Dye penetrant inspection

Read more about our Dye Penetrant Inspection services below:

What is Dye Penetrant Inspection?

Dye penetrant inspection (DPI), also called liquid penetrate inspection (LPI) or penetrant testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials (metals, plastics, or ceramics).

How does Dye Penetrant Inspection Work?

One of the oldest and simplest methods of Non-Destructive Testing, dating back as far as the 19th century. Dye Penetrant Inspection is used to detect any surface connected discontinuities such as cracks from fatigue, quenching, and grinding, as well as fractures, porosity, incomplete fusion, and flaws in joints.

After an initial pre-cleaning process, a liquid penetrant is applied to the inspection surface. The penetrant stays in contact for a pre-determined "dwell time", which allows the penetrant to soak into any flaws. The excess penetrant is then removed. Once the surface has been cleaned a developer is applied in a thin even coating. The developer acts to draw penetrant out of any surface flaws, leaving a visible indication in the location of the flaw.


This inspection method can be used to detect


• Porosity in castings and welds.
• Cracking in castings, ceramics, plastics wrought products and welds.
• Fatigue and stress related defects during in-service inspection.


Penetrant Testing can be carried out with both visible and fluorescent dyes for multiple inspection modes and sensitivity levels, viable for a variety of industries using conductive or non-conductive, magnetic or non-magnetic, metallic or non-metallic materials.


Advantages of Penetrant Testing


• Rapid, portable, low-cost test method on complex shapes.
• High sensitivity.
• Visual representation of indications Disadvantages of Penetrant Testing.
• Can only detect surface flaws.
• Pre and post cleaning reliant.
• Surface finish and roughness affect inspection.
• Multi-step process.
• Direct access required.

The penetrant may be applied to all non-ferrous materials and ferrous materials, although for ferrous components magnetic-particle inspection is often used instead for its subsurface detection capability

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