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LINIQIJE TECHNOCRATSSCHOOL OF NON-DESTRUCTIVE TESTING & WELDING

MAGNETIC PARTICLE TESTINGLEVEL - I/ LEVEL - II

S.H.DESTTPANDEASNT LEVEL - III

R-EGD, OFFICE;

UMQUE TECHNOCRATSNO.47, P.O.BOX NO,9153MAGADI ROAD STINKADAKATTEBANGALORE - 560091PH.NO. - 080 - 3486659 13489140FAX -080-3485374EMAIL - weldaids@yahoo.com

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M AG N ETI C PARTI CLE EXAMIN ATI O N

INTRODUCTION

The Magnetic particle examination method may be used for FERROMAGNETIC

materials to detect cract

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THEORY

Each material is considered to hqye lgveraf-11-l!3reas in it which are magneticatly

similar. These are called obfvrntNs' These are ranaomty oriented Wlgn a magnetrc

filed is applied, tn" ootuin''o'il'ii oin"t"ntrv-oepenJins on whether the material is

;; RR-o N|-ACN ir I c, PARAMAG N ET I c or D IAMAG N Er I c

HOW IS MAGNETIC FIELD APPLIED ?

THEORY OF MAGNETISM - All materials 1f" tlid to contain magnetic domains r'e"

behave like individuat t"g""tl" O"tliJrv ln: -"1::td all domains'gets annulled as

they are randomlv oistno'li""i] H"*"i'"1i1 tl:::l* bf an external magnetic fields'

these domains g", on"nr.l'in a particular way o"p"noing on the nature of the material'

Fig l

tt can be seen that, in ferromagnetic -materials' the north & south poles combine

tooether, producing "

,nong';i"Ji"tic effect Concepiually' such alignments cause tne

:;Y.ilil'il.iXn6nrH pdr-rs a sourH PoLES'UN-LIKE POLES ATTRAC;;;LH OTHER & LIKE POLES

REPEL EACH OTHER.

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Page2 of 37

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F i g ' 2 ' l g l i n e s

Dependinsonthestrensth;ilT ji5tJ?::*"#"jl'i,il'',ilf i:Elili:[{jl'*":t"iJi"" iE"u" rrom-Ie^ ,'";U;; t"e ir" l::j,.:!;j;ui:i."J ffilt.iffiil?iT";:lil""}!:'lf":$:'.'oiiii,'H;; a-nv point,i" g:'9; how much inruence tne masnetSThENG+i at"that point This property

determtneshas at that Point

There are some specific properties of these concepiual lines of force. They

are

i\ MAGNETIC LINES OF FORCE]'EAVE THE MAGNET AT THE NORTH POLE &

"

'ile:EN;Ln ni rHe sourH PoLE'

ii) THEY NEVER CROS$ EACH OTHER'

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REPE L

ATTRACI T

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ExamPles -

Var iousmater ia |sared i f fe ren t f romeachother in the i rmagnet icbehav io r .Thetermsused to describe these are

i ) P E R M E A B | L | T Y - T h e . . e a s e w i t h w h i c h a m a g n e t i c f l l e d i s e s t a b l i s h e d ' . . i n t h eii\ [Ell!'3io*at - opposition to the establishment of a magnetrc field'iiir RETENTIvITY r'rli l'friiiv oi-tt't" mut"rl"i t; ;iui'i

a certain amount or"'' t-"o*iitt when the external magnetic filed- ts removeo'iv) RES|DUAL rrancruiri3ili'--+n"""r"""t or r"-g;"ti.t retained in the

material

after the external magnetic filed is remove-d' -v )coERc tVEroRce . - rne reversemagne t i z ing fo rcenecessary to remove the

"flct ot residual magnetic filed

H|GH CARBON STEEL

PERMEABILITY LOWnElucrnuce HIGHdEienrvrrv HIGHnEsiounr- MAcNETISM HIGHHEiir-mvrw HIGHCoeCsrve FoRcE HIGH

LOW CARBON STEEL

HIGHLOWLOWLOWLOWLOW

|tcanbeobservedf tomlheabovetab|ethatmater ia |scanwide|yd i f fer invar iousmagnetic ProPerties.

Thereareothercharaderisticsofmagnetic|inesofforce.Theyare.i) ln highly permeable materials' the magnetic lines of force

can pack themselves

densely' n, r+ nf rhc maonet at the north pole' they look for leastiit On"" tit" lines of force are out of the magnel a"t

resistance path to the south pole'

Page 4 of 37

ln a horse shoe shapedMagnet the lines of forceleave the north Pole & enterthe south pole.

They attract magnetisablematerial only at north & south poles.

In a cylindrical magnet,the lines of force neverleave the magnet.

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FIE LD IS EH I IR El.Y

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I R O N P A i ; I C L : 5

lf there are cracks inthe magnet as shown'the lines of force lumPacross the crack to causea leakage field'

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LAKACE FI LO WILLATIf,ACI T.|AC8 TICP,II ICLES

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Sometimes' even defectsinside the magnet can . .cause leakage flux outsloethe magnet, which can. .H;';fi;;i .;snetisable materials

FLUX L I ^ (AG E

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UNITS OF MEASUREMENT

Flux Density refers to the no. of lines of magnetic frux per unit area at right angles

to the

Direction of the flux lines

GAUSS = 10a Webers / m2

1oE Lines of force passlng thro' 1 m2 area around the

point of interest'

104 Guass104 Lines of force / m-

MAGNETTG EFFecT oF ELECTRIG GURRENT fietd iswhenever erect.c,ty is!ssed JlXTSl"1:ffi !|rfi:Y[t"ruti$r?l;"#33l3llioroduced around the conot

This property is very useful in MAGNETIC PARTICLE TESTING'

RIGHT HAND RULE

Electrical current is considered to flow from positive terminal to negative termlnal'

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LEFT HAND RULE

Inelect ron ic theoryofElect r ic i ty , thedi rect ionofe|ect ronf |owis f rom- iveterminal to+ivetermina| 'That is ,erect ronnowis inopposi ted i rect iontoconvent iona|curren lIn this case, LEFT HAND RULE is applicable i e '

IF WE HOLD THE CURRENT CARRYING CUNDUCTOR WITH OUR LEFT HAND IN

SUCH A WAY THAT TTTE iHJT'NE IS POITTIUC IN THE D1RECTION OF FLOW OF

ELECTRONS & THE OrH;n"Fir'rcEns wnnpp_ro AROUND THE CONDUCTOR.THE DIRECTION OF rr-rEtiHiN FiII-CENS INDICATE THE DIRECTION OF THELINES OF FORCE.

PLEASE NOTE THAT BOTH THE RULES GIVE THE SAME DIRECTION FOR LINES

OF FORCE.

METHODS OF MAGNETISATION

Usingtheprincip|eofexistenceofamagneticfi |edaroundacurrentcarryingconductor.various techniques can De used for magnetization Some of them are'

1. PROD MAGNETISATION2. LONGITUDINALMAGNETISATION3. CIRCUI.AR MAGNETISATION4. YOKE MAGNETISATIONs;. MULTIDIREcTIoNALMAGNETISATIoN

1. PROD MAGNETISATION

ln prod magnetization, electric current is passed through two prods which are

held pressed "g;Ji

tr;-t""t surface, using an electric power source. sincecurrent is passed,iit""gh tiie pto, magnetiJfield is CIRCULAR as shown in theFig. 10.

Page B of 37

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Thetwoprodscanbeconneciedtotheendsof thetestp iece&magnet ized.EVenthenthe magneiic fieto is circJra*i, ;" th; magnetic fierd is perpendicular

to the current

carrying conductor. See sketch below

To avoid arcing, a remote control switch is built into the prod handles to ensure current

i;;*tch"d oninly after the prods are firmly positioned'

The open circuit voltage of the power source should nol be very high 1o prevent

possibility of electric.no"x' Sind welding power sources are also low O C'V power

producers, they can O" u""O-*iGin-ine &pacity of the welding machine. However'

modern MT equipments are jeneralty built with much lower OCVS'

The current to be used is Direct / rectified current and the magnitude is related to PROD

iil;iiic.-iRoD sPAclNG never exceeds 8" generallv'

Current requirement for adequate magnetization is calculated using

90-1 10 Amps / inch of prod spacing foj t!f, d component < 3/4"'r oo-i is Atiip. / inch oi prod spaciig tor thk of component > 3/4"'

Reduction of prod spacing may be.require$ io a93,1moOate component geometry or loincrease sensitivity. pnoii'Spacing < 3,, is rarely used as the banding of

magnettcparticles interferes with indications'

The tips of the prods are made of soft materials so that a proper contact is easlly

""ni"Go & the piod tips can be readily dressed.

Page 9 of 37

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LONGITUDINAL MAGNETISATION

When curreni is passed through a coil, magnetic field will be perpendicular to thedirection of curreni and will entei a test specimen placed inside the coil longitudinally'

Whenanumbero f t u rnsex i s t i naco i l , each tu rnp roduces | i neso f f l u xo f i t sown i . e ' ,two tu rnsco i | sw i | l p roduce tw i ce the l i neso f f l u xasaone - t u rnco i | .As tanda rdco i lg"n"iifly consists oi5tums, even though more or less turns could be used'

THE MAGNETIC FIELD IS GREATEST AT THE INSIDE $URFACE OF THE COIL

coNcLUS|oN : Parts for lnspection shou|d be near the inner surface of the coil.OrnebiOCnECTtFlED CUR{ENT shall be used for longitudinal magnetization'The required field strengtn or cunent required can be calculated for a component basedon the lengih L & Diameter D of the component'

PARTS WITH L/D > 4.

Amoere-turns = 35.000(UD\+2

lf L> 18',, the component should be examined in more than one position i.e'' max lengthto be examined in a srngle shot is l s". The value of L =

'l S" even for longercomoonents.

For non-cylindrical parts, D is the max cross - section diagonal'Page 10 of 37

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Exampte 1 - A part of 16" length & 2" diameter is to be longitudinal magnetized using a5 turn coil calculate the cunent required ?

LID = 1612-8>4

:: Ampere-turns = 35000 =L I D + 2

L = ' 1 8 " 0 = 2 "

U D - 1 8 1 2 = 9 > 4

Ampere turns = @.QQ =UD+2

No., of turns = 5

Amperes=Ampere- turnsNo., of turns

PARTS WITH UD between 2 & 4.

Ampere-turns = 45000UD

35000 350009 + 2 1 1

3200 = 640 Amps.

