Penetrant Testing (PT)

Penetrant Testing (PT) is one of the oldest methods of finding indications in parts which are not visible by eye.
This method utilizes a visible or fluorescent dye solution which penetrates into open surface discontinuities via capillary action. The excess dye must be removed completely from the surface.

A developer which bleed out the trapped penetrant and the inspector might found the discontinuities easily.
With the correct application, it will detect discontinuities ranging in size from the large to the microscopic.