Liquid Penetrant Testing

Pt (dye penetrate testing)
dye penetrant inspection (dpi), also called liquid penetrant 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). 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. Lpi is used to detect casting, forging and welding surface defects such as hairline cracks, surface porosity, leaks in new products, and fatigue cracks on in-service components.
Dpi is based upon capillary action, where low surface tension fluid penetrates into clean and dry surface-breaking discontinuities. Penetrant may be applied to the test component by dipping, spraying, or brushing. After adequate penetration time has been allowed, the excess penetrant is removed and a developer is applied. The developer helps to draw penetrant out of the flaw so that an invisible indication becomes visible to the inspector. Inspection is performed under ultraviolet or white light, depending on the type of dye used - fluorescent or nonfluorescent (visible).
Pt applications include
metals (aluminum, copper, steel, titanium, etc.)
glass
many ceramic materials
rubber
plastics
following defects are find out by pt
liquid penetrant inspection can only be used to inspect for flaws that break the surface of the sample. Some of these flaws are listed below
fatigue cracks
quench cracks
grinding cracks
overload and impact fractures
porosity
laps
seams
pin holes in welds
lack of fusion or braising along the edge of the bond line
as mentioned above, one of the major limitations of a penetrant inspection is that flaws must be open to the surface.