350008 + 2

= 350001 0

3500

No., of turns = 5

Current required = Ampere turns = 3500 = 700 Amps.No., of turns 5

Example 2 - A part of 24" length & 2" diameter is to be longitudinal magnetised using a5 turn coil calculate the current required ?

Length of part = 24" > 18"

The part has to be magnetized twice.

= 3200 approx.

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Page 11 of 37

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Example 3 - A part of 12" length & 4" dlameter is to be longitudinal magnetized usrng a

Il"ini.ir calculate the current required'

LtD = 12"t4" = 3 i 'e' ' between2&4

AmPere-turns= 4?0:90 = 45900

U D o= 15000 AmPere - turns

current required = Amperc-:-tulns 1.9Pq = 3000 A

No. of turns c

The current actualty used for testing should be + 10% of calculated value'

CIRCULAR MAGNETISATION

Circular magnetizatlon can be induced in a slecimefl by two methods

r HEAD SHOT / DIRECT CONTACT-TECHNIQUE2. ' iEf i i r i r lCor ' loucronrEcHNrQUEHEAD SHOT ' D]RECT CONTACT TECHNIQUE

Magnetization is accomplished bv passing t]:?ll,iltounnThemagne t i chneso r ' ' u x 'wn i c -na repe rpend i cu l a r t o r l

the Partwill get

to be examined'induced circularlY

around the sPecimen'--,- ^. .J'.Ix aaLD

Direct Contacl Method ot Magnetiring Bings

Fig 12

Page 12 ot 37

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Direct / rectified cunent is used for this technique. The current used for magneiizatron

InJJ n" "i"rnd

Boo A per inch of cross - section'

ln case of non-circular components' tl"- S*.?t::L:i:.ts - sectional diagonal in a plane

oft"i^cLi"i to ine citectioh of cunent flow is considered

rn the case of some ooo shapes,.the diniension obtained by PERTMETER can also be

used to determine tne magneiizaiion current' 3 14

CENTRAL CONDUCTOR TECHNIQUE

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Magnetization is accomplished in this technique by. passing thro' a cential conductor

around which tne "ompon"nit ""JiiJi"s

in! conouctor pid'""t a circular.magneticfietd. which magnetizes t#;;li'.}n; cl-nductorsnoutJ U'e located close

to the inside

surface of the cyrincler. rnr.iltn"iqr" L-"*ti*."rv u.eful for parts like rings / cylrnders

/ bores. The current ,"q;;;;;;biaining requiieo magnetization is.to b-e_ carcurated

using the Direct contacl t"in"i p'J"io"S ;t'l^n':::tduCtor is used lf more than one

turn is used in tne centrai condlctor' then the "tp"i"g" required would have to be

divided bY to the no., of turns'

Page 13 of37

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YOKE METHOD

ln this method, the magnetization produced is lonqitudinal Yoke is essentially

horseshoe shaped tugnut"'li f"n either be a periranent magnet or magnetlsm

produced in the soft f'on noi="tfto" by a multiturn coil carrying current'

Fig. 14

Thismethodisextremetyusefu|for' 'deteclionofdiscontinuit iesopentothesurface.Forthis technique, altemating #;;ii JireJ cu'rent

eteciiomagnetic yoke is used -

Above

6 mm thk., alternating *"?nilir"l are superior to direcicurrent yokes / permanent

magnet Yokes-

MULTI - DIRECTIONAL MAGNETISATION

Multi - directional magnetization is accomplished by high amperag" q:Y:: pu"nt

ooerating three circuits tnuil'" tn"'g'.t"d o1"-^?1,;'time'in rapid succession The

combined effect of these rapidly alternating magnetizilg ;it"nt is to produce an overall

magnetizatlon in the comPonent'

Three phase, full wave rectified current. P ,*?9. for magnetization'

.The current

reouirement for eacn crrcuit.is to be establisheO usiig tne"appropriate longitudinal /

"itirt"t magnetization principles'

Page 14 of 37

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This method is extremety useful in the testing of complex shaped components' Despitethis method, there are situations where all surface to be examined do not developadequatef ie ldst rengthfnt 'c f tcase,addi t ional test ingmethodsforsuchareasneedto be develoPed.

MAGNETISING CURRENT

Most power is transmitted as Alternate Current (AC) of 50 cycles / Sec'

The voltage required for magnetic particle testing is quite low comOgre! to transmittedpo*.r.

-"U.ing' efficiently O"esigneO transformeis

.can bring about this reduction In

voltaoe. The reduceo uoriug""r in magnetic particle testing equipment substantially*nitiUut" to the safety of operation of these equipments'

AC current tends to flow in the surface of the condudors only This leads to a situation

where magnetic fields asiociated with. AC cunent also are strong only at the surface

and rapidlv reduce rnwards' Hence, AC is best suited for detection of surface

;;;;"^til;iii".. A tvpical AC waveform is as shown in Fig

Fig. 15

Since a|ternate current cnanges direction several times in a second, it tends to providean aoitation to the magnetrc'Fu'ti"f

"i, *ni"h makes them more mobile and hence helps

tnem-to show leakage fields more clearly'

DIRECT CURRENT can be obtained by rectificatior of AC current by various methodslike using bridge circuits, iio-J"i, inu"ti"rs etc' -The method in which bottom

half of

each cycle is eliminated "iiog"in"i

i* "alled

Half-wave rectification and the waveformp.O""to is discontinuous

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HALF . WAVE DIRECT CURRENT

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Such half - wave DC has some advantages :Mh AC & DC and is very useful in

maonetic particle t"sting r il Jepin ot perietration of magnetic field produced with such

warTeforms is substantiaily ,ii;* iin" iil'iiaiion ot nc waie forms is almost eliminated

iur-i wnve DlREcr cURRENT

Fig 17

This type of waveform.can be obtained by reversing the bottom half of the waveform

rather than eliminatlng n' "nit

it called full wave rectification.

The deoth of penetration of magnetic field from the surface is improved' but mobility of

.i"giJii" p"ntlei is substantiallv hampered'Page 16 of 37

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lag between the 3offers the highest

( \ l AGN ET tZ l t l 6FORCE}{A IA6NETIZ ING FORCE OF

OPP OSTTE POLARITY 70 I ] . ,

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THREE PHASE FULL WAVE D.C'

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Even 3-phase power,(which consist of 3-individual plrases having a

ohases) can be full wave t""titi"O Full wave rectified current

[iili'#i.tii"i-is otten n"ipi']ln J"i""tion of deep lvins defects'

HYSTERISIS LOOP

lf we Place a Piece of matenal in

8 . i FLUx OENSITY I

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A magnetic field & measure the flux density caused by it in the material, we canunderstand the influence Of the magnetic field on the material. lf we gradually increasethe magnetic field, the flux density developed in the steel also keeps increasing. Butbeyond a point, increase in the magnetic field will no longer produce increased fluxdensity in ihe matelal. This is called the saturation point. OA shows the shape of thecurue bbtained if a graph were lo be drawn. In a typical AC waveform, this is whathappens when AC iuirent keeps increasing in the 1o Quarter. When the current(Mignetizing force H) keeps reducing in the second half, the flux density also.reducesbut tottows the path AB rather than retracing the original path. When current becomeszero at the end of second half, the flux density is not zero, but a finite value. This fluxdensity is called the RESIDUAL FLUX DENSITY. When the current starts increasing inthe reverse direction in the 3'd quarter, the flux density keeps reducing till such time itreaches O at point 'C' and then reverses direction as the current keeps increasingfurther. When the curfent teaches max., the flux density would have reached the point'D'. tn the fourth quarter, when the current starts falling in the reverse direction' thecurve follows DE. \A/hen current starts increasing again in the first quafter of the secondcycle, the curve tracs EFA.

HYSTERISIS LOOP described above shows that there is a lag between the flux densityin the part and the magnetizing force.

o c &o B &

OFOE ---> Residual magnetism

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" ' r o a c E r

B + ( F L U X O I N 5 I T Y I

COE RCIVE FOR CE

R S IOU ^Ll r A c t i f r l S M

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R S IOU^L MA6NE T I5M

Fig 2l

Fioure A, represents a marerial having high q:n::llitv' high residual field' & requiring

a 6igh coercive torce. Sucj'niateriatJarJsrited for making "permanent magnels '

Fisure B represents a materiarhavins high q:'ile:!:"$oL'iilHJ";fH?'3?Es;:::[::l.i:,*J'."' :: Jil%,*"l,[3'"J T'::: ;:tTfi l'%"T'l;;

-' ffi '"'i ""

n ""

to s etti n gdemagnetized.

We can draw the followtng conclusions from the above discussion'

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When electricity is passed througnlnauceO in them lags electric currenl

'il?ff'Ji::ffi!:iEFi"tlmagnetic fielc

Beyond SATURATION POINT' materials lose the ability to a$ract lrnes of force

further.

HIGH PERMEABILTY & HIGH SATURATION POINT are characteristrcs o

materials that can get magnetized easily & sufficiently

H|GH RELUCTANCE / HIGH RESIDUAI l-lE*lD^:,H|GH COERCIVE FORCT

are characieristics ot materiatt in"i""n retain magnetism in them'

Page 19 o f 3

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5. Different Ferro-magnetic materials differ in their permeability, reluctance &coercive force and their values will determine their suitability to magnetic particletesting.

EFFECT OF PASSING ELECTRIC CURRENT THROUGH CONDUCTORS

Now, we need io study the effect of electricity on various types of conductors. We alsoneed to understand what happens when different iypes of current are passed thro'them. These aspects are very important to determine where the magnetic field inducedin the part is highest & hence where the MAGNETIC PARTICLE TESTING would bemost effective,

1. NON-MAGNETIC SOLID CONDUCTOR CARRYING D.C.

where D.c. current is passing through a non-magnetic conductor like copper. thesketch below shows how magnetic field exists in & around it.

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FEIDSTAEn6rlr ^I SUAFAcE tFl

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As magnetizing D.C. current is introduced in sollD NON-MAGNETIC CONDUCTOR

Magnetic field induced at the centre of the conductor is always ZERO'within the conductor, magnetic filed strength linearly incfeases upto its suriace.At the surface, the value is the highest.

iii) outside the surface, the magnetic field strength reduces inversely with thedistance from the centre of the conductor-

FERRO - MAGNETIC SOLID CONDUCTOR CARRYING D'C.

