MPI_ Magnetic Particle Inspection

MPI_ Magnetic Particle Inspection

1. MET312 NONMET312 NON--DESTRUCTIVE DESTRUCTIVE
TESTINGTESTING
MM
ODULEODULE
--3 3 ––MM
AGNETICAGNETIC
PP
ARTICLEARTICLE
II
NSPECTIONNSPECTION
ME312 NDT_SUKESH O P/ APME/JECC
SukeshO P
AssitantProfessor
Department of Mechanical Engineering,
JyothiEngineering College, Cheruthuruthy
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ME312 NDT_SUKESH O P/ APME/JECC

2. MET312 N
ON
-D
ESTRUCTIVE
T
ESTING
Introduction to NDTIntroduction to NDT--Visual Visual
InspectionInspection--Liquid Penetrant Liquid Penetrant
InspectionInspection--
Magnetic Magnetic
Particle Particle
ME312 NDT_SUKESH O P/ APME/JECC
Particle Particle
InspectionInspection
--Ultrasonic Ultrasonic
TestingTesting--Radiography TestingRadiography Testing--Eddy Eddy
Current Testing.Current Testing.
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3. MODULEMODULE--33
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4. INTRODUCTION

MPIMPIisgovernedbythelawsofmagnetismandis
thereforerestrictedtotheinspectionofmaterialsthat
cansupportmagneticfluxlines,metalscanbeclassified
asferromagnetic,paramagnetic,ordiamagnetic.

Ferromagneticmetalsarethosethatarestrongly
attractedtoamagnetandcanbecomeeasily
ME312 NDT_SUKESH O P/ APME/JECC
MPI-it is not
applicable to
non-magnetic
materials
attractedtoamagnetandcanbecomeeasily
magnetized.Ex:iron,nickel,cobalt.

Paramagneticmetalssuchasausteniticstainlesssteel
areveryweaklyattractedbymagneticforcesof
attractionandcannotbemagnetized.Ex:Aluminum

Diamagneticmetals whichhaveaweak,negative
susceptibilitytomagneticfields.Diamagneticmaterials
areslightlyrepelledbyamagneticfieldandthe
materialdoesnotretainthemagneticpropertieswhen
theexternalfieldisremoved.Ex:copper,silver,gold
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5. INTRODUCTION

TheonlyrequirementFortheinspectionthroughthis
techniqueisthatthecomponentsbeinginspectedmust
bemadeofa ferromagneticmaterial(amaterialsthat
canbemagnetized)suchasiron,nickel,cobalt,orsome
oftheiralloys.

Themethodisusedtoinspectavarietyofproductforms
ME312 NDT_SUKESH O P/ APME/JECC

Themethodisusedtoinspectavarietyofproductforms
includingcastings,forgings,andweldments.

ManydifferentindustriesuseMPIsuchas structural
steel,automotive,petrochemical,powergeneration,and
aerospaceindustries.

Underwaterinspectionisanotherareawheremagnetic
particleinspectionmaybeusedtotestitemssuchas
offshoreoffshorestructuresstructuresandandunderwaterunderwaterpipelinespipelines..
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6. ME312 NDT_SUKESH O P/ APME/JECC
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7. I
NTRODUCTIONTO
M
AGNETISM
ME312 NDT_SUKESH O P/ APME/JECC
Magnetismistheabilityofmatterto
attractothermattertoitself.Objects
thatpossessthepropertyofmagnetism
aresaidtobemagneticormagnetized
andmagneticlinesofforcecanbefound
inandaroundtheobjects.Amagnetic
poleisapointwheretheamagneticline
offorceexitsorentersamaterial.
Magnetic field lines:
•Form complete loops.
•Do not cross.
•Follow the path of least
resistance.
•All have the same strength.
•Have a direction such that they
cause poles to attract or repel.
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Magnetic lines of
force around a bar
magnet
Opposite poles
attracting
Similar poles repelling

8. F
ERROMAGNETIC
M
ATERIALS

Amaterialisconsideredferromagneticifitcan
bemagnetized.Materialswithasignificant
Iron,nickelorcobalt contentaregenerally
ferromagnetic.

Ferromagneticmaterialsaremadeupofmany
regionsinwhichthemagneticfieldsofatomsregionsinwhichthemagneticfieldsofatoms
arealigned.Theseregionsarecallmagnetic
domains.

Magneticdomainspointrandomlyin
demagnetizedmaterial,butcanbealigned
usingelectricalcurrentoranexternalmagnetic
fieldtomagnetizethematerial.
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Demagnetized
Magnetized

9. H
OW
D
OES
M
AGNETIC
P
ARTICLE
I
NSPECTION
W
ORK
?
Aferromagnetictestspecimenismagnetizedwitha
strongmagneticfieldcreatedbyamagnetorspecial
equipment.Ifthespecimenhasadiscontinuity,the
discontinuitywillinterruptthemagneticfield
flowingthroughthespecimenandaleakagefield
willoccur.

10. H
OW
D
OES
M
AGNETIC
P
ARTICLE
I
NSPECTION
W
ORK
? (C
ONT
.)
Finelymilledironparticlescoatedwithadyepigment
areappliedtothetestspecimen.Theseparticlesare
attractedtoleakagefieldsandwillclustertoforman
indicationdirectlyoverthediscontinuity.This
indicationcanbevisuallydetectedunderproper
lightingconditions.lightingconditions.

