X-R-I Testing, NDT Testing Experts
Liquid Penetrant Nondestructive Testing

Liquid Penetrant (NDT) Testing

Also known as: Dye Penetrant Inspection (DPI), Liquid Penetrant Inspection (LPI), Penetrant Testing (PT), Fluorescent Testing

Liquid penetrant testing is one of the oldest methods of nondestructive testing still in use today because of its simplicity and remarkable sensitivity to locating very fine surface discontinuities. Used on ferrous, nonferrous, and even nonmetallic materials, dye penetrant inspection is the most common and cost effective of all NDT inspection methods.


  • Fast
  • Portable
  • Cost-Effective
  • High Sensitivity
  • Flaws are visually indicated on surface
  • Appropriate for large & complex shapes

How does Liquid Penetrant NDT work?

As the name implies, Liquid Penetrant testing involves a colored penetrating liquid that is applied to the surface of the material being tested. The liquid is drawn into defective areas in the material’s surface through capillary action and then drawn out to reveal itself to detection using UV lights or other methods, depending upon the type of penetrant and dye coloring used.

X-R-I Testing Laboratories provide a full range of economical liquid penetrant NDT services. Whether it’s high-volume production or testing individual, large, and complex objects, we offer quick turn-around and a high degree of reliability.

The Penetrant Testing Process

Step 1: Preparation
The surface is prepared by removing any contaminants that could interfere with the process.
Step 2: Application of Penetrant
The penetrant is applied by spraying, brushing or immersing in a bath. It is then left to site for an amount of time to allow as much dye penetration as possible.
Step 3: Removal
In this step, the inspector carefully removes excess penetrant without removing penetrant from the defects. Water or emulsifiers are sometimes used.
Step 4: Application of Developer
A layer of developer is applied to the surface, drawing penetrant out of flaws and to the surface, making it visible.
Step 5: Inspection
With the aid of proper lighting, visual inspection is performed to detect any indications that may be present.
Step 6: Cleaning
The last step is to remove the developer material from the areas of the surface lacking in defects.

Superior Testing

As an industry leader in nondestructive testing, XRI Testing is proud to be the name that people turn to when their application requires testing with honesty, integrity and a superior attention to detail. For over 75 years, XRI has provided quality NDT inspection services to a wide variety of industries, including critical fields such as aerospace and defense.

Our reputation for detail and precision is further supported by our extensive accreditation and certifications, including NADCAP and ISO. In addition to our outstanding services, our company is supported by a philosophy that focuses on honesty, integrity and responsibility.

To provide further value, we offer our extensive selection of testing services with competitive pricing and fast turnaround, as well as additional services, such as consultation, training, and on-site testing. For quality assurance with a proven track record and superior customer care, give us a call today.

Liquid Penetrant NDT in action.
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