F - F|LD Al TtlE StJAf^cIXEK 2E FROM TH CENTEA IHE f l f IO

v.rtr- e: t. erc

IIIII

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@As magnetizing D.C. current flows through Ferro - magnetic conductor,

i) Magnetic field induced at the centre of the conductor is always still ZERO.i;) Witiin tne Ferro-magnetic conductor, magnetic field strength linearly increases

upto its surface, but io a much higher value depending on the permeability of theFerro-magnetic conductor.

iii) At the surface, the value immediately drops to the same value as what wouldhave been in the case of a non-magnetic conductor'

iv) Outside the surface, the magnetic field reduces inversely with thethe centre of ihe conductor.

distance from

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U N I O O ENON-MAGNETIC HOLLOW CONDUCTOR CARRYING D'C.

WHERE R r RAOT(JSF - FIELO AI IHE SURFACE

THER 2R FROM THE CEIf iEN IHE FIELOW I I 8 E I - F T C2

2 A 3 RorsT ANcE

' Fig.24

AsmagnetizingD.C.Currentflowsthro'non-magneticho||owconductor,e*

,) Magnetic field inside the entire hollows portion (including centre) is alwaysZERO.

ii) Inside the non-magnetic conductor, the field linearly increases from zero at theinside wall of nofl6* portion to maximum at the surface of the non-magneticconductor.

iii) Away from the non-magnetic conductor surface, the field strength reducesinversely with the distance from centre'

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FERRO - MAGNETIC HOLLOW CONDUCTOR CARRYING D'C'

TVHERE R - hAotusF - FEtO AT THE SURFACE

IHEN 2R fROM tHE CN]ER THE FIELOwrLL 8E i. eTcT

?op

I;1II

orsT^Nc6

Fig. 25

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As magnetizing D.C current flows through hollow Ferro-magnetic conductor'

i) The generated field at the centre is always zero'

ii) Inside the hollow.portion' a slow growing magnetic field exisis as you move

towards the materlal

i i i ) |n thesol idpor t ionof theho| |owferro-magnet icconductor ,magnet ic f ie |dgrowsat a rapid pace to

"

nigi't t"i;tdependingin permeability) linearly'

iv) At the surface, magnetic field is highest a Opgs vertically down to a lower value

and, then ,t",t, o'opping inv"rs"ty'*itn the distance from the centre'

Page 23 ol 37

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oA ' r A / 1 ,;{iy. - - - -| ( IN lo ( |EII soLlD / HoLLOW NON-MAGNETIC coNDUcroR

CARRYING A'c'

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; = F r E L o A T t H L s u R F A c E

IHEN ?R FFO|I . ' i HE CINIER THE FTELO

wrrr Br !. rc

Fig' 26

As magnetilng A.C' Cunent flows thro' solid/hollow non-magnetic conductor'

i )

i i )

Magnetic field upto the inner wall of the hole (including centre) will always oe

ZERO.

l ns i de thenon -magne t l cma te r i a l ' t he f i e l dsw i l l ve r vo radua l l y i nc reasenon -linearly, but suddenly '"""iiliitiig'h"ti u"iu" near thL

Jurface & is maximum at

the surface.

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Page 24 of 37

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( |N lo ( JESOLID / HOLLOW FERRO . MAGNETIC CONDUCTOR CARRYING A'C'

PEA( FLUX OEI{SITY

F I f L O S I R E N C T X

OC FLUXOI S TRIEU TIOH

^C FLUX0r5 IR r8u l r0H

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0 ;orSI^ f {cE

ITEL 8^R

F IE IO 5 I RE

orsT^r.cE .

-

sr tL 8^R

Field Dislrlbtrt loo In and Around a Hollow Magnetlc Conductor Carrylng AC

'PEl( FLUx oExslTY

OC FLUXotsTRrEuTlol{

AC FLUXOISIRIEUTrcfl

Page 25 ot 37

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( I N l a o EWhen magnetizing A.C. Current flows thro' ferro-magnetic conductor carrying A C.,

1. Hollo portion (including the centre) wil l have negligible f ield which is growing alsovery slowly.

2. Suddenly at the surface of Ferro-magnetic conductor, the field rapidly increasesto a very high value (depending on permeabil i ty) and rapidly fal ls to a valuecorresponding to p = 1 , just outside the surface

3. As you move away from the surface, the magnetic field will drop inversely withthe distance from the centre.

We can draw ihe following conclusions :

1 .

2.

4.

Magnetic field produced is restricted to mainly the surface of the conductor inboth ferro & non - magnetic conductor when A C Current is used.

Magnetic field produced at the centre of a current carrying conductor is alwaysZERO (both for A.C. & D.C. as also solid & hollow conductor).

Magnetic field produced is always the highest at the surface of conductor, thepeai value dep'ending on the permeability of the material in both A C & D C'

A very week & sheggishly increasing field exists in the hole of a hollow Ferro -magnetic condudor.

Our aim in magnetic particte testing is always to locate the object io be tested in thehighest field particle to get good results'

PROPERTIES OF MAGNETIC PARTICLES & SUSPENSION FLUIDS

Magnetic particles are classified based on the medium in which they are canied to thepart.

Carried in airCarried in i) water ii) oil

Visible & ii) FluorescentMagnetic particles can also be classified as i)

DRY PARTICLESWET PARTICLES -

Page 26 of 37

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( |N to (JEDRY PARTICLES

Magnetic particles can differ from each other ini) Permeability of the materiali i) Retentively of the materialiii) Size of particles .iv) Shape of particlesv) Density of particlesvi) Mobility of particlesvii) Visibility of particles & Contrast with the inspection surface.We have to leam that

1. The magnetic particte should have the HTGHEST posstBLE pERMEABlLlry.This will enable week leakage fields to be detected by the particles.

2. The magnetic particles shoutd have the LowEST posslBlE RETENTtvtry.High retentively leads to clumping of particles affecting their mobility, a neavyback ground and subsequenfly a reduction of sensitivit!. lt would aiso stick tothe surface after testing is over due to residual magnetism and hence makePOST CLEANING DEFFICULT.

3' PARTICLE slZE should be the LowEST slZE possibte. An extremety fine sizewould cause clumping due to moisture or rough surface of the object inspected.An elitremely coarse particle would be difficult to be caried. would noi collectenough leakage flux to cause indication etc.

4. PARTICLE SHAPE is best when a combination of globular & elongated particlesare used. Globular particles would provide maximum flexibility in uniformdispersal of particles over the test surface whereas long, slender particlesprovide stronger poles for the same leakage field.

lf the surface to be tested is rough, more long and slender particles should beused, but rounded particles would be suitable for smooth surfaces. A suitableCOMPROMISE needs to be made between both the above factors.

5. DENslry oF THE PARTTCLES should be the {owest oossible so that theparticles have a higher chance of floating without setiling.

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( I N t a o EMOBILITY of the particles should be highest so that they stand a higher chanceof catching even week leakage fields effectively.

VlSlBlLlTY & CONTRAST of the particles depends on the colour of the particles,the colour of the inspection surface, the amount & type of lighting in which it isseen.

Dry particles are generally available in black and red, and, can also be made inyellow and shades of grey by pigmentation. Dry particles can also be made withfluorescent coatings so that they can be obseryed under black light or UV light

IT IS NOT ADVISABLE TO RECYCLE DRY PARTICLES

WET PARTICLES

All the above considerations stated above are also applicabte for wet particles. Inaddition, wet particles can be used in much finer sizes because they are now caried ina liquid medium. The fluidity of the liquid adds to the mobility of the particles, withoutfear of clumping.

Few properties of the liquid also should be considered additionally when wet particlesare used.'1. Liquid should be odourless.2. Liquid should have a high flash point3. Viscosity of the liquid should be lowest. (Generally 3-5 centistockes).4. Liquid should not be conosive to either magnetic particles or to ihe Inspection

surface.5. Liquid should not be reactive to the skin of the operator.

6. Suitable conditioners may have to be added to improve mobility of particlesthrough addition of wetting agents, rust inhibitors, dispersing agents & anti-foamagents.

Having understood the various properties of liquid carriers, it is now important to knowthat bath concentration is very important. Too strong a bath may hide few indicationsdue to a heavy background & too week a bath may provide too less particles to locateall leakage fields. The best method of determing ideal bath concentration is to carry outexperiments on a specimen having known discontinuities.

7.

Page 28 of 37

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( I N t o o EBATH CONCENTRATION can be measured in what is known as a SETTLING TESf.In this test, 100 ml of the welfagitated liquid containing magnetic particles can beallowed to settle in a pear - shaped centrifuge. The volume of solid that settles out after30 mins. (considered long enough for most particles to settle) can be read out from thegraduated cylindrical portion at the bottom. lt is generally possible to differentiatemagnetic particles & other dirt particles, which settle because of colour difference &density differences.

Fig. 29

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Page29 of 37

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U N I O O EAcceleration of this test is possible by forcing particles to settle quickly through the useof.either a magnetic fietd / through the use of a CENTRIFUGE. ihis iecrrniqie is oftenadopted when continuous Magnetic particle testing has to be canied out on large no., ofcomponents.

IT IS POSSIBLE TO RECYCLE THE WET BATH BY ADDING MORE SOLIDPARTICLES WHEN THEY ARE LOST

FLUORESCENT PARTICLES

Fluorescent particles are nothing but dry powder particles, which have been coated withsome suitable fluorescent materials and are readily available as such.

Fluorescent particles are designed to receive light energy (from special bulbs calledBLACK LIGHT / u.v. LTGHT) in rhe range ot eoS A" wav6 tbngtn ano give out visiblelight. when this is done in the dark, the presence of particles is iery cleaily indicated.The characteristics described earlier for dry & wet powders are also applicable to

. fluorescent particles. However, much finer particles can be used in both the drv & wetmethod as they can be easily spotted in dark because of their brilliant glow.Dryfluorescent particle testing is not very common and is used only in a limited range ofapplications.

wet fluorescent particle testing is very common as the brilliant glow allows much lowerconcentration of particles to be used aid the wet method also allows use of very fineparticles. combination of these two fac{ors gives the advantage of HlGHEsrSENSITMIry IN WET FLUORESCENT MAGNETIE PARTICLE TESTING.BLACK LIGHT / ULTRAVIOLET LIGHT

$_mercury 9rc lamp is a convenient source of Ultraviolet light (also called black light).\Mren used with specially desjo.ngd filters, a narrow band'of Ultraviolet tignt 6fapproximately.3650 A" (1A' = 10 cm) wave is emifted. A length CRAcKED FILTERwould also allow UNDESIRABLE ULTMVIOLET LTGHT to come out, and, henceshould be avoided. These wavelengths are absorbed by the fluorescent material andvisible light is given out by them.