11. B
ASIC
P
ROCEDURE
-MPI
Basic steps involved:
1.Component pre-cleaning
2.Introduction of magnetic field
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2.Introduction of magnetic field
3.Application of magnetic media
4.Interpretation of magnetic particle
indications
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12. 1. P
RE
-
CLEANING

Wheninspectingatestpartwiththemagnetic
particlemethoditisessentialfortheparticlestohave
anunimpededpathformigrationtobothstrongand
weakleakagefieldsalike.Thepart’ssurfaceshould
becleananddrybeforeinspection.
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Contaminantssuchasoil,
grease,orscalemaynot
onlypreventparticlesfrom
beingattractedtoleakage
fields,theymayalso
interferewith
interpretation
ofindications.

13. 2. I
NTRODUCTIONOFTHE
M
AGNETIC
F
IELD
The required magnetic field can be introduced into a component
in a number of different ways.
1.Using a permanent magnet or an electromagnet that
contacts the test piece
2.Flowing an electrical current through the specimen
ME312 NDT_SUKESH O P/ APME/JECC
3.Flowing an electrical current through a coil of wire around
the part or through a central conductor running near the
part.
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14. 3. Application of Magnetic Media (Wet
Versus Dry)
MPIcanbeperformedusingeither
dryparticles,orparticles
suspendedinaliquid.WithWiththethe
drydrymethod,method,thetheparticlesparticlesareare
lightlylightlydusteddustedonontotothethesurfacesurface..
Withthewetmethod,thepartis
floodedwithasolutioncarryingthe
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Withthewetmethod,thepartis
floodedwithasolutioncarryingthe
particles.
Thedrymethodismoreportable.
Thewetmethodisgenerally more
sensitivesincetheliquidcarrier
givesthemagneticparticles
additionalmobility.
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15. 4. I
NTERPRETATIONOF
I
NDICATIONS
Afterapplyingthemagneticfield,indicationsthat
formmustinterpreted.Thisprocessrequiresthat
theinspectordistinguishbetweenrelevantand
non-relevantindications.
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16. C
RANE
H
OOKWITH
S
ERVICE
I
NDUCED
C
RACK
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Fluorescent, Wet Particle Method
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17. G
EARWITH
S
ERVICE
I
NDUCED
C
RACK
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Fluorescent, Wet Particle Method
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18. D
RIVE
S
HAFTWITH
H
EAT
T
REATMENT
I
NDUCED
C
RACKS
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Fluorescent, Wet Particle Method
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19. S
PLINED
S
HAFTWITH
S
ERVICE
I
NDUCED
C
RACKS
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Fluorescent, Wet Particle Method
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20. T
HREADED
S
HAFTWITH
S
ERVICE
I
NDUCED
C
RACK
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Fluorescent, Wet Particle Method
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21. L
ARGE
B
OLTWITH
S
ERVICE
I
NDUCED
C
RACK
ME312 NDT_SUKESH O P/ APME/JECC
Fluorescent, Wet Particle Method
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22. C
RANK
S
HAFTWITH
S
ERVICE
I
NDUCED
C
RACK
N
EAR
L
UBE
H
OLE
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Fluorescent, Wet Particle Method
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23. L
ACKOF
F
USIONIN
SMAW W
ELD
Indication
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Visible, Dry Powder Method
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24. T
OE
C
RACKIN
SMAW W
ELD
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Visible, Dry Powder Method
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25. T
HROATAND
T
OE
C
RACKSIN
P
ARTIALLY
G
ROUND
W
ELD
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Visible, Dry Powder Method
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26. BASIC PHYSICS OF BASIC PHYSICS OF
MAGNETISMMAGNETISM
261.
POLARITY

Inmagnetism,polarityreferstothe
orientationofnorth&southpolesin
space.
ME312 NDT_SUKESH O P/ APME/JECC
space.

E.g.,Ifamagnetizedrodissuspended
atitscentre,itwilleventuallyalign
itselfwiththeearth’smagneticfieldso
thatonesidepointstogeographicnorth
&otherendtothesouth.
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27. 27
2.MAGNETICFORCE

It’saforceofattractionorrepulsionthatone
bodyhasuponanother.

E.g.,WhentheNpoleofamagnetizedrodis
BASIC PHYSICS OF BASIC PHYSICS OF
MAGNETISMMAGNETISM
ME312 NDT_SUKESH O P/ APME/JECC

E.g.,WhentheNpoleofamagnetizedrodis
placedcloselytotheSofanother,theyattract
eachother.
3.MAGNETICFIELD

It’stheareaaroundamagnetwherethe
magneticforcesareobserved.
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28. 28

BASIC PHYSICS OF BASIC PHYSICS OF
MAGNETISMMAGNETISM
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29. 29
5.FLUXDENSITY

It’sdefinedastheno.oflinesofforceperunitarea,measuredin
‘Gauss’&denotedby‘B’.
BASIC PHYSICS OF BASIC PHYSICS OF
MAGNETISMMAGNETISM
ME312 NDT_SUKESH O P/ APME/JECC
6.MAGNETIZINGFORCE

Thetotalno.oflinesofforcemakingupamagneticfielddetermines
thestrengthoftheforceofattractionorrepulsionexertedbythe
magnet.Thisisknownasmagnetizingforce.

