An Insider Guide to Fluorescent Penetrant Inspection
Engineers and technicians across major manufacturing industries use fluorescent penetrant inspection (FPI), a non-destructive testing method utilizing black light and a dye penetrant, to identify surface flaws in materials like plastics and metals. If left undetected, surface cracks can spread, which can ultimately cause part failure – and even catastrophic damage. This is why this inspection is so important.
How Does Fluorescent Penetrant Inspection Work?
Fluorescent penetrant inspection is sometimes referred to as “dye penetrant inspection” or “liquid penetrant inspection”, but they are all one in the same. Two types of penetrant liquids are commonly used: fluorescent and visible. Regardless of the liquid used, the process is similar:
- Clean the surface: The surface must be cleaned of any dirt or debris before testing begins. This can be accomplished using wire brushing, grinding or solvent degreasing.
- Apply the penetrant: The technician or engineer applies a dye penetrant that fluoresces under UV-A black light onto the surface of the material under testing. The penetrant is applied by spray gun or brush and must be allowed to dwell on the surface for up to 30 minutes to allow it to penetrate any surface openings.
- Remove excess penetrant: Using a clean cloth or water rinse, excess penetrant is carefully removed from the surface. Of course, close attention is paid here to ensure the penetrant is not removed from surface openings.
- Apply the developer: If there are any surface cracks or openings, the penetrant seeps into them and a developer is then applied to the surface.
- Inspect the surface area for indications: The developer draws the penetrant to the surface, making surface damage visible to the naked eye. The indication may be faint depending on the sensitivity level, so the technician or engineer performs a careful examination.
For specific instructions, please reference our Fluorescent Penetrant Method Guides: Method A, Method B, Method C, and Method D.
Common Applications
This testing is used across several industries where you find safety-critical components. It’s important to perform routine evaluations to spot issues early and ensure safe operations. Some common applications are outlined below.
Aerospace
The aerospace industry relies upon fluorescent penetrant systems for the detection of defects in aircraft and engine components during maintenance and overhaul operations.
Automotive
The automotive industry uses penetrant testing primarily during nonferrous parts design and maintenance of production equipment.
Energy
Within the energy industry, sectors such as gas & oil, nuclear, gas turbine and wind rely heavily on liquid penetrant for the inspection of welds, valves, vanes and blades.
Marine & Shipping
Classification societies require ship manufacturers to perform non-destructive examination of new, re-built and repaired ships. So, penetrant testing is used frequently in the marine and shipping industry, such as during inspections of ship weldments, propellers and pipes.
Types of Fluorescent Penetrants
We offer several series of penetrants, all of which are QPL-certified. A few of our most requested penetrant systems are outlined below:
Fluorescent Penetrants – Biodegradable
- Biodegradable Penetrants by Met-L-Chek® are water-washable and solvent-removable and are used for the detection of fine cracks, porosity, and through-leaks on metals, composites, synthetic materials and even plastics. The materials used are low in sulfur, halogens, VOC-free and safe for use on all metal surfaces.
- Met-L-Chek® FBP Series Penetrants are bright yellow, smooth washing and non-gel forming, allowing them to wash cleanly from rough surfaces.
Fluorescent Penetrants – Water Washable
- All Met-L-Chek® Method A[i] & C[ii] Fluorescent Water Washable Penetrants are SAE AMS 2644 QPL certified, meeting the requirements of AMS 2647, ASTM E1417, ASTM E165, ASTM E1209, ISO/FDIS 3452.
- Met-L-Chek® Method A & C Fluorescent Water Washable Penetrants are also solvent-removable and used for the detection of fine cracks, porosity, and through-leaks on metals, composites, synthetic materials and plastics. The materials used are low in sulfur, halogens and safe for use on all metal surfaces.
- Met-L-Chek® Method A & C Fluorescent Water Washable Penetrants are bright yellow, smooth washing and non-gel forming, allowing them to wash cleanly from rough surfaces.
Fluorescent Penetrants – Post Emulsifiable
- All Met-L-Chek® Post Emulsifiable Penetrants are SAE AMS 2644 QPL-certified, meeting the requirements of AMS 2647, ASTM E1417, ASTM E165, ASTM E1209, ISO/FDIS 3452.
- Met-L-Chek® Post Emulsifiable Penetrants are used in Methods B[iii], C & D[iv] for the detection of fine cracks, porosity, and through-leaks on metals, composites, synthetic materials and some plastics. They are low in sulfur and halogens and safe for use on all metal surfaces.
Why Incorporate FPI in Your Quality Control Plan
Fluorescent penetrant inspection is a cost-effective and non-destructive method of accurately detecting surface damage and defects, making this an essential part of a quality control system.