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What is a liquid penetrant test?

A liquid penetrant test (LPT), also known as dye penetrant inspection (DPI) or penetrant testing (PT), is a non-destructive testing method used to detect surface defects, such as cracks, porosity, laps, and seams in materials.

In this test, a liquid penetrant (dye) is applied to the surface of the material being inspected. After a specified period of time, the excess penetrant is removed, and a developer is applied to the surface to draw the penetrant out of any surface-breaking defects. The developer forms a visible indication on the surface, making it easy to identify the location and extent of any defects.

LPT is widely used in the aerospace, automotive, and manufacturing industries to inspect materials such as metals, plastics, ceramics, and composites. It is a cost-effective method of detecting surface defects and is commonly used as a follow-up inspection after visual inspection or other non-destructive testing methods.