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NDT Level-3 ( Pual E. Mix - By Wilay & Sons) > 3- Electromagnetic Testing Method > Flashcards

3- Electromagnetic Testing Method Flashcards

1
Q

Eddy current testing involves the use of ,,,,, and can be applied to any ,,,,

A

alternating magnetic fields

conductor

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2
Q

Leakage flux testing involves the use of a

,,,, and can be applied only to ,,,,

A

permanent magnet, DC or AC electromagnetic fields,

ferromagnetic materials

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3
Q

Ferromagnetic materials are the materials that are ,,,, They are able to create ,,,,,.

A

magnetic

permanent magnets

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4
Q

In eddy current testing, the alternating magnetic field sets up ,,,,, in the test part

A

circulating eddy currents

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5
Q

The magnetoelastic technique is used for characterizing and determining the amount of residual stress in magnetic materials by ,,,,, or ,,,,,

A

measuring magnetic

“Barkhausen noise.”

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6
Q

Eddy Current and magnetoelastic techniques an be combined with other methods, such as ,,,,, and ,,,,, to achieve multifunction high-speed testing

A

ultrasonic testing

laser dimensional measuring

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7
Q

High-speed automatic testing is possible using multiple ,,,,

A

NDT methods

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8
Q

When an alternating current is used to excite a coil, an ,,,, field is produced and magnetic lines of flux are concentrated at the ,,,, of the coil.

A

alternating magnetic

center

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9
Q

as the coil is brought near an electrically conductive material, the ,,,,,, penetrates the material and generates continuous, ,,,,,,

A

alternating magnetic field

circular eddy currents

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10
Q

As the penetration of the induced field

increases, the eddy currents become ,,,,,

A

weaker

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11
Q

The induced eddy currents produce an in a test coil,,,,,

A

opposing (secondary) magnetic field

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12
Q

The opposing magnetic field of, coming from the material, has a weakening effect on the ,,,,, and the test coil can sense this ,,,,

A

primary magnetic field

change.

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13
Q

In effect, the impedance of the test coil is ,,,proportionally as eddy currents are increased in the test piece.

A

reduced

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14
Q

A crack in the test material ,,, the eddy current flow ,,,,, the eddy current path, ,,,,, the secondary magnetic field, and increases the coil ,,,,,

A

obstructs
lengthens
reduces
impedance

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15
Q

Changes in magnetic flux density may also be detected by ,,,,, devices,

A

Hall effect

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16
Q

the conductivity of a material has the greatest effect on coil ,,,,,

A

impedance

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17
Q

Coil impedance is dependent on the vector sum of the coil’s ,,,,,, and the test part’s resistance to the ,,,,,

A

inductive reactance

eddy current field.

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18
Q

Another important influence on coil impedance is the clearance or lift-off between the ,,,, and the,,,,

A

coil

conductive material surface

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19
Q

coil impedance remains unchanged regardless of any conductivity changes in the ,,,,

A

material

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20
Q

as the coil approaches the surface in the stepwise fashion, ,,,,,,eddy currents are induced in the material

A

stronger

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21
Q

When attempting to measure changes in conductivity, changes in spacing or lift-off are highly ,,,,,

A

undesirable

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22
Q

In order to minimize variations in lift-off, eddy current coils may be recessed a,,,,, into the eddy current probe head, and the probe head may be ,,,, to maintain surface contact

A

short distance

spring loaded

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23
Q

However, since the lift-off effect is ,,,, over a limited probe clearance range, eddy current probes can
be designed to measure ,,,,, coating thickness over uniformly conductive materials.

A

linear

nonconductive

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24
Q

Coil impedance can be calculated for any known combination of ,,,,, and ,,,,,

A

conductivity

probe clearance

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25
Q

The planar diagram shows that it is more difficult

to distinguish between ,,,, and ,,,,, with low conductivity materials.

A

defect indications

lift-off indications

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26
Q

,,,,,, coils are used more frequently than surface-mounted coils

A

Encircling

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27
Q

The degree of filling is the ratio of the ,,,, to the ,,,,,

A

test material cross-sectional area

coil cross-sectional area

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28
Q

For most applications, two coils are employed—the primary (field) coil generates the ,,,,, and the secondary (pickup) coil detects the ,,,,,,caused by the changes in conductivity and permeability

A

eddy currents

change in coil impedance

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29
Q

Eddy currents are generated in the material in accordance with ,,,,,

A

Maxwell’s law

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30
Q

according to Lenz’s law, these eddy currents must flow

in the ,,,,, to the current in the field coil

A

opposite direction

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31
Q

the magnitude of the eddy current depends on ,,,,,,of the test part

A
  • frequency of the field current,
  • conductivity and permeability of the test material,
  • and geometry
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32
Q

When ferromagnetic materials are magnetized, magnetic lines of force (or flux) ,,,,, through the material and complete a ,,,, between the pole pieces.

