Electromagnetic Testing

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Discussion Subject 1: Shielding, while improving resolution, usually sacrifices some amount of penetration into fue part. Subject 2: A disadvantage of high conductivity, low or no permeability shielding is that the coil's impedance is reduced when the shielding material is placed around the test coil. The net effect is that the coil's “Q” factor is less than it was when the coil was surrounded by air. Charlie Chong/ Fion Zhang
Saturation Approach Another coil design used for inspection of ferromagnetic materials is the saturation approach. A predominant variable that prevents eddy current penetrating in ferromagnetic material is called permeability. Permeability effects exhibited by the test object can be reduced by means of magnetic saturation(Figure 3.4). Saturation coils for steels are usually very large and surround the test object and test coil. A steady state (DC) current is applied to the saturation coil. When the steel test object is magnetically saturated it may be inspected in the same manner as a nonferromagnetic material. In the case of mild steel many thousands of tesla are required to produce saturation. In some inherently nonferromagnetic tubing materials like high temperature nickel chromium alloy there may be low level permeability variations because of manufacturing discontinuities. In this case the use of small permanent magnets adjacent to the bobbin probe coils may improve the inspection quality by reducing the permeability effects. Figure 3.5 shows the use of disk type magnets placed close to the coil. It is also possible to use an array of bar magnets arranged around the probe housing if higher magnetic potential is required to offset the material permeability characteristics. Charlie Chong/ Fion Zhang
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Electromagnetic Testing Study Guide
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E&P Applications Charlie Chong/ Fio
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Charlie Chong/ Fion Zhang
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乱七八糟 - 随看随记 C
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Charlie Chong/ Fion Zhang http://ww
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IVONA TTS Capable. Charlie Chong/ F
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EDDY CURRENT an Overview Descriptio
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Tangential Probe Charlie Chong/ Fio
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Electromagnetic Testing Advantages
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Factors Affecting Eddy Current Resp
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from this it can be seen that depth
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http://www.eng.morgan.edu/~hubert/I
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Robotic Charlie Chong/ Fion Zhang
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Measurement Techniques (EN!) a) Abs
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Figure 1.1 Arago’s Experiment Cha
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Oersted discovered the presence of
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Figure 1.3: Induced current electro
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Charlie Chong/ Fion Zhang http://en
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Charlie Chong/ Fion Zhang http://en
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The law of physics describing the p
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Charlie Chong/ Fion Zhang http://hy
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Magnetic Force The magnetic field B
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Generation of Eddy Currents When a
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Factors Affecting Inductance There
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COIL LENGTH: All other factors bein
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Coil Inductance L An approximation
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Note the direction of the primary c
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Generation of Eddy Current With a p
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Charlie Chong/ Fion Zhang Permeabil
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A Dual Variable inductors Figure 1:
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Figure 3: Here is another inductor
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Figure 4: The two inductors on this
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Grundig radio satellit 750 ■ http
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Figure 1.7: Phasor Diagram of Coil
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Current Density The distribution of
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Figure 1.8: Relative eddy current d
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Relative Magnetic Permeability Perm
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It should be observed at this point
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δ = (π x 100 x 10 3 x 4 x π x 0.
