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NON DESTRUCTIVE TESTING
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What is NDT ?
Is procedure , covers the inspection and testing of anymaterial , component or assembly by means which do
not effect ultimate serviceability.
SCOPE OF NDT
Covering the fields : Design , safety engineering.
Quality control of product specifications .
Condition monitoring and maintenance
Industrial standards .
What is the aim of NDT ?
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NDT
The aim of NDT:
Deficiencies in materials and products.
Determination of physical and geometrical properties of
materials and products. Structural behavior of materials , products and installations.
What are the test methods ?
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Visual Inspection. Radiation methods
Leak testing
Liquid penetrate testing
Magnetic particle testing
Ultrasonic testing.
What U R going to see during visual inspectionof Welds and How ?
NDT
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NDT( Visual inspection )
Before welding :Dents , Burrs , scales,
dirt , grease and mill scale on the
fusion faces.
During fit-upGeometry of edge andjoint preparation(Root face ,root
gap, bevel and angle )
After welding :
Removal of spatters and slag.
Appearance of ripples on the weld.
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NDT( Visual inspection )
Undercuts and overlaps.
Unfilled crater.
Gas pockets or porosities.
External cracks.
Size and shape of the bead.
The appearance of the weld
is considered to be goodifripples are spacedregularly.
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NDT (MPT)
Used for detection of surfaceand near surface flaws inferromagnetic materials primarily for crack detection.
Magnetic reluctance Surfacebreaking flaw Magnetic field
will be distorted.
Cause local flux leakagearoundthe flaw.
Magnetic Flux is displayed byvery fine iron particles dry or
wet.
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NDT ( MPT )
Magnetizationcan be produced :
Applying a permanent or electro-magnet to the surface ( Magnetic
flow) Passing a large current to the
specimen or locally by means ofcurrent flow.
Putting the specimen inside acurrent coil or forming a coilaround the specimen.
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NDT ( MPT )
Used may beAC or DCof any wave
form.
Important - current used is correct
for the specimen size.
Dry powder or liquid magnetic inc.
Will be applied while magnetic
current is flowing . or
Residual magnetismis sometimesused when the particles are applied
after magnetization.
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NDT ( MPT )
Magnetic inks are used widelyby low pressure spray, dippingor brushing.
Important to use plenty of inkand to allow time for particlesto flow over the surface andmigrate to any cracks.
On dark surfaces a very thinlayer ofwhite paintcan beapplied to give a heightcontrast indication.
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NDT (MPT)
Defects detected: Surface cracks which may be missed by naked eye .
Give indication of subsurface flaws.
Advantages; Relatively low cost.
Portable
Gives clear indication.
Limitations ;
Only surface cracks
Used only on ferromagnetic materials
No permanent record.
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LIQUID PENETRANT TESTING
Principle is the liquidpenetrant drawn in to thesurface flaw by capillaryaction.
Surface flawssuch ascracks,laps , porosity.
One step up from visualinspection.
Advantages :
Speed ,large area coverage andlow cost.
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LIQUID PENETRANT TESTINGTesting is usually six stages.
1. Surface cleaning (Degreasingetc)
2. Application of penetrant
(Dipping ,spraying or by brush)3. Removal of excess penetrant
(solvent )
4. Application of developer
5. Inspection of test surface
6. Post inspection cleaning.
Matls : Penetrant /developer /cleaner.
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LIQUID PENETRANT TESTING
Can be applied to anynon-porous cleanmaterial ,metallic or non-
metallic. Unsuitable for the dirty or
very rough surfaces.
Surface cleaning is avitalpart of LP testingtechnique.
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RADIOGRAPHY EXAMINATION
Detectingdiscontinuities in testobjects by passing
ionizing radiationonradiography films.
Permanent record.
Industrial radiographycan be Gamma ray and X-ray.
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RADIOGRAPHY EXAMINATION Source Half life
Iridium 192 74days
Cobalt60 5.26 years
Cesium 137 30 years
Thorium 170 127days
X-ray source needs electricpower and continuous
cooling.
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RADIOGRAPHY EXAMINATION Strength of the source:
The old unit is curie(Ci) ,newunit is Bequeral (Bq)
1 curie = 3.7 x 1010disintegrations /sec
1 Bequeral = one transmission/second
1curie = 37G Bq ( G stands for
Giga = 109 Radiography film will be
measured in Densitometrerange 1.5 to 3.0.
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RADIOGRAPHY EXAMINATION Techniques:
Single wall image :Center is
not accessible ,source can be
off the center .
Double wall single image:Noaccess to the inside .Source
can be kept away from the
job.Source film distance
required and accessible.
Double wall double image:
small size below 21/2 inch
.diameter.Elliptical shot.
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RADIOGRAPHY EXAMINATION
Exposure time will be calculated based on the
strength of the source , thickness of the job.
As radiation is harmful , no workmen is
allowed during radiography. As Gamma is
scattered radiation.
Distance coverage depends on the source and
direction.
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Ultrasonic testing
Detection of discontinuitiesgenerally by pulse echomethod.
Using straight and angularbeams.
Flaw can be identified bynoting the reductionin thestrength of the transmittedvibration.
signal will be transmitted atright angleto the surface.
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Ultrasonic testing
Absence of the defect ,travelthrough the thickness andreflected on the other face andreturnto the probe.
Defect shorter distance totravel.
Set the distance between twoechoes as thickness.
Knowing the geometry of thesystem exact location can becalculated.
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THANKS