good

1. Magnetic particle testing :
Magnetic particle testing is a non destructive testing method for
detection of surface and near surface discontinuities in
ferromagnetic materials.
* Applicable only to :
* ferromagnetic materials, Iron, Cobalt, Nickel and their magnetic
alloys.
* Detection sensitivity diminishes rapidly with depth.
* If the flaw is deeper, it must be larger to produce indication.
* Deeper flaws produce broad and fuzzy indication which require
careful interpretation.

2. Magnetic particle testing :
detection of ‘surface and sub surface’ flaws
[ depth of detection depends on the type and size of the flaw ]
Leakage field above the flaws collects and hold magnetic particles to form
caterpillar like visible indication pattern.

3. Discontinuities at or near the surface produce magnetic leakage field on the
surface :
Magnetic flux in a magnetized part pass through the body of the part.
Discontinuities at or near the surface of the part disturb the normal flow of
magnetic flux and leakage flux fields are produced on the surface above the
discontinuities. These leakage fields attract iron particles and are detected
by applying iron powders.

4. Leakage field :
flaws at or near the surface of a magnetized part produces leakage field at
the surface which is detected by sprinkling iron powders.

5. Magnetic lines of force is entirely within the part for a flawless specimen.

6. Leakage field :
flaws at or near the surface of a magnetized part produces leakage field at
the surface which can be detected by sprinkling iron powders.

7. Detection of leakage field :
Finely divided iron particles are used for detection of leakage field.
Leakage field at the surface collects and hold the iron particles together to
form visible indication patterns.
• Flaws at or near the surface
disturb the magnetic flux flow and
produce leakage field at surface
above the flaw.
• Magnetic particle build up at the
leakage field produces recognizable
patterns which are interpreted.
• Color of the particles must be
chosen to provide adequate
contrast against the part’s natural
color.

8. Surface discontinuities produce strong leakage field, which produces
sharp indications, which are easy to recognize.
Sub surface discontinuities produce wide and fuzzy indications, which are
difficult to recognize as the depth of the discontinuities increases. Thus
there is a loss of sensitivity with increasing depth from the surface.

9. Magnetized : Particles applied :
Magnetic particle testing :
leakage field produced by tight cracks are indicated by accumulation of
colored dry particles.

10. Flaw depth to width ratio for good detection sensitivity
flaws should be deeper than the opening.
• For detection sensitivity, the depth of the flaw should be at least 3 times
deeper than the surface roughness of the part.
• For good detection sensitivity the ratio of
width: depth: length should be : 1 : 5 : 10

11. Test Process :
1. A suitable technique of magnetization is chosen.
2. The part is magnetized in the desired direction.
3. While the magnetizing field is present, iron powders
are applied dry or wet.
4. Iron powders bridge the leakage fields, if present, to produce
indications.
5. Powder patterns produced by flaws are identified and
accept reject decision is made.

12. Advantages :
* Detects flaws up to ¼ inch below the surface.
[ not the ultimate limit ]
* Detects flaws filled with foreign matter.
* Detects cracks below plating or paint.
* Immediate indication.
* Testing possible up to 3000C part temp using dry powders.
* Indications can be recorded.
Limitations :
* Applicable only to ferromagnetic materials.
* Limited depth of detection.
* Depth or size of flaw not indicated.
* Sensitivity varies with test surface position and roughness.
* Sensitivity diminishes rapidly with depth.

13. Magnetic Field Strength :
Magnetic field is produced by Magnetic lines of force.
* Lines of force is known as Flux.
* Unit of flux is weber.
* 1 line of flux is 1 weber.
* Flux per unit area is flux density and is measured in
Gauss.
* 1 Gauss is 1 line of flux per sq Cm.
* 104 Gauss is 1 Tesla [ 108 lines per sq meter ]

14. Magnetic behavior :
A magnet has two poles. North and South poles.
Opposite poles attract each other.
Like poles repel.

15. Magnets :
A bar magnet has a magnetic field within and around.
The Magnet has two poles. Magnetic field is strongest near the poles. The
field runs along the length of the magnet and is known as longitudinal field.
• The field strength decreases with distance
from the poles.
• Magnetic field seeks the path of least
magnetic resistance.
• The flux lines form a closed loop and they
do not cross each other.
• Number of lines per unit area is the
strength of the field and is a measure of
flux density.

16. Ferromagnetic materials have domains. Domains are smallest known
permanent magnets. A domain has one South and one North pole. When the
poles are aligned under the influence of an external magnetic field, the
material behave as a magnet and attracts other ferromagnetic materials.
When all domains are aligned, the material becomes magnetically saturated.

18. Magnetic lines of force around a Bar Magnet revealed by sprinkling iron
powders around the magnet. Dense lines indicate strong magnetic field.

19. Longitudinal & Circular Magnetic field :
A Bar magnet has Longitudinal magnetic field.
A Ring magnet has Circular magnetic field.

20. Magnetic field of a Bar magnet :
Flux lines have a direction, inside the magnet they travel from the South pole
to the North pole and outside they travel from the North pole to the
South pole.

21. If a Bar magnet is bent into ‘ U ‘ shape, the poles still remain.

22. Bar magnet being formed into a Ring :
• If a bar magnet is shaped into a ring, the magnetic flux lines concentrate
at the gap between the poles.
• If iron powders are sprinkled on the ring, particles will be collected at the
ends.

23. Magnetized Ring :
• If a bar magnet is formed into a ring, and the ends are fused, the poles
vanish and the field becomes circular and remains within the ring.
• If iron powders are sprinkled on the ring, there is very little attraction of the
particles.
• Circular field exhibit no poles.

