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Liquid Penetrant Testing  (PT)

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PT is a widely applied NDT method that is utilized to detect surface breaking flaws in ferrous & non-ferrous materials. PT is based on capillary action which is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. Because PT is based on capillary action pre-cleaning is of the up most importance when using PT as an examination method.

PT can be used to examine small parts, large parts, parts with complex geometry, and welds

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After penetrant is applied it has to stay on the part for specified dwell time usually ranging from 5 to 60 minutes depending on the specification. The dwell time allows the penetrant time to enter the discontinuity. After the dwell time the excess penetrant is carefully removed and a developer is applied.

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The developer is also given a specified dwell time usually ranging from 5-60 minutes depending on the specification. The developer causes reverse capillary action also referred to as bleed out. Bleed out draws the penetrant out from discontinuity. The developer also provides a contrasting background when utilizing the  visible penetrant testing method. making discontinuities to be easily seen by the technician.

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Advantages of PT

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Works on complicated geometric shapes

sensitivity 

Cost-Effective 

Visual results

Few materials Limitations

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Disadvantages of PT 

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Works on porous surface materials only

No depth sizing

Environmental concerns

Surfacing breaking flaws only

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