What is the Nondestructive Testing? (Part 1)

Nondestructive Testing  (NDT) has been defined as comprising those test methods used to examine or inspect a part or material or  system without impairing its future usefulness.
The term is generally applied to nonmedical investigation of material integrity. Strictly speaking, this definition of nondestructive testing includes noninvasive medical diagnosis, X-rays, ultrasound and endoscopes are used by both medical and industrial nondestructive testing, however, has come to be treated by a body of learning so separate that today most physicians never use the word nondestructive.
(In Medical branch, is common listen the phrase "Non Invasive" for explain a method what don´t need a manipulation of the human body or some tissue.)

Nondestructive testing is used to investigate specifically the material integrity of the test object. A number of other technologies -for instance, radio astronomy, voltage and amperage measurement and rheometry (flow measurement)- are  nondestructive but are not used specifically to evaluate  material properties. Radar and sonar are classified as nondestructive testing when used to inspect dams, for instance, but not when they are used to chart a river bottom.

Basicly, Nondestructive testing asks "Is there something wrong this material?". Various performance and proof test, in contrast, ask "Does this component work?" This is the reason that it is not an inspector checks through it. Hydrostatic presure testing is another of proof testing, one that may destroy the test object.
Another gray area that invites various interpretations in defining nondestructive testing is future usefulness. Some material investigations involve taking a sample of the inspected part for testing that is inherently destructive. A noncritical part of pressure vessel may be scraped or shaved  to get a sample for electron microscopy, for example. Although future usefulness of vessel is not impaired by the loss of material, the procedure is inherently destructive and the shaving itself -in one sense the true tes objetc- has been removed from service permanently.