Liquid Penetrant Testing (PT) is one of NDT (Non-Destructive Testing) techniques that is dedicated to detecting surface defects in all non-porous materials. A PT 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. The principle of PT is: draw the liquid indicator on the surface-breaking crack by capillary action; remove excess surface penetrant; apply a dry powder to the surface; draw out the penetrant in the crack and produce a surface indication.
Reference Definition by Nationalboard.org: Liquid Penetrant Testing (PT) is one of the most popular Nondestructive Testing (NDT) methods in the industry. It is economical, versatile, and requires minimal training when compared to other NDT methods. Liquid penetrant exams check for material flaws open to the surface by flowing very thin liquid into the flaw and then drawing the liquid out with a chalk-like developer. Welds are the most common item inspected, but plate, bars, pipes, castings, and forgings are also commonly inspected using liquid penetrant examination.
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