A

flow

magnetic path

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33
Q

These magnetic lines of flux,,,, from zero at the center of the test piece and,,,, in density and strength toward the outer surface

A

increase

increase

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34
Q

By measuring the ,,,,,,of this leakage flux, we can

determine to some extent the severity of the defect

A

intensity

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35
Q

heavy buildup of magnetic particles is a ,,,,,pattern at the poles

A

three-dimensional

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36
Q

All of the fine magnetic particles near the magnets are drawn to the ,,,,, pieces

A

pole

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37
Q

The ideal permanent magnet should be easy to magnetize and hard to ,,,

A

demagnetize

38
Q

If the material is not ,,,,,, some flux may also exit the far surface

A

too thick (<0.3in.)

39
Q

For longitudinal flaw detection on round bars and tubes, a ,,,, yoke DC-MFL system is used.

A

rotational

40
Q

for longitudinal and round bar/tube, The magnetic poles of the yoke are ,,,, apart with a series of magnetic sensors ,,,,,from the poles

A

180° degree

90°

41
Q

Transverse flaws are detected by passing the tube through a ring yoke that produces ,,,,,,,magnetization

A

longitudinal

42
Q

The frequency of the alternating field is about ,,,, to ,,,

A

1 to 30kHz

43
Q

Increases in intensity increase the depth of ,,,,,

A

saturation

44
Q

with the differential coil (two-coil) system, the magnetic

lines of flux in the coils (shown by directional arrows) ,,,, each other

A

oppose

45
Q

The differential method is also known as the self-,,,,, method because the adjacent sections of the material are compared to each other

A

comparison

46
Q

The crack distorts the eddy currents, weakens the ,,,,, and increases the,,,,, and ,,,,,, of the pickup coil

A

primary magnetic field

impedance and voltage output

47
Q

crack distorts the eddy current ,,,,,

A

path

48
Q

Wide coils are used to measure ,,,, and narrow coils are used ,,,, detection

A

changes in conductivity

primarily for flaw

49
Q

The majority of Flux Leakage sensors are ,,,,,or ,,,,,

A

inductive coil sensor

solid-state Hall effect sensors

50
Q

For an induction coil to detect a magnetic field, the magnetic field must be,,,,,,, or ,,,,,

A

alternating or pulsating

51
Q

A greater electromotive force (emf) will be induced into

the coil if the number of turns of wire is ,,,,,,,

A

increased

52
Q

,,,,,,,probes are popular magnetic flux measuring devices

A

Hall effect

53
Q

,,,,,,,,, is described as, strong magnetic fields skewed the equal potential lines in a conductor, thus producing a miniature voltage perpendicular to the direction of current flow

A

Hall effect

54
Q

Hall effect principle:
When a current-carrying conductor is placed in a magnetic field, a ,,,,, is produced, which is,,,,,,, to both the direction of current and the magnetic field.

A

Hall voltage

perpendicular

55
Q

Since a 1 gauss (G) field produces a Hall voltage of about ,,,,,

A

30 mV

56
Q

The more highly magnetized the ferromagnetic object, the higher its ,,,,,, will be for a given defect.

A

leakage flux field intensity

57
Q

longitudinal defects in tubes, rods, and bars will be

more easily detected with ,,,, magnetic fields

A

circular

58
Q

For typical Hall effect probes, operating speed is listed as ,,,,,maximum

A

100kHz

59
Q

Test Frequency:

test frequency affects the ,,,,, of the coil

A

inductance

60
Q

Test Frequency:

Lowering the test frequency ,,,, the depth of eddy current penetration

A

increases

61
Q

Test Frequency:

Lower test frequencies are typically used with ,,,,, materials because of their,,,,,,

A

ferromagnetic

low permeability

62
Q

Test Frequency:
At a fixed frequency, eddy current penetration
will be the ,,,,, in a metal with the ,,,,,,, International Annealed Copper Standard (% IACS) conductivity

A

greatest

lowest-percentage

63
Q

Test Frequency:
,,,,,, is the frequency at which additional increases in frequency do not produce additional increases in eddy current losses.

