Which inspection method involves a liquid that is applied to the surface to reveal cracks?

Dye penetrant inspection is a widely used non-destructive testing method specifically designed to identify surface defects, such as cracks, in non-porous materials. In this method, a colored or fluorescent dye is applied to the surface of the material. The dye penetrates any cracks or voids present in the surface due to capillary action. After a specified dwell time, during which the dye has time to seep into the defects, the excess dye is removed from the surface, usually with a solvent.

A developer is then applied, which draws the penetrated dye back out from the defects and makes them visible against the background of the material. This visibility allows inspectors to easily detect and evaluate the extent of any surface-breaking flaws. The simplicity, low cost, and effectiveness of dye penetrant inspection make it a common choice for many applications where surface integrity is critical.

In contrast, the other methods listed do not utilize a liquid in the same manner to reveal cracks. Magnetic particle inspection relies on magnetic fields and ferromagnetic particles to identify surface and near-surface discontinuities. Ultrasonic inspection uses high-frequency sound waves to detect irregularities within the material rather than just on the surface. Visual inspection relies solely on the inspector’s ability to visually