intro_to_mag (1) - copy.ppt
TRANSCRIPT
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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
Fluorescent, Wet Particle Method
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6plined 6)aft #it)
6erice Induced Crac&s
Fluorescent, Wet Particle Method
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0)readed 6)aft #it)
6erice Induced Crac&
Fluorescent, Wet Particle Method
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8arge Bolt #it)
6erice Induced Crac&
Fluorescent, Wet Particle Method
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Cran& 6)aft #it)
6erice Induced Crac& =ear 8u*e "ole
Fluorescent, Wet Particle Method
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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+