Liquid Penetrant Testing (Fluorescent Penetrant Inspection - FPI)

Fluorescent penetrant inspection (FPI) is a highly effective method for identifying surface-breaking flaws, cracks, and defects that might otherwise go unnoticed. This non-destructive testing (NDT) technique is widely used in various industries, including aerospace, automotive, medical, and power generation. The FPI process involves the careful cleaning of the object's surface before a fluorescent dye is applied. The dye penetrates any cracks or defects, and after a set amount of time, excess dye is removed, leaving the defect outlined in vivid, contrasting colour. This makes it easy for technicians to detect any flaws that might otherwise be difficult to see with the naked eye.

In the aerospace industry, FPI is a crucial step in ensuring the safety and reliability of aircraft components. During the manufacturing process, FPI is used to check the quality of raw materials, such as sheet metal, forgings, and castings, before they are assembled into larger structures. In-service aircraft are also inspected using FPI to detect any signs of wear and tear, stress, or other forms of damage. In the medical industry, FPI is used to detect defects in components such as medical implants, prosthetics, and surgical instruments. This ensures that these products are safe and reliable for use in medical procedures. In addition to FPI, liquid penetrant testing (LPT) encompasses other NDT techniques such as water-washable penetrant testing and solvent-removable penetrant testing. These techniques use different types of penetrants and cleaning methods to identify flaws on the surface of objects.

FPI Solutions for Manufacturing and MRO

Our systems are designed to meet the ASTM E1417 FPI standard that is commonly used in both the aerospace and medical industries. Kemet provides a comprehensive range of standardised systems that offer the flexibility to combine automated and manual operation. This enables streamlined and maintainable non-destructive testing (NDT) inspections with integrated waste water handling and extraction systems as optional features that result in significant cost savings on process chemicals, labour, and energy consumption.

Finnsonic has been providing fully automated systems for inspecting critical airframe components, turbine blades, and medical implants, as well as smaller manual systems for less critical parts. A well-designed combination of automation and manual handling can significantly reduce labour requirements, while an adjustable layout can provide a small footprint. These FPI systems are durable, safe, ergonomic, and user-friendly, just like Finnsonic's cleaning machines.

Kemet offer a range of systems to suit different inspection needs. Our flexible manual roll track spray lines have a small footprint, while our fully automated roll conveyor immersion lines are suitable for high-capacity mass production with dipping penetrant application, "Dust Storm" developer chamber, and integrated pre- and post-wash. Kemet also provide additional options such as material handling, batch traceability via data log, fully automated penetrant and developer spray, basket rotation, basket trolleys, and automatic loading/unloading conveyors.

Automated FPI Line

  • The automatic FPI line ensures process safety and high capacity with minimal operator involvement.
  • User friendly operator interface with data collection of each batch for quality control and traceability.
  • Buffering infeed conveyor, various conveyor sizes available on request.
  • Pre-cleaning with ultrasonic technology provides precision cleaning with automatic tuning feature.
  • Water wash with dedicated spray nozzles, penetrant residues removed from the waste water in a separate storage tank.
  • Emulsifier, PLC controlled time critical treatment.
  • Automatic electrostatic developer spray with rotation of the carrier, PLC controlled contact time.
  • The carriers can hold parts with various sizes and shapes.

FPI solution concepts

Manual roll track spray line

  • Ideal for inspection of wheel and brake parts
  • Flexible with a small footprint
  • Optional dip or electrostatic spray methods

Roll conveyor immersion line

  • Automated high capacity system for mass production
  • Penetrant application by dipping
  • “Dust Storm” type developer chamber

Manual chain hoist line

  • Higher throughput with minimum foot print
  • Double FPI line for turbofan MRO

Automated line

  • Integrated process with pre and post wash
  • Automated process control and material handling
  • Batch traceability via data log

Booth line

  • A manual monorail system
  • Inspection of large parts such as aero-structures

Key features and benefits

  • Intelligent combination of automation and manual handling provides labour cost savings
  • Traceable and reliable inspection
  • Adjustable layout provides small footprint
  • Low consumption of process chemicals
  • Low operational costs
  • Durable and safe
  • Ergonomic/User-friendly

Optional features include

  • Fully automated penetrant and developer spray
  • Basket rotation
  • Upgraded ventilation systems
  • Integrated Pre-cleaning and cleaning after FPI processes
  • Basket trolleys and automatic loading/unloading conveyors

Main applications

  • Engine parts
  • Aerostructures
  • Wheel hubs
  • Brake parts
  • Landing gear
  • Automotive parts

Fluorescent Penetrant Inspection machine

General Questions regarding Fluorescent and Liquid Penetrant Testing

Fluorescent Penetrant Inspection vs Magnetic Particle

Fluorescent Penetrant Inspection (FPI) and Magnetic Particle Inspection (MPI) are two different non-destructive testing techniques used to detect surface and slightly subsurface discontinuities in metallic materials. The primary difference between the two techniques is the way they detect these discontinuities.

In Magnetic Particle Inspection (MPI), a magnetic field is applied to the part being inspected. Ferromagnetic particles are then applied to the surface, which is then magnetised by the applied magnetic field. Any discontinuities in the material will cause a leakage of magnetic flux, which will attract the particles, forming an indication. This technique is typically used to detect surface and subsurface discontinuities in ferromagnetic materials, such as cracks, laps, seams, and porosity.

What does Fluorescent Penetrant Inspection detect

FPI can detect surface-breaking cracks and discontinuities that are open to the surface of the material being inspected. It can be used to inspect a variety of materials, including metals, plastics, ceramics, and composites. FPI is commonly used in industries such as aerospace, automotive, and manufacturing to ensure the quality and integrity of critical components.

When is Fluorescent / Liquid Penetration Testing required

  • Quality control: FPI is often used as a part of quality control procedures in manufacturing and maintenance operations. It can help to ensure that components are free from surface cracks, porosity, laps, and other discontinuities that could compromise their safety and reliability.
  • Regulatory compliance: FPI may be required by regulatory agencies such as the Federal Aviation Administration (FAA), the Nuclear Regulatory Commission (NRC), and the Department of Defence (DoD). These agencies may require FPI to be performed on critical components to ensure their safety and reliability.
  • Failure analysis: FPI can be used to investigate the causes of component failures. By inspecting failed components, FPI can help to identify the location and extent of any surface discontinuities that may have contributed to the failure.
  • Routine maintenance: FPI can be used as a part of routine maintenance procedures to ensure the continued safety and reliability of components over time. By regularly inspecting components using FPI, maintenance personnel can identify and address surface discontinuities before they become a safety or reliability issue.

Dye Penetrant Inspection vs Fluorescent

Dye Penetrant Inspection (DPI) uses a coloured dye that penetrates into surface discontinuities by capillary action. The excess dye is then wiped off, and a developer is applied that draws out the dye from the discontinuities, making them visible to the inspector. The dye used in DPI is typically visible to the naked eye and does not require a UV light source for detection.

Fluorescent Penetrant Inspection (FPI), on the other hand, uses a fluorescent dye that is applied to the surface of the part being inspected. The dye penetrates into surface discontinuities by capillary action. After a dwell time, excess dye is removed, and a developer is applied. The developer draws the penetrant out of the discontinuities, causing them to show up as bright indications under UV light. FPI can detect smaller and shallower surface discontinuities than DPI, and it can provide greater contrast between the indication and the background surface.

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