Liquid penetrants are generally not effective at detecting which kind of defect?

Liquid penetrant testing (also known as dye penetrant inspection) is a widely used non-destructive testing method that identifies surface-breaking defects in non-porous materials. This method relies on the ability of a liquid dye to seep into cracks or voids to reveal their presence when viewed under ultraviolet light or with a contrasting color background.

Subsurface defects, by their nature, are located below the surface of the material and are not accessible for the penetrant to effectively enter. Since liquid penetrants can only detect flaws that are open to the surface, they will not be able to identify any defects that are buried within the material. This limitation is crucial to understand when selecting a testing method for specific types of inspections.

In contrast, surface cracks, weld slag inclusions, and manufacturing defects predominantly manifest at or near the surface. These defects are detectable by liquid penetrants since the testing method is designed to reveal issues that are open and accessible at the surface, making it unsuitable for identifying subsurface shortcomings.