24. Surface discontinuities in a magnetized ring produce leakage
fields :
A crack at the surface of a magnetized ring produces leakage field which
attracts and accumulate ferromagnetic particles.

25. Field direction for flaw detection :
For maximum detection sensitivity the magnetic field should be 900 to the
major dimension of the flaw. However magnetic field direction up to 450 to
the major dimension may produce detectable indications.

26. Flaw orientation to the magnetic field :
magnetic field 45 - 900 to the major dimension of the flaw produces leakage
fields of varying strength. Field parallel to the flaw does not produce leakage
field. A second magnetization direction, 900 to the first applied field is
required.

27. Flaw orientation to the magnetic field :
magnetic field 45 - 900 to the major dimension of the flaw produces leakage
field. Field parallel to the flaw does not produce leakage field.

28. Field direction for flaw detection :
To produce a leakage field, magnetic field must intercept between 450 to 900
to the major dimension of the flaw.
• A 900 magnetic field
produces stronger
indication.
• A 450 magnetic field
produces weaker
indication.
• A parallel magnetic
field produces no
leakage and no
indication.

29. Magnetizing direction :
Ideal magnetic field direction is
900 to the major dimension of
the discontinuity.

30. Magnetizing direction :
A longitudinal magnetic field will detect the crack on this weld.
Circular field may produce very weak or no indication.

31. Magnetizing direction and detectable discontinuities :

32. Magnetizing direction and detectable discontinuities :

33. Magnetizing Current :
Types of current used to magnetize a part are ;
Alternating Current
Half wave rectified Direct Current
Full wave rectified Direct Current
Three phase rectified Direct Current
[ for generating very high currents > 3000 amps ]

34. Alternating Current [ AC ] :
This is the common supply current to the Industry.This current continuously
reverses direction [ Positive and Negative transition ] hence it is known as
alternating current.
When a part is magnetized by alternating current, the magnetic field remains
near the surface. This is known as SKIN EFFECT
For 50 Cycles AC, field penetration is within 1 mm. Hence, alternating
Current is used for detection of surface flaws only and provides maximum
sensitivity for such flaws in combination with wet particles.
Alternating current is extensively used for demagnetization of parts.

35. Half wave rectified Direct Current [ HWDC ] :
When alternating current is rectified, the negative transition is blocked
and current flows in one direction only. This is current known as HWDC.
HWDC penetrates deeper in the part and is used for detection of surface
and sub-surface defects.
HWDC is pulsating in nature and is very suitable for detection of deeper
defects using dry particles.

36. Full wave rectified Direct Current [ FWDC ] :
When the negative transition is inverted to positive transition by
rectification, all the current flow in one direction only. This current known
as FWDC and is used for generating very high currents
[ > 6000 amps ].
FWDC penetrates deeper in the part but is not pulsating, hence this
current is less suitable for use with dry particles.
FWDC is used for detection of surface and sub-surface defects.

37. Magnetizing a part :
Circular magnetization.
Produced by passing current through a part

38. • A conductor carrying electric current has a
magnetic field around it which is 900 to the
direction of current flow :

39. The magnetic field is 900 to
the direction of current flow :

40. Right Hand Rule :
for determining the direction of magnetic flux flow.
* If a conductor carrying
current is grabbed as
shown in the picture.
* If the thumb points
towards the direction of
current flow [ + to –
terminal ] then the
fingers shows the direction
of the magnetic flux lines.
The above right hand rule
is based on current flow
theory

41. Left Hand Rule :
Based on electron flow
for determining the direction of magnetic flux flow.
In this case, the thumb is to be pointed towards the direction of electron
flow, I. E. from negative to positive terminal.

42. For a given current flow
the magnetic field strength is
uniform throughout the length of
the conductor. Test sensitivity is
same throughout the length of the
conductor.

43. Magnetic field around a
conductor revealed by iron
powders :
A current carrying conductor
produces a circular magnetic
field.

44. The circular Magnetic field around a current carrying conductor revealed by
iron powders :

45. Circular magnetic field :
can be established by passing current directly through
a long part.
• Passing Current
through the part
produces circular field
around the part.
• The field strength is
maximum at the
surface and uniform
throughout the length.
• Magnetic field
strength reduces to
zero at the center of
the part.
• Circular field can be
used to detect
lengthwise defects.

46. Circular magnetic field :
can be established by passing current directly through a long part. Flaws
along the length of the part can be detected by this technique.

47. Detectable flaw orientations for circularly magnetized part :
must be 450 to 900 to the magnetic field.

48. A long part can be circularly magnetized by passing
current along the length of the part in a head shot
machine.

49. A current is passed through an axle to produce circular magnetization.
Lengthwise discontinuities can be detected by this technique.

50. If a current is passed through an axle to produce circular magnetization,
Field strength is maximum at the surface. At the center, field strength is
zero.

51. If a current is passed through a hollow conductor, the inside of the bore is
not magnetized and can not be tested.

52. Central conductor :
For magnetizing the inside surface of a cylindrical part.
Field strength is maximum at the inside surface.
•A central/offset
conductor is used to
magnetize the inside bore
of a hollow part.
•Flaws at the outer
surface may be detected
if the wall thickness of
the part is not large.
•Strength of the magnetic
field reduces with
distance between the
conductor and the inner
surface, hence for large
part, conductor must be
close to the inside wall.

