liquid penetrant testing

Liquid Penetrant Testing (LPT)

Magnetic Particle Testing

Liquid Penetrant Testing (LPT), also known as visible dye penetrant testing, uses fluorescent dye to indicate and detect surface flaws in parts and components that might not be visible to an inspector’s eye. It is a relatively simple process and one of the least expensive methods of non-destructive testing.


The technique is based on capillary action, or the ability of liquid to flow into a narrow space without the assistance of external forces. This property allows the dye to mark any surface flaws for inspection.

After thoroughly cleaning components to remove any contaminants that might interfere with the testing, we apply the penetrant using aerosol spray cans in our mobile darkrooms. The penetrant is allowed to remain on the surface for a sufficient amount of time to penetrate and detect any damages.

Once that time has elapsed, we carefully remove the excess penetrant from the component, and apply a developer. This allows the dye to fluoresce under ultraviolet light, making it ready for examination by one of our highly-trained technicians.


Liquid Penetrant Testing can detect very small flaws. We use fluorescent penetrants because they are more sensitive than other systems and better mark any potential damage in components.

The process is also fast, portable and fairly inexpensive for rapid inspection of large areas or complex geometrically-shaped components. It can be used on almost anything that is not extremely rough or porous -- including metals, certain plastics and ceramics -- so there are few material limitations.


In the industries we serve, LPT is commonly used in the aerospace, automotive and power sectors. It can be used to test parts critical to safety, such as turbine blades on an airplane, as well as non-ferrous power generation components, including large castings or forgings.


Are you in need of Liquid Penetrant Testing? USINDT’s mobile darkrooms bring any needed materials to you as part of a full suite of testing, inspection and certification services for the construction, manufacturing, power generation, oil and gas, aviation and infrastructure sectors.