Non-destructive testing

The terms "non-destructive testing" (NDT) or "non-destructive testing" (NDT) evoke the diagnosis made by a doctor when examining a patient. The same principle is applied to industrial parts: investigative methods are used to assess their state of health without destruction, and to formulate an opinion on their suitability for their intended function.

From the point of view of fitness for use, the definition of NDT presupposes a sound knowledge of all the phenomena involved, in particular the harmfulness of defects, their evolution over time, and the general laws of fracture mechanics. In practice, NDT specialists are faced with the problem of interpreting test results in relation to criteria established in conjunction with the part designer.

A definition of non-destructive testing closer to industrial reality would therefore be to say that it involves "qualifying, without necessarily quantifying, the state of a product, without altering its characteristics in relation to recipe standards".

Performing this task requires a sound knowledge of the investigative methods used, their limitations and, above all, a perfect match between the detection power of each method and the criteria applied for its implementation. Understandably, great importance is attached to training non-destructive testing operators.

The Confédération Française des Essais Non Destructifs (COFREND) is the national body which issues certifications demonstrating the ability of operators to carry out the tasks entrusted to them. It now applies European regulations. Standardization is also a fundamental aspect of defining methods and their application, and numerous national, European and international texts exist. Some of the most important are listed below. .

The aim of this dossier is to present, without going into too much detail, the physical principles involved in the main methods, highlighting their specific features and the fields of application concerned. In-depth information on the methods will be provided in more specialized documents, or through training courses such as those offered by CETIM (Centre Technique des Industries Mécaniques).