The amount of height that is required by the operator for getting a clear view of theindication is presently thought to be around 1500 p WCm2 (micro watts / sq. Cm.) at theinspedion surface. However, up to 3000 p wcm2 can be used for verv critical

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Page 30 of 37

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inspection. Inspectors should acclimatize to dark condition for at least 5 mins. & blacklight should be on for at least 5 mins, to stabilize before viewing is done.U-LTMVIOLET light quantum can be measured using a specially designed-UV ttcHt|yFTFR Relevant Specification should be consulted before using the ibove values forlight intensity as lhe same can vary from specification to specificatJon.INDICATIONS & THEIR INTERPRETATION

An indication is an accumulation of magnetic particles on the inspection surface that isf ormed during inspection.

Indication can be of three types

RELEVANT, NON-RELEVANT, & FALSERELEVANT INDICATIONS are those indication which can be attributed to errors macteduring or after metal processing.

NON-RELEVANT INDICATIONS are not attributed to enors in materials. but are due toleakages fluxes which are disturbed. These indications bear no relation to the errors inthe part.

FALSE lNDlcATloNS are those in which the magnetic particles are held by gravity orsurface roughness without any magnetic attraction.

One of the most common,problems of magnetic particle testing is the classification ofindications into one of the above three catelories. '

Given below are a few typical examples & their interpretation.

1- Excessive particles are found adhering to corners, ridges etc. with the magneticparticles standing 1 to the surface.- This is non-relevant indication caused by excessive magnetizing current in

longitudinal magnetization.

2. Regular patterns of iron powder all around the surface everywhere.- This is a non-relevant indication caused by excessive cunent in circular

magnetization.

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Page 31 of37

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( |N tooE3. Build up of particles at edges of mill scale sticking to the inspection.

- This is a non-relevant indication due to mechanical stoppage of particlesas well as magnetic permeability difference between steel & scale.

4. Paft configuration like splices, threads, key ways etc., also may cause indications

- These are non-relevant indications & should be associated with theirphysical shapes.

Indication which are attributable lo sudden changes in magnetic properties like HAZ inwelds, dissimilar base metals, differently heat treated portions (case carburising) alsocause NON-RELEVANT indication.

MAGNETICWRITING

When magnetized materials having good residual magnetism are to be tested, they canbe first magnetized & then tested using residual magnetism. In such conditions, whenparts touch each other, they alter the leakage flux pattems. When tested, someindications conesponding to these changes will appear. These are non-relevantindications which dis-appear when re-tested avoiding these contacts.

In the case of relevant lndications, we need to know the nature of materials & the natureof defects caused during those operations. Then we will be able to say what kind ofindications we expect. lt is necessary for us to know the various defects, which canoccur in process like welding, casting, forging, pressing, forming etc. These aredescribed separately. Students are advised to acquire good working knowledge ofthese phenomenon by a thorough study.

ADEQUACY OF FIELD

When various methods of magnetization are used on complex engineering items, it isimpossible to say whether adequate magnetic lines are introduced in the material or not.It is not possible to see the magnetic lines nor is it possible too count them. We needsome indirect method of ensuring that adequate field strength exists where the test isbeing canied out. This can be accomplished by the use of

i) Pie-shaped Magnetic Field lndicatorii) Artificial flaw shims, and,iii) Hall - effect Tangential - Field probe.

Page 32 of 37

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The aim of magnetization is always to introduce adequate lines of flux to producesatisfactory indications. lt should not be too low to miss some indications nor to high tocause inelevant indications which would then mask the true indications. The factorswhich affect the required field strength are size, shape & nature of the part, technique ofmagnetization, technique used for testing, coating present on the surface, expectedtype of discontinuities & their probable location, permeability & reluctance of the part,permeability of magnetic particles etc.

However, basic guideline to be followed for FIELD ADEQUACY CHECK is that, whenone of the indicators is used under actual test conditions, it should show evidence ofexistence of sufficient field.PIE - SHAPED MAGNETIC PARTICLE FIELD INDICATOR

Eighl lo\ir:.bon neet piesect ;ons f ! rnace o.aredtoqethr

nd copp. pta led

{ 1 9 . 1 m m r o: 5 . 1 m m ,

Nonler .ous ha^dte!

lengrh and.hape

//.//\,//

10.79 Nohterrous truoions

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PIE.SHAPEO MAGNETIC PARTICLEFIELD INDICATOR

Coppe. plele 0.016 in. . 0.mt in.{O.25 mrn : 0.025 mm) rhict

F i g . 3 1

Page 33 of 37

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The indicator shown above essentially consists of eight sections of pie-shape made oflow - c steel furnace brazed together to form an octagon. lt is them copper plated,When this indicator is positioned on the surface io be examined so that the copperplated surface is away from the inspection surface. The fleld strength is consideredadequate if " one or more clearly defined lines of magnetic particles appear across theindicator when magnetic particles are applied simultaneously with the magnetic field''.This is a GO - NO GO QUALITATIVE TEST.

ARTIFICIAL FLAW SHIMS

-T0.t5 in.(20 mml

S.clion A-A

- r+ 0.002 ;n.ii (0.0s mfttlJ{';3ti-.,Jll r ,Ye,c.'

J* o.oooe ;n.(0.019 mml

'-+ a - f+0 m2 rnr--r- t-T ii r0 05 h6,

l ,At l o. , r ' ,n. 11l l l r l , l l l r z o m m ) l lI f \\Irlf | , tJl l r ] l - r l I I l n

'ii/ r-o

--{t -0.@o6.;n.4 o-9 in-

{!2.5 mm, S.ction A-A

0,4 ia.(10 m|n)rm

15 mln)Type {

GENERA! NOTE:Abov6 .16 exampl6g ol :dificial ll.w shimi used in m.9ne!icpattbl. inspcction .yrtem vcrilicsrion {not drawn to scate).Ths 6him5.re mede of low c:rbon steel i lo05 r teel lo i t l .Thc./rificill fl.w i: tchod o. ma.hinod on one i;de of th.foil to. dcpah o,30.Ja ot thc loil thicl(ncls.

FlG. T-753.r.2 AR'tlFlClAL FLAW SHltvlS

lllIT-T'li 10.005 in.l l 10_125 rnlnt

l l 'ye'cal-+lF+ 0.0006 ;n.

10.015 rnml

Page 34 of 37

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The shims shown above are made of low - c steel foil & the artificial flaw is etched onthe side bf a foil to a depth of 30% of the foil thk. These shims are to be placed on thearea to be inspected such that artificial flaws face the Inspection surface. Whenmagnetic particles are applied simultaneously with the magnetic field "a clearly definedIine representing 30% depth should appear on the other sides.

HALL. EFFECT TANGENTIAL - FIELD PROBE

A gauss meter and the above probe can be used for measuring the peak value of atangential filed. The probe shall be positioned on the Inspection surface such thatmaximum field strength is determined. When the measured field is 30G to 60 G withthe magnetizing force ON, the field is considered adequate.

PROCEDURES, EVALUATION & RECORDS

PROCEDURES

Magnetic particle procedures should contain at least the following :

1. Material shapes & size to be examined.2. Extent of examinaiion - 100o/o or otherwise.3. Magnetic technique employed.4. Equipment io be used for magnetization.5. Surface preparation.6. Type & concentration of magnetic powder to be used - Manufacture, Brand.

Colour etc.7. WET / DRY method.8. Magnetization culrent - AC / DC & Amperage (if measurable).9. Demagnetization procedure, if required.

Procedure may contain any additional information like field adequacy check requirementetc., which will help the operator conectly perform the test.

EVALUATION

Evaluation consists of inspecting the surface to be inspected and classifying theindiCations- into FALSE, NON - RELEVANT & RELEVANT INDICATIoNS. Afterclassifying, relevant indications are to be compared with the acceptance standardsgoverning the Inspection, which normaily are the DESIGN CODE for Ex. ASME Sec.Vlll Div.1. Acceptance standards for Magnetic Particle Examination are given in theSPECIFICATIONS book supplied.

Page 35 of 37

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oN roo EIt students are advised to study simirar acceptance standards from BS, DrN, Jrs, etc., toa

familiarize themselves with these requirements.

I RECORDTNG OF lNDtcATroNs

O Normally recording of indications are done by marking out the indicalons on a Drg. /t,

Sketch of the mmponent inspected.

a 5."J.::"t, other methods are often used to record & preserve the indication when

I TAPETRANsFERTEcHNIQUECiI JffJl'lflillin'""rT,1fl:i:ii".H?:,.,1,,X$T'jlT::",#":.ffij",:',i3:""fl:lty,T:a

paper where all other information is documented.

O STRIPPABLE LACQUERa strippabre racquer is sprayed on to the indication in.severar thin rayers. on drying, theI li*u"t

strip can be pulled out and stored along with all other intoimation pertaining toI pHorocRApHyIa [s5'#1flf,9fiflt":phs of indication as found on components is arso a userur way or

DEMAGNETISATION

l1l:s-!:rll ail aspects of Magnetic particre Examination, it is important to rearn rhermportance of Demagnetization and also how it can G accomplished.

[l:I?r"g*Jic materiars, of high. retentivity, substantiar residuar fierd can remain aftercompletion of examination. inis mav iiriJrrerl *ith subsequent processing rikemachining, werding etc. For exampre,.during ma;nining, chips may tend to stick to they-?t ,pi"T causing poor surface nniin

-

or"ring *"iiing, the magnetic field can causearc blow teading to werding d."f-".ar __rr magdtic tia"r.ing o"ui"E iu'rrJioiwetaing,device may not work satisiactoriry. r-r"*""Er,-iJra'gnetization may not be importanty!-"l.tl" Lo_s.e_oyent proce$sing is neat ireitment-'aboue the cuRlE potNT of thematerial- CURIE porNT is that t,emperature iuove wnich ierromag-neil ,I"iLr. ror"

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their.magnetic properties. Therefore, it is very important that examination proceduresshould specify clearly if demagnetization is required.

