Electromagnetic Testing Chapter 3- Electromagnetic Testing

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3.17 BARKHAUSEN NOISE/MICROMAGNETIC TESTING The Barkhausen noise/micromagnetic testing method characterizes and determines the amount of residual stress in magnetic materials by measuring Barkhausen noise (BN). BN measuring instruments measure positive and negative stress units in N/mm 2 , ksi, or relative magnetoelastic parameter (MP) units. MP units over the range of 0 to 140 correspond to a stress range of about -650 to +450N/mm 2 .Tensile stresses are positive and compressive stresses are negative. Charlie Chong/ Fion Zhang
3.17.1 Introduction In 1911, Dr. Heinrich G. Barkhausen became the world’s first professor in the Communications Branch of Electrical Engineering at Dresden’s Technical Academy. He worked on the theories of spontaneous oscillation and nonlinear switching elements. He also formulated electron-tube coefficients and experimented with acoustics and magnetism, which led to his discovery of the Barkhausen effect in 1919. In 1920 Barkhausen and Karl Kutz developed the Barkhausen-Kutz ultra high-frequency oscillator, which eventually led to the development of the microwave tube. Barkhausen learned that a slow, smooth increase in magnetic field applied to a ferromagnetic material caused it to become magnetized in a series of minute steps. 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
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3.3 EDDY CURRENT SENSING PROBES For
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As the probe moves over the defect,
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Figure 3.17 Differential surface co
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Figure 3.19 shows an encircling coi
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The application of eddy current sen
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Baffles and tube sheets. Charlie Ch
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Another important consideration for
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3.4.1 Induction Coils For an induct
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If the diameter of a surface coil i
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3.4.2 Hall Effect Sensors Hall effe
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Figure 3.21 illustrates the Hall ef
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Hall voltage Charlie Chong/ Fion Zh
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Since a 1 gauss (G) field produces
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Figure 3.22 Effect of magnetic fiel
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3.5 FACTORS AFFECTING FLUX LEAKAGE
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Defect & Flux Distribution Charlie
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The distance between adjacent defec
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3.6 SIGNAL-TO-NOISE RATIO The signa
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With flux leakage testing, signal-t
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As shown in Eq. (3.6), test frequen
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The characteristic frequency for a
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Charlie Chong/ Fion Zhang
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Figure 3.23 Magnetization or magnet
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By taking the product of B and H fo
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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
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Page 135 and 136: 3.11 INSTRUMENT DESIGN CONSIDERATIO
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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
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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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Page 175 and 176: Permanent magnets are the preferred
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Page 183 and 184: Typical roll failures are caused by
Page 185 and 186: This technique has been found to be
Page 187 and 188: Figure 3.38 A comparison of Barkhau
Page 189 and 190: Figure 3.39 Three-channel Rollscan
Page 191 and 192: The appropriate depth of measuremen
Page 193 and 194: 3.17.5 Calibration and Testing Bark
Page 195 and 196: Comparative studies by Kirsti Titto
Page 197 and 198: 3.17.6 Current Applications Barkhau
Page 199 and 200: 3.17.9 Pipe/Tubing/Sheet/Plate Manu
Page 201 and 202: EMATs overcome many common ultrason
Page 203 and 204: 3.18.1 EMATs Advantages Over Piezoe
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Page 207 and 208: Figure 3.44 Courtesy of Weld Inspec
Page 209 and 210: 3.19 ALTERNATING CURRENT FIELD MEAS
Page 211 and 212: 3.19.1 Acfm Principles Of Operation
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Page 215 and 216: 3.19.2 Bx and Bz Components The pre
Page 217 and 218: 3.19.3 Butterfly Plot To aid interp
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Page 225 and 226: Other applications include: • Ins
Page 227 and 228: 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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