53. Central conductor :
For magnetizing the inside surface of a cylindrical part.
Field strength is maximum at the inside surface.
•The circular field around
the central conductor is
collected at the inside
surface of the bore.
•This method is called
indirect magnetization.

54. Central conductor :
For magnetizing the inside surface
of a cylindrical part.
Field strength is maximum at the
inside surface.

55. Central conductor :
A central conductor producing a surface indication on a thin
wall tubing. Central conductor detects inside flaws and
outside flaws also if the tube wall is not very thick.

56. Crack detected by central conductor magnetization :
When the wall thickness is not large, longitudinal defects at the
outside surface are also indicated.

57. Magnetizing a part :
Longitudinal magnetization can be
achieved,
1. By a coil
2. By permanent magnet
3. By electromagnets

58. A loop produces longitudinal field : If
a current carrying wire is formed into a loop the magnetic field threads the
opening of the loop.
The field is longitudinal.

59. Magnetic field of a single turn loop :
field distribution revealed by iron powders.

60. When a linear part is placed
inside the loop, a lengthwise field
is induced on it.

61. Magnetic field strength increases with number of turns and the
magnitude of the current flow.

62. Magnetic field of solenoid :
Solenoid is a coil with many loops. field strength increases with number of
turns and the current flowing through it. Magnetic field strength is
expressed in Ampere – Turns. When a linear part is placed inside the loop,
a lengthwise field is induced on it.

63. For a coil, Magnetic field strength is maximum at the inside
surface and reduces towards the center.

64. Magnetic field of a multi turn coil shown by iron powders.

65. When a Ferro magnetic material is placed within the coil, strong longitudinal
magnetic field is induced in the material:

66. A long part can be tested by placing it within a coil.

67. Because the field is longitudinal, only flaws along the
circumference will be detected.

68. Lengthwise flaws can not be detected by this technique.

69. Magnetic field of a multi turn coil :

70. Magnetic field of a multi turn coil :

71. Detectable flaw orientations for coil magnetization.

72. Magnetic field of a multi turn
coil :

74. Coil method for longitudinal magnetization in the part :
In coil method Selection of
current is based on
NI = 45000/(L/D)
N denotes Number of turns in
the coil
L denotes Length of the
material
D denotes diameter of the
specimen
For example 16 inch long bar
with 2 inch OD and 5 turn
coil, the current required is
5I = 45000/(16/2)
or I = 1125 Amperes

75. Longitudinal magnetization detects circumferential flaws.
* When using the formula
NI = 45000 / (L/D), the following
conditions apply;
* Part diameter should be within
10% of the coil opening and the
part must be placed near the
inside wall of the coil where the
field strength is maximum.
* L shall be maximum 18 inches
* Test length shall be 9 inches on
either side of the coil. For long
parts, testing shall be performed
18 inches at a time.

76. Increasing the L / D ratio.

77. Circumferential crack detection in long parts :
By using longitudinal
magnetization in coil method
any indication which is
circumferential produces
strongest indication
Magnetic field is zero at the
center, maximum at the inside
wall.
Any object which is more than
18 inches need more than
one shot of magnetization.l
Current selection is
determined by
NI = 45000/(L/D)

78. Portable coil magnetization :
small coils of different diameter can be made and operated directly from
the mains supply.
• Smaller parts whose
length predominates,can be
magnetized in a small
portable coil operating
directly from mains.
• L / D ratio should be
3 or more.

79. Magnetic Particles are:
Finely divided iron powders, colored to provide contrast
against the part surface.
Dry powders - used dry, good for sub surface flaws.
Wet powders - used as suspended, good for surface
flaws.
Powders must have :
High permeability [ easily magnetized ]
Low retentivity [ does not remain magnetized ]
Non toxic [ relatively harmless to the user ]
Powders are available as
Visible - viewed under ordinary light.
Fluorescent type – viewed under ultraviolet light.

80. Magnetic Particles :
Are packed in different forms;
Dry powders
Coarse or Fine particles to be used dry.
Wet powders
as particles to be suspended in carrier.
as paste or concentrates with wetting agent and corrosion inhibitors, to be
mixed thoroughly with the carrier.

81. Dry Particles :
colored to provide contrast with the part’s natural surface.
Require clean and dry surface.
Good on rough surface.
Fine powders are used on vertical or
overhead surface.
Coarse powders are used on
horizontal surface and provide
maximum sensitivity to subsurface
flaws. Dry particles require mobility
and is used with pulsating current, AC
& HWDC.
Sensitivity to subsurface flaws much
more than wet powders when applied
to the surface by floating with
minimum of motion.
require suitable powder blowers for
correct application.

82. Fine dry particles may be applied by a rubber puffer but is not easily
controlled :
Sensitivity of dry particles depends on technique of application.

83. A Blower for applying fine dry
powders,
from Parker research corpn :

84. A Crane Hook being tested by an electromagnetic yoke and
red dry powder

85. Powder Blower from Parker research corpn :
for efficient application of dry particles. The head floats the particles using
compressed air. Excess dry particles around the indications can be
removed by gentle plain air blast also available from the blower.

86. Dry particle flaw indication :
Red colored Dry particles formed a crack indication on the face
of a cutter blade.

87. Wet Powders :
colored to provide contrast with the part’s surface.
Particles are fine to be remained in suspension.
Black particles are most sensitive.
Wet particles are fine powders
to be suspended in kerosene /
water.
Require smooth surface.
High sensitivity to fine surface
cracks.
Sensitivity to subsurface flaws
much less than dry powders.
May require the use of white
contrast paint on normal steel
surface.
Available as visible and
fluorescent powders.

