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Non-Destructive Testing


									                          Non-Destructive Testing


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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