Disclosure to Promote the Right To Information

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इंटरनेट मानक

“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda

“Invent a New India Using Knowledge”

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“Step Out From the Old to the New”

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“The Right to Information, The Right to Live”

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“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 3703 (2004): Recommended practice for magnetic particleflaw detection [MTD 21: Non-Destructive Testing]

!-”-l

IS 3703:2004

Indian Standard

RECOMMENDED PRACTICE FOR MAGNETICPARTICLE FLAW DETECTION

(Second Revision)

ICS 77.040.20

0 BIS 2004

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

December 2004 Price Group 8

Non-destructive Testing Sectional Committee, MTD 21

FOREWORD

This Indian Standard (Second Revision) was adopted by the Bureau of Indian Standards, after the draft finalizedby the Non-destructive Testing Sectional Committee had been approved by the Metallurgical Engineering DivisionCouncil.

Magnetic pafiic]e flaw detection maybe used to locate cracks, discontinuities, non-meta]]ic inclusion and segregationat or just below the surface in ferromagnetic material. However the method cannot be used on non-magneticmaterial. It is hoped that the use of this recommendation would help in establishing a unified practice formagnetic particle testing within the country.

This standard does not cover the acceptance criteria for magnetic particle testing which should be subject tomutual agreement between the contracting parties.

This standard was first published in 1966 and subsequently revised in 1980. While reviewing the standard thecommittee felt to revise this standard keeping in view the latest development in the field of magnetic particleflaw detection. .

In this revision, following modifications have been made:

a) Title of the standard has been modified;

b) Scope has been modified;

c) Reference clause has been added;

d) Clause on types of magnetic fields has been modified; and

e) A new clause on Optimum Sensitivity has been added.

For the purpose of deciding whether a particular requirement of this standard is complied with, the final value,observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance withIS 2 : 1960 ‘Rules for rounding off numerical value (revised)’. The number of significant places retained inthe rounded off value should be the same as that of the specified value in this standard.

IS 3703:2004

Indian Standard

RECOMMENDED PRACTICE FOR MAGNETICPARTICLE FLAW DETECTION

(Second

1 SCOPE

1.1 This standard specifies techniques andrecommended procedure for both dry and wetmagnetic particle flaw detection, a non-destructivetesting method, for detecting cracks and otherdiscontinuities which are open to surface or just belowthe surface in ferro-magnetic materials. The method isapplicable only to material which can be easilymagnetized notably iron, steel, cobalt, nickel and theiralloys. Techniques described may be applied toraw material, semi-finished material, finishedmaterial and welds regardless of heat treatment.

1.2 This practice may be used to prepare proceduresfor magnetic particle flaw detection of materials andparts.

2 REFERENCE

The following standard contains provisions whichthrough reference in this text, constitutes provisionsof this standard. At the time of publication, the editionwas valid. All standards are subject to revision, andparties to agreements based on this standard areencouraged to investigate the possibility of applyingthe most recent edition of the standard indicated below:

1S No. Title

3415:1998 Glossary of terms used inmagnetic particle flaw detection(second revision)

3 TERMINOLOGY

For the purpose of this standard, the definitions givenin IS 3415 shall apply.

4 PRINCIPLE OF TEST

The magnetic particle method is based on the principlethat magnet ic lines of forces, when present in a ferro-magnetic material will be distorted by a local changein the permeability due to the presence of anydiscontinuity having permeability different to that ofthe test piece. These distorted magnetic lines of forcesresult in leakage flux which leaps through air fromone side of the discontinuity to the other side creatingmagnetic north and south poles at these points ofexit and re-entry respectively. If freely divided ferro-magnetic particles are applied to the surface of thetest piece they are attracted by these poles to form apattern of the discontinuity.

Revision)

5 DRY AND WET TECHNIQUES

Depending upon the type of ferro-magnetic particle,whether free flowing dry powder or suspension ofpowder in a suitable liquid medium, the method isclassified into dry and wet magnetic particle flawdetection respectively.

6 METHOD

In the application of the method, three essential stepsare involved.

6.1 The part must be properly magnetized.

6.2 Suitable magnetic particles must be applied overthe surface of the part in such a way that they canmove to collect at leakage fields occurring atdiscontinuities.

6.3 Any accumulation of magnetic particles mustbe observed and interpreted.

7 TYPES OF MAGNETIC FIELDS

7.1 The magnetic force can be produced bymeans of either the magnetic effect of electriccurrent or by the magnetic field of a permanentmagnet. Depending upon the types of magnetizingmethods used, generally three types of magneticfields are produced: (a) circular magnetization,(b) longitudinal magnetization, and (c) multi-directional magnetization.

7.2 Circular Magnetization

In this method, electric current is passed through apart or by use of a central conductor through a centralopening in the part, inducigg a magnetic field at rightangles to the current flow. The magnetic field isessentially contained within the contours of the part.(see Fig. 1).

7.3 Longitudinal Magnetization

When electric current is passed through a multi-turncoil (either rigid or cable formed) which encloses thepart or section of the part to be examined a longitudinalfield parallel with the axis of the coil is induced inthe part. Longitudinal magnetization is also known ashi-polar magnetization (see Fig. 2).

7.4 Multi-direction Magnetization

It is not possible to have more than one direction of

1

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1S 3703:2004

MAGNETIC FIELD

MAGNET IZINGCURRENT

\\

\/LTEST plECE

FIG. 1 CIRCULARMAGNETIZATIONOFA TESTPIECETHROUGHWHICHA MAGNETIZINGCURRENTPASSES

TMAGNETIC FIELD /-WIRE COIL

NETIZIN~CURRENT

FIG. 2 LONGITUDINALMAGNETICFIELDWITHINA CURRENT-CARRYINGMAGNETIZINGCOIL

magnetic field present in a part at any given time.However, in multi-direction magnetization method,magnetic fields having different directions may beinduced in the part in very rapid sequence, followingeach so rapidly that magnetic particles attracted by onefield do not have time to fall away before the field isrepeated. In this method, magnetic field is made tooscillate, or move, within the part from one directionto another, usually approaching 90°, which permitsbuild up of indications in more than one direction.

8 OPTIMUM SENSITIVITY

8.1 Direction of Field

Maximum sensitivity is achieved when the flaw lies atright angles to the magnetic flux, but the sensitivity isnot reduced below the effective level if the flaw isoriented at an angle of up to 45° from the optimumdirection. Beyond 45°, the sensitivity is diminishedapparently. For this reason, the complete examinationof any surface requires the flux to be passed in twodirection at right angle to each other in separateoperation.