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Using 1.35 mm as depth x from surfa
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Standard Depth for Different Conduc
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Current (?) Lagging Voltage lagging
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σº∙πμ■δ∝∞ωΩθ√ρβ
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Figure 1.9 should be used as a rela
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Figure 1.8: Relative eddy current d
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Q.1.1 Generation of eddy currents d
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Q.1.5 Eddy current generated a test
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Q.1.9 Refer to Figure1.9 using exam
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Chapter 2 The Coil Arrangements Cha
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Probe coils and probe coil forms ca
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Encircling Coils Encircling coil, o
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Discussion Subject; Encircling Coil
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Bobbin Coils Bobbin coil, inside di
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Figure 2.5: Test coil configuration
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Differential coils Differential coi
Page 113 and 114: Figure 2.6: External reference diff
Page 115 and 116: Figure 2.7: Hybrid coil (through tr
Page 117 and 118: Additional Coil Characteristics Coi
Page 119 and 120: Q.2.1 Differential coils are usuall
Page 121 and 122: Q.2.6 An absolute coil measurement
Page 123 and 124: The Answers Charlie Chong/ Fion Zha
Page 125 and 126: As discussed earlier test coil desi
Page 127 and 128: Demonstration model of a moving iro
Page 129 and 130: Thus, the resistance of a 10 ft len
Page 131 and 132: SPECIFIC RESISTANCE OR RESISTIVITY
Page 133 and 134: Problem: What is the resistance of
Page 135 and 136: The inductance of a multilayer air
Page 137 and 138: Example: A coil whose dimensions ar
Page 139 and 140: Example: Using the 32 μH coil calc
Page 141 and 142: Impedance To explain the addition o
Page 143 and 144: Maximum transfer of power is accomp
Page 145 and 146: Rectangular Notation Because reacta
Page 147 and 148: Vectors With Polar Notations. Stand
Page 149 and 150: Rectangular Notation - Prefix “j
Page 151 and 152: Imaginary Component In “rectangul
Page 153 and 154: Imaginary Charlie Chong/ Fion Zhang
Page 155 and 156: To convert from rectangular to pola
Page 157 and 158: More Reading on Polar & Rectangular
Page 159 and 160: Eddy current coils with included im
Page 161 and 162: Permeability and Shielding Effects
Page 163: Another technique of shielding uses
Page 167 and 168: Figure 3.5: Magnetic bias probe Cha
Page 169 and 170: Materials must be chemically compat
Page 171 and 172: Q.3.1 A coil's resistance is determ
Page 173 and 174: Q.3.7 The Q or merit of a coil is d
Page 177 and 178: Jackfruit Tree Charlie Chong/ Fion
Page 179 and 180: Electrical Conductivity σ In elect
Page 181 and 182: As previously discussed, conductivi
Page 183 and 184: Figure 4.1; Conductivity curve Char
Page 185 and 186: The coil's inductive reactance is r
Page 187 and 188: Effects of Heat Treatment on Conduc
Page 189 and 190: Permeability Permeability of any ma
Page 191 and 192: When increases in the magnetizing f
Page 193 and 194: Skin Effect Charlie Chong/ Fion Zha
Page 195 and 196: Discussion Subject: Response to the
Page 197 and 198: Lift Off Electromagnetic coupling b
Page 199 and 200: Fill factor will always be a number
Page 201 and 202: Figure 4.4: Fill factor ratios When
Page 203 and 204: Example: Calculate the resultant lo
Page 205 and 206: Figure 1.8 is again useful to illus
Page 207 and 208: Signal-to-Noise Ratio Signal-to-noi
Page 211 and 212: Q.4.4 A (?) prime factor affecting
Page 213 and 214: Q.4.10 Temperature changes, vibrati
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Test Frequencies It is the responsi
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Single Frequency Systems Unfortunat
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Eddy Current Density Since the sens
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Applicable Scenario Eddy Current De
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Standard Depth δ Formula The depth
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Example 1: As an example of how thi
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Frequency Selection - Ferromagnetic
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A frequency can always selected to
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Figure 5.1(a) shows the effect on p
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Figure 5.1: Effects of frequency ch
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Figure 5.2: Normalized impedance di
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Figure 5.3: Impedance variations ca
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Figure 5.4: Impedance variations ca
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Multiparameter Techniques It become
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Multiparameter Techniques - Multipl
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First, a frequency is selected to g
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More Reading on Characteristic Para
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Figure 1: Eddy Current Testing Char
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Figure 2: Types of Probes Charlie C
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Surface (Pancake) Probes Surface pr
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Encircling Probes Encircling probes
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Design of eddy current probes In mo
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In brief, probe design is usually d
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Analytical Approach (Pc & f g ) Ana
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RECENT TRENDS IN EDDY CURRENT PROBE
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Pressurized Heavy Water Reactors (P
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The Answers Charlie Chong/ Fion Zha
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Q.5.4 Calculate the limit frequency
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Q.5.7 Primary resistance is subtrac
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Q5.9 A 25% deep crack open to the n
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Chapter 6 Instrument Systems Charli
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Eddy Current Instrumentation Most o
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Figure 6.1: Internal functions of t
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Chernobyl Nuclear Power Plant Charl
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Figure 6.2: Four types of simple ed
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Figure 6.2(b) shows an impedance br
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Figure 6.2(d) illustrates a balanci
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Eddy current testing - Signal Analy
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Impedance Testing With impedance ma
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Phase Analysis Testing - Vector Poi
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Phase Analysis Testing - Ellipse As
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Figure 6.4: Cathode ray tube displa
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Figure 6.5: Screen image of a linea
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Impedance Plane Testing - Mode of O
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Figure 6.6: Null balance instrument
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Figure 6.7: Typical surface riding
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For deep subsurface crack detection
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Multiple circuits are used througho
