Electromagnetic Testing Chapter 3- Electromagnetic Testing

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ith the differential coil arrangement, defect sensitivity is retained while clearance sensitivity is reduced by a factor of two or three. The differential method is also known as the self-comparison method because the adjacent sections of the material are compared to each other. Differential encircling coils are shown in Figure 3.16. As shown, one section is compared to an adjacent tube section, which provides automatic compensation for probe clearance and gradual changes in tube diameter. Figure 3.17 shows a surface scanning probe with a differential detector coil located inside a larger excitation coil. Magnetic flux from the excitation coil passes through both coils of the differential detector into the test piece, and sets up circular eddy currents near the surface.The crack distorts the eddy currents, weakens the primary magnetic field, and increases the impedance and voltage output of the pickup coil. A number of these surface-mount coils can be used to scan irregularly shaped objects. Charlie Chong/ Fion Zhang
Figure 3.17 Differential surface coil showing that primary and detector coils share the same primary field. Note that crack distorts the eddy current path. Courtesy of Institut Dr. Foerster. Detector coil#1 Detector coil#2 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.
Page 23 and 24: Figure 3.2 Schematic diagram of bas
Page 25 and 26: Figure 3.3 The effect of conductivi
Page 27 and 28: Figure 3.3 The effect of conductivi
Page 29 and 30: Another important influence on coil
Page 31 and 32: If the conductivity of the material
Page 33 and 34: Figure 3.5 The effect of a crack on
Page 35 and 36: FIGURE 8-49 Conductivity curve: (a)
Page 37 and 38: So far, we have described how eddy
Page 39 and 40: Figure 3.6 The effects of (a) condu
Page 41 and 42: 3.1.2 Limiting Frequency f g of Enc
Page 43 and 44: Figure 3.7 The effect of degree of
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Page 47 and 48: Eddy Current Heating Charlie Chong/
Page 49 and 50: Eddy Current Heating Charlie Chong/
Page 51 and 52: 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: As the probe moves over the defect,
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 and 122: Figure 3.23 Magnetization or magnet
Page 123 and 124: By taking the product of B and H fo
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The rate of change of the opposing
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Figure 3.25 Encircling coils establ
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Figure 3.27 DC-MFL sensor illustrat
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Fill factors apply only to encircli
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For best results with encircling co
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3.11 INSTRUMENT DESIGN CONSIDERATIO
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Charlie Chong/ Fion Zhang Figure 3.
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TABLE 3.2. Comparison of Instrument
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Some general categories of equipmen
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Figure 3.29 UniWest-454 EddyView mu
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Scanner operation uses a separate c
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Figure 3.30 E-Lab model US-450 full
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3.12.3 ETC-2000 Scanner Because of
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ETC-2000 scanner features include:
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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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Electromagnetic Testing Chapter 3- Electromagnetic Testing

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