8.2 Type of Field

Type of magnetic field is also an important factor whileconsidering the sensitivity. For a given magnetizingforce, a stronger circular field is produced than if itwere producing a longitudinal field. This is due to thecircular field being completely contained within thepart, which has a low reluctance path. The longitudinalfield must use an air path to return from north pole tosouth pole. Hence a high reluctance path. Further,the external poles of a longitudinal field attract

magnetic particles and produce confusingindications. Adequate inspection in the vicinity ofsuch poles is impossible. For these two reasons thecircular method of magnetization is preferredwhenever it can be used.

8.3 Location of Flaw

If a flaw is open to the surface, the flux leakage,therefore sensitivity will be a maximum for a givensize and shape of discontinuity. When a flaw is belowthe surface, flux leakage diminshes giving diffusedindications. For sub-surface flaw, sensitivity decreasesrapidly with the depth of the flaw below the surface.

8,4 Su/face Coatings

It is possible to inspect components that have beentreated with a non-magnetic coating (that is cadmiumplate or paint) not greater than 50 pm thick, withonly slight loss in sensitivity.

8.5 Magnetic Field Strength

The lines of force must be of sufficient strength toindicate those discontinuities which are unacceptable,yet must not be so strong that an excess of particlesis accumulated locally (known as furring), therebymasking relevant indications. This optimumcondition can be achieved if the magnetic particleflaw detection is carried out at levels of magnetic fluxdensity equal to or greater than 0.72 T. For most ofengineering steels, ferritic or tempered martensiticstructures, the permeability exceeds 240 at relevantfield intensity levels and the above said criteria cantherefore be satisfied at ambient temperature, with

2

an applied field at 2400 A/m tangential to the surfaceunder inspection and in close proximity to it.

9 TYPES OF MAGNETIZING CURRENTS

9.1 The three basic types of current used in magneticparticle examination to establish part magnetizationare alternating current (a.c.), single phase half-waverectified alternating current (HW) and three phasefull-wave rectified direct current (FWDC). Theinductance associated with a.c. results in a ‘skineffect’ that confines the magnetic field to the surfaceof a part. In contrast, both HW and FWDC produce amagnetic field having maximum penetratingcapabilities and are used when near surfacediscontinuities are of concern.

9.1.1 Part magnetization with this current is limitedto those applications where examination requirementscall for the detection of discontinuities that areopen to the surface. Alternating current is alsoextensively used for the demagnetization of parts afterexamination. The through-coil technique is normallyused for this purpose due to its simple, fast nature.

9.1.2 Direct Current

Years ago, batteries and d.c. generators were used toproduce a magnetizing current and were used forrelatively small operations. They have given way,however, to HW and FWDC.

9.1.3 Half-wave rectified alternating current is usedprimarily with prod type examination but is alsoapplicable to examinations involving both coil andthrough current techniques. When usedin conjunctionwith dry powder, its pulsating characteristic providesan additional degree of mobility to the particlesgiving a great deal of sensitivity to sub-surfacetype discontinuities. It is usually associated withportable and mobile type equipment, although it issometimes incorporated into the design of horizontalwet particle units.

9.1.4 FuI1- Wave Rectijied Direct Current

As a source of part magnetization, FWDC is applicable

IS 3703:2004

for the detection of both surface and near surfacediscontinuities. It is often used with high amperageon the orderof6000to20000 A. This type of magneticparticle testing equipment (wet horizontal or stationarypower packs) provides the high magnetizing currentsnecessary for the magnetic particle inspection of largecomponents such as castings and forgings.

10 PARh MAGNETIZATION TECHNIQUES

10.1 A part can be magnetized either directly orindirectly. For direct magnetization, the magnetizingcurrent is passed directly through the part creating acircular magnetic field in the part. With indirectmagnetization technique, a magnetic field is inducedin the part, which can create a circular, longitudinal,or multi-directional magnetic field in the part.

10.2 The choice of direct or indirect magnetizationwill depend on such factors as size, configuration, orease of processing. Table 1 compares the advantagesand limitations of the various methods of partmagnetization.

10.2.1 Direct Contact Magnetization

For direct magnetization, physical contact must bemade between the ferromagnetic part and the currentcarrying electrodes connected to the magnetizing powersource. Both localized area magnetization and overallpart magnetization are direct contact means of partmagnetization achieved through the use of prods, headarid tailstock, clamps and magnetic leeches.

10.2.1.1 Localized area magnetization

a) Prod technique — The prod electrodes(generally solid copper or braided copper tips)are first pressed firmly against the test part.The magnetizing current is then passed throughthe prods and into the area of the part in contactwith the prods. This establishes a circularmagnetic field in the part around and betweeneach prod electrode, sufficient to carry outa local magnetic particle examination (seeFig. 3).

AGNETIZING

CURRENT

FIG,3 CIRCUI,ARMAGNETIZATIONWITHPRODTYPECONTACTS

3

IS 3703:2004

Table 1 Advantages and Limitations of the Various Ways of Magnetizing a Part

(Clauses 10.2 and 14.1.1)

Types ofi$lngnctization rsrsdParts Detail Advantages Limitations

(1) (2) (3)

1. Direct Contact Piwt Magnetization

A. Heud/Tai[stock Contact

1. Solid, relatively small parts 1. Fast and easy technique, 1. Possibility of arcing exists if proper

(castings, forgings, machined) 2. Complete circular magnetic field contact conditions are not made.

that can be processed on a ;urrounds entire current. 2. Long parts should be magnetized

horizontal wet unit, 3. Good sensitivity to surface and near in sections to facilitate bath

surface discontinuities. applicationwithout resorting to an

4. Simple as well as relatively complex overly long current shot.

parts can usually be easily processed

with one or more shots.

5. Complete magnetic path is conducive

to maximizing residual characteristics

of material.

2. Large castings and forgings Large surface areas can be processed

and examined in relatively short time.

3. Tubular-type parts such as 1. Entire length can be circularly

tubing, pipe, hollow shafts, etc magnetized by contacting end to end.

2. Ends must be conducive to electrical

contact and capable of carrying

required current without excessive

heat.

4. Long solid parts such as

billets, bars, shafts, etc

B. Prods

1. Welds

2. Large castings or forgings

High amperage requirements

(16 000 to 20000 A) dictates

special d.c. power supply.

Effective field limited to outside

surface and cannot be used for

inside diameter examination.

1. Entire length can be circularly 1. Voltage requirements increases asmag]letizedby contacting end to end. length increases due to greater

2. Current requirements are independent impedsmee of cable and part.

of length. 2. Ends must be conducive to contact

3. No end loss. and capable of carrying required

current without excessive heat.

1. Circutar tield can be selectively

directed to weld area by prod place-

ment.