It’stheforcewhichsetsupmagneticfluxinamaterial.
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30. 30
6.COERCIVEFORCE

It’sameasureoftheabilityofaferromagneticmaterialto
withstandanexternalmagneticfieldwithoutbecoming
demagnetized.
BASIC PHYSICS OF BASIC PHYSICS OF
MAGNETISMMAGNETISM
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demagnetized.
7.RETENTIVITY

Theabilityofacoiltoretainsomeofitsmagnetismwithinthe
coreafterthemagnetizationprocesshasstopped.
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31. 31
8.HYSTERESISLOOP

Byexposinganunmagnetizedpieceofmaterialto
magnetizingcurrent,wecanplotthedensityBofthefield
inducedbyappliedmagnetizingforceH&theresultantcurve
BASIC PHYSICS OF BASIC PHYSICS OF
MAGNETISMMAGNETISM
ME312 NDT_SUKESH O P/ APME/JECC
inducedbyappliedmagnetizingforceH&theresultantcurve
iscalledHysteresisloop.
9.RESIDUALMAGNETISM

It’sdefinedastheamountofmagnetismleftbehindafter
removingtheexternalmagneticfieldfromthecircuit.
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32. HYSTERESIS LOOPHYSTERESIS LOOP
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33. M
AGNETIC
P
ARTICLES
/
MEDIA

Theparticlesusedinmagneticparticletestingare
madeofferromagneticferromagneticmaterials,materials,
usuallycombinationsof ironironandandironironoxides,oxides,
havinghavingaahighhighpermeabilitypermeabilityandandlowlowretentivityretentivity..
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
Particleshaving highpermeabilityare
easilyattractedtoandmagnetizedbythelow-
levelleakagefieldsatdiscontinuities.
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34. 
Lowretentivityisrequiredtopreventthe
particlesfrombeingpermanentlymagnetized.

Stronglyretentiveparticleswillcling
togetherandtoanymagneticsurface,
resultinginreducedparticlemobilityandinc
reasedbackgroundaccumulation.
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M
AGNETIC
P
ARTICLES
/
MEDIA
resultinginreducedparticlemobilityandinc
reasedbackgroundaccumulation.

Acommonparticleusedtodetectcracksis iron
oxide,forbothdryandwetsystem
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35. D
RY
M
AGNETIC
P
ARTICLES
Magneticparticlescomeinavarietyofcolors.A
colorthatproducesahighlevelofcontrastagainst
thebackgroundshouldbeused.
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36. W
ET
M
AGNETIC
P
ARTICLES
Wetparticlesaretypicallysupplied
asvisibleorfluorescent.Visible
particlesareviewedundernormal
whitelightandfluorescentparticles
areviewedunderblacklight.
ME312 NDT_SUKESH O P/ APME/JECC
areviewedunderblacklight.
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37. Dry
●Common, relatively
cheap
●Generally applied to
rougher surfaces
●Particle types
Wet
●More expensive,
accurate
●Painted or sprayed
onto surfaces
●Wet dye
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●Particle types
○Elongated -align
well with
magnetic fields
○Rounded -move
freely across a
surface
●Wet dye
classifications
○Light (UV or
fluorescent)
○Removal type
(water, solvent, or
emulsifier)
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38. T
YPESOF
M
AGNETIZATION
Twogeneraltypestypesofofmagneticmagneticfieldsfields(longitudinal
andcircular)maybeestablishedwithinthespecimen.
Thetypeofmagneticfieldestablishedisdetermined
bythemethodusedtomagnetizethespecimen.
ME312 NDT_SUKESH O P/ APME/JECC
•
A longitudinal magnetic fieldlongitudinal magnetic fieldhas magnetic
lines of force that run parallel to the long
axis of the part.
•
A circular magnetic fieldcircular magnetic fieldhas magnetic lines
of force that run circumferentially around
the perimeter of a part.
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39. I
MPORTANCEOF
M
AGNETIC
F
IELD
D
IRECTION
Beingabletomagnetizethepartintwo
directionsisimportantbecausethebest
detectionofdefectsoccurswhenthelinesof
magneticforceareestablishedatright
anglestothelongestdimensionofthe
defect.
Flux Leakage
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defect.
Thisorientationcreatesthelargest
disruptionofthemagneticfieldwithinthe
partandthegreatestfluxleakageatthe
surfaceofthepart.Anorientationof45to
90degreesbetweenthemagneticfieldand
thedefectisnecessarytoformanindication.
No Flux Leakage
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40. ME312 NDT_SUKESH O P/ APME/JECC
Sincedefectsmayoccurinvariousandunknowndirections,
eachpartisnormallymagnetizedintwodirectionsatright
anglestoeachother.
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41. METHODS OF MAGNETIZATIONMETHODS OF MAGNETIZATION
41

Thebasicprincipleofmagnetizationistoproducemagnetic
linesofforceacrosstheexpecteddirectionofcracks.

Ifthelikelycrackdirectionisunknown,thenthetestmustbe
performedin2directionsatrightangles.
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performedin2directionsatrightangles.
1.
Magneticflow
2.
Currentflow
3.
Inducedcurrentflow
4.
ElectromagneticInduction
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42. 42
1.
Magneticflow:Tomakethecomponentofamagneticcircuitby
effectivelyusingitasthebridgeofapermanentorelectromagnet.
2.
Currentflow:Topassanelectriccurrentthroughthespecimen,
alongthedirection&throughtheregionwherecracksareexpected.
METHODS OF MAGNETISATIONMETHODS OF MAGNETISATION
ME312 NDT_SUKESH O P/ APME/JECC
alongthedirection&throughtheregionwherecracksareexpected.
3.
InducedCurrentflow:Usedforringspecimensbyeffectively
makingthemthesecondaryofamaintransformer.
4.
Electromagneticinduction:Passanelectriccurrentthrougha
conductorwhichisthreadedthroughahollowspecimenorplaced
adjacentorwrappedaroundit.
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43. 43
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44. M
ETHODSOFMAGNETIZATION

