The Basics of Dye Penetrant Testing

Dye penetrant testing helps determine flaws in a structure’s integrity, including metal, glass, ceramics, plastic and rubber.


As a builder, architect, or other professional overseeing a structure’s integrity, you want to make sure you deliver a quality product. This means that you need to find any existing flaws before you let anyone near your buildings. Not only do you want to avoid lawsuits, but you don’t want anyone to sustain injuries either. So you’ve turned to non-destructive testing for help.

You may have thought of non-destructive testing or NDT as simple before, but suddenly you have a variety of testing options before you. You see ultrasonic, radiographic, or magnetic particle testing in the list, and you may even see some other options, like dye or liquid penetrant testing. And as you look at this list, you think to yourself, “How do I know which one works best in my situation?”

You can only get an answer to that question by asking a professional or studying the various testing techniques. To help you with your decision, we at 20/20 NDT have outlined one of those techniques – dye penetrant testing – below. Read on to discover if this testing technique can help you with your project.

What Is Dye Penetrant Testing?

The Basics

Dye penetrant testing uses a coloured liquid to reveal pores, cracks, fractures, seams, and other flaws in a structure’s integrity. Testers can use it on a variety of materials, including metal, glass, ceramics, plastic and rubber. However, this testing method can only reveal flaws that break the structure’s surface, including:

  • Impact or stress fractures
  • Quench and grinding cracks
  • Chips
  • Porosity
  • Pinholes
  • Seams
  • Laps
If a material has any flaw on its surface, dye penetrant testing can find it. Simply contact our helpful staff at 20/20 NDT to learn more.

The Process

During the testing process, NDT professionals will take the following steps:
  • Preparing the surface: This step may seem simple, but it matters just as much as the other ones. After all, if the surface has contaminants on it, the dye will pool around them, and you could mistake a contaminant for a flaw. To prepare the surface, professionals will remove all oil, grease, water, and other contaminants, and then they may etch it. Etching removes any debris from sanding and other machining processes.
  • Applying the dye: Once the professionals have cleaned the target surface, they’ll apply the dye penetrant. They may spray or brush it on, or they could immerse the entire object in the dye.
  • Letting the dye sit: The dye has to sit on the surface for enough time to seep down into any flaws. This step could last anywhere between five and 60 minutes—the time varies on the dye and the target surface. This step could also take more time, but no matter what, the dye must not dry.
  • Removing the excess dye: This step often proves tricky because professionals have to remove as much dye as possible without scraping it out of the defects. They may use a water rinse, an emulsifier, or a solvent to remove the excess dye.
  • Applying a developer: Once the NDT professionals remove the excess, they apply a powder or liquid developer, which draws out the dyes trapped in cracks and other defects. This helps them see the flaws better.
  • Letting the developer sit: The dye has to sit, and so does the developer. This step can take 10 minutes or more, especially if you want to check for tight cracks.
  • Inspecting: Once the developer draws out the dye and makes all the flaws visible, the professionals will analyze the surface to determine its integrity.
  • Cleaning: Finally, if the target surface has sufficient structural integrity, the NDT testers will remove the developer and any remaining dye. If the target surface or structure lacks sufficient integrity, the professionals will instruct you from there. You may need to repair or replace the entire structure.

This process may sound simple to you, but don’t try to do it on your own. You could probably handle the application and cleaning processes, but only an experienced NDT professional should handle the inspection. He or she will know better how to spot and interpret structural flaws.

What Are the Advantages and Disadvantages of Dye Penetrant Testing?

So why would you choose this testing over other kinds of testing? It has the following advantages:
  • It can find even the smallest flaws.
  • You can use it on virtually any material.
  • You can use it on complex shapes.
  • You can inspect large surface areas in little time.
  • It has a lower cost than other methods.

However, this method doesn’t come without its disadvantages. As before mentioned, you can only test for cracks that break the surface. Your structure could still have other flaws. Dye penetrant testing can’t reliably test naturally porous materials either, and this method runs into problems if you don’t prepare the surface.

That being said, dye penetrant testing can provide reliable results in virtually any application as long as its facilitators do it properly. Call our helpful staff at 20/20 NDT if you have any questions and to see if this technique will work for you.