Dye Penetrant Inspection (DPI), also known as Liquid Penetrant Inspection (LPI), is a Non-Destructive Testing process used to detect surface breaking defects in all non-porous materials e.g. metal, plastics and ceramics.

DPI is a very cost effective method of inspecting castings, forgings and weldments and is regularly used in many industries including (but not limited to) steel fabrication, renewable energy, aerospace, power generation, transportation and in the gas and oil sectors.

Dye Penetrant Inspection can be applied to both non-ferrous and ferrous materials but Magnetic Particle Inspection (MPI) is usually used to examine ferrous materials because it can also detect defects which may be just below the surface but not actually breaking the surface of the item being examined.

The dye penetrant is very portable, which enables easy on-site inspections to be completed.

Dye Penetrant Inspection is performed by the application of a visible or fluorescent solvent or water based dye to the surface of the test component and left for a ‘dwell’ or ‘soak’ time. During this dwell time the dye penetrates any surface breaking defects through capillary action.

Once the dwell time is complete any excess dye is removed from the test component and a developer is applied. The developer draws the dye out of the surface defect. A visual inspection is then performed by the Inspector under ultraviolet or white light, depending on the type of penetrant used (fluorescent or visible colour contrast). DPI is useful in detecting hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.

IACS NDT use PCN Level 2 qualified personnel to perform any inspections with dye penetrants. All inspections are carried out with approved procedures which follow the most recent international British Standards and/or any client specifications. Risk assessments are undertaken and are issued to the client with the relevant COSHH data sheets.

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