Electromagnetic Testing Chapter 3- Electromagnetic Testing

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With integrated Hall effect transducers, voltage or current regulation, temperature compensation, output voltage ratioing, current sinking, and digital (on/off) outputs from Schmitt triggers can be provided. In addition, these transducers can be used with biasing magnets and interfaced with other amplifiers, comparators, or computers in thousands of applications. Other methods of detecting magnetic flux leakage include the magnetic powder method, the oldest known method, and the magnetic rubber method, which is relatively new. Charlie Chong/ Fion Zhang
3.5 FACTORS AFFECTING FLUX LEAKAGE The more highly magnetized the ferromagnetic object, the higher its leakage flux field intensity will be for a given defect. Both continuous and residual magnetic fields can be used. However, leakage flux testing should not be used with ferromagnetic objects that have weak residual fields and poor retentivity because test sensitivity may be too low to detect small discontinuities. The amount of leakage flux produced depends on defect geometry. Broad, shallow defects will not produce a large vertical component of leakage flux; neither will a defect whose long axis is parallel to the lines of flux in the test object. For these reasons, longitudinal defects in tubes, rods, and bars will be more easily detected with circular magnetic fields. 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
Page 53 and 54: 3.2 MAGNETIC FLUX LEAKAGE THEORY Wh
Page 55 and 56: 3D Magnetic Field Charlie Chong/ Fi
Page 57 and 58: 3D Magnetic Field Fig.1 THE PRINCIP
Page 59 and 60: Based on what we have learned about
Page 61 and 62: Charlie Chong/ Fion Zhang Figure 3.
Page 63 and 64: Magnetic Field - Simple Semi Ellipt
Page 65 and 66: Flux leakage sensors have small dia
Page 67 and 68: The frequency of the alternating fi
Page 69 and 70: Figure 3.14 Rotating magnet arrange
Page 71 and 72: 3.3 EDDY CURRENT SENSING PROBES For
Page 73 and 74: As the probe moves over the defect,
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: Figure 3.22 Effect of magnetic fiel
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 and 122: Figure 3.23 Magnetization or magnet
Page 123 and 124: By taking the product of B and H fo
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
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It is possible to provide 100% eddy
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Figure 3.33 ET testing of hot coppe
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For maximum sensitivity, the Circog
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3.14 MAGNETIC FLUX LEAKAGE TESTING
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ASTM E 570 describes magnetic flux
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Charlie Chong/ Fion Zhang Figure 3.
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Applications involving physical par
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Inexpensive 60 Hz eddy current comp
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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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