There are a variety of methods that can be used
to establish a magnetic field in a component for
evaluation using magnetic particle inspection. It
is common to classify the magnetizing methods
as either direct or indirect.
ME312 NDT_SUKESH O P/ APME/JECC
as either direct or indirect.
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45. MM
AGNETIZATIONAGNETIZATION
UU
SINGSING
DD
IRECTIRECT
II
NDUCTIONNDUCTION
(D(D
IRECTIRECT
MM
AGNETIZATIONAGNETIZATION
))

Withdirectmagnetization, currentispassed
directlythroughthecomponent. Theflowof
currentcausesacircularmagneticfieldtoform
inandaroundtheconductor.

Whenusingthedirectmagnetizationmethod,
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
Whenusingthedirectmagnetizationmethod,
caremustbetakentoensurethatgoodelectrical
contactisestablishedandmaintainedbetween
thetestequipmentandthetestcomponentto
avoiddamageofthecomponent (duetoarcingor
overheatingathighresistancepoints).
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46. 
MagnetizationMagnetizationUsingUsingDirectDirectInductionInduction
(Direct(DirectMagnetization)Magnetization)

Clampingthecomponentbetweentwo
electricalcontacts(HEAD(HEADSHOTSHOTMethod)Method)

Usingclampsorprods
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
Usingclampsorprods
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47. C
LAMPINGTHECOMPONENTBETWEENTWO
ELECTRICALCONTACTS
(HEAD SHOT (HEAD SHOT
MM
ETHODETHOD
))
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48. 
Currentispassedthroughthecomponentanda
circularmagneticfieldisestablishedinand
aroundthecomponent.Whenthemagnetizing
currentisstopped,aresidualmagneticfieldwill
remainwithinthecomponent.
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remainwithinthecomponent.

Thestrengthoftheinducedmagneticfieldis
proportionaltotheamountofcurrentpassed
throughthecomponent.
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49. HEAD SHOT TECHNIQUEHEAD SHOT TECHNIQUE
49

Thistechniqueproducescircularmagnetizationbypassing
electriccurrentthroughthepartitself.

Aroundbarisheldbetweentheheadsinawethorizontalunit.
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
Asthecurrentflowsfromoneendtotheanotherendofthe
bar,themagneticlinesofforcegetscirculatedaroundthebar.

Thecirculationofmagneticfluxaroundthebarisknownas
circularmagnetism&thetechniqueisknownasheatshot
technique.
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50. 50
(Wethorizontalunitisastationaryunitinwhichlongitudinal&
circularfieldsareproduced.Theunithasafixedheadstock&
slidingtailstock.Thepartcanbeplacedb/wthesebyadjusting
thetailstock.)
HEAD SHOT TECHNIQUEHEAD SHOT TECHNIQUE
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thetailstock.)

Onedisadvantageisthat,itproducesheating&arcingatthe
junctureduetothepassageofhighcurrentthroughasmall
contactarea.

Toavoidoverheating&arcing,thecontactfacesshouldbe
madeflexible.
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51. U
SINGCLAMPSORPRODS
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
whichareattachedorplacedincontactwiththe
component.Electricalcurrentflowsthroughthe
componentfromcontacttocontact.

Thecurrentsetsupacircularmagneticfieldaround
thepathofthecurrent.
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52. MM
AGNETIZATIONAGNETIZATION
UU
SINGSING
II
NDIRECTNDIRECTII
NDUCTIONNDUCTION
(I(I
NDIRECTNDIRECT
MM
AGNETIZATIONAGNETIZATION
) )

Indirectmagnetizationisaccomplishedbyusing
astrongexternalmagneticfieldtoestablisha
magneticfieldwithinthecomponent. Aswith
directmagnetization,thereareseveralwaysthat
indirectmagnetizationcanbeaccomplished.
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indirectmagnetizationcanbeaccomplished.
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53. 22..MagnetizationMagnetizationUsingUsingIndirectIndirectInductionInduction
(Indirect(IndirectMagnetization)Magnetization)

Useofpermanentmagnets

Electromagnets(usingyokes)

Centralconductormagnetization
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
Centralconductormagnetization

Useofcoilsandsolenoids
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54. UU
SESEOFOFPERMANENTPERMANENTMAGNETSMAGNETS
54

Theuseofpermanentmagnetsisalowcostmethod
ofestablishingamagneticfield.However,theiruse
islimitedduetolackofcontrolofthefieldstrength
andthedifficultyofplacingandremovingstrong
permanentmagnetsfromthecomponent.
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55. E
LECTROMAGNETS
(
USINGYOKES
)
55
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
Electromagnetsintheformofanadjustablehorseshoe
magnet(calledayoke)eliminatetheproblemsassociated
withpermanentmagnetsandareusedextensivelyin
industry.

Electromagnetsonlyexhibitamagneticfluxwhenelectric
currentisflowingaroundthesoftironcore.Whenthe
magnetisplacedonthecomponent,amagneticfieldis
establishedbetweenthenorthandsouthpolesofthe
magnet.
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56. C
ENTRALCONDUCTOR
MAGNETIZATION
56

Anotherwayofindirectlyinductingamagneticfield
inamaterialisbyusingthemagneticfieldofa
currentcarryingconductor.Acircularmagneticfield
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currentcarryingconductor.Acircularmagneticfield
canbeestablishedincylindricalcomponentsbyusing
acentralconductor.