2. In conjunction with HW current and

dry powder provides excellent sensiti-

vity to sub-surface discontinuities as

well as surface type.

3. Flexible, in that prods, cables and

power packs can be brought to test site.

1. Entire surface area can be examined

in small increments using nominal

current values.

2. Circular field can be concentrated in

specific areas that historically are

prone to discontinuities.

3. Equipment can be brought to the

location of parts that are diftlcult to

move.

4. 10 conjunction with HW current and

dry powder provides excellent sensiti-

vity to near surface sub-surface type

discontinuities that are difficult to

locate by other methods.

1. Only sarrdl area can be tested atone

time.

2. Arcing due to poor contact.

3. Surface must be dry when dry

powder is being used.

4. Pm~ spacing must be in accordance

with magnetizing current level.

1. Coverage of large surface areas

require a multiciplicity of shots that

cast be very time consuming. ‘

2. Possibility of are strike due to poor

contact.

3. Surface should be dry when dry

powder is tilng used.

4

...-1

IS 3703:2004

Table 1 (Continued)

Types of Magnetization and Parts Detail Advantages Limitations

(1) (2) (3) ~

IL Indirect Part Magnetization

A. Central Conductor

1. Miscellaneous parts having

holes through which a

condoctor can be threaded

soch as:

Bearing race

Hollow cylinder

Gear

Large nat

Large clevis

Pipe coopling

2. Tubular type parts such as:

Pipe

‘robing

Hollow sllatl

3. Large valve body and similar

parts

B. CoiI/CabIe Wrap

1. Miscellaneous medium sized

parts where the length pre-

dominates such as a crank shatl.

2. Large castings, forgings, or

shafting

3. Miscellaneous small parts

C, I)lduced Current Fixtures

1, Examination ofring-shaped

part for circumferential-type

discontioaities.

1.

2.

3.

4.

5.

1.

2.

3.

1.

2.

3.

1.

2.

3.

No electrical contact to part and

possibility of arcing is eliminated.

Circumferentially directed magnetic

field is generated in all” surfaces

surrounding the conductor (inside

diameter, outside diameter, faces etc).

Ideal for those cases where the residual

method is applicable.

Light weight parts can be supported by

the central conductor.

Multiple turns may be used to reduce

current required.

No electrical contact of part required.

Inside diameter as well as outside

diameter examination.

Entire length of part circularly mag-

netized.

Provides good sensitivity for detection

of discontinuities located on internal

surfaces.

All generally longitudinal surfaces are

longitudinally magnetized to effecti-

vely locate transverse discontinuities.

Longitudinal field easily attained via

cable wrapping.

Easy and fast, especially where

residual magnetization is applicable.

Non-contact.

Relatively complex parts can usually

be processed with same ease as those

with simple cross section.

No electrical contact.

All surface of part subjected to

toroidal type magnetic field.

Single process for 100 pereent coverage.

1.

2.

3.

1

2.

3.

4.

5.

1.

2.

Size of conductor must be ample to

carry required current.

Ideally, conductor should be

centrally located within hole.

Larger diameters require repeated

magnetization with conductor

against inside diameter and rotation

of part between processes. Where

continuous magnetization

technique is being employed,

inspection is required after each

magnetization.

Outside diameter sensitivity may be

somewhat diminished relative to

inside diameter for large diameter

and extremely heavy wall.

Outside diameter sensitivity may be

somewhat diminished relative to

inside diameter for extremely heavy

wall.

Length may dictate multiple shot as

coil is repositioned.

Multiple magnetization may be

required due to configuration of

part.,

L/D (length/diameter) ratio

important consideration in

determining adequacy of ampere-

turns.

Effective L/D ratio can be altered

by utilizing pieces of similar cross-

sectional area.

Use smaller coil for more intense

field.

Sensitivity diminishes at ends of

part due to general leakage field

pattern.

‘Quick break’ desirable to

minimize end effect on short parts

with low L/D ratio.

Laminated core required through

ring.

Type of magnetizing current must

be compatible with method.

5

\ “1

IS 3703:2004

Table 1 (Concluded)

Types of Magnetization and Parts Detail Advantages Limitation

(1) (2) (3)

~. Ball examination

3. DISK and gears

4.

1.

2.

3.

1.

2.

3.

Can be automated. 3.

4.

No electrical contact.

100 percent coverage for discontinuities

in any direction with three step process

and proper orientation between steps.

Can be automated.

No electrical contact. 1.

Good sensitivity at or near periphery

or ring.

~ensitivity in various areas can be 2.

varied by core or pole piece selection.

Other conductors encircling field

must be avoided.

Large diameters require special

considerations.

For small diameter balls limited to

residual magnetization.

100 percent coverage may require

two steps process with core or pole

piece variation or both.

Type of magnetizing current must

be compatible with part geometry. .

D. Yokes

1. Examination of large surface

areas for surface-type

2. Miscellaneous parts requiring

examination of localized areas

1.2.

3.

1.

2.

3.

4.

5.

No electrical contact. 1.

Highly portable. 2.

Can locate discontinuities in any

direction with proper orientation.

No electrical contact. 1.

Good sensitivity to direct surface

discontinuities.

Highly portable. 2.

Wet or Dry technique.

Alternating current type can also 3.

serve as demagnetizer in some

instances. 4.

Time consuming.

Must be systematically repositioned

in view of random discontinuity

orientation.

Must be properly positioned

relative to orientation of

disrmntinuities.

Relatively good contact must be

established between part and poles.

Complex part geometry may cause

difflcldty.Poor sensitivity to subsurface-type

discontinuities except in isolated

areas.

1)

2)

Alternating current limits the prodtechnique to the detection of surfacediscontinuities. Half-wave rectified directcurrent is most desirable since it will detectboth surface and near surface dis-continuities. The prod technique generallyutilizes dry magnetic particle materials dueto better particle mobility. Wet magneticparticles, however, are not generally usedwith the prod technique because of potentialelectrical and flammability hazards.

Proper prod examination entails a secondplacement with the prods rotatedapproximately 90° from the first placementto assure that all existing discontinuities arerevealed. Depending on the surface coveragerequire-ments, overlap between successiveprod placements may be necessary.

Caution: Extreme care should be taken to maintain

clean prod tips to minimize heating at the point of

contact and to prevent arc strikes and local overheating

on the surface being examined since these may cause

adverse effects on material properties. Steel or

aluminium or copper braided tip prods or pads rather

than the solid copper tip prods are recommended where

the possibility of copper penetration exists. Open-

circuit voltages sh@sld not exceed 25V.

