Which of the following is a limitation of NDT methods?

The limitation of non-destructive testing (NDT) methods that is identified here is that they may not detect all types of defects. NDT techniques are designed to evaluate the properties of a material without causing any damage. However, each NDT method has its strengths and weaknesses, and some types of defects may not be identifiable with certain methods due to factors like the size, orientation, or type of defect, as well as the material properties themselves.

For example, techniques like ultrasonic testing may not reliably detect surface cracks if they do not intersect with the sound wave path. Similarly, other methods, such as magnetic particle testing, can be limited to detecting only surface or near-surface discontinuities in ferromagnetic materials. Therefore, a comprehensive assessment often requires the use of multiple NDT methods to ensure that a wide variety of potential defects are addressed.

The other options present characteristics that do not accurately reflect the nature of NDT methods, either by overstating their capabilities or misrepresenting the necessary expertise required for their operation.