Typically,oneormorecylindricalcomponentsare
hungfromasolidcopperbarrunningthroughthe
insidediameter.Currentispassedthroughthecopper
barandtheresulting circularmagneticfield
establishesamagneticfieldwithinthetest
components.
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57. U
SEOFCOILSANDSOLENOIDS
57
ME312 NDT_SUKESH O P/ APME/JECC

Whenthelengthofacomponentisseveraltimeslarger
thanitsdiameter,alongitudinalmagneticfieldcanbe
establishedinthecomponent.

Thecomponentisplacedlongitudinallyinthe
concentratedmagneticfieldthatfillsthecenterofacoilor
solenoid.Thismagnetizationtechniqueisoftenreferredto
asa"coilshot".
ME312 NDT_SUKESH O P/ APME/JECC

58. L
ONGITUDINAL
&C
IRCULAR
M
AGNETIC
F
IELDS
Longitudinal
1.
Permanent magnets
2.
Electromagnetic yokes
3.
Using a Coil(COIL SHOT)
Circular
1.Clamping the component
between two
electrical contacts(HEAD
SHOT)
3.
Using a Coil(COIL SHOT) SHOT)
2.Using clamps or prods
3.Central conductor
magnetization

59. T
YPESOF
M
AGNETIZING
C
URRENT
59

Asmentionedpreviously,electriccurrentisoften
usedtoestablishthemagneticfieldin
componentsduringmagneticparticleinspection.
Alternatingcurrent(AC)anddirectcurrent(DC)
arethetwobasictypesofcurrentcommonly
ME312 NDT_SUKESH O P/ APME/JECC
arethetwobasictypesofcurrentcommonly
used.
ME312 NDT_SUKESH O P/ APME/JECC

60. 1. D
IRECT
C
URRENT
60

Directcurrent(DC)flowsflowscontinuouslycontinuouslyininoneonedirectiondirection
atataaconstantconstantvoltagevoltage..Abatteryisthemostcommon
sourceofdirectcurrent.

Thecurrentissaidtoflowfromthepositivetothe
negativeterminal,thoughelectronsflowinthe
oppositedirection.
ME312 NDT_SUKESH O P/ APME/JECC
oppositedirection.

DCisverydesirablewheninspectingforsubsurface
defectsbecauseDCgeneratesamagneticfieldthat
penetratesdeeperintothematerial.

Inferromagneticmaterials,themagneticfield
producedbyDCgenerallypenetratestheentirecross-
sectionofthecomponent.
ME312 NDT_SUKESH O P/ APME/JECC

61. 2. A
LTERNATING
C
URRENT
61

Alternatingcurrent(AC)reversesindirectionat arateof
50or60cyclespersecond.SinceACisreadilyavailablein
mostfacilities,itisconvenienttomakeuseofitfor
magneticparticleinspection.

However,whenACisusedtoinduceamagneticfieldin
ferromagneticmaterials,themagneticfieldwillbelimited
ME312 NDT_SUKESH O P/ APME/JECC
ferromagneticmaterials,themagneticfieldwillbelimited
toathinlayer atthesurfaceofthecomponent.This
phenomenonisknownasthe "skineffect"andoccurs
becausethechangingmagneticfieldgenerateseddy
currentsinthetestobject.

Theeddycurrentsproduceamagneticfieldthatopposes
theprimaryfield,thusreducingthenetmagneticflux
belowthesurface.Therefore,itisrecommendedthatACbe
usedonlywhentheinspectionislimitedtosurfacedefects.
ME312 NDT_SUKESH O P/ APME/JECC

62. 3. R
ECTIFIED
A
LTERNATING
C
URRENT
62

Clearly,theskineffectlimitstheuseofACsince
manyinspectionapplicationscallforthe
detectionofsubsurfacedefects.

Luckily,ACcanbeconvertedtocurrentthatis
verymuchlikeDCthroughtheprocessof
ME312 NDT_SUKESH O P/ APME/JECC
verymuchlikeDCthroughtheprocessof
rectification.Withtheuseofrectifiers,the
reversingACcanbeconvertedtoaone
directionalcurrent.
ME312 NDT_SUKESH O P/ APME/JECC

63. 63
ME312 NDT_SUKESH O P/ APME/JECCME312 NDT_SUKESH O P/ APME/JECC

64. H
ALF
W
AVE
R
ECTIFIED
A
LTERNATING
C
URRENT
(HWAC)
64

Whensinglephasealternatingcurrentispassedthrougha
rectifier,currentisallowedtoflowinonlyonedirection.

Thereversehalfofeachcycleisblockedoutsothataone
directional,pulsatingcurrentisproduced.

Thecurrentrisesfromzerotoamaximumandthen
returnstozero.Nocurrentflowsduringthetimewhenthe
reversecycleisblockedout.
ME312 NDT_SUKESH O P/ APME/JECC
returnstozero.Nocurrentflowsduringthetimewhenthe
reversecycleisblockedout.

