnetic Testing 4 Electromagnetic tests are an important and widely used method within the broad field of nondestructive materials testing.
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  • Fall '19
  • The Land, Nondestructive testing, electromagnetic testing

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