The various methods of demagnetizalion possible are

i) Withdrawal from A,C. Coillf we pass the part to be demagnetized thro' on A.c. coil; the magnetic field willbe varying in direction continuously and also varying in intensity,

'ihrs oppos,ng

residual magnetic field. This is a very fast & efficient way of demlgnetizatron.i i) DecreasingAlternatingcurrent

lf a decreasing alternating current is passed, then the opposing magnetic fieldwill eliminate the remnant magnetism.

lll) Demagnetization using yokes can be done. In this method, ihe yoke is placed onthe surface, moved. around & then slowly withdrawn from the object cusing areduction in the fielo

iv) Reversing Direct current is another efficient method for demagnetizingcomponents which have been magnetized by D.c. method. ThJ specia-lequipment periodically changes the direction oi D.c. current and also reducesthe cunent gradually

All these methods are effective and can be used depending and availability ofequipment & ease of operation. lt is to be rememberec tnat ctnculARLyMAGNETISED COMPONENTS DO NOT EASILY SHOW EVIDENCE OF NESIOUNIFIELDS. lf defects become open on subsequent processing teakage netoi couta9g.vgLgq_r1.ing probrems. rr rs ALWAYS PREFERABT-E fo r_or.r"criuoiruar_r_vMAGNETISE A PART BEFORE DEMAGNETTSATTON. riris nerps in-"i.'J"'ting tn"extent of demagnetization effectivelv.

Page 37 of 37

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T-710T-'t20T_730

'f - '7 31

"t-7 40

T-?-s0T-?51T-152r - / ) JT-'154

T-'t 56'r',760

T-761T -162'I'-763

T-770'r_17 |'1"712

T-17 31'-'/l I't

-17 5' I - t76

1'7'7'11.1',/8

T-7801'-'79C

T-79I

lf igut csT,753.1 . IT -753.1 .2T- ,475.2

ARTICLE 7

E.f,amination Medium, -. . .. . . .. . ,Requ i rements . . . . . . .Surface CondirioningProcedure Requiremeots ... ,. . . ,.. .. . , , .Method o f Examinat ion . . . . . . . .Techn iques and Mater ia ls , . . . . . .Magnetizing Field Adequacy and DirectionRect i f ied Cur ren t . . . , . . . . .DemagnctizationPosGexamina t i on C lean ing . . . . . . . . . . ,Ca l i b ra t i on o f Equ ipmenr ._ . . . . ] . . . .F requency o f Ca l i b ra t i on . . . . - . . , . .L i f t i n g P o w e r o f y o k e s . , . . . . . . . .

Examination.Direc(ion of Magnetization . . . . - . . . . .Examination Coverage. . _. . . . . . _ .

Loo8itudinal Magnctizarion Tcchnique. . . - . . , , . .Circular Magnetization Technique... , .Y^kF T ' .hn i^ , ' .

Multidircctionlrl Mngnctizxtion Tcchniquc . . , . . . . . , .

r r $ ! r P r ! r a U v u

Mulridirecrional Magnerizarion Techniquc Skerch . . .

Single-Turn and Two-Tum Central Conductor Technique. . . . . . .

1 3 1t 3 ll 3 tt 3 rt 3 1

t32t32t32t32) 3 3t34t34t34134134t 3 4t341 3 4l ]4134r35t 3 5r 3 613613'tt37t37137

133133

h{andatory AppendicesAppcndix I

I . 7 I Ot-120

t-'72rt'731)r-750

Magnetic Panicle Examinarion on Coared Ferritic Materials Using theAC Yoke Technique lj8

Scopc. . . . . . . . , . . . . - t j8C e n e r a l . . . . . , B l tP c r s o n n c l Q u n l i l i c a r i o n . , . . . . . . . . , . . - , . l l t iEquiprncnt. - - . . . t l l lProccdurc/Techniquc l l8

129

oa

t-751.t-752J-753

r-'770t.?80I-790

Appendix IIrr-7 to

-170II-730

Appendix IIIIII-7IO

l .1I It-720

t-'721lI- '122nr.723

n-730Iu-740I -?60I|- '710IIt-780I II- 790

F'iguretlt-']22

Appendix A

A-720A-730A-750A-790

Coating Thickness Measurcment.... . t3gP r o c e d u r e D e m o n s t r a t i o n . . - . . . . . . . , . . . . . . , . . . . . . . . . . . , . . 1 3 9Procedure Qualificarion . , , , . . . . . . . . . l3gExamination . . . . . . . , 139Evaluation. . . ,, , . .. . 139Documenta t ion /Reco.ds . . . . . - . . , . , . . . . . 139Glossary of Terms for Magneric Parricle Examinarion 139Scope. . . . . . . . . . . . . . l3gCeneral Requirements 140Requirements . . . , . . . . . . . . . . . . . . . . , , . _.. 140Magnetic FIux Leakage (MFL) Examinarion t4lScop . . . . . . . . . . . . . . t4lReferences l4lC e n e r a l . . . , . . . . . . . . l 4 lP c r s o n n c l Q u a l i f i c a t i o n R c q u i r c n r c n t s . _ . _ . . , . . . , , . . . . , . . . . , , l 4 lEqu ipmeot Qua l inca t ioo Requ i rements . . . . . , . . . . . . . . . . . . . . . l4 lW r i ( c n P r o c e d u r e R e q u i r e m e n t s . . . . . . . . , . . . . . , . . . . . , . . . . . , I 4 lEquipmer(. . . . . . . . . . t42Requirements . , . , , . . 143Calibration 143E x a m i n a t i o n , . . . . . . . - . . . - - . . . . _ . . . . . . . . t 4 3Evaluation. . . . . . . , . . 143Docuq,entation. . . . . . l4l

Requiremenrs of an MFL Examinal ion

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ARTICLE 7

T.?IO SCOPEWhen specified by the referencing Code Section, the

magnetic particle examination techniques described inthis Anicle shall be used. In general, this Anicle is inconformance with SE-709, Standard Guide for MagneticI'i l(iclc l:xirnri[ation. This docunent provides dctails'10 be considered in the procedures used.

When this Articte is specified by a referencing CodeSection, the magnetic particle method described in thisAnicle shall be used together with Anicle l, GeneralRequiremeots. Definition of terms used in this Aniclearc in Mandatory Appendix IL

T-720 GENERALThe magnetic particle examination method may be

applied to detect cracks and olher discontinuities onor near the surfaces of fermmagnetic matedals. Thesensitivity is greatest for surface discontinuities anddiminishes rapidly with inoeasing depth of subsurfacediscontinuities below the surface. Typical types ofdiscontinuities that can be deteded by this melhod arecracks, laps, seams, cold shuts, and laminations.

In principle, this method involves magnetizing anarea to be examined, and applying fenomagnetic parti-cles (the examinations medium) to the surface, Theparticles wilt form pattems on the surface where cracksand other discontinuities cause distortions in the normalmagnetic Reld. These patterns arc usually characteristicof the type of discontinuity thar is detected.

Whichever technique is used to produce the magneticflux in the part, maximum sensitivity will be to lineardiscontinuities oriented perpendicular to the lines offlux. For optimum effectiveness in detecting all typesof discontinuities, each area should be examined atlcast twice, with the lines of flux duiing one examinationapproximately perpendicular to the lines of flux duringthe other.

MAGNETIC PARTICLE EXAMINATION

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T.730 EQUIPMENT

A suitable and appropdate means for producilg thenecessary magnetic flux in the part shall be employed,using one or ..nore of the teciiniques listed in T-752and described in T-770-

T-731 Examination lt{ediumThe Snety divideC fenonagnetic panicles used for

the examination shall meet the following rcquirements.(a) Particle Typcs. The pil icles shall be trcatcd

to impan color (f luorescent pigrnents, nonfluoresccntpigments, or both) in order to nrake thenr highly visible(contrasting) against the background of the surfacebeing exan]ined.

(b) Particles. Dry and llet panicles, including wetpa(icle suspension vehicles, aod particle concentrationsshall be in accordance with SE-709.

(c) Temperature Limitations. Pa(icles sltall be usedwirhin the tmperature range limitations set by themanufacturer. Altematively, particles may be used out-side the manufacturet's recommerldations providing theprocedure is qualified in accordance with Anicle l,T -150.

"T-740 REQUIREMENTST:741 Surface Conditioning

T-741.1 Preparation(a) Satisfactory resulr are usuxlly obtained when

the surfaces are in the as-welded. as-rolled, as-cast, oras-forged conditions. However, surface preparation bygrinding or machining may be ncccssary whcrc surfaccinegularities could mask indications due to discontinu-ities.

(b) Prior to magnetic particle exanrination, thc surfaceto be examined and all adjacent areds within at leastI in. (25 mrn) shall be dry and ftee of all dirt,grease, lint, scale,. welding flux and spatter, oi), or

r 3 l

T-741.r

orher extraneous matter that could interfere with theexaminarion.

, (c) Cleaning may be accor,rplished using detergents,organis solvents, descaling solutions, paint removers,vapor degreasing, sand or grit blasting, or ultasoniccleaning methods.

(dJ If coatings are left on the pan in the area beingexamined, it must be demonstrated that indications canbe detected through the existing maximum coatingthickness applied. When AC yoke technique is used, thedemonsfation must be in accordance with MandatoryAppendix I of this Article.

T-741.2 Surface Contrast Enhancement. Whencoatings are applied temporarily to uncoated surfacesonll, in amounts sufficient to enhance particle contrast,it nust be demonstrated that indications can be detecredthrough the enhancement coatlng.

NOTE: Rcfer ro T-150(a) for tuidanic for the dcmonstration rcquiredin T-7Jl . l (d) and T-741,2.

.T.750 PROCEDURE REQUIREMENTS

Magnetic particle examination shall be performed ioaccordance with a written prccedure.

Eaclr procedure shall include at least the followinginformation, as applicable:

(d) the materials. shapes, or sizes to be examined,and the extent of the examination;

(b) magnetization techniques to be used;(c) equipment to be used for magnetization;(d) surface preparation (finishing and cleaning);(e.) type of fenomagnetic particles to be used: manu-

facturer, color, wet or dry, etc.;fJ maxirnum allowable tempetature for ferromag-

netic particles to be used: per manufacturer recommen-dation or by qualif ication;

(g) magnetization cunents (type and arnperage);{hJ d(rrnagnetization;(i) post-examination cleaning.

T-751 Method of Examination

Examinaaion shall be done by the continuous method;that is, the olagnetizing current remains on while theexamination medium is being applied and while excessof the examinution medium is beins removed.

T-753.1.2

T-752 Techniques and Materials

The fenomagneaic particles used as an exanrinationmedium shall be either wet or dry, and may be eitherfluorescent or nonnuorescent.