3) A remote-control switch, which may bebuilt into the prod handles, should beprovided to perr@ the current to be turnedon after the prods have been properlyplaced and to turn it off before the prodsare removed in order to minimize arcing.

b) Manual clamplmagnetic leech technique —Local areas of complex component may bemagnetized by electrical contact manuallyclamped or attached with magnetic leeches tothe part. As with prods, suftlcient overlap maybe necessary if testing of the contact location isrequired.

10.2.1.2 Overall magnetization

a) Head and tailstock contact — Parts maybe clamped between two electrodes (such as a

6

‘ ‘~

IS 3703:2004

b)

c)

head and tailstock of horizontal wetmagnetic particle equipment) and themagnetizing current applied directly through thepart. The size and shape of the part willdetermine whether both field directions can beobtained with such equipment (see Fig. 4)..

Clamps — The magnetizing current may beapplied to the test parts by clamping the currentcarrying electrodes to the part producing acircular magnetic field.

Multi-directional magnetization technique —With suitable circuitry, it is possible to producea multi-directional (oscillating) field in a partby selectively switching the magnetic fieldwithin the part between electrode contacts/clamps positioned approximately 90° apart.The wet method technique is generallyemployed.

10.2.2 Indirect Magnetization

Indirect part magnetization involves the use of apreformed coil, cable wrap, yoke, or a centralconductor to induce a magnetic field. Coil, cable wrap

and yoke magnetization are referred to as longitudinalmagnetization in the part.

10.2.2.1 Coil and cable magnetization

When a magnetic material is placed within a currentcarrying rigid coil of several turns, the magneticlines of force created by the electric current concentratethemselves in the part and induce a longitudinalmagnetic field as indicated in Fig. 5. Parts too large tofit in a fixed coil may be magnetized longitudinallyby making a coil of several turns of flexible cable(cable wrap) around the parts (see Fig. 6).

10.2.2.2 Central conductor and threading cablemagnetization

Indirect circular magnetization of hollow pieces/partscan be performed by passing the magnetizing currentthrough a central conductor passed through a centralopening in the part (see Fig. 7A and 7B).

10.2.2.3 Induced current jlow method

This is a technique of setting up circumferentialcurrent flow in large ring specimens by making it,

-CONTACT PLATES T

FIG.4 CIRCULARMAGNETIZATIONOFTESTPLECEBYPASSINGELECTRICCURRENTTHROUGHTHETESTPIECEFROMMACHINECONTACTPLATES

P ELECTRIC CURRENT

---- A MAGNETC DIRECTION OF

~ PARTICLE INDICATIONS “COIL

MAGNETIC FIELC)

I \II ——— —- —— ----- “-----

\ {

\

—

FIG. 5 LONGITUDINALMAGNETIZATION

7

IS 3703:2004

AGNETIZING

CURRENT

FIG. 6 LONGITUDINALMAGNETIZATIONOFTESTPIECEWITHCorL

fCRACK

r’~MAGNETIZING-,,-A-..- L MAGNETIC FIELDLUKtft Nl

7A Circular Magnetization of Passing CurrentThrough a Central Conductor

+PECIMEN

7B Threading CoilTechnique

... -

FIG. 7 CENTRALCONDUCTORANDTHREADINGCABLEMAGNETIZATION

8

in effect, the secondary of a mains transformer. Theoptimum flaw direction is basically circumferentialas shown in the Fig. 8.

10.2.2.4 yokes

a) Yokes are essentially C-shaped electro-magnets which create a longitudinal magneticfield between the poles. The dry magneticparticles are generally employed with yokemagnet ization technique and are applied whilethe electromagnetic yoke is energized (seeFig. 9).

IS 3703:2004

b) Alternating current electromagnetic yokesprovide effective means of part magnetizationfor the detection of surface discontinuities. Half-wave rectified direct current electromagneticyokes, however, provide an effective means fornear surface discontinuities as well.

11 CURRENT REQUIREMENTS

To produce satisfactory indications, the magnetic fieldin the part shall have suftlcient strength as mentionedin 8.5. Factors that affect the strength of the field arethe size, shape and material of the part, and the

●

PRIMARY COIL FLAWS

FIG. 8 INDUCEDCURRENTFLOWTECHNIQUE

.D

- ~ DISCONTINUITIES

NOTE — Electromagneticyoke,showingpositionand magneticfield fordetectionofdiscontinuitiesparalleltoa weldbead. Discontinuitiesacrossa weld bead may bedetectedbyplacingthecontactsurfaceof the yokenextto andoneithersideof the bead (rotatingyokeabout9V frompositionshownhere).

FIG.9 ELIXTROMAGNETICYOKE

9

‘ (“”-’-

IS 3703:2004

technique of magnetization. Since these factors varywidely it is difficult to establish rigid rules for thefield strengths for every conceivable partconfigurations, itis usually best to experiment withthe parts having known discontinuities determiningthe actual requirements. In general, however,following guidelines can be effectively applied tocalculate the current value for establishing properlevels of circular and longitudinal magnetization.

11.1 Circular Magnetization

11.1.1 Overall Magnetization with Head and TailStock Contact (Head Shot Metkoa)

a)

b)

c)

d)

For all solid and hollow sections value of FWDCand HW current shall be as given below:

S1 Part Diameter Current Value inNo. D Ampere/mm of

in mm Part Diameterf h

Min Max

1 D< 125 28 36

2 125< D<375 20 28

3 D >375 4 12

Alternating magnetizing current can be usedat approximately half these values for detectionof surface discontinuities.

For parts with geometric shapes other thanround, the greatest cross-sectional diagonal ina plane at right angles to the current flow shallbe taken as D in above formulae.

The head shot method produces the maximumcircular field at the O.D-.but a greatly reducedfield at the I.D. surface of a part for a givencurrent.

11.1.2 Central Conductor Technique

a)

b)

c)

Assuming that the central conductor islocated centrally, the values given in 10.1.1may be used taking the outside diameter orperimeter of the component as the criteria forselecting current value. The resulting field isconcentric relative to the axis of the part andthis permits the entire circumference to beprocessed at one time. In this technique, themaximum field is obtained at the insidediameter of the part.

When several bars or cable are passed throughthe component, the current value shallbe reduced in proportion to the number ofwindings.

Off-setting the central conductor is most oftenrestored to when the magnetizing currentcapabilities are lacking, for example in thecase of large outside diameter parts. As a matterof convenience if small ring like parts areallowed to rest against their inner wall on a

central conductor, this method provides highspeed of testing because all parts aremagnetized in a single shot. In such instancesfor the purpose of current calculation as per11.1.1, part diameter D is taken as diameter ofcentral conductor plus twice the wall thicknessof the test part. The entire circumferenceshould be inspected by re-positioning thepart(s) on the central conductor allowingfor approximately 10 percent magneticoverlap. The distance along the circumferencethat is effectively magnetized is approximatelyfour times the diameter of the centralconductor..

