LIQUID PENETRANT INSPECTION (LPI, PT)
Our nondestructive testing technicians certified according to ISO 9712 use liquid penetrant inspection method that reveals surface breaking flaws by bleed out of a penetrating liquid colored with a visible or fluorescent dye from the flaw.
The technique is based on the ability of a liquid to be drawn into a “clean” (in other words, unobstructed) surface breaking flaw by capillary action. After an appropriate period of time for penetration has passed, called the “dwell time,” excess penetrant on the surface is removed and a developer applied. The developer acts as a blotter and draws the penetrant from the flaw to reveal its presence. Penetrants with a visible dyed added (color contrast) require sufficient white light to ensure proper inspection, while penetrants with a fluorescent dye added need to be used in darkened conditions with an ultraviolet or “black light”.
This method according to ISO 3452, ISO 23277 is used to inspect a variety of product forms including castings, forgings, and weldments. It is one of the most portable of the surface inspection methods and also has the advantage of being able to detect flaws in non metallic and non ferromagnetic materials.