Penetrant Testing (PT), is a widely applied and low-cost inspection method used to locate surface-breaking defects in all non-porous materials.
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.
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. PT 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 (about 10 minutes) 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 non-fluorescent (visible).
Normative references of the liquid penetrant method are:
- UNI EN ISO 17635: Non-destructive examination of welds - Examination with Penetrant - General principles.
- UNI EN ISO 23277: Non-destructive examination of welds - Penetrant testing of welds - Acceptance levels.
- UNI EN ISO 3059: Non-destructive testing - Examination with penetrant and magnetic particle inspection - Terms of vision.
- UNI EN 10228-2: Non-destructive testing of steel forgings - Control of penetrant.
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