What can liquid penetrant testing be used to locate?

Liquid penetrant testing is specifically designed to identify open surface defects in materials. This non-destructive testing method involves applying a liquid dye to the surface of the material. The dye penetrates any cracks, voids, or other surface imperfections, making them visible upon inspection after the excess dye is removed and a developer is applied. This enables inspectors to find issues such as surface cracks, porosity, and other faults that are open to the surface.

The other options pertain to defects that are either beneath the surface or related to structural characteristics, which cannot be detected by liquid penetrant testing. For instance, subsurface discontinuities and internal stress points relate to defects that lie below the material's surface and would require other testing methods, such as ultrasonic testing or radiographic testing, to detect. Material thickness variations can be measured through techniques like ultrasonic thickness gauging, which is not a function of liquid penetrant testing.