Intro_to_Mag (1) - Copy.ppt

7/26/2019 Intro_to_Mag (1) - Copy.ppt

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Outline

Magnetism and Ferromagnetic Materials Introduction of Magnetic Particle Inspection

Basic Procedure and ImportantConsiderations

1. Component pre-cleaning2. Introduction of magnetic field3. Application of magnetic media4.

Interpretation of magnetic particleindications

!amples of MPI Indications


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"o# $oes Magnetic Particle

Inspection %or&'

A ferromagnetic test specimen is magneti(ed #it)a strong magnetic field created *+ a magnet orspecial e,uipment. If t)e specimen )as adiscontinuit+ t)e discontinuit+ #ill interrupt t)emagnetic field flo#ing t)roug) t)e specimen and alea&age field #ill occur.


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"o# $oes Magnetic Particle

Inspection %or&' Cont./

Finel+ milled iron particles coated #it) a d+epigment are applied to t)e test specimen. 0)eseparticles are attracted to lea&age fields and #illcluster to form an indication directl+ oer t)e

discontinuit+. 0)is indication can *e isuall+detected under proper lig)ting conditions.


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Pre-cleaning

Contaminants suc) as oilgrease or scale ma+ notonl+ preent particles from*eing attracted to lea&age

fields t)e+ ma+ alsointerfere #it) interpretationof indications.


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Introduction of t)e Magnetic Field

0)e re,uired magnetic field can *e introduced into acomponent in a num*er of different #a+s.

1. sing a permanent magnet or an electromagnet t)atcontacts t)e test piece

2. Flo#ing an electrical current t)roug) t)e specimen

3. Flo#ing an electrical current t)roug) a coil of #irearound t)e part or t)roug) a central conductor runningnear t)e part.


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$irection of t)e Magnetic Field

0#o general t+pes of magnetic fields longitudinaland circular/ ma+ *e esta*lis)ed #it)in t)especimen. 0)e t+pe of magnetic field esta*lis)ed isdetermined *+ t)e met)od used to magneti(e t)especimen.

A longitudinal magnetic field )asmagnetic lines of force t)at run

parallel to t)e long a!is of t)e

part. A circular magnetic field )as

magnetic lines of force t)at run

circumferentiall+ around t)e

perimeter of a part.


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Importance of Magnetic Field $irection

Being a*le to magneti(e t)e part in t#odirections is important *ecause t)e *estdetection of defects occurs #)en t)e lines ofmagnetic force are esta*lis)ed at rig)t angles tot)e longest dimension of t)e defect. 0)isorientation creates t)e largest disruption of t)emagnetic field #it)in t)e part and t)e greatestflu! lea&age at t)e surface of t)e part. Anorientation of 4 to 5 degrees *et#een t)emagnetic field and t)e defect is necessar+ toform an indication.

6ince defects ma+occur in arious andun&no#n directionseac) part is normall+magneti(ed in t#odirections at rig)tangles to eac) ot)er.

Flux Leakage

No Flux Leakage


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7uestion

?? From t)e preious slide regarding t)e optimum

test sensitiit+ #)ic) &inds of defect are easil+

found in t)e images *elo#'

Longitudinal (along the axis) Transverse (perpendicular the axis)


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Producing a 8ongitudinal Magnetic

Field sing a Coil

A longitudinal magnetic fieldis usuall+ esta*lis)ed *+placing t)e part near t)e

inside or a coil9s annulus.0)is produces magneticlines of force t)at areparallel to t)e long a!is oft)e test part.

Coil on Wet Horizontal Inspection Unit

Portable Coil


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Producing a 8ongitudinal Field sing

Permanent or lectromagnetic Magnets

Permanent magnets andelectromagnetic +o&esare also often used to

produce a longitudinalmagnetic field. 0)emagnetic lines of forcerun from one pole to t)eot)er and t)e poles are

positioned suc) t)at an+fla#s present run normal

to t)ese lines of force.


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Circular Magnetic Fields

Circular magnetic fields are produced *+passing current t)roug) t)e part or *+placing t)e part in a strong circularmagnet field.

A )eads)ot on a #et )ori(ontal test unit

and t)e use of prods are seeral commonmet)ods of in:ecting current in a part toproduce a circular magnetic field.Placing parts on a central conductorscarr+ing )ig) current is anot)er #a+ toproduce t)e field.

Magnetic Field

lectric

Current


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Application of Magnetic

Media %et ;ersus $r+/

MPI can *e performed using eit)erdr+ particles or particlessuspended in a li,uid. %it) t)edr+ met)od t)e particles are

lig)tl+ dusted on to t)e surface.%it) t)e #et met)od t)e part isflooded #it) a solution carr+ingt)e particles.

0)e dr+ met)od is more porta*le.

0)e #et met)od is generall+ moresensitie since t)e li,uid carriergies t)e magnetic particlesadditional mo*ilit+.


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$r+ Magnetic Particles

Magnetic particles come in a ariet+ of colors. A

color t)at produces a )ig) leel of contrast

against t)e *ac&ground s)ould *e used.


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%et Magnetic Particles

%et particles are t+picall+ supplied

as isi*le or fluorescent. ;isi*le

particles are ie#ed under normal

#)ite lig)t and fluorescent particles

are ie#ed under *lac& lig)t.


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Crane "oo& #it)

6erice Induced Crac&

Fluorescent, Wet Particle Method


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$rie 6)aft #it)

"eat 0reatment Induced Crac&s



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6plined 6)aft #it)

6erice Induced Crac&s



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0)readed 6)aft #it)




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8arge Bolt #it)




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Cran& 6)aft #it)

6erice Induced Crac& =ear 8u*e "ole



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8ac& of Fusion in 6MA% %eld

Visible, Dry Powder ethod

Indication


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0oe Crac& in 6MA% %eld

Visible, Dry Powder ethod


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0)roat and 0oe Crac&s in

Partiall+

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