Electromagnetic Testing Chapter 3- Electromagnetic Testing

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Figure 3.8 Simulation of a defect by a hypothetical defect dipole. Test Piece Charlie Chong/ Fion Zhang
3.2 MAGNETIC FLUX LEAKAGE THEORY When ferromagnetic materials are magnetized, magnetic lines of force (or flux) flow through the material and complete a magnetic path between the pole pieces. These magnetic lines of flux increase from zero at the center of the test piece and increase in density and strength toward the outer surface. When the magnetic lines of flux are contained within the test piece, it is difficult if not impossible to detect them in the air space surrounding the object. However, if a crack or other defect disrupts the surface of the magnetized piece, the permeability is drastically changed and leakage flux will emanate from the discontinuity. By measuring the intensity of this leakage flux, we can determine to some extent the severity of the defect. Figure 3.9 shows magnetic flux patterns for a horseshoe magnet and flat bar magnet. Note the heavy buildup of magnetic particles is a three dimensional pattern at the poles. Charlie Chong/ Fion Zhang
Page 1 and 2: Electromagnetic Testing Chapter 3-
Page 3 and 4: Submarine Applications Charlie Chon
Page 11 and 12: Fion Zhang at Shanghai 6th April 20
Page 13 and 14: IVONA TTS Capable. Charlie Chong/ F
Page 15 and 16: Chapter 3. ELECTROMAGNETIC TESTING
Page 17 and 18: Barkhausen effect The Barkhausen ef
Page 19 and 20: Barkhausen Noise Charlie Chong/ Fio
Page 21 and 22: 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
Page 45 and 46: Charlie Chong/ Fion Zhang
Page 47 and 48: Eddy Current Heating Charlie Chong/
Page 49 and 50: Eddy Current Heating Charlie Chong/
Page 51: Eddy currents weaken the original m
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
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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
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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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