11.1.3 Localized Magnetization

a) Prod technique — With prod, the fieldstrength of- circular magnetization isproportional to the amperage used but varieswith the prod spacing and thickness of thesection being inspected. The following valuesare generally recommended:

sl Section Current Values inNo. Thickness Amperdmm of

‘t’ in mm Prod Spacing

‘Min Max’

b)

1 t<zo 3.5 4.5

2 t>zo 4.0 5.0

Prod spacing should not exceed 200 mm. Prodspacing less than 75 mm is usually not practicaldue to banding of the particles around the prods.

Yoke techniques — The field strength of yokecan be empirically determined by measuring itslifting power.

11.2 Longitudinal Magnetization

Longitudinal part magne-tization is produced bypassing a current through a multitum coil encirclingthe part or section of the part to be examined. Thefield strength in the part is det~rmined primarily by theampere-turns N] of the cod (the actual amperage 1multiplied by the number of turns N of the encirclingcoil or cable).

The effective field extends on either side of thecoil for a distance approximately equal to the radiusof the coil being employed. Long parts shouldbe examined in sections not to exceed thislength. Depending upon the coil size and length todiameter ratio (L/D) of the components there are threebasic longitudinal magnetization formulae as givenbelow:

When the part diameter is less than 10 percent ofthe coil inner diameter of a fixed encircling coilthen

.’-...

10

IS 3703:2004

a) for test object positioned to the side of the from 2000 A up to 20000 A at a safe open voltagecoil, ampere turn is given by, between 6 V and 27 V are usually suitable.

~1 = 45000( q 10 percent) 12.1.2 The current flow may be derived from either

(L/D) d.c., a.c., full or half-wave rectified a.c. supplies or acombination of these. Rectified a.c. supplies may be

b) and for test object positioned in the centre of obtained from either single-or three-phase mains.the coil, ampere~tum-is given by,

12.1.3 It is recommended that all parts of the equipment

~1= 3000R (q 10 percent)should be capable of continuously carrying the rated

6 (L/D) -5current available from the apparatus, for an operatingcycle of 5s ‘on’ and 20s ‘off’, without overheating.

c) if the outer diameter of the part completely 12.1.4 The equipment should, normally, be providedor nearly completely fills the inner diameter of with controls for adjusting the excitation currents eitherthe encircling coil then the ampere turn is continuously from zero to the maximum, or in stepsgiven by such that any required current values may be obtained

within +1Opercent of the nominal.NI =

35000(q 10 percent)

(L/D) + 2 12.1.5 When d.c. or rectified a.c. supplies are employed,the equipment should be provided with a current

In formulae (a), (b) and (c) above reversing switch to facilitate demagnetization.

where 12.1.6 The apparatus should be equipped with an

L = part length; ammeter for measuring the current used in any test.For d.c. supplies, and for rectified a.c. supplies, it shall

D = part diameter; be of the permanent magnet moving coil type markedR = coil radius; in direct current amperes. For a.c. supplies it shall be

N = number of turns in the coil; of the moving iron, electrodynamicsor induction type,

I = coil current to be used, A; andmarked in rms amperes. Ammeter shall be calibratedfor variations not exceeding *1 O percent of the

NI = ampere turns. nominal.

These equations are valid only for parts having lengthover diameter ratio @/D) between 3 and 15. For J!/Dratio less than 3, the formulae given above results iniarge values of current. To minimize the current,extenders of ferro-magnetic material approximatelythe same diameter as part should be used to effectivelyincrease the L/D ratio. For L/D ratios greater than 15,a maximum L/D value of 15 should be used for a!lformulae cited above.

NOTE — For hollow cylinder test object diameter D shall

bereplacedbyaneffectivediameterDeff calculatedby

Def =2 [At – Ah]’

c

where

At= cross-sectional area of the test object, and

12.1.7 The installation for wet magnetic testing shouldnormally have a reservoir tank to contain the magneticpowder. The tank should preferably be fitted with apowered agitatoq but if this is not provided, the tankshould be so designed that adequate agitation by amanually operated paddle may be carried outfrequently during the operation of the equipment. Airagitation of the powder is not recommended.

12.1.7.1 Suitable means should be provided forapplying the detecting media to the component undertest. For liquid media, a powered pump system shouldbe used.

12.1.8 The apparatus Shall be equipped with meansfor firmly clamping the component under test betweenthe current carrying contacts or electromagnet~oles,

Ah = cross-sectional area of the hollow portion of the ‘test object. 12.2 Mobile and Portable Apparatus

12 EQUIPMENT FOR MAGNETIC PARTICLE 12.2.1 Mobile and portable apparatus consistsbasically

FLAW DETECTION of a high current low voltage source. Alternatively, ad.c. battery maybe used provided the test requirements

12.1 Fixed Equipment are met.

12.1.1 Thg equipment should be capable of enabling 12.2.2 The magnetizing force of a yoke can be testedthe component or material to be tested in accordance by determining its lifting power on a steel plate.with the specified technique. Current flow sources, Alternating current electromagnetic yokes should havesuch as transformers, giving maximum current values a Iifling force of at least 4.5 kg with a 30 cm pole

11

IS 3703:2004

spacing. For d.c. yokes at a maximum pole spacingof 150 mm, a lifting power of 18 kg is recommended.

12.2.3 Unless otherwise agreed, the mobile or portableapparatus should also conform to the requirements offixed equipment, as specified in 11.1.

12.3 Ancillary Equipment

The following ancillary equipment should norrnalllybe required for magnetic particle inspection:

a)

b)

c)

d)

e)

0

g)

Bars of various diameters of solid copper,brass or aluminium rod, or of larger sizesplugged aluminium tubing;

Rigid coil of 100 mm, 20(I mm, 300 mm andupward in diameter having five or more turnsof cables;

Copper gauge faced C-Clamps;

Heavy duty welding cables for leads, to beused with the ‘prod’ technique;

Wooden blocks for supports;

Jigs and fixtures; and

Magnetic field indicators.

12.4 Associated Equipment

The following associated equipment shall also berequired:

a) a demagnetizer of adequate size and powerto satisfactorily demagnetize the componentuncle?test, and

b) suitable sources of white or black light forviewing the flaw indication.

