Penetrant inspection / crack detection

Penetrant inspection frequently asked questions

What is penetrant inspection?

Penetrant Flaw Detection (PFD), also known as Dye Penetrant Inspection (DPI) or Liquid Penetrant Inspection (LPI) or Fluorescent Penetrant Inspection (FPI) is a non-destructive testing method used to find surface-breaking defects like cracks and porosity in non-porous materials such as Aluminium. It works via capillary action, where a fluorescent liquid penetrant is drawn into flaws, then later revealed using a developer. The developer acts like a blotter, drawing the trapped penetrant out of the flaws (“bleed-out”) and making the defects clearly visible under UV light.

In Aluminium castings, PFD is essential for evaluating part integrity because casting processes can easily introduce microscopic surface defects.

What defects can penetrant testing find?

PFD has its Limitations. It can only detect flaws that break through to the surface of the Aluminium. It cannot detect internal, subsurface porosity. Highly porous, cast surfaces can sometimes trap penetrant, causing “false indications”. Castings typically require machining before testing for high-sensitivity requirements such as sealing faces or ‘O’ Ring grooves.

Is this method suitable for castings?

PFD is a highly effective and cost‑efficient Non‑Destructive Testing (NDT) method designed to reveal surface‑breaking defects on a casting. It’s ideal for quickly identifying issues that the naked eye would miss — such as hairline cracks, fine porosity, cold shuts or through defects on thin walled castings – ensuring your components meet the required quality standards before moving forward.

One of the biggest advantages of PFD is its versatility. It works on almost all non‑porous materials, including both ferrous and non‑ferrous metals, and can be carried out easily directly on-site. With minimal equipment and low operating costs, it offers excellent value without compromising accuracy.

Like any inspection method, PFD has its limits. Because it only detects defects that reach the surface, it cannot identify deeper internal issues such as hidden gas porosity or internal shrinkage. It also relies on proper surface preparation — the casting must be thoroughly cleaned to ensure contaminants don’t mask potential flaws.

For components that require inspection beyond the surface, we recommend complementary NDT methods. Radiographic Testing (X‑Ray) is ideal for detecting deep internal defects, while Magnetic Particle Inspection (MPI) is better suited for locating just‑below‑surface flaws in ferrous materials.

How are results recorded and reported?

Our NADCAP-approved Penetrant Flaw Detection (PFD) facility, the inspection results must be recorded in a controlled and traceable manner that complies with customer specifications, Nadcap requirements, and the applicable standards such as AMS 2644, ASTM E1417, EN4179, NAS410, or customer-specific procedures.

Typical inspection records include:

Job Identification; Process Parameters; Inspection Results; Defect Mapping; Inspection Disposition (Accept/reject/rework/concession); Personnel Traceability; Equipment Traceability; Retention of Records (In aerospace foundries and machine shops, retention periods of 7–30 years are common depending on the customer and end application).

Is penetrant inspection done in-house?

Non-Destructive Testing (NDT): Maycast-Nokes provides fully accredited Non-Destructive Testing (NDT) services, on-site here in Halstead. This includes Radiographic Testing (X-Ray) and Liquid Penetrant Inspection (LPI), to verify the integrity and quality of castings and precision-engineered components.

Penetrant Flaw Detection (PFD) – Expertise and Certification: Our NDT personnel are certified to NAS 410, EN4179, and PCN Level II standards and are trained to operate across multiple inspection disciplines. The team is supported by an in-house Level III specialist, providing complete control over procedure development, qualification, and technical oversight.

Both our Radiographic Testing and Liquid Penetrant Inspection facilities are fully Nadcap accredited. Reflecting our ongoing commitment to quality, compliance, and continuous improvement.

In addition to supporting our own manufacturing operations, Maycast-Nokes offers independent subcontract NDT inspection services for externally manufactured components. Inspections can be performed to customer-specific requirements, aerospace standards, and other applicable industry specifications.

For further information about our NDT capabilities or subcontract inspection services, please contact our team.