One or nrore of the following five ntagnetizationtethniques shall be used:

(a) prod techaique;(D) longitudinal magnetization rechnique;(c) circular magnetization technique;(d) yoke technique;(e) multidirectiooal nragnetizarion technique.

T-753 Magnetizing Field Adequacy andDirection

T-753,1 Magnetic Field ittequacy. Tbe appliedmagnetic field shall have sufncient strength to producesatisfactory indications, but it shall not be so strongthat it causes the masking of relevant indications bynonrelevant accumulations c,f magnetic pilrticlcs. Factorsthat infiuence the required field strength includc thcsize, shape, and material permeabil ity of the panl t ltetechnique of magnetizatian; coatings; the n)ethod oipa.ticle application; and the type and location of discon-tinuities to be detected. When it is necessary ro veril1,the adequacy of magnetic f ield strengdr, it shall beverif ied by using one or more of the followinc threemcthods.

T-753.1.f Pie-St apcd l\{agnctic Particle }' icldIndicator. The indicator, shorvn in Fig, T-753.1 , l, shallbe positioned on the surface to be examined, such thatd|e copper-plated side is arvay from the inspectedsurface, A suitable field strength is indicated when aclearly defined line (or l ines) of magneric particlesform(s) across the copper facc of the indicator rvhenthe magnetic pafticles are applied simultaneously wi(hthe magnetizing force. When a clearly defined line ofparticles is not formed, the nragnetizing technique sballbe changed as needed. Pie-rype indicators are besl usedwith dry panicle procedures.

T-753.1.2 Artif icial Flarv Shims. The shim. shownin Fig. T-753.1.2, shall be attrched to the surihce tobe examined, such that the anificial flaw side of thcshim is toward the inspcc(ed surt'rce. A suitablc lleldstrength is indicated when a clerrly delined line (orlines) of magnetic panicles, representing the 30% depthflaw, appea(s) on the shinr face when nragnetic particlesare applied simultaneously wilh the milgnetizing fbrce.When a clearly defined line of pirrt icles is not fonned,the magnelizilg techniquc shall hc charged as nccdcd.

2OOI SECTION V

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T.753.t.2

t/. in. to I in-(19 .1 mm ro25.4 mml

Eight low c..bon lteEl pieaectioni lurnacg b{gadto9elhe. and copper platedE

, +l F- 0.002 in.ii (0.0s mmrl l f , o . m s i n .l (+ (0.12s mm)l l l + wc;*rq]

-dt - 0.0006 i..{0.015 mm}

Section A-A

ARTICLE 7 - MAGNETIC PARTICLE EXAMINATION T-754

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lensrh .nd shape

mml, \-Nonfsrrouttrunions

Nonte.rour handlgs --'l F- 0.002 in.i i {0.0s mm)t (t lt )IT

-JL o.moe in.{ 0 . 0 1 5 m m }

. TYp6 c section a-A

1/, in.(3.175 mmJ

FIG. T.753. I .1 PIE.SHAPED MAGNETIC PARTICLEFIELD IN DICATOR

Shirn-type indicators are best used with wet particleprocedures.

T-753,1.3 Hall.Effect Tangential-Field Probe. Agaussmeter and Hall-Effect tangential-field probe shalibe used for measuring the peak ralue of a tangentialfield. The probe shall be positioned on the surface tobe examined, such that the maximunr field strength isdetermined. A suitable field stren$h is indicated whenthe measured neld is within the range of 30 G to 60G (2.4 Mm-' to 4.8 ?:Am-l) while the magnetizingforce is being applied. See Afiicle ?, NonmandatoryAppendix A.

T-753.2 Magnetic Field Directlon. The direction ofmagnetization shall be determined by particle indicationsobtained using an indicator or shims as shown in Fig.T-753.1.1 or Fig. T-753.1.2. When a clearly definedline of particls is not formed in the desired dircction,the magnetizing technique shall be changed as needed.

T-753.2.1 For multidirectional_magnetization tech-nique.s, the orientation of the lines of flux shall be inat least two nearly perpendicular' directions. Whenclcarly defined lines of particles are not formed in at leasttwo nearly perpendicular directions, the mignetizingtechnique shall be changed as needed.

0.005 in.(0 ,1?5 mm)

Type I

Copper plaie0.010 in. t 0.001 in.(0.25 mm t 0.025 mml thick

r t t r t t t r l

n) -.1i f- o oo2 inD i " i s i o n I l l ( o o s m m )

Typ R

GENERAL NOTE:ALrove sre ex.mples ol ar t i l ic is l l lsw shims !sed in magnet icperlicle ingpection sygtem verificstion (nol drawn ta scal).

. Ths rh ims Bre made of low carbon s leel 11005 steel lo i l ) .The lrtificisl flw ir tchsd or mschined on ohe 3ide of theloil to . depth of 3096 otth6 foil th;clnctr.

FIG. T.753. I ,2 ARTIFICIAL FLAW SHIIVIS

T-7533 Determination of the adequacy and directionof magnetizing fields using magnetic field indicatorsor artificial flaws are only permitted when specificallyreferenced by the magnetizing technique in T-774.2(c'l.,^t

-7 7 4.2(d), T-775. I (bX3), T -7 7 5.2(a), T-775.2(b), and

T-754 Rectified Current(a) Whenever direct current is required rectificd cur-

rent nay be used. The rectified current for magnc(izationshall be either three-phase (full-wave rectifled) current,or single phase (half-wave rec(ilied) cunent.

(/r) The amperage required with threc-phasc, full-wave rectified current shall bc verilied bv mcasuringthe nverage current.

T-754 2001 sEcTIoN v

(c) The amperage required with single-phase (half-wave rectified) cunent shall bc verified by measuringthe avera8e current output during lhe conducting halfcycle only.

(d) When measurirg half-wave rectified curent witha direct cuncnt test meter, readings shall be multipliedby two.

T-755 DemagnetizationWhen residual magnetism in fte pan could interfere

with subsequent processing or usage, (he pan shallbe demagnetized any time after completion of thecxanllnairon.

T-756 Post-cxamination CleaningWhen postexamination cleaning is required by the

procedurc, it should be conducted as soon as ptacticalusing a process that does not adverscly affect lhe pan.

T-770T-77 |

"f.760 CALIBRATION OF EQUIPMENTT-761 Frequency nf Calibration

(a) Frequency. Each piece of magnetizing equipmentwith an amrueter shall be calibrated at least once ayear, or whenever the equipment has been subjectedto major electric repair, periodic overhaul, or damage.If equipment has not been in use for a year ot more,calibration shall be done prior to first use.

(b) Procedure. The accuracy ofthe unit's meter shallbe verified annually by equipment traceable to a nationalstandard. Comparative readings shall be taken for atleast three different current output levels encompassingthe usable range,

(c) Tolerance. The unit's meter reading shall notdeviate by more than ilo% of -fuu scale, relrrdve tothe actual current value as shown by the test meter,

T-762 Lifting Power of Yokes

(aJ Prior to use, the nagnetizing power of electro-magnetic yokes shall have been checked within thepast yar. The magnetizing Power of permanedt mag-netic yokes shall be checked daily prior to use. TheInagnetizing power of all yqkes shall be checked when-ever the yoke has been danrlged or repaired.

(D) Each alternating curent electromagnetic yokeshall have a l ift ing power of al least l0 lb (4.5 kg)t the mrxinrunt pole .spacing that wil l be used

T -173.2

(c, Each direct cufient or pennanent nagnetic yokeshall have a l ift ing power of at least a0 lb (18.1 kg)al the naximum pole spacing that wil l be used.

(d) Each weight shall be weighed with a scale from areputable manufacturer and sterciled with the applicablenominal weight prior to frrst use. A weight need onlybe verified again if damaged in a manner that couldhave caused ootential loss of material.

T-763 Gaussmeters

Hall-Erfect probe gaussmeten used to verify mag-netizing 6eld strength in accordance with T-753 shalltre calibrated at least once a yerr o: whencvcr thcequipment has been subjected to a najor repair, periodicoverhaul, or damage. If equipment has not been i usefor a year or more, calibration shall be done prior tofirst use.

BXAMINATIONDirection of Magr.etization

At lerst two separate examinations shall be perforrnedon each area. During the second examinalion, the l lnesof magnetic f lux shall be approxinrately peqrendicularto those used during the Rrst exan)ination. A dil lerenttechnique for magnetization may be used for the secondexamination.

'T:772 Examination Coverage

All examinations shall be conducted with sufllcientfield overlap to ensure 1007o coverage at the requlredsensitivity (T-753).

T-773 Prod Tcchnique

T-773.1 Magnetizing Procedure. Fo. the prod tech-nique, magnetizalion is accomplished by portable ptodtype electrical contacts pressed:rgainst the surface inthe area to be examined. To aloid arcing, a rerl]otecontrol switch, which may be built into the prod hrndlcs,shall be provided to pennit lhe currcnt to bc lurncdon after the prods have been properly positioned.

T-7?3.2 Magnetizing Current. Direct or rectifiedmagnetizing cunent shall be used. The currcnt shallbe 100 (minirnunr) amp/in. (3.9 amp/mnr) to 125(maximurn) rnrp/in. (4.9 arnp/nlnl) of prod spircing l i)rsections l4 in. (i9 nrrn) thick or greater. For scctions

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ARTICLE 7 - MAGNETIC PARTICLE EXAMINATION T.7?5.1T-77 3,2

less than % in. (19 mm) thick the cunent shall be 90anrp/in. (3.5 amp/mm) lo I l0 amp/in' (4'3 amP/mm) ofprod spacing.

T-773.3 Prod Spacing' Prod sPacing shall not erceed8 in. (?03 mm). Shorter spacirg may be used toaccommodate the geomelric timitations of the areabeing examined or to increase the sensitivity, but Prodspacings of less than 3 in. (76 mm) are usually notpractical due to banding of the particles around theprods. The prod tips shall be kept clean and drcssed'If the open circuit voltage of the magnetizing currcntsource is greater than 25 V, lead, steel, or aluminum(ratlrer than copper) tipped prods are recomnended toavoid copper deposits on th part being eramined'

'l'-774 LongitudinalMagnetizationTechniquT-77 4.1 Magnetizing Procedure. For this technique,

magnetization is accomplished by passing arnentthrough a rdulti+um fixed coil (or cables) that iswmpped around the pan or section of the part to be

"*"niine.l. This produces a longitudinal magneiic field

parallel to the axis of the coil.If a lixed, prewound coil is used, the part shall be

nhced rterr the side of the coil during inspection Thisis of special irnportance when tLe coil opening is norethao l0 times the cross-sectional area of the Part'

T-774.2 Magnetic Field Strength. Direct or retifiedcurrent shall be used to magnetize parts examined bythis technique. The required field strengih shall becalculated based on the length L and the diameter Dof the part in accordance with (a), (b), or as establishedin (c), Glow. t-ong parc shall be examined in sectionsnot to exceed l8 in. (45? mm)' and l8 in' (457 mm)shall be used for the part L in calculating the requircdfield strength. For noncylindrical pans, D shall be themaximum cross-sectional diagonal.