TheHWACrepeatsatsamerateastheunrectifiedcurrent
(50or60Hz).Sincehalfofthecurrentisblockedout,the
amperageishalfoftheunalteredAC.Thistypeofcurrent
isoftenreferredtoashalfwaveDCorpulsatingDC .The
pulsationoftheHWAChelpsmagneticparticleindications
formbyvibratingtheparticlesandgivingthemadded
mobilitywherethatisespeciallyimportantwhenusingdry
particles.HWACismostoftenusedtopower
electromagneticyokes.
ME312 NDT_SUKESH O P/ APME/JECC

65. F
ULL
W
AVE
R
ECTIFIED
A
LTERNATING
C
URRENT
(FWAC) (S
INGLE
P
HASE
)
65

Fullwaverectification invertsthenegative
currenttopositivecurrentratherthanblockingit
out.ThisproducesapulsatingDCwithno
intervalbetweenthepulses.Filteringisusually
performedtosoftenthesharppolarityswitching
ME312 NDT_SUKESH O P/ APME/JECC
performedtosoftenthesharppolarityswitching
intherectifiedcurrent.

Whileparticlemobilityisnotasgoodashalf-
waveACduetothereductioninpulsation,the
depthofthesubsurfacemagneticfieldis
improved.
ME312 NDT_SUKESH O P/ APME/JECC

66. T
HREE
P
HASE
F
ULL
W
AVE
R
ECTIFIED
A
LTERNATING
C
URRENT
66

Threephasecurrentisoftenusedtopower
industrialequipmentbecauseithasmore
favorablepowertransmissionandlineloading
characteristics.

Thistypeofelectricalcurrentisalsohighly
desirableformagneticparticletestingbecause
ME312 NDT_SUKESH O P/ APME/JECC
desirableformagneticparticletestingbecause
whenitisrectifiedandfiltered,theresulting
currentverycloselyresemblesdirectcurrent.

Stationarymagneticparticleequipmentwired
withthreephaseACwillusuallyhavetheability
tomagnetizewithACorDC( threephasefull
waverectified),providingtheinspectorwiththe
advantagesofeachcurrentform.
ME312 NDT_SUKESH O P/ APME/JECC

67. E
QUIPMENT
'
SUSEDFOR
MPI
67

MPI equipment serves the following purposes, it
provides

Sufficient power of right type

Suitable contact and coils

Convenient means for accomplishing proper
ME312 NDT_SUKESH O P/ APME/JECC

Convenient means for accomplishing proper
magnetization with respect to field strength and
direction.

Means of applying the magnetic particles

Well lighted space for careful examination of the part
of indication.
ME312 NDT_SUKESH O P/ APME/JECC

68. 68
1. Simple equipment:1. Simple equipment:
for occasional
testing of small casting or machine parts for
detection of surface cracks, small and easily
portable equipment is most convenient.
ME312 NDT_SUKESH O P/ APME/JECCME312 NDT_SUKESH O P/ APME/JECC

69. P
ERMANENT
M
AGNETS
69

Theuseofindustrialmagnetsisnotpopular
becausetheyareverystrong( theyrequire
significantstrengthtoremovethemfromthe
surface,about250Nforsomemagnets )andthus
theyaredifficultandsometimesdangerousto
handle.
ME312 NDT_SUKESH O P/ APME/JECC
handle.

However,permanentmagnetsaresometimes
usedbydiversfor inspectioninspectionininunderwaterunderwater
environmentsenvironmentsororotherotherareas,areas,suchsuchasasexplosiveexplosive
environments,environments,wherewhereelectromagnetselectromagnetscannotcannotbebe
usedused..

Permanentmagnetscanalsobemadesmall
enoughtofitintotightareaswhere
electromagnetsmightnotfit.
ME312 NDT_SUKESH O P/ APME/JECC

70. E
LECTROMAGNETIC
Y
OKES
70

Anelectromagneticyokeisaverycommonpiece
ofequipmentthatisusedtoestablishamagnetic
field.Aswitchisincludedintheelectricalcircuit
sothatthecurrentand,therefore,themagnetic
fieldcanbeturnedonandoff.
ME312 NDT_SUKESH O P/ APME/JECC
fieldcanbeturnedonandoff.

TheycanbepoweredwithACfromawallsocket
orbyDCfromabatterypack.Thistypeof
magnetgeneratesaverystrongmagneticfieldin
alocalareawherethepolesofthemagnettouch
thepartbeinginspected.
ME312 NDT_SUKESH O P/ APME/JECC

71. 71
2. Large portable equipment: it is used where
higher power is required or heavier duty cycles
make the small kits inadequate. One of the
smallest of this series operates at 120V AC and
delivers up to 700amperes, either AC or half wave
ME312 NDT_SUKESH O P/ APME/JECC
delivers up to 700amperes, either AC or half wave
DC
ME312 NDT_SUKESH O P/ APME/JECC

72. P
RODS
72

Prodsarehandheldelectrodesthatarepressed
againstthesurfaceofthecomponentbeinginspected
tomakecontactforpassingelectricalcurrent(ACor
DC)throughthemetal.
ME312 NDT_SUKESH O P/ APME/JECC

Prodsaretypicallymademadefromfromcoppercopperandandhavehaveanan
insulatedinsulatedhandlehandletotohelphelpprotectprotectthetheoperatoroperator..Oneof
theprodshasatriggerswitchsothatthecurrentcan
bequicklyandeasilyturnedonandoff.Sometimes
thetwoprodsareconnectedbyanyinsulator,to
facilitateonehandoperation.Thisisreferredtoasa
dualprodandiscommonlyusedforweldinspections.
ME312 NDT_SUKESH O P/ APME/JECC

73. P
ORTABLE
C
OILSAND
C
ONDUCTIVE
C
ABLES
73
Coilsandconductivecables areusedto
establishalongitudinalmagneticfieldwithin
acomponent.Whena preformedcoil is
used,thecomponentisplacedagainstthe
insidesurfaceonthecoil.Coilstypicallyhave
threeorfiveturnsofacoppercablewithinthe
moldedframe.Afootswitchisoftenusedto
ME312 NDT_SUKESH O P/ APME/JECC
moldedframe.Afootswitchisoftenusedto
energizethecoil.

