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CHAPTER 3: Liquid Penetrant Inspection (LPI) [Part 2, 3, 4, 5, 6] - Coggle…
CHAPTER 3: Liquid Penetrant Inspection (LPI) [Part 2, 3, 4, 5, 6]
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Density/Specific
Gravity
of a penetrant material has a slight to negligible effect on the performance of a penetrant. The gravitational forces acting on the penetrant liquid can be working either with/against the capillary forces depending on the orientation of the flaw during the dwell cycle
Increasing the specific gravity by decreasing the % of solvent in the solution which will increase the penetration speed
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Fluorescent
Penetrant
When fluorescent materials are involved, the effect of the color & fluorescent are not straight forward
PT materials fluoresce because they contain 1/more dyes which absorb EM radiation over a particular wavelength & the absorption of the photons leads to changes in electronic configuration of the molecules
The radiation absorption & emission could take place in a no. of times until the desired color & brightness is achieved. 2 different fluorescent colors can be mixed to interact by the mechanism called cascading
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Emulsifiers
When removal of the penetrant from a defect due to over-washing of the part is concern, a post-emulsifiable penetrant system can be used
Post emulsifiers penetrant requires a separate emulsifier which could break the penetrant down & make it water washable
Most penetrant inspection specifications classify penetrant systems into 4 methods of excess penetrant removal
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Method B: Post emulsifiable, lipophilic
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Method D: Post emulsifiable, hydrophilic
Penetrant
Removal Method
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Water washable penetrants are removed by using spray water & easiest to employ & most cost effective when inspecting large areas
Post-Emulsifiable penetrants are water-washable only after they have reacted with an emulsifier solutions. This system is used when washing the penetrant out of the defect is a concern
Developers
Role of developers is to pull trapped penetrant out of the flaw/defect & spread it out on the surface for the NDT officer to be seen. Also provides light background to increase the contrast when the visible penetrants is used
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