Electromagnetic Testing

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The Standard Depth of Penetration δ The Standard Depth of Penetration can be expressed as: δ = (πfμσ) -½ Where: δ = One standard depth of penetration; 1/e of the surface current density (37%) in meter, m f = Frequency of the AC primary current in Hz μ = Permeability of the test object in Henry per meter, H∙m -1 σ = Conductivity of the test object in Siemens per meter, S∙m -1 Charlie Chong/ Fion Zhang
It should be observed at this point that as frequency, conductivity or permeability is increased, the penetration of current into the test object will be decreased. The graph in Figure 1.8 is used to demonstrate many eddy current characteristics. Using an example of a very thick block of stainless steel being interrogated with a surface or probe coil operating at a test frequency of 100 kHz, the standard depth of penetration can be determined and current densities observed at other depths. Stainless steel (300 Series) is nonferromagnetic. Magnetic permeability (μ) is 4πX 10 -7 H∙m -1 , the conductivity σ is 0.14 X 10 7 siemens (mhos) per meter for 300 Series stainless steel. δ = (πfμσ) -½ δ = (π x 100 x 10 3 x 4 x π x 0.14) -½ δ = 0.00135m or 1.35mm # 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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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
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Page 41 and 42: The law of physics describing the p
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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
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Page 69 and 70: Figure 1.7: Phasor Diagram of Coil
Page 71 and 72: Current Density The distribution of
Page 73 and 74: Figure 1.8: Relative eddy current d
Page 75: Relative Magnetic Permeability Perm
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Page 81 and 82: Using 1.35 mm as depth x from surfa
Page 83 and 84: Standard Depth for Different Conduc
Page 85 and 86: Current (?) Lagging Voltage lagging
Page 87 and 88: σº∙πμ■δ∝∞ωΩθ√ρβ
Page 89 and 90: Figure 1.9 should be used as a rela
Page 91 and 92: Figure 1.8: Relative eddy current d
Page 93 and 94: Q.1.1 Generation of eddy currents d
Page 95 and 96: Q.1.5 Eddy current generated a test
Page 97 and 98: Q.1.9 Refer to Figure1.9 using exam
Page 99 and 100: Chapter 2 The Coil Arrangements Cha
Page 101 and 102: Probe coils and probe coil forms ca
Page 103 and 104: Encircling Coils Encircling coil, o
Page 105 and 106: Discussion Subject; Encircling Coil
Page 107 and 108: Bobbin Coils Bobbin coil, inside di
Page 109 and 110: Figure 2.5: Test coil configuration
Page 111 and 112: 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
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Page 125 and 126: 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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The Answers Charlie Chong/ Fion Zha
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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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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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