(a) Parts With L/D Ratios Equal to or Greater Than4. The magnetizing cunent shall be within tlO% ofthe ampere-tums' value determined as follows:

35'000Ampcre-rums = G/Df z

For example, a part l0 in. long x 2 in. diameter has{n L/D ralio of 5. Therefore,

25 aYlI)ffit = 5M *P"t"-tu*"

(D Pa s Wirh L/D Ratios lzss That 4 but NotLess Thut 2. The nragnetizing amPcre-lums shall be

within tl0% of,the ampere'tums' value determined asfollows:

45,000Ampere-turns =

Ic) If the area to be magnetized extends beyond 6in. on either side of the coils, field adequacy shall bedemonshated using the magnetic field indicator perT-'153.

(d) For large Parts due to size and shape, the mag-netizing current shall be 1200 ampere-tums to 4500amDe;turns. The field adequacy shall be demonstratedusing artificibl flaw shims or a pie-shaped nagneticfield indicator in accordance with T-753 A Hall-Effectprobe gaussmeter shatl not be used with encircling coilmagnetization tecitniques'.

T-774.3 Magnetizing Current' The current requiredto obtain the necessary nragnetizing field strengrlr shal)be determired by dividing the ampere-turns obt inedin steps (a) or (b) rbove hy the ntrnrber of lttrns inthe coil as follows:

Amperes (meter reading) = 3l91il!!j

For example, if a 5-turn coil is used rnd the 'rnlperctums required are 5000' use

1000 amperes (t 107c)50005

T-775 Circularl\tagnetizationTechniqueT-775.1 Dircct Contact Technique(a) Magnetizing Procedure. For this technlque' mag-

n"ii-tiotii. acco:mplished by passing current throughthe part to be examined' This produces a cit'cularmasnetic field that is apProximately perPendicular tothe direction of curent flou' in the part

(b) Magnetizing Current' Dircct or rectified (half-wave rectified or full-wave rectified) magnetrzrng cur-rent shall be used.

(1) The cunent shall be 300 amp/in (l2A/rnnt)to 800 amp/in. (3lA/mm) of outer diametcr'

(2) Parts with geontetric shapes other than roundwith the greatest cross-sectional diagona) in I phnc alright angles to the cufient flow shall detertDine thcinches to be used in (b)(l) above'

(J) If the cunent levels required for (bXl) ctnnotbe obtained, the nuxinrunl current obtajnatrle shall be

1 3 5

'1.77 5.1

used and the field adequacy shall be demonstrated inaccordance with T-753.

'l'.775.2 Ccntral ConductDr Technique(a) Megnetiai,lg Procedure. For this technique, a

ccnlrirl conduclor is uscd to examine the intemal surfaccsof cylindrically or ring-shaped parts. The central conduc-tor tcchnique nlay also be used for examining theoutside surfaces of these shapes. Where large diametercylinders arc to be exanlined. the conductor shal bepositioned close to the intemal surface of the cylinder.When the conductor is not centered, the circumferenceof the cylinder shall be examined in iFcrements. Fildstrength measurements in accordance with T-753 shallbe used to detemtine the extent of the arc that maybe examined for each conductor position. Bars or cables,passed through the bore of a cylinder, may be usedto induce circular magnetization.

(b) Magnetizing Current."lhe field strength requiredshall be equal to rhar detern ined in T-775.1(b) for asingle-tum central conductor. The magnetic field willIncrease in proportion to the number of times the centralconductor cable passes through a hollow part. Forexample, if 6000 ampercs are required to examine aprrt using a single cantral conductor, then 3000 amperesare required when 2 tums of the throughrable arcused, and 1200 amperes are required if 5 tums areused (see Fig. ^l-7'15.2). When the central conductortechnique is used, magnetic lield adequacy shall beverif ied using a magnetic particle field indicator innccordance with T-?53.

'f-776 Yoke Technique'l-776.1 Application. This method shrll only be

xpplied to derect discontinuil ies that are open to thesurface of thc pan.

T -717.2

T-776.2 Magnetizing Procedure. For this techniquealternating or direct current electromagnetic yokes, orlrrrnaneat magnet yokes, sball be used,

NOTET Excep( for m:rrcrials Z in. (6 nrnr) or tcss in lhicknirss.r l tcrnr t ing cu.r(nt yol is are suncr i in r , , J r ( ,1 dr tc f ln: ,nc r nrr l .n. lyokes ofequal lifiing power far lhe derecrion ofsurface disco rilllrilies.

^t-7^t7 Multidirectional Nlagnctizrt ionTechnique

T-777.1 Magnetizing Procedure. For tJris techniqucmagnetization is accomplished by high amperage porverpacks operating as many as three circuits that areenergized one at a time in rapid succession. The eflcctof these rapidly alternating mlgnetizing currenrs is toroduce an ovenll magnettzation of the part in multipledirections. Circular or longitudinal magneric fields maybe generated in any combination using rhe varioustechniques described in 'f-774 and't-775,

T-777.2 M^gnetlc Field Strength. Only three phase,full-wave rectifred cunent shall be used (o magnetizelhe pan, The init ial magnetizing currenr requiremenlsfor each circuit shall be esrablished using the previouslydescribed guidelines (see T-774 and T-77-5). The adc-quacy of the magnetic f ield shalJ be demonstr:rred usingartif icial naw shims or a pic-shapcd nu_qneric particlcfield indicator in accordance with T-753. A Il l l ,Eftccrprobe gaussrncter shall not bc used to nreasure ficldadequacy for thc multidirectional magletizalion tcch-nique. An adequate l ield shall be obtained in rr lcrsrtwo nenrly perpendicular directions, and rhe field inreosi-ties shall be bllanced so tl ' tr( a stronq lield iD oncdirection does not overwhelm the field in rhc olhcrdirection. For areas where adcquute l icld slrelgtltscrnno( be dentonstrated, additional nta{nctic Dilrl iclc

2001 sEcTtoN v

FIG. T.775.2 SINGLE-TURN AND TWO.TURN CENTRAL CONDUCTOR TECHNIQUE

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techniques shall be used todirectional coverage.

ARTICLE ? - MAGNETIC PARTICLE EXAMINATION

obtain the required two-

T-778 InterprebtionT-778.1 Nonfluorescent pafticles. With nonfluores-

cent panicles, the examination is performed using visiblelight. A minimum light intensity of 100 fc O000 Lx)rs requrred to ensure adequate sensitivity during theexamination and evaluation of indications. Ttre lightsource, technique used, td Iight levet verification isrequired to be detnonstrated one time' documented, andmaintained on file.

T-778.2 Fluo..,escent particls, With nuorescnt Dar-ticles rhe examination is performed using an ultravioletlight, called black light. The examination shall beperformed as follows:

(a) It shall be performed in a darkened area.(6) Tlre examiner shall be in the darkened area for

at least 5 min prior to prforming the examination toennble his eyes to adapt ao dark viewing. If the examinerwears glasses or lenses, $ey shall not be photosensitive.(c) The black light shall be allowed to warm up fora minimum of 5 min prior to usi: or measurement ofthe intensiry of the ultraviolet light emitted.

(dJ The black light intensiry shall be measured witha black light meter. A minimum of 1000 pWlcm2 onthe surface of the part being examined shall be required.Thc black lighr intensity shall be measured at Ieast

once every 8 hr, and wheneverchanged.

T-791

the work station is

T-780 EVALUATION(a) AII indications shall be evaluated in terms of the

acceptance standfids of the referencing Code Section.(r) Discontinuities orl or near the surface are indi-

cated by retefltion of the examination medium. However,localized surface inegularities due to machining marksor other surface conditions may produce false indica-ti.ons..(c) Broad areas of particlc accumulation, which mlght

mask indications from discontinuides, are prohibited,and such aleas shall be cleaned and re-examined.

T.790 RECORDS"t-791 Multidirectional Masnetization

Technique SketchA teclrniquc sketch shall be prcpared for erch diflcrcrr

geometry examined, showing the oart georuetry, cableaflangement and connections, magnetizing current foreach circuit, and the areas of examination where ade-quate field strengttls are obtained. Parts with repctirivegeometries, but different dimensions, rnay be exanrinedusing a single sketch provided that rhe magnetic lieldstrength is adequate when demonstmtcd in accordance

' with T-771.2.oaooIIoaoooooaI

ARTICLE 7MANDATORY APPENDICES

APPENDIX I _ MAGNETICPARTICLE EXAMINATION ON

COATED FERRITIC MATERIALSUSING THE AC YOKE TECHNIQUE

r.7r0 scoPEThis Appendix provides the Magnetic Padicle exami-

nation methodology and equipment re4luircments appli-cable for performing Magnetic Particle examination oncoated ferritic materials.

GENERALPersonnel Qualification

Personnel qualification requirements shall be in ac-cordance with the referencing Code Section.

I-730 EQUIPMENTI-730.1 The magnetizing equipment shall be in ac-

cordance with Anicle ?.

I-730.2 W}en the dry powder technique is used, apowder blower shall be utilized for powder application.Hand squeezed particle applicators shall not be usedwhen the dry powder technique is utilized.

I-730.3 Magnetic particles shall contrast wifi theconrponent background.

1.730.4 Nonconductive materials such as plastic shims(ock nray be used to simulate nonconductive coatingsfor procedure and personnel qualification.

