Electromagnetic Testing

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Proximity / Lift-off The closer a probe coil is to the surface the greater will be the effect on that coil. This has two main effects: The "lift-off" signal as the probe is moved on and off the surface. A reduction in sensitivity as the coil to product spacing increases. Depth of penetration The eddy current density, and thus the strength of the response from a flaw, is greatest on the surface of the metal being tested and declines with depth. It is mathematically convenient to define the "standard depth of penetration" where the eddy current is 1/e (37%) of its surface value. The standard depth of penetration in mm is given by the formula: Where: δ is standard depth in mm ρ is resistivity in μΩ.cm f is frequency in Hz μ r is relative permeability Charlie Chong/ Fion Zhang http://www.eng.morgan.edu/~hubert/IEGR470/eddycurrent.html
from this it can be seen that depth of penetration: 1. Decreases with an increase in frequency 2. Decreases with an increase in conductivity 3. Decreases with an increase in permeability: this can be very significant penetration into ferrous materials at practical frequencies is very small. δ δ The graph above shows the effect of frequency on standard depth of penetration. It is also common to talk about the "effective depth of penetration" usually defined as three times the standard depth, where eddy current density has fallen to around 3% (5%?) of its surface value. This is the depth at which there is considered to be no influence on the eddy current field. Charlie Chong/ Fion Zhang http://www.eng.morgan.edu/~hubert/IEGR470/eddycurrent.html
Page 1 and 2: Electromagnetic Testing Study Guide
Page 3 and 4: E&P Applications Charlie Chong/ Fio
Page 5 and 6: Charlie Chong/ Fion Zhang
Page 7 and 8: 乱七八糟 - 随看随记 C
Page 9 and 10: Charlie Chong/ Fion Zhang
Page 11 and 12: Charlie Chong/ Fion Zhang http://ww
Page 13 and 14: IVONA TTS Capable. Charlie Chong/ F
Page 15 and 16: EDDY CURRENT an Overview Descriptio
Page 17 and 18: Tangential Probe Charlie Chong/ Fio
Page 19 and 20: Electromagnetic Testing Advantages
Page 21: Factors Affecting Eddy Current Resp
Page 25 and 26: http://www.eng.morgan.edu/~hubert/I
Page 27 and 28: Robotic Charlie Chong/ Fion Zhang
Page 29 and 30: Measurement Techniques (EN!) a) Abs
Page 31 and 32: Figure 1.1 Arago’s Experiment Cha
Page 33 and 34: Oersted discovered the presence of
Page 35 and 36: Figure 1.3: Induced current electro
Page 37 and 38: Charlie Chong/ Fion Zhang http://en
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Page 41 and 42: The law of physics describing the p
Page 43 and 44: Charlie Chong/ Fion Zhang http://hy
Page 45 and 46: Magnetic Force The magnetic field B
Page 47 and 48: Generation of Eddy Currents When a
Page 49 and 50: Factors Affecting Inductance There
Page 51 and 52: COIL LENGTH: All other factors bein
Page 53 and 54: Coil Inductance L An approximation
Page 55 and 56: Note the direction of the primary c
Page 57 and 58: Generation of Eddy Current With a p
Page 59 and 60: Charlie Chong/ Fion Zhang Permeabil
Page 61 and 62: A Dual Variable inductors Figure 1:
Page 63 and 64: Figure 3: Here is another inductor
Page 65 and 66: Figure 4: The two inductors on this
Page 67 and 68: Grundig radio satellit 750 ■ http
Page 69 and 70: Figure 1.7: Phasor Diagram of Coil
Page 71 and 72: 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
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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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Charlie Chong/ Fion Zhang
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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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