13 INSPECTION MEDIUM (MAGNETICPOWDERS AND FLUIDS)

13.1 The inspection medium shall consist of finelydivided ferromagnetic particles, which may besuspended in a suitable liquid medium (wet method)or used in dry powder form (dry method). The mainrequirements for magnetic powders are highpermeability and low retentivity and a very small sizeand proper shape to be readily mobile over the surfacebeing tested. The colour of the magnetic particles(non-fluorescent) to be used should have adequatecontrast with background colour of the surface to betested for clear identification of flaws.

13.1.1 The dry powder method is more sensitive thanthe wet method in the detection of near surfacediscontinuities, but is not as sensitive in detecting finesurface discontinuities. It is also convenient to usein conjunction with portable equipment for theinspection of large areas or for field inspection. Thedry powder method is, therefore, often used forthe inspection of large parts, such as large castings,forgings or weldments or parts with rough surfaces.It is not normally used for the inspection of smaller

parts, such as automotive or aircraft parts, in whichcase the wet method with stationary equipment isusually more convenient and effective.

13.2 Dry Powders

Dry powders are designed to be used as suppliedand are applied by spraying or dusting directly on tothe surface of the part being examined. Dry powdersmay also be used under extreme environmentalconditions. They are not affected by cold; thereforeexamination can be carried out at temperatures thatwould thicken or freeze wet baths. Dry powders arealso heat resistant and can be used up to 315 “C.Genarally dry powders are available in light gray,black, red, or yellow colours. The choice is basedon maximum contrast with the part to be examined.These materials are not generally fluorescent, andexamination is done under white light.

13.3 Wet Powders

Wet magnetic particles are designed to besuspended in a vehicle such as water or oil at a givenconcentration for application to the test surface byflowing, spraying or pouring over the surface, orthe specimen under inspection may be immersed inan agitated bath of the inspection medium. Two typesof wet magnetic particles may be used as follows:

a)

b)

Fluorescent Magnetic Particles — The particlesused in the wet fluorescent magnetic particlesbath are coated with a dye which causes themto fluoresce brilliantly when exposed to nearblack light. The purpose of the dye is to providemaximum contrast between the indications andtheir background so that fine discontinuitiesmay be detected.

Visible Magnetic Particles — The visiblemagnetic particles normally used in wet-bathsare either reddish or black and are observedunder normal white light. There is no differencein sensitivity with respect to dry powdermethod, and the colour should be so selectedas to provide the best, contrast against thebackground of the p~ being inspected.

13.3.1 Liquid Vehicle

Generally the particles are suspended in a low viscosityoil or conditioned water.

a)

b)

12

Water vehicles — Water may be used forsuspending wet magnetic particles providedsuitable conditioning agents are added whichprovide proper wet dispersing, in addition tocorrosion protection to the parts being testedand the equipment in use. Water vehicle is safeto use as it is nonflammable.

Oil vehicles — The oil used in preparing thebath is a light, well-refined petroleum distillateof low sulphur content, preferably treated to

reduce any unpleasant odours, and havingapproximately the following characteristics:

Viscosity (kinematic at4380C) 3 CS,Max

Flash-point (closed cup) 57”C, Min

Initial boiling point 200”C, Min

End point 260°C

Colour (Saybolt) + 25

Where oil is used as a vehicle for fluorescent particles,it should have the minimum amount of naturalfluorescence and should not degrade suspendedparticles. Uniform dispersion of magnetic particlesin oil vehicles and corrosion protection to parts andequipment are the chief advantages of the use of oilvehicles. Principal disadvantages are flammability.Commonly employed oil for suspending bothfluorescent and non-fluorescent magnetic particles iskerosene.

13.3.2 Bath Strength

The concentration of magnetic particles in the bathshould be maintained at the proper level if theinspection results are to be reliable and consistent.The concentration is periodically checked by taking a100 ml sample from a well-stirred bath and aliowingit to settle for 30 min in a pear-shaped centrifuge tube.The volume settling out at the bottom is indicative ofthe particle concentration. With red or black material,the recommended concentration from a 100 ml sampleis 1.2 to 2.4 ml. For fluorescent material therecommended concentration is 0.1 to 0.7 ml. Careshould be taken to see that the inspecting medium isnot contain inated with grease, oil, water or foreignmatter. If a clear line of demarcation is seen betweenthe sediment and the liquid when the medium isallowed to settle in the centrifuge tube, it may be takenas being free from contamination.

14 TEST PROCEDURE

14.1 General

All tests consist of the following processes whichshould be carried out in the given order:

a)

b)

c)

d)

e)

f)

~)h)

j)

Surface preparation;

Initial demagnetization;

Decreasing and cleaning;

Applying the excitation current for generatingthe magnetic field;

Applying the detecting media;

Viewing;

Marking position of indications;

Assessment and recording the nature of flaws;

Demagnetization;

13

IS 3703:2004

k) Repetition of the tests, if necessary;

m) Cleaning; and

n) Preparation for storage.

14.1.1 Selection of Test Method

A suitable test technique should be selected as perthe recommendations given in Table 1,for examinationof a component with a specific geometric shape. ,

14.2 Surface Preparation

14.2.1 The surface to be inspected shall be clean, dryand free from rust, oil, scale, excessive slag and otherextraneous matter which may interfere with efficientinspection. Machined or plated surfaces normally donot require any preliminary surface treatment otherthan degreasisng. However rough surfaces such asvery rough weld bead make the interpretation difficultdue to mechanical trapping of the magnetic powderthereby producing false indications. In such casessurface preparation by wire brushing, sand blasting,

.,

grinding, machining or other suitable method isnecessary.

14.2.2 Painted Parts

a)

b)

Parts, which are to be painted, should preferablybe tested before application of the paint.Otherwise, subject to mutual agreementbetween the manufacturer and the buyer, paintshall be removed locally, so as to provideadequate contact areas for the current flow tests.Other painted areas will only require decreasing.

Poor contrast is likely to be obtained if thecolour of the paint is the same as that of theparticles in the ink to be used. In such cases, anapproved contrast aid may be applied. Acontrast aid is normally a thin white adherentcoating which is compatible with the ink and~eadily removed after use.

14.2.3 Loose rust and scale should be removedfrom components before testing by suitable mechanicalor chemical methods.

14.3 Initial Demagnet@ation

All components should be demagnetized beforetesting, in order to release any adhering magneticswarf and to remove any magnetic fields such as thosewhich cause magnetic writing.

14.4 Decreasing and Cleaning

All components should be thoroughly cleaned beforetesting, as adhering grease and dirt may mask thedefects and also contaminate the ink.

14.4.1 For cleaning unassembled parts, it is essentialto subject them to a decreasing operation, followedby a mechanical wiping operation to remove adherentsolid residues.