88. Fluorescent pigment glowing under UV light
Fluorescent chemicals can be used to enhance the visibility of the
magnetic powders :
1. Florescent pigments are used for coating magnetic powders.
2. Fluorescent materials glow brilliantly under ultraviolet illumination.
3. No contrasting medium is required for fluorescent powders.

89. Fluorescence enhances the visibility of the indications :

90. Fluorescent magnetic particles illuminated by an ultraviolet light.

91. Fluorescent magnetic particle examination requires a darkened
examination area.

92. Wet suspension application :
In stationary machines the suspension is applied to the parts by a hose
with the help of re-circulating motor pump. The suspension is called bath.

93. Automatic Wet suspension application :
Fluorescent examination can be carried out in daylight condition under
high intensity UV light source.

94. Fluorescent suspension is
being used during a test :

95. The particle suspension of required concentration is stored in a
tank and is re-circulated by a pump and a hose. The particle
concentration gradually reduces and the suspension gets
contaminated with use :

96. For manual use in field
condition, Pressurized Can,
which can be refilled, is
normally used for wet
suspension
application.

97. Pressurized Cans for wet suspension application in the field :

98. Aerosol spray Cans
with ready mix black
powder suspension
application :

99. Aerosol Cans with
ready mix
fluorescent powder
suspension
application :

100. Wet particle use :
When Kerosene is used as
the suspending medium,
Rubber Gloves for Hand
protection is very
necessary.
Continuous exposure to
kerosene or petroleum
products causes serious
skin infection.

101. ASTM Centrifuge :
Pear shaped centrifuge tube is used to check particle
concentration in the suspension or bath.
The amount of particle in the suspension is important
for flaw detection.
Low concentration produces weak indication.
High concentration mask flaw indications.
For visible powders 1.2 to 2.4 ml of powder per 100
ml liquid is recommended.
For fluorescent powders .1 to .5 ml of powder per 100
ml liquid is recommended.
Lower concentration may be used on horizontal test
surface.
Higher concentration is required for vertical or
overhead test surface.

102. • The stem of the tube has an
engraved scale which is used to
read the volume of powders
settled out of suspension.

103. A thoroughly agitated
suspension is poured into the
Centrifuge up to the 100 ml
mark and allowed to settle for
30 minutes.
The settled volume is read
from the stem.

104. ASTM Centrifuge & stand :
Particles must be allowed to settle undisturbed. Vibration may compact
the settled powder and the reading would be erroneous.

105. Contamination of fluorescent suspension :
Recycled suspension gradually becomes contaminated during use.
Abnormal coloration of the suspension liquid indicates
contamination.Contaminated suspension must be discarded. Indications
are not visible when contaminated suspension is used.

106. Magnetized ring [ MTU 3 ]:
for checking relative quality of the suspension.
•The ring is pre
magnetized to retain a
residual field.
•The liquid suspension
to be tested is flowed on
the surface and the
indications are
compared.
•Clarity of indications is
a relative measure of
bath quality.
•Fluorescent indications
of the cracks are visible
on the ring.

107. MTU 3 ring for testing wet particle suspension

108. Accumulation of wet suspension can produce false
indications and mask weak indications.

109. Accumulation of wet suspension can produce false
indications and mask weak indications.

110. Magnetized ring [ MTU 3 ]:
for checking relative quality of the suspension after hours of use.

111. Visibility of indications :
Color of the test surface may not provide adequate contrast when visible
powders are used. Red and Black wet powders do not provide adequate
contrast when natural steel surface is examined.

112. Visibility of indications :
Fluorescent particle indications are examined under ultraviolet illumination
in a darkened condition and does not require contrast medium. The
indications glow in a dark background and are easily seen.

113. Visibility of indications :
Faint Fluorescent particle indications are easily seen.

114. Visibility of indications :
Faint Fluorescent particle indications are easily seen.

115. Contrast of indications :
Application of White paint on the test surface provides contrast for steel
examination when visible powders are used.
•Brown-Red and Black particles
provide less contrast while
testing steel.
•White contrast paint enhances
the contrast.Small indications
are easily seen.
•Fluorescent particles glow in
the dark and do not require
contrast paint.

116. Ready made quick drying White contrast paint in aerosol cans :

117. Applying white contrast paint for
weld examination.

118. White contrast paint applied
on welds for magnetic
particle examination.

119. Performing examination on white contrast paint.

120. Crack indication on a valve body casting. Black indications on white
contrast paint is easy to see.

121. White contrast paint enhances the indications on otherwise blackish part
background.

122. Cracks indicated by black particles on white
paint. High particle concentration produces
black patches.

123. Magnetizing Equipments :
Stationary Horizontal Units
this machine uses a combination of Current flow [ circular ] and Coil [
longitudinal ] method of magnetization. A re-circulating particle suspension is
applied to the part using a hose and a pump. The machine provides AC and
HWDC with high currents. Standard lights for visible particle and ultraviolet
lights for fluorescent particle examination are provided in the machine.
Prod Units
These are portable high current sources and use a pair of prods
[ electrodes ] to circularly magnetize a local area of a part by current flow
method.
Permanent Magnets
Use a pair of very strong permanent magnets to introduce a longitudinal
magnetic field in a local area of a part.
Electromagnetic Yokes
Use an electrically energized coil to magnetize a C- Shaped laminated
adjustable core, which is used to introduce the magnetic field in the local area
of a part.

