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Fun Fact Friday: Liquid Penetrant Testing

By July 17, 2020No Comments3 min read

This week’s Fun Fact Friday will focus on Liquid Penetrant Testing (LPT) and Examination, one of the Non-Destructive Examination (NDE) inspection services that Encorus Group offers. LPT is used to detect discontinuities that are on the surface of ferromagnetic (materials that are attracted to magnets) or non-ferromagnetic materials. This type of testing is one of the most widely used NDE inspection methods in the construction industry and any other situation where the surface of materials could be subject to discontinuities.

According to NDT Resource Center, there are several steps involved in the liquid penetrant inspection process.

Surface Preparation

During this step, the surface that will be tested is thoroughly cleaned to prevent any contaminants from potentially blocking the penetrant from entering into the flaw. This is a vital step in the process because without it, a flaw could go undetected. Once the area is cleaned and dried, the inspector moves to the next step.

Penetrant Application

The next step involves applying the penetrant to the surface by spraying, brushing, or dunking the surface into the penetrant.

Penetrant Dwell

After the penetrant is applied, it is allowed to sit and seep into the surface for a period of time, sinking into the defect. This period of time can range from 5 minutes to an hour depending on the type of penetrant that is being used and the material that is being tested.

Excess Penetrant Removal

When it is time for the next step, the penetrant around the defect needs to be gently removed. To do this, a solvent, water, or an emulsifier is used to remove the excess without disturbing the penetrant within the defect.

Developer Application

When the excess penetrant is gone, a layer of developer is applied to the surface to make the penetrant inside the flaw visible.

Indication Development

This step allows the developer to sit on top of the penetrant for a long enough time in order to be able to accurately detect the flaw.


After the penetrant is visible, the inspector can begin to examine the area with the flaw and determine the size and where it is located. Proper lighting is very important so that the inspection can be as accurate as possible.

Clean Surface

After the flaw is noted, the penetrant is cleaned off of the surface and plans are made for repairs.

If you would like to learn more about LPT or other NDE processes, the NDT Resource Center has more in-depth information. If you have a project that needs Liquid Penetrant Testing and Examination services, contact Director of NDE Jim Handzlik at or (716) 592-3980 ext 148.