penetrating testing

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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



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.



Surface tension

wetting ability

good surface tension low

bad surface tension great additional dependence:

Viscosity

surface roughness



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.



Capillarity



Description of the process



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



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



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



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



developing

Dry developers

Dry developers are to be applied in combination with

fluorescent penetrant only! electrostatic spraying, f1uidisers, …



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



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!)



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



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



Testing devices (testing system)

From: EN 571-1



OutwardOutward imperctionimperction of an angle Vof an angle V-- butt weld butt weld



This imperfections predominantly step out by the following

procedures and are ascertainable by visual inspection:



Interior imperfection of an single VInterior imperfection of an single V-- butt weld butt weld

penetrating testing

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