124. Stationary Horizontal units are used with wet particles.
Supplies both AC and HWDC adjustable current. Has built in visible light
as well as ultraviolet lights for fluorescent examination. A re-circulating
pump supplies the particle bath through a hose.
Other features ;
Two Contact heads, one
fixed and the other is
movable to accommodate
the test part.
Coil for longitudinal
magnetization.
High current capability.
Foot switch for current
trigger.
May be used to
Demagnetize.

125. Stationary Horizontal units are used with wet particles.
Supplies both AC and HWDC adjustable current. Has built in visible light as
well as ultraviolet lights for fluorescent examination. A re-circulating pump
supplies the particle bath through a hose.
Other features ;
* Two Contact heads, one
fixed and the other is
movable to
accommodate the test
part.
* Coil for longitudinal
magnetization.
* High current capability.
* Foot switch for current
trigger.
* May be used to
Demagnetize.

126. Stationary Horizontal units :
Contact heads may use lead liner for improving contact. A nozzle and
hose is used for applying suspension.

127. Stationary Horizontal units :
Heads also use copper braids for uniform contact.

128. Contact Heads :
For passing current through the part.
Contact heads lined with lead for improving electrical contact. It also
has support for the test part.

129. Stationary Horizontal units : In addition to contact, the heads may contain
coils such that the heads can be used as yokes for longitudinal
magnetization of parts.

130. Stationary Horizontal units :
Foot switches are used to activate the magnetizing current.

131. Coil magnetization :
A Coil is provided on the stationary magnetizing unit for longitudinal
magnetization of parts. The coil may be of 5 turns.

132. The Coil

133. Components in the stationary unit :
Heads and coil for magnetizing part
Rollers for positioning coil and rotating cylindrical part
Grid for draining liquid in to the storage tank

134. The coil in the unit is heavy. A trolley supports the coil and help
to position at the desired location.

135. The coil which is used in the stationary horizontal unit. The
base is fixed to the roller support. The supply connections
are removed from the heads and connected to the copper
pads of the coil.

136. Roller support for fixing and positioning the coil.
Roller support for rotating cylindrical parts during examination.

137. Attachments for the Contact Heads for holding different types of
test parts during the examination.

138. Small part fixing adapters :
to be attached to main contact heads for holding small diameter parts
and for passing current through them.

139. Motor Pump for re-circulating the particle suspension
through the hose :

140. Mobile Pump and tank system for applying re-circulated
particle suspension through a hose :

141. Bath Circulating Pump, high current generating main
Transformer and control Electronics in the stationary horizontal
unit :

142. UV lighting system in a
Stationary magnetizing
unit :

143. The Coil and the small part adapters mounted on the
Stationary Horizontal unit :

144. Central conductors for magnetizing inside diameter of hollow
parts:
Copper and Aluminum rods of different diameters are generally used as
central conductors.
Steel rods can be used but heating effect and electrical resistance will
increase the load on the machine.
For a given current and rod diameter, magnetic field distribution outside
any electrical conductor is same.

145. The Central conductor arrangement :

146. The Central conductor magnetization of hollow parts.

147. Head shot unit for small parts :

148. The braided contact Heads of the small horizontal machine :

149. Prod magnetizing units : A low voltage, high current transformer for
magnetizing local area of large parts. Provides maximum sensitivity for sub
surface defects when HWDC and dry method is used. Major problem Arc Burn
at the prod contact points.

150. Prod magnetizing units :
During use, current can be switched On or Off by the remote control
switch and is used to minimize arcing at the contact points.

151. Mobile magnetizing Power Units :
For 3000 Amps and above for field use.

152. Mobile Magnetizing Power Units :
For 6000 Amps and above on shop floor use.

153. Mobile Magnetizing Power Units :
For 6000 Amps and above.

154. Permanent magnet :
A pair of strong permanent magnets, separate or mounted in an adjustable
fixture can be used to produce local magnetization in a part. Magnets
produce steady longitudinal field, which does not contribute to particle
mobility, therefore less sensitive for detection of sub surface flaws. Field
strength can not controlled easily.
• Permanent magnets are used
when electric current can not
be used.
• Wet particles are normally
used with this magnet.
Inspection area is centrally 1
inch dia between the poles.
• Qualifying Lifting power 40
lbs or 18.1 kg.
• Useful when the flaw
locations are known.

155. Electromagnetic Yokes :
A laminated soft iron C shaped core is magnetized within a coil and is
used to introduce magnetizing field in the part. AC and HWDC
magnetization are generally used. Yoke eliminates electric arcing problem
of the direct current flow methods.

156. AC / DC Electromagnetic Yoke :
A laminated soft iron C shaped core is magnetized within a coil. The leg
spacing is adjustable.

157. The Electromagnetic Yoke is switched on from a push
switch.:

158. Yoke in use with wet particle aerosol spray can :

159. Electromagnetic Yokes from Parker :
for AC or HWDC local longitudinal magnetization of a part.
AC is used for surface and HWDC for sub surface.
AC operating mode can be used for demagnetizing operation.
• Electric yokes use coils wound
on C shaped laminated soft
iron core.
• Opening of the core [ leg ] is
adjustable.
• Magnetizing field switches off
with the current.
• Required lifting power, 4.5 kg
AC and 18.1 kg DC.
• Recommended Pole spacing
3 to 8 inches.
• Detects surface and sub
surface flaws.

160. Induced Current magnetization :
for rings shaped parts using AC or DC surge current to produce a torroidal
magnetic field.
The ring is used as a short circuit secondary in a transformer
arrangement. Discontinuities along the ring are indicated.