[S 3703:2004

14.%2 When a component istobetested in-situ inastructure, the following cleaning procedure isrecommended:

a) The heavier soil should be removed using aclean rag or cotton waste moistened with asuitable solvent, preferably white spirit orparaffin. Liquid chlorinated hydrocarbons arehazardous and should not be used.

b) Thecleaning,shoul dbecontinue dwit hafreshlint-free rag and fresh solvent, until a satisfactoryclean surface is obtained.

14.5 Application of Magnetizing Current

Magnetic flux should be generated in the componentby any one of the methods specified in 10, which issuitable for the individual requirement. Depending uponthe sequence of application of the magnetic particleson the test object, with respect to magnetizing currentthere are two variations in the method as follows.

14.5.1 Continuous Method

In (his method, the inspection medium is applied to thesurface under inspection while the full magnetizationcurrent is flowing.

14.5.2 Re.siduo[ Method

In this method, the inspection medium is applied tothe surface under inspection after the magnetizingcurrent has been turned off. This method may be used,when specified, on parts having a relatively highmagnetic retentivity. It depends upon the residualmagnetic field in the part to produce indications, andis usually limited to the detection of surface cracks.Residual method offers some advantage whennumerous small parts ofhigtt retentivity material suchas high carbon or hardened steel are being tested bythis method. Parts may be magnetized rapidly and thenimmersed in a wet bath, or powder applied; thereforereducing the inspection time as compared to thecontinuous method.

14.6 Application of the Detecting Media

Unless residual magnetization methods have beenageed upon, the detecting medium should be appliedimmediately before and during excitation. Theapplication should stop before the magnetizationcurrent is switched off. Sufficient time, not less than3 s. should be allowed for the indications to build upbefore moving or examining the component undertest.

14.6.1 Dry powder, when used, should be applied ina manner so as to prevent disturbance of indications.

14.6.2 When an immersion procedure is used,parts must not be allowed to touch each other as hard,magnetized parts in contact with each other createlocal spots of magnetism (magnetic writing) which will

hold particles giving false indications. Precautionsshould be taken to avoid disturbance of the indicationupon removal from the ink bath.

14.6.3 When hose or ladle application is used themagnetic ink should be allowed to flow on to thecomponent with very low pressure, so that the particlesare allowed to adhere to a defect indication withoutbeing washed off.

14.6.4 The component should be allowed to drain, afierinking, for improving the contrast of flaw indications,

14.7 Viewing Conditions

14.7.1 The lighting used for inspection purposesshould be adequate without creating strong shadowsor highlights. There should be an even illumination toa level of not less than 500 htx daylight or artificiallight to permit proper evaluation of the indicationsrevealed on the test surface. This level of lighting maybe achieved by using either a fluorescent tmbe of ?-.

80 W at a distance of about 1 m or a tungsten filamentlamp of 100 W at a distance of about 0.2 m.

14.7.2 When using fluorescent inks and powders,the inspection area should be darkened and level ofillumination due to white light should not exceed10 htx. The inspection should be carried out underultraviolet radiation with a predominant wave lengthof 365 nm (3650 AO),that is,’black light’ conditions.The intensity of backlight at the test surface (380 mmfrom the face of the light lens filter) shall be not lessthan 800 fW/cm and unnecessary reflection ofultraviolet radiation from the test surface should beavoided.

14.8 Marking of Flaws

Where necessary, flaws shall be indicated by anapproved means, such as red-wax pencil.

14.9 Assessment of Indications

The indications obtained by magnetic particle flawdetection are all of a general form — a ‘piling up’ ofthe magnetic particles at the lines of flaws, variationsbeing of size, shape and p~sition. The accurateinterpretation of flaw indications is a matter requiringconsiderable experience. The service conditions ofa componant should always be borne in mind whenspecifying flaws. The common flaws are easilyidentifiable, but in some cases, false indications maybe obtained. Typical examples of these are:

a) grain flow indications caused by over-magnetizing;

b) over heavy indications on small diameters oraround holes caused by magnetizing whenusing the magnetic flow method;

c) indications caused by abrupt changes of section,for example, indications on the outside diameter

14

IS 3703:2004

of a tube shaft caused by internal key way orsplines;

d) magnetic ‘writing’ caused by the rubbing ofanother magnetized part during handling or theuse of a magnetized scriber; and

e) indications occurring at the interface of two

$, metals of differing magnetic permeability which

h have been welded together,

14.9.1 The most common types of imperfections, thatP are identified by magnetic particle inspection, are

grinding cracks, cracks caused by incorrect heat-treatment, seams due to rolling flaws, subsurfaceinclusions and shrinkage cracks in casting.

14.10 Demagnetization

I14.10.1 Ferromagnetic components which have beentested by magnetic particle flaw detection method, ofienremain magnetized for a considerable time after testing.

f This may be exceedingly troublesome if the componentis to be built into machinery or is likely to operate inclose proximity to sensitive electrical instruments. Inthe former case the local poles formed at projectionsand extremities will attract ferrous particles, causingexcessive wear due to abrasive effects, or makingmachining extremely difficult owing to the pick-upof metal chips, by clinging to the tool and causingscratching and other damage to the metal surface.Strong magnetic field may blow the weld metal as itis deposited. In aircraft construction, steel parts in theproximity of the aeroplane compass should bedemagnetized to eliminate any effect on the compass.Demagnetization takes place automatically if thespecimen is heated above the transformationtemperature (curie point). But, for the majority ofspecimens which are tested in finished condition,demagnetization methods which will not interfere withthe metallurgical condition of the material will haveto be used. However, complete demagnetization isdifficult if not impossible to obtain, thus the process islimited to reducing the residual field in specimensthat must be demagnetized to an acceptable levelspecified in drawings specification or purchase order.For general engineering application interferenceCaused by magnetism equal to or less than 0.1 mT(1 G) is negligible; therefore it is considered as anacceptable level for the residual magnetism.

14.10.2 For a longitudinally magnetized component,it is easy to measure the residual magnetism sincetlux leakage takes place at both the poles. However,a part may retain a strong magnetic field afterhaving been circularly magnetized and exhibitlittle or no external evidence of this external field as~he flux lines do not leave the part. Therefore,before demagnetizing circularly magnetized article,it must be magnetized longitudinally with a strongerlongitudinal field so that the residual field will be inlongitudinal direction.

14.10.3 Demagnetization is usually accomplishedby subjecting the specimen to a magnetizing forcethat is continually reversing in direction anddecreasing in strength so that the hysteresis loop isreduced to virtually zero. A simple and effectivemethod of accomplishing this is to insert the piece inthe field of an alternating-current solenoid ,andgradually to withdraw it from the field. It is importantthat the demagnetizer be set up with its axis in amagnetic East-West orientation.