Also,flexibleconductivecables canbe
wrappedaroundacomponenttoformacoil.
Thenumberofwrapsisdeterminedbythe
magnetizingforceneededandofcourse,the
lengthofthecable.Normally,thewrapsare
keptasclosetogetheraspossible.Whenusing
acoilorcablewrappedintoacoil,amperageis
usuallyexpressedinampere-turns.Ampere-
turnsistheamperageshownontheamp
metertimesthenumberofturnsinthecoil.
ME312 NDT_SUKESH O P/ APME/JECC

74. P
ORTABLE
P
OWER
S
UPPLIES
74

Portablepowersuppliesareusedto
providethenecessaryelectricitytothe
prods,coilsorcables.Powersupplies
arecommerciallyavailableina
varietyofsizes.Smallpowersupplies
generallyprovideupto1,500Aofhalf-
ME312 NDT_SUKESH O P/ APME/JECC
generallyprovideupto1,500Aofhalf-
waveDCorAC.Theyaresmalland
lightenoughtobecarriedandoperate
oneither120Vor240Velectrical
service.
ME312 NDT_SUKESH O P/ APME/JECC
Whenmorepowerisnecessary,mobilepower
suppliescanbeused.Theseunitscomewithwheels
sothattheycanberolledwhereneeded.Theseunits
alsooperateon120Vor240Velectricalserviceand
canprovideupto6,000AofACorhalf-waveDC.

75. 75
3.Stationarymagnetizingequipment: Alarge
varietyofstationary,bench-typeunitsisavailable,
withvariouscharacteristicstofitdifferenttesting
requirements.
Thesmallersizeequipmentisusedforsmallparts
ME312 NDT_SUKESH O P/ APME/JECC
Thesmallersizeequipmentisusedforsmallparts
thatcanbeeasilytransportedandhandledby
hand.Thelargeronesareusedforheavyparts
suchaslongdieselenginecrankshafts,where
handlingmustbecrane.
ME312 NDT_SUKESH O P/ APME/JECC

76. S
TATIONARY
E
QUIPMENT
76

Stationarymagneticparticleinspectionequipmentisdesignedfor
useinlaboratoryorproductionenvironment.Themostcommon
stationarysystemisthewethorizontal(bench)unit.Wethorizontal
unitsaredesignedtoallowforbatchinspectionsofavarietyof
components.Theunitshaveheadandtailstocks( similartoalathe)
withelectricalcontactthatthepartcanbeclampedbetween.A
circularmagneticfieldisproducedwithdirectmagnetization.
ME312 NDT_SUKESH O P/ APME/JECC
circularmagneticfieldisproducedwithdirectmagnetization.

Mostunitsalsohaveamovablecoilthatcanbemovedintoplaceso
theindirectmagnetizationcanbeusedtoproducealongitudinal
magneticfield.Mostcoilshavefiveturnsandcanbeobtainedina
varietyofsizes.Thewetmagneticparticlesolutioniscollectedand
heldinatank.Apumpandhosesystemisusedtoapplytheparticle
solutiontothecomponentsbeinginspected.Someofthesystems
offeravarietyofoptionsinelectricalcurrentusedformagnetizing
thecomponent(AC,halfwaveDC,orfullwaveDC ).Insomeunits,a
demagnetizationfeatureisbuiltin,whichusesthecoilanddecaying
AC.
ME312 NDT_SUKESH O P/ APME/JECC

77. 77
4. Large heavy duty DC equipment: very
versatile types of heavy duty stationary equipment
are those DC units designed for application of the
“overall” method of magnetizing , for the inspection
of very large and complicated castings. Rectified
ME312 NDT_SUKESH O P/ APME/JECC
of very large and complicated castings. Rectified
three-phase AC is delivered with current values
running as high as 20,000 amperes.
ME312 NDT_SUKESH O P/ APME/JECC

78. SENSITIVITY
78

MPIMethodsaresensitivemeansoflocating
smallandshallowsurfacecracksin
ferromagneticcomponents.Manyincipient
fatiguecracksandfinegrindingcrackshaving
sizelessthan0.02mmdeepandsurfaceopenings
ME312 NDT_SUKESH O P/ APME/JECC
sizelessthan0.02mmdeepandsurfaceopenings
ofonetenthofthatorlesscanbelocatedusing
MPI.

Detectabilitygenerallyinvolvesarelationb/w
surfaceopeninganddepth.

Ifdefectssoughtareusualcracks,comparatively
lowlevelofmagneticforcewillgivesufficient
build-up.
ME312 NDT_SUKESH O P/ APME/JECC

79. 79

However,tofindminutecracksorsubsurface
flaws,thefluxlevelshouldbehigh.Theoretically,
aleveljustbelowsaturationwouldgivethemost
sensitiveresults.Butthisisimpracticalowingto
thenon-regularshapesofthecomponents
ME312 NDT_SUKESH O P/ APME/JECC
thenon-regularshapesofthecomponents
encountered.

Sensitivityalsodependsonthetypeofcurrent
used.
ME312 NDT_SUKESH O P/ APME/JECC

80. 80

Various tests have conclusively proved the
following information:

AC magnetization is most effective for surface
defects.