161. Induced Current magnetization :
for rings shaped parts using AC or DC surge current to produce a torroidal
magnetic field.
The ring is used as a short circuit secondary in a transformer
arrangement. Discontinuities along the ring are indicated.

162. A fixture for
Induced Current
magnetization :
for annular discs such as
rotary cutters, DC surge
current is used to produce
a residual circular
magnetic field.
Radial discontinuities on
the face the disc can be
detected.

163. Chain Testing :
by coil magnetization
using Fluorescent particles
as detecting medium.

164. Magnetizing Techniques :
Head shot magnetization [ Circular magnetization by passing
current through the part ]
Coil magnetization [ Longitudinal magnetization by placing
the part within the coil ]
Central conductor [ to magnetize the inside bore of hollow
parts ]
Prod method [ Circular magnetization of local area of a part ]
Permanent magnet [ Longitudinal magnetization of local area
]
Electric yokes [ Longitudinal magnetization of local area ]
Induced current magnetization [ for ring shaped parts ]

165. Head shot magnetization uses AC, HWDC and high current FWDC for
circular magnetization. Current is passed from one end to the other end.
12 to 32 Amps per mm of cross section diameter is recommended. This
technique detects lengthwise discontinuities.

166. Head shot machine for long / heavy parts :
Long parts are tested in 12” increments.
If there is difference in cross section,currents applicable to each cross
section is used in ascending order.

167. Current flow in the conductor produces circular field.
Applicable current 12 – 32 Amps per mm diameter for a circular part.

168. If there is difference in cross section,currents applicable to each cross
section is used in ascending order.

169. Head shot machine for long / heavy parts :
Axle testing using high intensity UV flood lamp under day light condition.

170. An axle surface is being scanned with an UV hand lamp :

171. An axle under examination using ‘Head Shot ‘ magnetization :
[ Circular magnetization ]

172. Coil magnetization of the axle :
[ longitudinal magnetization ]

173. Crack Indication [ fluorescent ] at the head of a bolt
produced by head shot circular magnetization :

174. Testing in a head shot machine : Generally, the suspension is applied
when the magnetizing current is flowing. This is known as continuous
method. For retentive parts suspension may be applied after switching off
the current. This is residual method and is less sensitive.

175. Rotor cracks :
Revealed by head shot technique [ circular magnetization ]
Fin indications at the left are non relevant.

176. Rotor cracks :
detected by
head shot
circular
magnetization.

177. Central conductor magnetization :
Passing current directly through a hollow part does not magnetize the inside
bore. A conductor running through the bore is used to magnetize the inside
surface of ring shaped and hollow parts.
Current is passed through
a conductor which is placed
along the hole of the part
thereby producing a
circular magnetic field
along the inside
circumference of the part.
This technique detects
flaws at the inside surface
and outside surface also if
the part is not too thick.
Current to be selected is 12
to 32 Amps per mm outside
diameter of the part.

178. Central conductor magnetization :

179. Central conductor magnetization :
A gear being tested by central conductor magnetization.

180. Crack detected by central conductor magnetization :
A central conductor or a flexible cable can be used to magnetize this part

181. Central Conductor magnetization :
[ in this case, conductor is offset ]. Used for testing Nuts, Rings and hollow
Cylindrical parts.

182. Close up view of central conductor magnetization :
[ in this case, conductor is offset ].

183. Crack indications [ marked by white circles ] produced
by central conductor Magnetization :
Magnetized by a cable through the hole.

184. Cracks around the holes[ within red marks ] revealed by central
conductor magnetizing technique :
white contrast used to enhance the indications.

185. A helical spring can be tested by central conductor magnetization.

186. Using a coil [ low fill factor ] :
Coil may be large or small and have 3 to 5 turns.
For a coil, Flux density is maximum near the inside surface of the
coil.Smaller parts are to be positioned near the inside wall of a large coil.

187. Coil magnetization of small parts [ low fill factor ]:
When length predominates.

188. Coil magnetization of small
parts :
When length predominates.
A part can be longitudinally
magnetized by placing it within a coil
Current I is
NI = 45,000/ [ L / D ]
N number of turns in coil
L length of the part
[ max 18” ]
D diameter of the part.
For long parts, test is carried
out with increments of 18”

189. Close up view of coil magnetization :

190. Coil magnetization by flexible cables :
A flexible Cable can be wrapped around a part to produce local
longitudinal magnetization. The current may be taken from a prod
machine.

191. Coil magnetization by flexible
cables :
Cable wrapped around the Lug for
longitudinal magnetization.

192. Flexible cable being used for magnetizing a crane hook :

193. Prod magnetization machines :
A transformer provides the current and a pair of prods are used to pass
current and produce local circular magnetization in the part.

194. Prod contacts and remote control switch :
A pair of prod contacts for single handed operation. The current carrying
cables are to be screwed into the terminals.

195. Copper Prod contacts and remote control switch :

196. Copper Prod contacts and accessories :

197. Braids for Copper Prod contacts for minimizing arc burn :

198. Prod magnetic field :
Circular magnetic field generated by prod contacts are revealed by
sprinkling iron powder.

199. Prod technique of
magnetization :

200. Prod placement for weld testing :

201. Prod placement for weld testing :

202. A prod unit detected a crack on a welded test plate :
Dry powder indication on white contrast paint.

203. A Flat coil attachment for prod units for longitudinal
magnetization of small parts :
Very useful for testing fasteners like parts.