A

The limit frequency

64
Q

Test Frequency:

The limit frequency is also known as the ,,,,,,frequency of the material

A

“characteristic”

65
Q

Test Frequency:

If the characteristic frequency is 100Hz, the test frequency that is required for an f/fg ratio of 10 is ,,,,,,

A

1.0kHz.

66
Q

MFLT;

A

MAGNETIZATION FOR FLUX LEAKAGE TESTING

67
Q

MFLT;

for MFLT testing to be effective, ferromagnetic parts must be magnetized to ,,,,,,,

A

saturation

68
Q

MFLT:

Magnetic lines of flux exit the ,,,,, pole of a magnet and enter the ,,,,, pole

A

north

south

69
Q

MFLT:

units of flux density will be given in ,,,, units or ,,,,

A

centimeter gram second (cgs)

gauss (G)

70
Q

MFLT:

The characteristics of magnetic materials can be described by reference to ,,,,,or,,,,,,,

A

the materials’ magnetization or hysteresis curves

71
Q

MFLT:

magnetization curve is a plot of,,,,,,,, on the vertical axis as a function of ,,,, on the horizontal axis

A 
flux density (B) in guass
magnetizing force (H) in oersteds
72
Q

MFLT:

In a magnetizations curve, Non magnetized ferromagnetic material is represented by the origin, ,,,

A

point 0,0

73
Q

MFLT:
In a magnetization curve, As this material is gradually
subjected to increasing magnetizing force, the magnetic flux density in the material increases from ,,.to ,,,,,

A

0 to Bmax

74
Q

MFLT:
In a magnetization curve, The force required to demagnetize the ferromagnetic part is known as the ,,,,,and the second quadrant of the magnetization curve is known as the ,,,,,

A

coercive force

coercive demagnetization curve.

75
Q

MFLT:
In a magnetization curve, The permeance or permeability (m) of a magnetic material depends on many factors, but for any set of conditions is defined as the ,,,,,

A

ratio of B/H

76
Q

MFLT:

In a magnetization curve, As a general rule, hard materials have a ,,,, force and are not easily demagnetized

A

high coercive

77
Q

Coupling:

In eddy current testing, the test piece is coupled to the test coil by the ,,,,,,

A

coil’s magnetic field

78
Q

Coupling:

coupling efficiency is 100% when lift-off is ,,,,,

A

zero

79
Q

Coupling:

Lift-off describes the change in electromagnetic coupling as a function of ,,,,,,

A

probe clearance

80
Q

Coupling:

,,,,,,,changes both the amplitude and phase of the eddy current signal

A

Lift-off

81
Q

EMT

A

Electromagnetic Testing

82
Q

EMT:

,,,,,,, produced by DC saturation coils, is used when ferromagnetic materials are tested with encircling coils

A

Direct current (DC) saturation

83
Q

EMT:
When a coil’s magnetizing force is applied to ferromagnetic materials, the flux density in the material is much than the flux density generated by the test coil

A

greater

84
Q

EMT:

the eddy current test coil detects the leakage flux emanating from ,,,,,, and,,,,,, defects.

A

small surface and near surface

85
Q

EMT:
Increases in alternating current field strength
decrease the eddy current ,,,, in magnetic materials to some minimum value.

A

penetration

86
Q

EMT:

When magnetic penetration is maximized, the part is magnetically ,,,,,,

A

saturated

87
Q

MFLT:

A

MAGNETIC FLUX LEAKAGE TESTING

88
Q

MFLT:

The magnetic flux leakage method is ,,,,,, and recommended by the ,,,,, for tubes with ,,,,, to,,,, wall thickness

A

dry, fast, online
API
small to medium

89
Q

MFLT:

,,,,,, is used over the entire cross section of pipes transversely for ,,,,,,,,and ,,,,,,,, flaws

A

DC field magnetization

internal and external

90
Q

MFLT:
,,,,,, describes magnetic flux leakage as the most efficient method for integration of an automated, nondestructive test for detecting ,,,, flaws during
the production of ,,,,,,, tubes.

A

ASTM E 570
rolling
seamless, hot-rolled

91
Q

GECA

A

General Eddy Current Applications

92
Q

GECA:

General eddy current applications can be further subdivided into applications:

A
  • Measurement of physical property differences
    ( such as; flaws & thickness)
  • Measurement of parameters relating more to
    conductivity (such as; hardness)
  • Application of permeability changes in ferromagnetic
    parts

NDT Level-3 ( Pual E. Mix - By Wilay & Sons) (14 decks)

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