AC magnetization is not effective for subsurface
ME312 NDT_SUKESH O P/ APME/JECC

AC magnetization is not effective for subsurface
defects.

DC( straight or half wave) must be used for
subsurface defects.

Half wave DC gives superior penetration as
compared to straight DC

Half wave DC dry method gives the greatest
penetration.
ME312 NDT_SUKESH O P/ APME/JECC

81. 
fast, simple and inexpensive

direct, visible indication on surface

unaffected by possible deposits, e.g. oil, grease or other
metals chips, in the cracks

can be used on painted objects
A
DVANTAGESOF
MPI
81
ME312 NDT_SUKESH O P/ APME/JECC

results readily documented with photo or tape impression

Post-cleaning generally not necessary.

A relatively safe technique; materials generally not
combustible or hazardous.

Indications can show relative size and shape of the
discontinuity.

Easy to use and requires minimal amount of training.
ME312 NDT_SUKESH O P/ APME/JECC

82. L
IMITATIONSOF
MPI

Non-ferrous materials, such as aluminum, magnesium, or
most stainless steels, cannot be inspected.

Examination of large parts may require use of equipment
with special power requirements.

May require removal of coating or plating to achieve
desired sensitivity.

Limited subsurface discontinuity detection capabilities.
82
ME312 NDT_SUKESH O P/ APME/JECC

Limited subsurface discontinuity detection capabilities.

Post-demagnetization is often necessary.

Alignment between magnetic flux and indications is
important.

Each part needs to be examined in two different
directions.

Only small sections or small parts can be examined at one
time.
ME312 NDT_SUKESH O P/ APME/JECC

83. T
ESTINGTECHNIQUES
83

In MPI, various methodologies for inspections are
used some are:

Dry particle inspection

Wet suspension inspection

Magnetic rubber inspection
ME312 NDT_SUKESH O P/ APME/JECC

Magnetic rubber inspection

Residual and continuous magnetization technique.
ME312 NDT_SUKESH O P/ APME/JECC

84. S
TEPSFORPERFORMINGDRY
PARTICLESINSPECTION
:
84

Surface preparation

Applying the magnetizing force

Applying dry magnetic particles

Blowing off excess powder
Terminating the magnetizing force
ME312 NDT_SUKESH O P/ APME/JECC

Terminating the magnetizing force

Inspection for indications
ME312 NDT_SUKESH O P/ APME/JECC

85. 85
ME312 NDT_SUKESH O P/ APME/JECCME312 NDT_SUKESH O P/ APME/JECC

86. S
TEPSFORPERFORMINGWETPARTICLE
INSPECTION
:
86

Surface preparation

Applying suspended magnetic particles

Applying the magnetizing force

Inspection for indications
ME312 NDT_SUKESH O P/ APME/JECCME312 NDT_SUKESH O P/ APME/JECC

87. 87
ME312 NDT_SUKESH O P/ APME/JECCME312 NDT_SUKESH O P/ APME/JECC

88. R
ESIDUALMAGNETIZATIONTECHNIQUE
88

Inthistechnique,componenttobeinspectedis
magnetizedfirst,thenbeforeapplicationof
magneticparticlemagnetizingforceisstopped.
Thusindicationisproducedbymagneticparticle
attractedduetoresidualfieldofmagnetized
ME312 NDT_SUKESH O P/ APME/JECC
attractedduetoresidualfieldofmagnetized
component.Thistechniqueis insensitiveto
componentsormaterialwithhighpermeability
andforlowpermeablematerialspecialcare
takentoensurethesufficientstrengthofresidual
fieldsothatindicationsmaybeproduced.
ME312 NDT_SUKESH O P/ APME/JECC

89. C
ONTINUOUSMAGNETIZATIONTECHNIQUE
89

Thistechniqueisusedwhen greatlevelof
sensitivityisrequired.Inthistechnique,
componenttobeinspectedismagnetizedand
magnetizationiscontinuedwhilethemagnetic
particlesareappliedonthesurfaceofcomponent.
Thetechniqueprovidesanadvantageofstrong
ME312 NDT_SUKESH O P/ APME/JECC

Thetechniqueprovidesanadvantageofstrong
leakagefield(strongmagneticfield). Thusa
strongmagneticfluxisproduced,whichforces
moreparticlestovibrateandslidedowntowards
thecracksurfaceorleakagesurface.

Onlylimitationwiththismethodisthat,it
producesheatwhichmaysometimedamagesthe
testcomponentwhendirectmagnetizationisused.
ME312 NDT_SUKESH O P/ APME/JECC

90. ME312 NDT
TASK TASK --3 (MODULE3 (MODULE--3) A3) A
SSIGNMENTSSIGNMENT
1.31.3
90

Importantterminologiesrelatedto
magneticpropertiesofmaterial.

WriteshortnotesonMagneticfield
indicators/Equipments
ME312 NDT_SUKESH O P/ APME/JECC
Submitonorbefore:29-06-2022 (inclassnote)
ME312 NDT_SUKESH O P/ APME/JECC

91. ME312 NDT
91
END OF MODULE -3
ME312 NDT_SUKESH O P/ APME/JECC
END OF MODULE -3
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ME312 NDT_SUKESH O P/ APME/JECC

92. 92
Quality & Process Control
Magnetic rubber inspection
ME312 NDT_SUKESH O P/ APME/JECCME312 NDT_SUKESH O P/ APME/JECC