Fluorescent Penetrant Inspection Services

FPI line

There are many ways to inspect parts. Fluorescent penetrant inspection (also known as liquid or dye penetrant inspection) is a form of non-destructive testing designed to detect surface defects on parts without destroying the parts themselves. This assists manufactures with their quality control, and helps prevent businesses from releasing defective parts into the market.

J&L Dimensional Services has two primary FPI lines dedicated to medical surgical implants and automotive part testing. In addition, we're working on an aerospace FPI line that is due to launch in 2020.

Due to the size and speed of our liquid penetrant inspection lines, we're able to handle large part sizes and large quantity orders without giving up quality. Contact us to learn more about our fluorescent penetrant inspection services, or request a quote for your project today. 

What Defects Does Penetrant Testing Reveal?

During the dye penetrant inspection process, we're on the hunt for discontinuities or interruptions in the normal structure of a part. There are 3 categories of discontinuities: inherent discontinuities, processing discontinuities, and in-service discontinuities. By identifying what kind of discontinuity exists, we can often understand what part of the manufacturing process produced the error. At J&L Dimensional Services, we're equipped to identify both inherent and processing discontinuities with fluorescent penetrant inspection.

Inherent Discontinuities

Inherent Discontinuities are formed during the initial processing, or casting, and solidification process. Types of inherent discontinuities include:

  • Inclusions
  • Pipes
  • Porosity
  • Cracks
  • Shrinkage
  • Hot Tears
  • Blowholes

Processing Discontinuities

During hot temperature forming processes like forging and welding, or cold processes like drawing, processing discontinuities sometimes occur. Processing discontinuities include bursts, laps, cracks and more.

How Fluorescent Penetrant Inspection Works

Fluorescent penetrant inspection is an eight step process. Each dye or liquid penetrant inspection line involves these steps: penetration, dwelling, rinsing, draining, drying, developing, a second round of dwelling, and the final inspection.


1. Penetrant Station

At the penetrant station, the parts must be prepared for the application of the penetrant. In order for the penetrant to adhere to the parts, they must be rinsed and cleaned. With the preparation complete, the parts are either placed into a basket and submerged in the liquid penetrant or sprayed with the fluorescent penetrant on the line.

2. Rest Station

At receiving the liquid penetrant, the part enters the first dwell station. As the parts rest, the penetrant has time to seep into any cracks, chips, grooves or other defects on the surface of the part.

3. Rinse Station

After the first rest, the parts move into the rinse station. Here, the excess penetrant is removed from the part. Some penetrant will remain in places where cracks, grooves, and other defects are present. This penetrant will illuminate in the inspection station, revealing any surface defects on the parts.

4. Drain Station

Parts must be completely dry during inspection. So, after the rinse, the parts enter a drain station where a majority of the rinse liquid drains away. The remainder of the liquid is then evaporated in the dryer station.

5. Dryer Station

During this phase, the parts are sent through a heated area of more than ___ degrees where they can dry.

6. Developer Station

At the developer station, developer is applied to the part according to customer specifications. We do not use a developer on the automotive line, but medical FPI requires a dry developer powder. The powder is applied to the entire inspection area, but only sticks to the areas where penetrant is present. This brings more penetrant to the surface and provides a contrasting white background to make any problematic indications more visible during inspection.

7. Rest Station 2

Once again, the parts take a rest so the penetrant has time to settle.

8. Inspection Station

Finally, the parts arrive in the inspection station. This area is filled with black lights. When the black lights turn on, any remaining penetrant reveals surface defects on the parts.

J&L's Fluorescent Penetrant Inspection Lines

Fluorescent penetrant testing (Liquid penetrant testing/dye penetrant testing) is a nondestructive method of finding defects in non-porous materials. Often times, FPI is a critical part of manufacturing lines that need to inspect the integrity of their parts. At J&L Dimensional, we have two distinct FPI lines - a small part line for medical FPI, and a large part line that’s primarily used for automotive FPI. Our third line, and aerospace FPI line, is expected to be active in our plant in 2020.

Small Part FPI Line

Medical - Surgical Implant Testing

Within the medical field, fluorescent, liquid, or dye penetrant inspection is most commonly used for surgical implants. Implanted devices with defects always cause issues in humans, and some of them are limb or life threatening. That's why fluorescent penetrant inspection is a vital part of the implant making process.

Our small part liquid penetrant inspection line is designed especially for medical applications. Due to the health risks associated with faulty surgical implants, choosing a quality fluorescent penetrant inspection line is crucial for surgical implant manufactures. This line is equipped to do quality inspections for a large quantity of parts.

Large Part FPI Line


Car manufacturers need to know that their vehicles are road ready. A variety of automotive parts are great candidates for dye penetrant testing. Using our automotive fluorescent penetrant inspection line, we can inspect small parts like brake disks and larger parts like exhaust systems.

The FPI line at J&L Dimensional has a large-object fluorescent penetrant inspection system that's one of the best in the midwest. The opening of our dryer allows up to 50" parts to fit through with ease. Due to the streamlined nature of the line, we’re able to send 36, 50" parts through the line in one hour, or 150, 12" parts through the line in one hour.

coming soon photo
Aerospace FPI Line

The need for nondestructive testing for aerospace parts is significant, which is why we're dedicated to bringing our Aerospace FPI line to the market in 2020.

Come back for more updates on our progress and capabilities for aerospace liquid penetrant testing.

When You Shouldn't Use Fluorescent Penetrant Testing

FPI isn’t the best solution for every application. If the material you’re inspecting has a rough or porous surface, it’s not a good candidate for FPI. That’s because penetrant will stick in the penetrant will hold in the rough surface and create a false indication.

If we tried to FPI parts that were meant to be rough or porous, the part would glow all over and we wouldn’t be able to get an accurate reading.

Additionally, FPI isn’t for detecting interior defects. So, if you need to inspect the integrity of a part below its surface, it’s best to use X-ray or CT scanning.

Case Study

FPI line 3

Finding Flaws and Fixing Parts on our Medical Fluorescent Penetrant Inspection Line

This year, one client wanted to use non destructive penetrant testing to inspect medical devices. Our team was able to use fluorescent liquid penetrant to discover any discontinuities on the surface of the parts. The feedback we were able to give helped them adjust their process in order to make their parts more accurately. Not only were we able to identify the errors, we were also able to correct some of them. Many of our FPI inspectors are also trained finishers so we were able to salvage the parts in house, re-inspect, and certify them without causing lengthy delays for our customer!

Meeting Quick Deadlines with Our Large Part FPI Line

J & L is proud to partner with major U.S. manufacturers. Sometimes, these manufacturers have a sudden demand for parts that they’re unable to fill on their own. Recently, one manufacturer needed to test 236 parts in a 24 hour window. Our automotive FPI line and inspectors were able to process all of the parts and get them back to the client in time to meet their deadline.

Helping Manufacturers with Limited Capacity Inspect Their Parts

Some of the region’s best manufactures have limited building space that can’t accommodate the size of a proper liquid penetrant testing station. Our team comes alongside those businesses and handles their penetrant testing for them so they can use their space for the manufacturing that they do best.