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LIQUID PENETRANT INSPECTION - Coggle Diagram
LIQUID PENETRANT
INSPECTION
Introduction
LPI method is used to reveal surface breaking flaws by bleed out of a colored or fluorescent dye from the flaw
the ability of a liquid to be drawn into a "clean" surface discontinuity or flaw by capillary action
Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity
Tendency of a liquid to penetrate or migrate into small openings such as cracks is due to capillary action
When a liquid wets a surface, the angle of contact or the wetting angle is less than 90°
Wettability reduces as the contact angle increase
How does PT work?
1) A liquid with high surface wetting characteristics is applied to the surface of a component under test.
2) Penetrant penetrates into surface breaking discontinuities via capillary action and other mechanisms
3) Excess penetrant is removed from the surface and a developer is applied to pull trapped penetrant back the surface
Basic Process of PT
1) Clean & dry component
2) Apply penetrant
3) Remove excess
4) Apply developer
5) Visual Inspection
Inspection
CAN be inspected
any material that has a relatively smooth, non-porous surface on which discontinuities or defects are suspected
CANNOT be inspected
Components with roughs surfaces, such as sand castings that trap and hold penetrant
Porous ceramics
Wood and other fibrous materials
Plastic parts that absorb or react with the penetrant materials
Components with coatings that prevent penetrants from entering defects
Types of Discontinuities can be detected
Castings: cold shuts, hot tears, porosity, blow holes, shrinkage
Forgings: cracks, laps, external bursts
Rolled products: cracks, seams, laminations
Welds: cracks, porosity, undercut, overlap, lack of fusion, lack of penetration