Liquid Penetrant Testing

So many things in the world around us are hidden from view. And if we can’t see something it doesn’t mean it’s not there. That’s where liquid penetrant testing comes in. 

This NDT method is used to find surface-breaking defects in all non-porous materials. Both ferrous and non-ferrous metals and alloys can be used with it. It’s also great for testing painted surfaces, ceramics, and plastics. But there’s a lot more to know about this method before you undergo liquid penetrant testing training. Keep reading.


What is Liquid Penetrant Testing?

In NDT, liquid penetrant testing (LPT) is a low-cost inspection method used to detect surface-breaking defects in non-porous materials. The process is relatively simple. Firstly, a liquid penetrant will be applied to the surface of the component that is to be inspected. 

The excess penetrant will be removed, and a developer is applied. The developer acts as a blotter, drawing the penetrant out of any defects that may be present. This makes the defects visible to the naked eye, allowing them to be inspected and repaired as necessary.

Types of Liquid Penetrant Testing

There are two main types of LPT: 

Visible Dye Penetrant Testing

In the process of this type, a visible dye is used as the penetrant. Once the developer has applied, the defects will be visible to the naked eye.  

Fluorescent Dye Penetrant Testing

This type uses a fluorescent dye as the penetrant. To see the defects, they must be viewed under ultraviolet (UV) light. This type is often used in difficult-to-inspect areas or when very small defects need to be found.

Process of Liquid Penetrant Testing

There are four steps in the process of liquid penetrant testing: 

  1. Pre-cleaning: The surface to be tested must be clean and free of any contaminants. This step is crucial to ensure the accuracy of the testing.
  1. Application of Penetrant: The penetrant is applied to the surface of the component. 
  1. Removal of Excess Penetrant: The excess penetrant is removed from the surface. This can be done using a cloth, paper towel, or other absorbent material.
  1. Application of Developer: The developer is applied to the surface. This will help to draw the penetrant out of any defects that may be present.

Importance of Liquid Penetrant Testing Training

It is important to undergo liquid penetrant testing training before carrying out this inspection method. This is because several factors can affect the accuracy of the testing. These include: 

  • The type of penetrant used
  • The type of developer used
  • The cleaning method used
  • The method of application
  • The drying time

All of these factors need to be taken into account in order to carry out the testing correctly. If you are not properly trained, you may not be able to carry out the testing accurately, which could lead to defects going undetected.


Liquid penetrant testing is an important process that helps ensure the quality of products we use every day. By understanding the different types and processes involved in this type of testing, you can be better equipped to spot potential problems before they become a bigger issue.

Finally, liquid penetrant testing training is essential for anyone looking to perform this type of testing – make sure you’re up to date on the latest techniques by enrolling in a course today!

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