Electromagnetic Testing

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Remote Field Eddy Current Technique (RFT) This process is well adapted to the inspection of small-bore ferromagnetic tubes such as carbon steel. Using electromagnetic techniques this is now the industry standard inspection for boilers and heat exchangers due to its low frequency (typically 50-1000Hz). The probe consists of two coils in a send-receive configuration which are inserted into the tube. The energized exciter coil transmits a signal to the detector coil located some distance away. This signal passes through to the outside tube wall returning to arrive at the detector coil. With wall thinning there is less shielding hence the return time (greater phase) and attenuation (greater amplitude) is shorter. Phase and amplitude traces are generated as the probe is pulled through the tube as recorded data identifies the metal loss. Flaw sizing is also possible with RFT enabling depth, length and circumference to be accurately calibrated. Charlie Chong/ Fion Zhang http://www.itcl.org.uk/itcl-services/tube-inspection/
The Remote Field Technique is an electromagnetic examination, which utilizes a through-transmission process. The resultant field is affected by either ID or OD tube wall anomalies. RFT signal measurements are made a few tube diameters away from the AC excitation coil without any attempt at tube wall magnetization or saturation. A pair of pick-up coils located in the remote field zone measures the resultant field to give both a differential and an absolute signal. The signal phase and amplitude information is used to determine defect depth and volume 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
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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
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Figure 2.6: External reference diff
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Figure 2.7: Hybrid coil (through tr
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Additional Coil Characteristics Coi
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Q.2.1 Differential coils are usuall
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Q.2.6 An absolute coil measurement
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The Answers Charlie Chong/ Fion Zha
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As discussed earlier test coil desi
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Demonstration model of a moving iro
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Thus, the resistance of a 10 ft len
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SPECIFIC RESISTANCE OR RESISTIVITY
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Problem: What is the resistance of
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The inductance of a multilayer air
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Example: A coil whose dimensions ar
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Example: Using the 32 μH coil calc
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Impedance To explain the addition o
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Maximum transfer of power is accomp
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Rectangular Notation Because reacta
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Vectors With Polar Notations. Stand
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Rectangular Notation - Prefix “j
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Imaginary Component In “rectangul
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Imaginary Charlie Chong/ Fion Zhang
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To convert from rectangular to pola
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More Reading on Polar & Rectangular
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Eddy current coils with included im
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Permeability and Shielding Effects
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Another technique of shielding uses
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Saturation Approach Another coil de
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Figure 3.5: Magnetic bias probe Cha
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Materials must be chemically compat
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Q.3.1 A coil's resistance is determ
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Q.3.7 The Q or merit of a coil is d
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Jackfruit Tree Charlie Chong/ Fion
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Electrical Conductivity σ In elect
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As previously discussed, conductivi
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Figure 4.1; Conductivity curve Char
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The coil's inductive reactance is r
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Effects of Heat Treatment on Conduc
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Permeability Permeability of any ma
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When increases in the magnetizing f
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Skin Effect Charlie Chong/ Fion Zha
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Discussion Subject: Response to the
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Lift Off Electromagnetic coupling b
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Fill factor will always be a number
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Figure 4.4: Fill factor ratios When
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Example: Calculate the resultant lo
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Figure 1.8 is again useful to illus
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Signal-to-Noise Ratio Signal-to-noi
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Q.4.4 A (?) prime factor affecting
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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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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
Page 381 and 382: Some other technologies that have b
Page 383 and 384: Alternating current field measureme
Page 385 and 386: Figure 8.1 shows the basic principl
Page 387 and 388: ACFM Principle Charlie Chong/ Fion
Page 389 and 390: ACFM Z X Bx =magnetic flux componen
Page 393 and 394: The technique in its simplest form
Page 397 and 398: Magnetic Flux Leakage Testing Prima
Page 399 and 400: Figure 8.2: Equipment for magnetic
Page 401 and 402: Magnetic Flux Leakage Testing Charl
Page 403 and 404: The most commonly used inservice in
Page 405 and 406: Magnetic Saturation Charlie Chong/
Page 407 and 408: The magnetization curve is not retr
Page 409 and 410: Magnetic Flux Leakage Testing Charl
Page 411 and 412: Magnetic Flux Leakage The basic pri
Page 413 and 414: Magnetic Flux Leakage Magnetic Flux
Page 415 and 416: Special hybrid (driver/pick up) coi
Page 417 and 418: At distances in excess of two tube
Page 419 and 420: Figure 8.4: Remote field testing en
Page 421 and 422: Remote-Field Energy Zones - in remo
Page 423 and 424: Remote-Field Zone Transition Zone C
Page 425 and 426: RFT - Flux distribution in pipe (a)
Page 427 and 428: Remote Field Zone - The third defin
Page 429 and 430: Amplitude (voltage) - The remote fi
Page 431: RFT Charlie Chong/ Fion Zhang http:
Page 435 and 436: Remote Field Eddy Current Technique
Page 437 and 438: More Reading: RFT Remote Field Test
Page 439 and 440: These eddy currents, in turn, produ
Page 441 and 442: The Zones Direct Couple Zone The re
Page 443 and 444: RFT Probes Probes for inspection of
Page 445 and 446: RFT Signal Interpretation The signa
Page 447 and 448: RFT Reference Standards Reference s
Page 449 and 450: Answers Charlie Chong/ Fion Zhang
Page 451 and 452: Q.8.4 A generally accepted definiti
Page 453 and 454: Q.8.8 The region of intense electro
Page 455 and 456: Chapter 9 Eddy Current Procedures,
Page 457 and 458: American Society for Testing and Ma
Page 459 and 460: Military Standard The United States
Page 461 and 462: EDDY CURRENT INSPECTION OF NONFERRO
Page 463 and 464: . Probe positioning and feeding sha
Page 465 and 466: 3. Tube Inspection General (Refer t
Page 467 and 468: F. INSPECTION RESULTS AND DOCUMENTA
Page 469 and 470: G. REFERENCES The following documen
Page 471 and 472: Answers Charlie Chong/ Fion Zhang
Page 473 and 474: Q.9.4 Military Standards are design
Page 475 and 476: Q.9.10 The system in QA3 is calibra
Page 477 and 478: More Reading http://www.allaboutcir
Page 479 and 480: 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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