What is the primary limitation of liquid penetrant testing?

The primary limitation of liquid penetrant testing is that it cannot locate subsurface discontinuities. This method is specifically designed to detect surface-breaking flaws, such as cracks, porosities, and laps in a material. Because it relies on the ability of the penetrant to enter and stay in these surface discontinuities, any defects that are below the surface cannot be detected. This limitation is inherent to the method itself, as penetrants work by being drawn into surface flaws but are unable to reveal issues that are hidden beneath the surface of a material.

Understanding this limitation is crucial for choosing the appropriate non-destructive testing method, as different techniques such as ultrasonic testing or radiographic testing may be more suitable for detecting subsurface defects.