Liquid penetrant testing is one of very common NDT methods. This method is suitable for detection of surface imperfections. The main application is in the automotive and aerospace industry, furthermore in energy and transport industry. This method is easy to perform and in basic application is cheap. PT allows detection of discontinuities on the surface (e.g. cracks, porosity, inclusions, laps, etc). Penetrant testing can be used for wide range of technical materials (steel, alloys of Al, Ni, Cu, Ti, glass, ceramics, plastics, ...) It is irreplaceable method for testing of non-ferromagnetic materials. This method can be used for part examination both in-process and in-service or maintenance.

Physical Background

Penetrant (the liquid with suitable properties) is deposited on the clean and dry surface of the part to be examined. Penetrant needs some "penetration" time to penetrate the surface opened imperfections. After this dwell time the excess penetrant shall be removed from surface and the developer is deposited on the surface. The developer is strong absorber, and withdraws the penetrant from discontinuities to the surface. After developing time it is possible to inspect presence of two-dimensional indications. Advantage is, that imperfections that are so small to be visible by human eyes, create larger indications. These indications create high contrast (color or brightness) on the background. Imperfection is detectable approximately from the width of microns (depending on the surface quality, type of the imperfection, penetration material used, etc.).