What does it mean when a type of NDE is referred to as a "volumetric" test?

When a type of non-destructive examination (NDE) is referred to as a "volumetric" test, it signifies that the examination method is capable of detecting flaws or irregularities within the interior volume of the test piece rather than just on its surface. This is crucial in materials testing because many defects, such as inclusions, voids, or cracks that originate internally, may not be visible from the outside.

Volumetric tests, such as ultrasonic testing or radiographic testing, utilize techniques that penetrate the material to provide information about the internal structure. These methods can reveal issues that, if left undetected, could lead to significant failures in structural integrity, especially under stress or load.

In contrast, methods that focus on the external surfaces can only identify flaws that are manifest on the outside, potentially missing critical internal defects. This key distinction highlights the importance of volumetric testing for a comprehensive evaluation of material integrity, especially in critical applications such as pressure vessels, pipelines, and structural components in engineering.