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7/13/2019 Magnetic Particle Testing ppt
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MAGNETIC PARTICLE
TESTING
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Magnetic particle inspection can
detect both production
discontinuities and in-service
damage
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INTRODUCTIONTOMAGNETISM
Magnetism is the ability of matter to attract other
matter to itself.
Objects that possess the property of magnetism are
said to be magnetic
magnetic pole is a point where the a magnetic line
of force exits or enters a material
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FERROMAGNETICMATERIALS
A material is considered ferromagnetic if it can bemagnetized
Ferromagnetic materials are made up of magnetic
domains
Magnetic domains point randomly in demagnetizedmaterial, but can be aligned using electrical current
Demagnetized Magnetized
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HOWDOESMAGNETICPARTICLE
INSPECTIONWORK?
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HOWDOESMAGNETICPARTICLE
INSPECTIONWORK? (CONT.)
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BASICPROCEDURE
Basic steps involved:
1 Component pre-cleaning
2 Introduction of magnetic field
3 Application of magnetic media
4 Interpretation of magnetic particleindications
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PRE-CLEANING
The parts surface should be clean and dry before
inspection
Contaminants being attracted to leakage
fields, they may also interfere with interpretation of
indications.
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INTRODUCTIONOFTHEMAGNETIC
FIELD
magnetic field can be introduced into a component
in a number of different ways.
A. Using a permanent magnet or anelectromagnet
B. Flowing an electrical current through the
specimen
C. Flowing an electrical current through a coil ofwire
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DIRECTIONOFTHEMAGNETICFIELD
Two general types of magnetic fields:
1) longitudinal magnetic field
2) circular magnetic field
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IMPORTANCEOFMAGNETICFIELD
DIRECTION
detection of defects occurs when the lines of
magnetic force are established at right angles to the
longest dimension of the defectFlux Leakage
No Flux Leakage
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Longitudinal (along the axis) Transverse (perpendicular the axis)
Kinds of defect
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PRODUCINGALONGITUDINAL
MAGNETICFIELDUSINGACOIL
placing the part near the
inside or a coils annulus.This produces magnetic
lines of force that are
parallel to the long axis of
the test part
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PRODUCINGALONGITUDINALFIELD
USINGPERMANENTOR
ELECTROMAGNETICMAGNETS
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CIRCULARMAGNETICFIELDS
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DRYMAGNETICPARTICLES
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WETMAGNETICPARTICLES
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Indications
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DEMAGNETIZATION
Possible reasons for demagnetization
include: May interfere with welding and/or machining
operations
Can effect gauges that are sensitive to magneticfields if placed in close proximity.
Abrasive particles may adhere to componentssurface and cause and increase in wear toengines components, gears, bearings etc.
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DEMAGNETIZATION
Magnetized
Demagnetized
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ADVANTAGESOF
MAGNETICPARTICLEINSPECTION
Can detect both surface and near sub-surface
defects
Precleaning of components is not critical
Fast method of inspection and indications are
visible directly
low cost compared to many other NDT methods
Is a very portable inspection
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LIMITATIONSOF
MAGNETICPARTICLEINSPECTION
Cannot inspect non-ferrous materials
Inspection of large parts may require use of
equipment
Some parts may require removal of coating
Limited subsurface discontinuity detection
Post cleaning, and post demagnetization is often
necessary
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TH NKYOU