Penetrant Testing

This testing method is used to detect surface defects in all metallic and non-metallic materials. For defects to be detected with this method, they must be open to the inspection surface. Defects that remain below the surface or whose opening to the surface has closed for any reason cannot be detected with this method. In addition, a highly porous structure of the test piece also rules out detection with this method.

Penetrant Testing is probably the most widely used NDT method. The part is coated with a visible or fluorescent dye; excess dye is removed and a developer applied. The developer acts like blotting paper, drawing the penetrant out of surface-breaking defects.

With visible dye, the bright color contrast makes the bleed-out visible; with fluorescent dye, ultraviolet light makes it glow. Penetrant liquids are usually red in color. The penetrant's characteristic is its ability to enter surface cracks and cavities.