Liquid Penetrant Testing is a nondestructive means of locating surface discontinuities based on capillarity and capillary action.

In the liquid penetrant method, the liquid is applied to the surface of the specimen and sufficient time is allowed for penetration of surface discontinuities. If the discontinuity is small or narrow, as in a crack or pinhole, capillarity assists the penetration.

After sufficient time has passed for the penetrant to enter the discontinuity, the surface of the part is cleaned. Capillary action is again employed to act as a blotter to draw penetrant from the discontinuity.

Penetrant Testing is successfully used on metals such as aluminum, magnesium, brass, copper, cast iron, stainless steel, and most other common alloys.

It can also be used to test other materials, including ceramics, plastics, molded rubber, powdered metal products or glass.

Penetrant testing is not too much depending on geometry and size of the part to be inspected: the surface must not be extremely porous and have to be very well cleaned.

Advantages of Penetrant Testing:

¨    May be applied to almost any kind of material

¨    It is easy to perform and read.

¨    May be applied also on parts with low accessibility.

¨    Low cost equipment required.

Limitations of Penetrant Testing:

¨    Only discontinuities open to the surface may be detected.

¨    Discontinuities containing alien substances (like sand after sandblasting) are not detected.

¨    Surface preparation must be more accurate than for other NDT Methods.