Liquid penetrant testing (LPT), which is also known as dye-penetrant inspection (DP), liquid penetrant inspection (LPI), or penetrant testing (PT), can be carried out using either visible or fluorescent dye penetrant. At Applus+, Liquid penetration inspection is one of the most common non-destructive testing (NDT) methods deployed because of its simplicity, effectiveness, and remarkable sensitivity to locating very fine surface discontinuities or flaws.

LPT involves applying a colored penetrating liquid to the surface of the material being tested. The liquid penetrant tests draw the dye into defective areas on the material’s surface through capillary action and then are revealed in detection using UV lights, or other methods depending upon the type of penetrant and dye coloring.

Fluorescent penetrant is typically more sensitive than the visible dye, and the DP test is ranked into 4 levels of sensitivity. In the field, fluorescent penetrant inspection requires special lighting conditions, containing UV-A lamps, blackout shades and power generators. Fluorescent-dye testing is easily performed under laboratory conditions.


Applus+ provides a full range of liquid-penetrant NDT services. Our Nadcap-accredited NDT services can offer fast project-turnaround times, with a high degree of reliability for high-volume production or for liquid penetrant testing on unique, large, and complex objects.

Trained to NAS410/EN4179 written practice, Applus+ has qualified technicians to meet our clients’ production requirements and Applus+ sources liquid penetrant testing materials from leading manufacturers who ensure their products meet code requirements.


Fluorescent dye penetrant is heavily utilized in the aerospace NDT sector and other industries that require a higher level of sensitivity achieved using visible dye. Liquid penetrant testing can be used on a variety of non-porous materials, including forgings, castings, ferrous and non-ferrous metals, and DP tests for welding.

Applus+ holds the Nadcap accreditation required to perform liquid penetrant testing on aerospace components.


Partnering with Applus+ helps assure our clients that their processes or products comply with industry regulatory requirements.

Liquid penetrant inspection and testing, when applied effectively, can:

  • Increase product reliability
  • Improve production processes by identifying problems quickly
  • Reduce costs through fewer returned items and less rework
  • Improve quality and assurance

Applus+ uses first-party and third-party cookies for analytical purposes and to show you personalized advertising based on a profile drawn up based on your browsing habits (eg. visited websites). You can accept all cookies by pressing the "Accept" button or configure or reject their use. Consult our Cookies Policy for more information.

Cookie settings panel