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This type of digital instrumentatio
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Read Out Mechanisms - Audio Alarms
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An qualitative meter response could
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Figure 6.13: A qualitative analog m
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Read Out Mechanisms - Cathode Ray T
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Figure 6.14: Numerical readouts/dig
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Read Out Mechanisms - Computer Eddy
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Probe Delivery System Instead of mo
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Chapter 6 Review Questions Charlie
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Q.6.1 Signal preparation is usually
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Q.6.7 Amplitude gates provide a tec
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Chapter 7 Eddy Current Applications
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Discontinuity Detection The theoret
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Heat Exchanger Charlie Chong/ Fion
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Heat Exchanger TSP Charlie Chong/ F
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Heat Exchanger TSP Charlie Chong/ F
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Figure 7.2: Phase-to-depth calibrat
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The geometry of real discontinuitie
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Figure 7.5: A multifrequency applic
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Aerospace Applications Charlie Chon
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The reference specimen and its asso
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Dimensional Measurements Dimensiona
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Figure 7.6: A single frequency hard
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Conductivity Measurements Conductiv
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Alloy Sorting Alloy sorting can als
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In addition, it is advisable to hav
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Answers Charlie Chong/ Fion Zhang
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Q.7.4 Using multifrequency techniqu
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Q.7.7 Response to multilayer varyin
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Chapter 8 Other Electromagnetic Tec
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Some other technologies that have b
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Alternating current field measureme
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Figure 8.1 shows the basic principl
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ACFM Principle Charlie Chong/ Fion
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ACFM Z X Bx =magnetic flux componen
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The technique in its simplest form
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Magnetic Flux Leakage Testing Prima
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Figure 8.2: Equipment for magnetic
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Magnetic Flux Leakage Testing Charl
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The most commonly used inservice in
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Magnetic Saturation Charlie Chong/
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The magnetization curve is not retr
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Magnetic Flux Leakage Testing Charl
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Magnetic Flux Leakage The basic pri
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Magnetic Flux Leakage Magnetic Flux
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Special hybrid (driver/pick up) coi
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At distances in excess of two tube
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Figure 8.4: Remote field testing en
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Remote-Field Energy Zones - in remo
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Remote-Field Zone Transition Zone C
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RFT - Flux distribution in pipe (a)
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Remote Field Zone - The third defin
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Amplitude (voltage) - The remote fi
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RFT Charlie Chong/ Fion Zhang http:
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The Remote Field Technique is an el
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Remote Field Eddy Current Technique
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More Reading: RFT Remote Field Test
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These eddy currents, in turn, produ
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The Zones Direct Couple Zone The re
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RFT Probes Probes for inspection of
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RFT Signal Interpretation The signa
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RFT Reference Standards Reference s
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Q.8.4 A generally accepted definiti
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Q.8.8 The region of intense electro
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Chapter 9 Eddy Current Procedures,
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American Society for Testing and Ma
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Military Standard The United States
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EDDY CURRENT INSPECTION OF NONFERRO
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. Probe positioning and feeding sha
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3. Tube Inspection General (Refer t
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F. INSPECTION RESULTS AND DOCUMENTA
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G. REFERENCES The following documen
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Q.9.4 Military Standards are design
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Q.9.10 The system in QA3 is calibra
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More Reading http://www.allaboutcir
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Discussion Subject: discuss on the
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Inspection from the Tube OD Most AS
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Approximately 25 years ago, the AST
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One additional advantage of OD ECT
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The baseline eddy current test The
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There is no standard accept/reject
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Pulsed Eddy Currents Systems Charli
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Although still an active research f
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LOI (Lift-Off point of Intersection
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Gap Point : Similar to the LOI, the
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Driving Coil Charlie Chong/ Fion Zh
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Hall effect sensors In opposition t
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Crack Detection using Pulsed Eddy C
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Fig. 1 (a) ARMANDA - Automated scan
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Fig. 2. Images of the Eddy current
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Reading 2: 4.9.2.3 Pulsed Eddy Curr
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Good Luck Charlie Chong/ Fion Zhang
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