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Penetrating Testing (PT)Penetrating Testing (PT)
General statements for Penetrant testing
Discontinuities have to be open to the surface
in principle indepe ndent to material but surface not excessively porous
important additional test method to magnetic particle testing which can only be
used by ferromagnetic material
indication is not coming equal to the real size of defect, it is a temporary bleed out
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Cohesion
Each of the particles of a substance (molecule) isattracted by its neighbouring molecules.
This attraction force is much lower with liquids than
with solid materials, with gases it is very much lower than with liquids .
Therefore, a liquid, e.g. takes every given room. inspite of this there is a residual cohesion (attraction
force) between the liquid particles. If one is aware of this, a variety of facts can be explained.
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Surface tension
wetting ability
good surface tension low
bad surface tension great additional dependence:
Viscosity
surface roughness
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Viscosity
As viscosity the "toughness" of a liquid is
meant.
highly dependent on the temperature
thermal limits of the penetration test
Adhesion Adhesion means a sticking
of different substances one
to the other.
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Capillarity
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Description of the process
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Description of the process
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Pre-cleaning and drying
All impurities such as rust, scale, oil, grease, varnishor contamination covering the surface imperfectionsare to be removed.
Removal
mechanical:Pay attention that surface will not be
compacted
chemical:no residuals which coul influence
the testing media
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Penetration procedure
Immersion, spraying, brushing, pouring
Important: surface must be sufficiently wetted
The penetration time depends on the propertiesof the penetrant, the testing temperature , the
material and the defect type:
5 - 60 minutes
testing temperature:
5 °C - 50 OC
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Excess penetrant removal
removal of excess penetrant from the surface
avoid washing out processes of the
penetrant from the surface discontinuities!
1- with solvent
2- with water and solvent
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3- three-step excess penetrant removal for post-emulsifiable penetrants using hydrophilic emulsifiers
(emulsifier makes penetrant suitable to be cleaned usingwater):
3 steps: coarse removal with H2O
application of the emulsifiers (Important: time of emulsifying!)
cleaning with H2O again
4- Two-step excess penetrant removal for post-emulsifable penetrants using hydrophilic emulsifiers
2 steps :• Immersion in emulsifier
(Important: time of emulsifying!)
• washing off with water
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developing
Dry developers
Dry developers are to be applied in combination with
fluorescent penetrant only! electrostatic spraying, f1uidisers, …
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solvent based developers
(powder suspendable in a solvent)
Water soluble developers
1- developer is slurried in water
2- uniform concentration of the developer isimportant (stirring and mixingprocesses)
3- application can be carried out by spraying or
electrostatically
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Drying of the surface
Important:
1- testing temperature max, 50°C
2- no pressurised air
developing time
the developing process starts as soon as the dry powder entersinto contact with the residual penetrant.
developing time between 10 and 30 minutes
(depending on the testing system used and the extend of the
defects to be proved!)
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inspection
The inspection should be carried out at an illumination
strength of 500IIx. Surface reflections as well as other
reflections should be avoided .
If fluorescent penetrants reused the surface should be
tested using a UV-A radiation source and a radiation
intensity of 1000 µW/cm2
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The surrounding radiation intensity should not exceed
20 Ix (darkened).Thus, a certa in adaptation time is
necessary for the human eye that in the standards is
indicated with 5 minutes. During the inspection the surface is sought for
indications. This should be done directly after drying
of the developer (larger defects) and then after
termination of the developing time 8 smaller defects).In individual cases intermediate inspections may be
necessary.
inspection
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Testing devices (testing system)
From: EN 571-1
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OutwardOutward imperctionimperction of an angle Vof an angle V-- butt weld butt weld
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This imperfections predominantly step out by the following
procedures and are ascertainable by visual inspection:
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Interior imperfection of an single VInterior imperfection of an single V-- butt weld butt weld