Electromagnetic Testing Chapter 3- Electromagnetic Testing

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If the magnetizing force is now gradually decreased to zero, the flux density decreases to point B r , which represents the residual flux density remaining in the material after the magnetizing force has been removed.The ferromagnetic part now has a significant amount of residual induction or magnetism. This condition represents the second condition under which satisfactory leakage flux testing can be done. If the magnetizing force is reversed in direction and gradually increased again, the residual magnetism can be reduced to zero point H c . The force required to demagnetize the ferromagnetic part is known as the coercive force and the second quadrant of the magnetization curve is known as the coercive demagnetization curve. In general, ferromagnetic parts should be demagnetized after flux leakage testing to assure that they do not attract minute iron particles that might interfere with subsequent machining operations. Charlie Chong/ Fion Zhang
By taking the product of B and H for every point on the demagnetization curve and plotting it against B, an energy product curve similar to the one shown in Figure 3.24, can be obtained. The peak energy product in million gauss-Oersted provides one important way of comparing magnetic materials. The permeance or permeability (m) of a magnetic material depends on many factors, but for any set of conditions is defined as the ratio of B/H. In many cases, it is possible to control the quality of ferromagnetic components by automatic measurement of coercive field strength because the coercive force is affected by alloy composition, structure, particle size, nonferrous inclusions, manufacturing techniques, heat treatment, and internal and external magnetic stresses. As a general rule, hard materials have a high coercive force and are not easily demagnetized. For automatic measurement of coercive force, the ferromagnetic parts are first magnetized to saturation with direct current pulses and an impulse coil arrangement. Magnetizing current in the coil is gradually reduced to zero, reversed, and increased until the residual flux density passes through zero. Charlie Chong/ Fion Zhang
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Electromagnetic Testing Chapter 3-
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Submarine Applications Charlie Chon
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Fion Zhang at Shanghai 6th April 20
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IVONA TTS Capable. Charlie Chong/ F
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Chapter 3. ELECTROMAGNETIC TESTING
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Barkhausen effect The Barkhausen ef
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Barkhausen Noise Charlie Chong/ Fio
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Figure 3.1 Eddy current principle.
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Figure 3.2 Schematic diagram of bas
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Figure 3.3 The effect of conductivi
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Figure 3.3 The effect of conductivi
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Another important influence on coil
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If the conductivity of the material
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Figure 3.5 The effect of a crack on
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FIGURE 8-49 Conductivity curve: (a)
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So far, we have described how eddy
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Figure 3.6 The effects of (a) condu
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3.1.2 Limiting Frequency f g of Enc
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Figure 3.7 The effect of degree of
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Charlie Chong/ Fion Zhang
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Eddy Current Heating Charlie Chong/
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Eddy Current Heating Charlie Chong/
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Eddy currents weaken the original m
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3.2 MAGNETIC FLUX LEAKAGE THEORY Wh
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3D Magnetic Field Charlie Chong/ Fi
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3D Magnetic Field Fig.1 THE PRINCIP
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Based on what we have learned about
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Charlie Chong/ Fion Zhang Figure 3.
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Magnetic Field - Simple Semi Ellipt
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Flux leakage sensors have small dia
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The frequency of the alternating fi
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Figure 3.14 Rotating magnet arrange
Page 71 and 72: 3.3 EDDY CURRENT SENSING PROBES For
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Page 75 and 76: Figure 3.17 Differential surface co
Page 77 and 78: Figure 3.19 shows an encircling coi
Page 79 and 80: The application of eddy current sen
Page 81 and 82: Baffles and tube sheets. Charlie Ch
Page 89 and 90: Another important consideration for
Page 91 and 92: 3.4.1 Induction Coils For an induct
Page 93 and 94: If the diameter of a surface coil i
Page 95 and 96: 3.4.2 Hall Effect Sensors Hall effe
Page 97 and 98: Figure 3.21 illustrates the Hall ef
Page 99 and 100: Hall voltage Charlie Chong/ Fion Zh
Page 101 and 102: Since a 1 gauss (G) field produces
Page 103 and 104: Figure 3.22 Effect of magnetic fiel
Page 105 and 106: 3.5 FACTORS AFFECTING FLUX LEAKAGE
Page 107 and 108: Defect & Flux Distribution Charlie
Page 109 and 110: The distance between adjacent defec
Page 111 and 112: 3.6 SIGNAL-TO-NOISE RATIO The signa
Page 113 and 114: With flux leakage testing, signal-t
Page 115 and 116: As shown in Eq. (3.6), test frequen
Page 117 and 118: The characteristic frequency for a
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Page 121: Figure 3.23 Magnetization or magnet
Page 125 and 126: The rate of change of the opposing
Page 127 and 128: Figure 3.25 Encircling coils establ
Page 129 and 130: Figure 3.27 DC-MFL sensor illustrat
Page 131 and 132: Fill factors apply only to encircli
Page 133 and 134: For best results with encircling co
Page 135 and 136: 3.11 INSTRUMENT DESIGN CONSIDERATIO
Page 137 and 138: Charlie Chong/ Fion Zhang Figure 3.
Page 139 and 140: TABLE 3.2. Comparison of Instrument
Page 141 and 142: Some general categories of equipmen
Page 143 and 144: Figure 3.29 UniWest-454 EddyView mu
Page 145 and 146: Scanner operation uses a separate c
Page 147 and 148: Figure 3.30 E-Lab model US-450 full
Page 149 and 150: 3.12.3 ETC-2000 Scanner Because of
Page 151 and 152: ETC-2000 scanner features include:
Page 153 and 154: 3.13 INSTITUT DR. FOERSTER Institut
Page 155 and 156: It is possible to provide 100% eddy
Page 157 and 158: Figure 3.33 ET testing of hot coppe
Page 159 and 160: For maximum sensitivity, the Circog
Page 161 and 162: 3.14 MAGNETIC FLUX LEAKAGE TESTING
Page 163 and 164: ASTM E 570 describes magnetic flux
Page 165 and 166: Charlie Chong/ Fion Zhang Figure 3.
Page 167 and 168: Applications involving physical par
Page 169 and 170: Inexpensive 60 Hz eddy current comp
Page 171 and 172: 4. Measure the length of nonwelded
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Some general applications for the f
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Permanent magnets are the preferred
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Robot Charlie Chong/ Fion Zhang
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3.17.1 Introduction In 1911, Dr. He
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3.17.2 Early Applications Stresses
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Typical roll failures are caused by
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This technique has been found to be
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Figure 3.38 A comparison of Barkhau
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Figure 3.39 Three-channel Rollscan
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The appropriate depth of measuremen
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3.17.5 Calibration and Testing Bark
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Comparative studies by Kirsti Titto
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3.17.6 Current Applications Barkhau
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3.17.9 Pipe/Tubing/Sheet/Plate Manu
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EMATs overcome many common ultrason
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3.18.1 EMATs Advantages Over Piezoe
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3.18.3 Recent Applications And Deve
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Figure 3.44 Courtesy of Weld Inspec
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3.19 ALTERNATING CURRENT FIELD MEAS
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3.19.1 Acfm Principles Of Operation
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Figure 3.45 Current flow and induce
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3.19.2 Bx and Bz Components The pre
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3.19.3 Butterfly Plot To aid interp
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3.19.4 Probe Design Standard ACFM p
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Figure 3.48 Flowchart selection of
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3.31 APPLICATIONS One active encode
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Other applications include: • Ins
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Eddy Current Testing at High Temper
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Good Luck Charlie Chong/ Fion Zhang
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Electromagnetic Testing Chapter 3- Electromagnetic Testing

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