Electromagnetic Testing Chapter 3- Electromagnetic Testing

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Calculation on the aforementioned scenario: Frequency = 100kHz maximum. In the worst case, the period of one full cycle would be 1/10,000 or 0.0001 second.With a ¼ inch diameter probe, we can move the probe or test object ¼ inch in 0.0001 second. Area of probe = π0.25 2 /4 Total test time for a 100% surface inspection 3-inch diameter by 30-ft-long tube, would: Area of pipe surface= (3π x 30 x 12) in 2 Total test time = 3π x 30 x 12 / (π0.25 2 /4) x 0.0001 = (3x4x30x12x4x4) x 0.0001 s = 6.912s Revolution to traverse 30’ by ¼ “ probe without overlapped = 30x12/0.25= 30x12x4=1440 revolution RPS= 1440/6.912 =208.3 RPS or 12498rpm. Charlie Chong/ Fion Zhang
3.6 SIGNAL-TO-NOISE RATIO The signal-to-noise ratio can be defined as the ratio of signal amplitude from a relevant indication to the signal amplitude received from the background noise or nonrelevant indications. A major problem associated with eddy current testing is that there are a large number of known and unknown variables that can affect the output indication. One of the greatest sources of noise is caused by lift-off variations. Spring-loaded eddy current probes are used to minimize the effects of lift-off. Other sources of noise or extraneous indications are varying test speed, gradual dimensional changes, and unwanted high frequency harmonics. Noise filtering or differentiation, phase discrimination, and signal integration can compensate for many of these sources of noise. For example, high-pass filters minimize the effects of gradual dimensional changes and low-pass filters are used to filter out unwanted high-frequency harmonics. Filters should not modulate the test frequency. 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
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 and 104: Figure 3.22 Effect of magnetic fiel
Page 105 and 106: 3.5 FACTORS AFFECTING FLUX LEAKAGE
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Page 109: The distance between adjacent defec
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
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
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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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