14.10.4 Many modern flaw detectors are providedwith continuous step less control for the a.c. circuit andthese may be used for demagnetization as follows:

a) Current from the flaw detector may be passedthrough a coil of two or three turns of heavy cablewound round the specimen and graduallyreduced to zero.

b) Alternatively, current may be passed directlythrough the specimen, as when testing by thecurrent flow method, and reduced to zero bymeans of the control.

14.10.5 Direct-current demagnetization is usuallyaccomplished by repeated reversal of the current whileit is being progressively weakend.

14.11 Cleaning

After testing and acceptance, all components shall becleaned to remove all traces of detecting ink, contrastaid, if used and temporary marking, if applied. Thismay be carried out by wiping or washing with solventlike white spirit, or by complete immersion in anapproved degreasinsg agent.

14.12 Preparation for Storage

A suitable temporary protective, as agreed to betweenthe contracting parties, may be applied to thecomponent after cleaning to prevent corrosive attack.

15 RECORDING OF TEST DATA

The following data should be recorded at the time ofeach test for future reference:

a) Material; thickness/diameter of the component;

b) Method used, dry or wet;

c) Type of magnetization;

d) Type of current; prod spacing and L/D value;

e) Amount of current; and

f) Nature and type of defects.

16 RECORDING INDICATION

16.1 When the examination of a specimen has beencompleted, flaws should be marked with a pencil, paintor some other suitable means.

16.1.1 Where permanent records of the indication are

15

IS 3703:2004

required, these may be obtained either by takingphotograph of the indications or by one of thefollowing methods:

a)

b)

The specimen should be allowed to drycompletely. A piece of transparent adhesive tapeshould then be pressed over the defectindication, and immediately peeled off. Thisrecord may be preserved by covering theadhesive surface with transparent paper.

A piece of tracing cloth is given an even coatingof gum, allowed to become almost dry, an~then pressed over the flaw indication on thedefective component. On stripping all theindications come away with the tracing cloth.When the latter is quite dry, it may be usedfor marking blue prints of the indications, ifnecessary.

i 7 EVALUATION OF SYSTEM PERFORMANCE/

SENSITIVITY

‘ro evaluate the overall performance/sensitivity of theflaw detecting machine and medium, it is desirable

that some form of test is conducted, preferably daily,before routine work is commenced. For this purpose,a test piece of same size and shape known to containdefects or an artificial test block may be used.

17.1 Test Ring Specimen,

This specimen (Fig. 10) should be fabricated from \

tool steel cut from annealed round stock having ..hardness in the range of 90 to 95 HRB. Using a ,.central conductor magnetizing technique overall 2performance and sensitivity of the magnetic flawdetector and the medium may be evaluated (seeTables 2,3 and 4).

I

17.2 Magnetic Field Indicators

A magnetic field indicator (see Fig. 11) may be usedfor checking the adequacy and direction of thepart magnetization. When fixed on the surface of thepart under test and magnetized simultaneously thisindicator will indicate suitable flux or field strength if ~ ,.

a clearly defined line of magnetic particles formsacross the copper face.

Hole 1 2 3 4 5 6 7 8 9 10 11 12

Diameter 07 07 07 07 07 07 07 07 07 07 07 07

“u 07 14 21 28 35 42 49 56 63 7(J 77 64

FIG. 10 RINGSPECIMENWITHARTIFICIALSUB-SURFACEDISCONTINUITIES

16

1S 3703:2004

Table 2 Advantages and Limitations of the Various Types of Magnetizing Current

(Clause 17.1)

Type of Current and Their Use Advantages Limitations

(I) (2) (3)

I. Direct (sf.c.)

Detection of’ both surface and sub-

sur~ace disco ntinuities. Primarily

used for sub-surface and relatively

small operations.

2. Alternating (a.c.)

Detection of surtace discontinuities.

Extensively used for the demagneti-

zation of parts atter examination.

3.

4.

Ilalf-Wave Rectilied Alternating

(l I\\’AC)

Detection of both surface and sub-

surface discontinuities. Most sensitive

for sub-surface discontinuities.

Primarily used with prod type exami-

nation associated with portable and

mobi Ie type equipment.

Full -\Vwe Rectified Direct

(FWDC)

Suitable for the detection of both

surfhce and Sab-surface discontinuities.

Primnrily ased for inspection of

large components on wet horizontal

or stationary power packs.

Maximum penetration of flux into object Difficult to demagnetize. Battery

permitting indications ofsub-surface maintenance. Fixed Voltage. Now-a-

discontinuities. days rarely used in industries

a.c, results in a ‘skin effect’ that confines Shallow penetration of flux making

the magnetic field to the surface ofa a.c. ineffective for sub-surface

part and thus making it most sensitive discontinuities

for detecting surface discontinuities.

High magnetic particle mobility is

attributed to its pulsating characteristics.

Relatively easy to demagnetize.

Higher flux densities for the same average Relatively difficult to demagnetize

current. Full penetration of flux into

object. Additional particle mobility in

conjunction with dry powder. Can be

easily obtained from a.c. power supply

by addition of rectifier and switch.

Suitable for field work.

Current of very high magnitude such Large power packs. Not suitable for

as 6000 to 20 000A are easily obtained. field work

Detection of surface and sub-surface

discontinuities impossible.

Table 3 Ring Specimen Indications with Wet Particles

(Cfuuse 17.1)

Type of Wet Suspension Magnetizing Amperage Minimum Number of Sub-SurfaceParticics (FWDC) Holes Indicated

(1) (2) (3)

I400 3Flourescent or non-tloarescent 2500 5

3400 6

1S 3703:2004.

AEIGHT LOW CARBON STEEL PIE SECTIONSFURNACE BRAZEO TOGETHER

L!(J:1k

\ ;/ NONFERROUS HANDLE OF

\ [ ,’ ANY CONVEtflENT LENGTH\l/

Y\----—-—— 1

/1,/

/ l\lx

?1/32 IN MAX.BRAZE WELO OR MECHANICALLYATTACH NONFERROUS TRUMNIONS

I /-COPPER PLATE O.OIOIN.THICK* O.OO1IN.

FIG. 11 MAGNETICFIELDINDICATOR

Table 4 Ring Specimen Indications with Dry Particles

(Clause 17.1)

Mtignctizing Amperage Minimum Number of(rmmc) Sub-Surface Holes Indicated

(1) (2)

500 4

900 4

I 400 4.

2500 6

.-

3400 7

18

A

f-- ~--q

1!I

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Amendments Issued Since Publication

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