During service at high temperature or in aggressive media, metallic structures andcomponents may suffer different types of changes or degradation. As an example, phasetransformations may occur, second phases may precipitate, and in consequence the mechanicaland chemical properties of the structure may change. Their behaviour will therefore differfrom that considered for the design of the component. A knowledge of the amount of a secondphase precipitated in a component should be an important tool in the hands of themaintenance engineer. And it would be very important to obtain this knowledgenondestructively and reliably.Eddy current testing is an adequate method for these assessments. However, the inducedvoltage in an eddy current probe, the measured quantity, is actually a superposition ofmany variables, and contains information on lift-off, resistance, etc. In order to sort outthis information, a model of the impedance plane was programmed in a PC. Use of thisprogram would provide a method for the calculation of the conductivity of materials, takinginto account the effect of specimen thickness. Adequate calibrations would allow for thenondestructive assessment of the amount of hydrogen in reactor components such as pressureand calandria tubes, a knowledge which will enable the experts to predict the degree offragilization of those components. This type of tests should be a natural complement to thenormal inspection procedures, which search for cracks and blisters.
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