Non-Destructive Testing Introduction Those tests described in the previous chapter are destructive tests carried out on samples which, it is hoped, are representative of a batch of manufactured material. In many cases such tests will be adequate, since properties are generally uniform throughout a large batch of material derived from a single cast ingot. Components which are produced individually, however, such as castings and welded joints, may vary in quality. Even with fairly rigorous on-line inspection, faulty components can arise due to the influences of many variable factors such as working temperature, surrounding atmosphere, and the operator skill. If the quality of such components is very important, as for example castings used in nuclear power plant, it may be necessary to test each component individually using some type of nondestructive examination, Non-Destructive Testing (NDT). During such testing’s faults and flaws are detected either at the surface or below it. And a number of suitable methods are available in each case. These tests give an overall assessment of the quality of the product; therefore, the term nondestructive testing is often replaced by Non-Destructive Evaluation (NDE). Tests for the Detection of Surface Cracks and Flaws Surface cracks may arise in a material in a number of ways. Some cracks show up during inspection using a simple hand magnifier, others may be far harder to detect. For example, steel tools may develop hair-line cracks which are not apparent during ordinary visual inspection; Castings may crack due to contraction during the period of solidification and cooling, etc.
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