What are the two general categories of NDT methods?

The correct answer identifies the two general categories of NDT methods as surface and volumetric examination methods. This classification is fundamental in non-destructive testing because it distinguishes how and where the examination is conducted on the test material.

Surface examination methods focus on detecting flaws or discontinuities that are located on or near the surface of the material. Techniques such as liquid penetrant testing and magnetic particle testing fall under this category. These methods are highly effective for identifying surface-breaking defects, which are often critical to the integrity of the component.

Volumetric examination methods, on the other hand, are designed to assess the integrity of the material throughout its volume. This includes methods like ultrasonic testing and radiographic testing, which can detect internal defects that may not be visible from the surface. These techniques provide a more comprehensive evaluation of the structural integrity of materials, making them essential for critical applications where internal flaws could lead to failure.

Understanding this distinction helps practitioners select the appropriate NDT method based on the specific needs of their inspection and the types of defects they are seeking to identify.