1.7-50 PROCEDURE/TECHNIQUEl-750.1 ProccdurcMngnctic paniclc exantination shall b Performed in

Iccorduce with ir writtcn procedure. The procedureshirl l includc thc following:

fa) identiication of surface confrgurations to be ex-amined, including coating materials, maximum qualifiedcoating thickness, and product forms (e.g., base materialor welded surface)

(b) surface condition requirements and preparationmethods

{c) manufacturer and model of AC yoke(d) manufacturer and type of magnetic particles(e) minimum and rnaximum yoke leg separation(/) method of measuring coating thickness(g) identification ofthe steps in perfornling thc cxarn-

irlation([J minimum ligitt ing aod AC yoke li l t ing power

requirements (as nreasured in accordancc $'i1h ProccdurcQualif ication I-752)

(i) methods of identifying fla* indications and dis-criminatirig between flaw indications and nonrelevantindications (e.g., magnetic writing or panicle heid bysurface irregularities)

f) instructions for identi6cation and conlirnation ofsuspected flaw indications

, (t) recording riteria(/J personnel qualif ication requirentents

(nrJ reference to the procedure- qualincation records(u) method of verifying that the yoke lifting power

and the illumination source used in the productionexaminatiol are at least as great as specified.

I-751 Coating Tltickness N{easurementThe procedure demonstration and perfornrrnce of

exarninations shall be preceded by rreasuremcot ol 'thecoxting thickness in the areas to bc cxanti ed. If lhccoating is noncondsclive, an eddy current techn'quemay be used to nreasure the coatinB thickness- If thecoating is conductive, a nlagnetic coating thicknesstechnique shall be used in accordance with ASTM l)1186. Coating neasurenlenl equipntenl shall be uscdin accordance with the equipment nra,ru l ictu rer's in-struclions. Co.lt ing thickness nlersurentcnts shil l betrken at the intersections of a 2 in. (i l mnr) nrrximunl

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I.75r ARTICI.E 7 _ MANDATORY APPENDICES II-?IO

before anil after coating. The coating thickness isqualified when the length of rhe indi;ation on thecoated surface is at least 50% of the length of theconesponding indication prior to coating.

{h) Requalificaiion of the procedure is required fora decrease in either the AC yoke lifting power or theillumination level, or for an increase in the coatinsthickness.

t-770 EXAMINATION(a) Surfaces to be examined, and all adjacent areas

within at least I in. (25 mm), shall be free of all din,grease, lint, scale, welding flux and spatter, oil, andloose, blistered, flaking, or peeling coating.

(b) Examine the coated item in accordance with thequalified procedure.

I.7EO EVALUATIONIf an indication greater than 507o of the maximum

allowable flaw size is detected, the coating in the areaof th6 indication shall be removed and the examinationrcDeated.

l:790Procedure qualification documentation shall include

the following:(a) identification of the procedure

' (r) identif ication of the personnel performing andwitnessing the qualification

(c) description and drawings or sketches of the quali-fication specimen, including coating !hickness measure-ments and ffaw dimensions

(d,) equipment and materials used(e) illumination level and yoke lifting power(/J qualification results, includin-s maximunr coating

thickness and flaws detected.

APPENDIX II - GLOSSARY OIT

It-710

TERMS FORMAGNETIC PARTICLE

EXAMINATIONSCOPE

This Mandatory Appendix is used for t lrc purlx)scof estabiishin-q stflndard terrns ald dclinit ion of (crrlts

grid pattem over tlie area of examination and at leastone-half the maximum yoke leg separation beyond theexamination area. The thickness shall be the mean ofthree separate readings within Z in. (6 mm) of eachintersection.

t-7sz Procedure DemonstrstionThe procedure shall be demonstrated to th: saGfac-

tion of rhe Inspector in accordance with the requiremenlsof the referencins Code Section.

I-753 Procedure Qualifi cation(a) A qualification specirnen is required. The speci-

men shall be of similar geometry or weld profile andcontain at least one surface crack no longer than themaximum flaw size allowed in the applicable acceptancecriteria, The mabrial used for the specimn shall bethe same specifrcation and heat treatment as the coatedfenomagnetic nraterial to be examined. As an alternativeto tl)c material requirement, other materials and heattreatments may be qualified provided;

(/) The measured yoke maximum lifting force onthe matcrial to be exrmined is equal to or greater thanrhe maximum lifting force on the qualification specimennaterial. Both valrres shall be determined with the sameor comparable equipment and shall be documented asrcquircd in paragraph (c).

(2) All the requiremens of paragraphs (6) thmugh(g) are nret for rhe altemate material.

(r) Examine the uncoated specimen in the mostunfavorable orienration expected during the performanceof the production examination.

(c) Documert rhe measured yoke maximum liftingpower, illuminarion levels, and the resul$.

(d) Measure the maximum coating thickness on theitem to be cxamined in accordance with lhe requirementsof l -751.

(e) Coat the specimen with the same type of coating,conduitive or nonconductive, to the maximum thicknessmeasured on the production ircm to be examined.Altern tcly, nonconductive shim stock may be used tosimulate nonconductive coatings.

(, Ex nlinc the coated specinren i:r the most unfavor-able orient tior cxpected during the performance ofthc production exanlinrtion. Document the measurcdyokc rurxirnurn lifting power, il lumination level, andcxilrt l ini lt ion rcsults.

(8) Conrplre lhc lcngth of the indication resultingfront thr' longest l l lw no longer than the maximumflaw sizc alkrwcd by the applicablc acceptance criteria,

DOCUMENTATION/ITECOITDS

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I-7 tO 2OOI SECTION V

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whicn appear in Anicle 7, Magnetic Particle Exami-nation.

II.7ZO GENERAL REQUIREMENTS{a/ The Standard Terminology for Nondestructive

Examinations (ASTM E f3l6) has been adopted bythe Committee as SE-I316.

(6) SE-1316 Section l0 provides the definitions ofterms listed in II-730(a).

(c) For general terms, such as Indication, Flaw,Discotttittuity, Evaluation, e!c., refer to Article I, Man-datory Appendix I.

(d.) Paragraph II-730(b) provides I list of terms anddefinitions, which are in addition to SE-1316 and areCode specific.

II.73O REQUIREMENTS(a) The following SE-1316 terms are used in conjunc-

tion with (his Article: ampere turns, black light, centralconductor, circular magnetization, demagnetization, drypowdeq full-*ave direct currenl half-wave current,longitudinal magnetization, magnetic field, magneticfield strength, ' magnetic particle examination, magneticparticle lield indicator, magnetic particles, multidirec-tional magnetization, permanent magnet, prods, sensitiv-ity, suspension, yoke.

II-?30

(b) The following Code terms are used in coniunctionwith ahis Anicle:

black ligh, intensit! - a quantitative expression ofultraviolet inadiance

&agnetic Jlax - the consept that the magnelic Reldis flowing along the lines of force suggests that theselines are thereforc "flux" lines, and they are calledmagneiic flux. The strengrh of rhe field is deflned bythe number of flux lines crossing a unit area taken atright angles to the direction of the lines.

recirted. magnetic curuent - by means of a devicecalled a rectifier, which permits current to flow in onedirection only, alternating current can be convcncd lounidirectional curent. This differs fronr direct cunenrin that the cunent yalue varies r.rom a steady level.This variation may be extreme, as in the case of thehalf-wave rectified single phase AC, or slighr, as inthe case of three-phase rectified AC.

half-wave recfirted current AC - when a single-phase altemating current is rectioed in the simplestmanner, the reverse of the cycle is blockcd out en(ircly.The rcsult is .r pulsating unidirccfional currcnt withintervals when no current at all is f lowing. This isoften referred to as "half-wa\:e" or pulsatinE directcunent.

lll-wave rec fed cuuc,ll - \\,hen the reverse halfof the cycle is turned around to flow in the samedirection as the forward half. The result is full-waverectif ied current, Three-phase ahernating cunent whenfull-wave rectif icd is unidirectional \r, irh very l itt lepulsation; only a ripple of varying voltage distinguishesit from straight DC single-phase, full rectif ied cunent isusually nol enrployed for magnetic particle examination.

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ARTICLET_APPENDIXI I IMAGNETIC F'LTIX LEAKAGE (MFL) EXAMINATION

III.TTO SCOPEThis Appendix describes the Magnetic Flux lrakage

(MFL) examination method equipment rcquirementsapplicable for perfonning MFL examinations on coatedand uncoated ferromagnetic materials from one surface.MFL is generally used as a post construction examina-tion merhod to evaluate the co[dition of plate materials,such as storage tank floors and piping for conosionor other forms of degadation. Other imperfections thatnray be detbcted are cracks, seams, dents, laps, andnonnlctallic inclusions, etc.

III-71I Referenceswhen the Magnetic Flux Leakage method of Arlicle

7, Appendix III is specified by a referencing CodeSection, the MFL method shall be used together withArticlc l, General Requirements.

ITI.72O GENERALlll-721 Personnel QualificationRequlrements

The user of ahis Appendix shall be responsible fordocunrentcd training, qualification, and cenification ofpersonnel performing MFL examination. Personnel per-tirmring supplenrental examinations. such as ultrasonic(UT) examinations, shall be qualified in accordanceu,ith the referencing Code Section

lll-722 Equipment Qualification RequirementsThe equipment operation shall be demonstrated by

successfully completing the unit verification and func-lion tcsts outlined as follows:

lu) Rq[erence Plate. All MFL examinations shallhrve a rcference plale to ensure the equipment tspcrfornring in lccordance with thd manufacturer's speci-ficiltions, prior to use, The reference plate shall consistof a Dlale that is made liom a mrterid of the samenonriirl thickncss, producl form, and cornposition as

the component to be exarnined. The plate shall havenotches" drilled holes, or other discontinuities machinedinto the bottom side of the plate, as slrown in Figurelll-7?2. Ttle depths and widths of artificial discontinu-ities should be similar to the sizes and physical charac-teristics of disconrinuitics to bc detccted. If coatinSsor temporary coverings will be present during theexamination, the reference plate shall be coated oicovered with the coatings or coverc representative ofthe maximum thickness that will be encountered duringthe examination.

(b) System Verifcatiott and Functiort C,ftecfts. Themanufacturct's verifrcation procedure shall be conductedinitially to ersure that the system is functioning asdesigned. The functional check shall be made by scan-ning the reference plate over the range of scanningspeeds to be utilized during the exanina(ion, Equipmentsettings shall be documented.

(c) Performance Confrnatiott. A functional chcckshall be conducted at the beginning and end of eachexamination, every eight hours, or when equipment hasmalfunctioned and been repaired. If it is determinedthat the equipment is not functioning proper)y, needed

, adjuslments shall be made and all areas examined sincethe last performance check shall be re-inspected

llI-723 WrittnProcedureRequirements

III-723.1 Requlremnts. Magnetic F