204. A Split coil attachment for prod units for longitudinal
magnetization of ends of tubular parts :
Useful for detection of lamination at pipe ends. The ends snap fit to form a
multiple turn continuous loop.

205. Cable Clamps for prod units for hands free operation :
• The ends snap fit to form a
multiple turn continuous loop.

206. A C-shaped strong permanent magnet can be used to produce
longitudinal magnetization in a local area of a part :

207. The permanent magnet contains two very powerful magnets
fixed in an adjustable fixture.

208. Permanent Magnets :
Crack on a plate surface detected by permanent magnets.

209. Permanent Magnets :
A pair of strong permanent magnets,
such as Neodymium – Iron - Boron,
suitably mounted, is useful for detecting
surface cracks on Ferro magnetic parts.

210. Permanent Magnets :
A pair of strong permanent
magnets, such as Neodymium –
Iron - Boron, suitably mounted,
is useful for detecting surface
cracks on ferro magnetic parts.

211. A surface crack detected by a permanent magnet.

212. A section of a part can be locally magnetized by placing two strong
magnets of opposite poles 3 to 8 inches apart.

213. Dry powder indication :
A Corner Crack detected by the magnets using red dry powder.

214. The electric yoke set:
Yokes can be powered by mains or a battery.

215. Controls of electromagnetic yoke.

216. A coil system generates the magnetic field in the core.

217. The coil is wound around the core.

218. Magnetic field of yoke :
produce a longitudinal magnetic field between the poles and radial field at the
poles. A single pole can be used to introduce a radial field.

219. Magnetic field of
yoke :
produce longitudinal
magnetic field between
the poles and leakage
field for surface and
near surface defects.

220. Test bar for checking lifting power of yokes :
A yoke is qualified by its weight lifting power.

221. A Yoke test bar with an artificial crack :
Can be used to check the performance of an yoke.

222. Test piece for yokes :
Small holes drilled at different depth [ 1 to 6 mm hole centers ] from the
surface is used to check the sensitivity of the Yoke – Particles
combination.

223. Indications from the holes by HWDC magnetization.

224. Yoke in use for testing weld:

225. Testing a crane hook with dry powder.

226. Testing a gear with dry powder.

227. Yoke in use for
testing a T joint.

228. Channel testing using an Yoke :

229. Welded Channel testing using an Yoke :

230. Axle testing using an Yoke :

231. Weld testing with yoke :
white contrast paint applied on the weld to improve the contrast of
indications.

232. Weld testing with yoke :
white contrast paint applied on the weld to improve the contrast of
indications.

233. Wire rope coupling testing with yoke :
white contrast paint applied on the weld to improve the contrast of the
indications.

234. Castings being tested with an yoke :
white contrast paint applied on the weld to improve the contrast of

235. Castings being tested with an yoke :
white contrast paint applied on the weld to improve the contrast of

236. To detect flaws of all orientation, Yoke is to be placed twice in
every test area, 900 to each other :

237. Yoke in use :
testing a crankshaft. AC is preferred for this application because of
irregular contour of the part.

238. Inspection
Booth with
hood for
fluorescent
examination
and a de -
magnetizing
tunnel for
small parts.

239. Unit for multidirectional magnetization of small / long parts :

240. Discontinuity Indications :
The interruption of normal physical structure in the material is defined as
discontinuity. Any discontinuity which is identified as not acceptable is a
defect.
The build up of iron powder attracted by a leakage field causes indication.
Indications are classified as Linear or Rounded, based on the formation of
powder pattern.

242. Network of cracks [ wet fluorescent method ]:

243. Crack :

244. Crack indications using Fluorescent powders :

245. Crack indications using black powders :

247. Crack indication on a rolled bar

248. The crack on the rolled bar.

249. Crack indications using Fluorescent powders :

250. Crack
indications at
nozzle weld :

251. Crack indications
using Fluorescent
powders :

252. A large Crack indication on a weld :

253. Crack indications on forged steering wheel :
Black & white image.

254. Casting cracks :

255. Casting cracks :

256. Crack indications on crane hook :

257. Crane Hook & crack indication:

258. Crack detected on a crane hook :

259. Crack detected on a crane hook :

260. Crack indications on a crank shaft.

261. Crack detected on a cast part.

262. Crack detected on a machined part.

263. Yoke placement for a weld.

264. Yoke positioned on the weld.

265. A Cross yoke for one step magnetization.

266. Gear & crack indication :

267. Cracks on a gear face.
Teeth indications are non relevant.

268. Central conductor magnetization :
Cracks on the face of a ring.
Fluorescent indications/ Black and White photograph.

269. Central conductor magnetization of rings :
Cracks on the rim of a ring.
Fluorescent indications.

270. Weld cracks detected by brown dry powder as indicator :

271. Fluorescent indications of weld cracks :

272. Longitudinal Crack in weld :
yoke magnetization with brown dry powders.

273. Longitudinal Crack in weld :
yoke magnetization with brown dry powders.

274. Longitudinal Crack in weld :
yoke magnetization with brown dry powders.

275. Longitudinal Crack in weld :
yoke magnetization with brown dry powders.

276. Longitudinal Crack in weld :
yoke magnetization with brown dry powders.

277. Longitudinal Crack in weld :
yoke magnetization with brown dry powders.

278. Longitudinal Crack in weld :
black powder indication with wet method.

279. Machined Parts [ Man Hole ] :
of a crack, detected by central conductor.

280. Fluorescent indications on a machined manhole :

281. Crack Indication :

282. Fluorescent indications :
of a crack, detected by central conductor.
Indications at the base of projections are non relevant indications.

