Advantages and Capabilities of Liquid Penetrant Inspection.
a. Liquid penetrant inspection is capable of examining all of the exterior surfaces of objects. Complex
shapes can be immersed or sprayed with penetrant to provide complete surface coverage. Other
nondestructive methods cover a specific area or location and must then be repeated to cover other areas
b. Liquid penetrant inspection is capable of detecting very small, surface discontinuities. It is one of the
more sensitive nondestructive inspection methods for detecting surface flaws.
c. Liquid penetrant inspection can be used on a wide variety of materials: ferrous and nonferrous metals
and alloys, fired ceramics, powdered-metal products, glass, and some types of organic materials.
Restrictions of the penetrant application are listed in paragraph 2.1.11.
d. Liquid penetrant inspection can be accomplished with relatively inexpensive, non-sophisticated
equipment. If the area to be inspected is small, the inspection can be accomplished with portable
e. Liquid penetrant inspection magnifies the apparent size of discontinuities making the indications more
visible. In addition, the discontinuity location, orientation, and approximate length are indicated on the
part, making interpretation and evaluation possible.
f. Liquid penetrant inspection is readily adapted to volume processing permitting 100 percent surface
inspection. Small parts may be placed in baskets for batch processing. Specialized systems may be
semi- or fully automated to process as many parts per hour as required.
g. The sensitivity of a penetrant inspection process may be adjusted through selection of materials and
technique. This allows suppression of indications from small, inconsequential discontinuities while
indicating larger discontinuities of more concern. Figure 2-3 shows indications from two penetrant
inspection processes of different sensitivity levels.
Figure 2-3. Cracked, Brittle Iron-Plated Coupon Showing the Inspection Results from Two Fluorescent
Penetrant Inspection Processes of Different Sensitivities.
Disadvantages and Limitations of Liquid Penetrant Inspection.
Penetrants, emulsifiers, and some types of developers have very good wetting and
detergent properties. They can act as solvents for fats and oils. If they are allowed
to remain in contact with body surfaces for extended periods, they may cause skin