Electromagnetic Testing Chapter 3- Electromagnetic Testing

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Figure 3.4 The effect of lift-off or probe clearance on coil impedance. Charlie Chong/ Fion Zhang
If the conductivity of the material is held constant and “A” is changed, the straight line from point “P1” to “Ao” is generated.When attempting to measure changes in conductivity, changes in spacing or lift-off are highly undesirable. In order to minimize variations in lift-off, eddy current coils may be recessed a short distance into the eddy current probe head, and the probe head may be spring loaded to maintain surface contact. However, since the lift-off effect is linear over a limited probe clearance range, eddy current probes can be designed to measure nonconductive coating thickness over uniformly conductive materials. Coil impedance can be calculated for any known combination of conductivity and probe clearance. 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: Another important influence on coil
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 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 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
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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
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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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