283. Crack on a connecting rod :
Fluorescent indication.

284. Crack on a connecting rod :
Fluorescent indication.

285. Magnetic particle indication of IGSCC :

286. Magnetic particle indication :
Crack indication on structural revealed by fluorescent powders.
Longitudinal magnetization.

287. Pipe Ends :
Laminar defect on the face of the pipe revealed by fluorescent powders.

288. Relevant and Non - relevant Indications :
• Relevant indications are
produced by
discontinuities such as
the crack.
• Non relevant indications
are produced by leakage
fields or discontinuities
not relevant to the
examination such as
corners, drilled hole near
the surface etc.

289. Surface marks which may produce non relevant
indications.

290. Relevant and non-relevant indications :
Fluorescent indication.

291. Relevant and Non - relevant Indications :

292. Relevant and Non - relevant Indications :

293. Relevant and Non - relevant Indications :

294. Relevant and Non - relevant Indications :

295. Material Failure :

296. Crack :

297. Inter Granular Stress Corrosion Cracking :

298. Forging burst :

299. Crack revealed after machining :

300. Crack revealed after machining :

301. Crack emnating from the hole.

302. A cracked component :

303. A cracked component :

304. A cracked Rail :

305. Cracks around a bolt hole :

306. A cracked
Ring :

307. A cracked component :

308. A cracked weld :

309. Test sensitivity :

310. ASTM Pie Gauge / Field indicator :
Indicates qualitative strength of the magnetizing field.
• 8 carbon steel triangles are
brazed together.
• The brazing deposit being non
magnetic simulates a
discontinuity.
• Indicates the adequacy of the
Magnetizing field.
• Does not indicate test sensitivity.

311. Pie gauge :
Brazing lines are clearly visible.

312. Pie gauge :
Brazing lines are clearly visible.

313. Brazing lines are covered
with a .010” thick copper
plate. The indications are
checked on the copper
face during check.

314. A pie gauge is being used with an yoke :
Brazing line indications with dry particles. Adequacy of magnetizing field is
indicated by formation of clear indications

315. A pie gauge is being used with an yoke :
Brazing line indications with dry particles. Adequacy of magnetizing field is
indicated by formation of clear indications

316. Fluorescent indications on the Field Indicator :

317. Castrol stripes :
Consists of an iron foil with three slits, sandwiched between two brass
foils.

319. Indications of the three slits on the castrol strip :

320. Qualitative Quantity Indicator shims :

321. Hall effect field meter :
for measuring magnetizing and residual fields using a hall effect electronic
sensor.

322. Hall effect field meter :
with sensor and zero field chamber.

323. Hall effect field meter and accessories :

324. Reference Magnets for checking field
meter calibration :

325. Hall effect field meter with sensor :

326. Coil for De-magnetization :
De magnetizing field may be 5000 to 10000 ampere-turns.

327. Coil De-magnetization :
De-magnetizing coil with motorized conveyor system. The part to be
demagnetized is passed through the coil opening while the alternating
current is flowing.

328. Coil De-magnetization :
A connecting rod is passing through the de magnetizing coil.

329. Large de-magnetization coil:
De-magnetizing coil with conveyor system for large parts. Field may be up
to 10,000 ampere-turns.

330. Small de-magnetization coil:
De-magnetizing coil with conveyor system for large parts. Field may be up
to 10,000 ampere-turns.

331. Heavy duty de-magnetization unit with round tunnel :

332. Heavy duty de-magnetization unit with square tunnel :

333. Inspection
and
demagnetizati
on of small
parts:
De-
magnetizing
coil attached
to the table.

334. Residual field meter :
is used for measuring residual
magnetic field before and after
demagnetization. Residual field after
De-magnetizing may be reduced to
less than 3 Gauss. Field is to be
measured at corners of the part.

335. Gauss meter :

336. Using a Residual field meter :
Field is to be measured at the ends and the corners of the part, where the
leakage field is maximum.

337. Residual field meter :
for measuring residual magnetic field before and
after demagnetization.

339. Demagnetization :
by wrapping coil around the part.
• Large objects such as a pipe
is difficult to demagnetize.
The residual field may create
arc blow during welding.
In such case, an A,C. de
magnetizing field is applied
simultaneously during the
welding operation.

340. Ultraviolet light :

341. 100 – 125 watts low power bulbs use internal deep purple coating
as ultraviolet and visible light filter.

342. High power bulbs. Requires external koop filter.

343. Koop filters for use with high power ultraviolet lamps.

344. Koop filters for use with high power ultraviolet lamps.

345. UV light meter :
for qualifying UV light intensity.
• UV light meter.
• For measurement
of ultraviolet
intensity in µW/Cm2
at the test surface.
• Minimum
1000 µW/Cm2 is
required at the
examination
surface,

346. UV / Vis light meter :
for measuring UV and
Visible light intensity.

347. Fluorescent Inspection Booth :
Small movable unit for fluorescent particle inspection.
• A darkened booth
using black curtains for
working with
fluorescent particles.

348. Fluorescent Particles :
Magnetic particles coated
with a fluorescent dye,
absorbs ultraviolet light and
emits brilliant yellow-green
or orange-red visible light.
• Absorbs energy near 365nm
and releases at 525 to 575
nm visible light.
• Small indications can be
seen easily.
• Examination is performed in
a darkened area of max 20
Lux visible light.

349. Fluorescent glow.

350. End of Slides