Electromagnetic Testing

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Phase - The phase change of the signals detected at the pick up coil can be used to estimate the loss of wall. A thinner wall allows the flux traversing the wall to arrive at the detector sooner (similar to the time of flight of ultrasonic testing signals). Discontinuities of differing depths can be evaluated accurately based on measured phase shift information. In eddy current testing there is a well defined difference in phase angle responses for inside diameter and outside diameter events; however, in remote field testing data inside diameter and outside diameter discontinuities of the same depth will have about the same phase angle. Charlie Chong/ Fion Zhang
Amplitude (voltage) - The remote field testing system senses a decrease in wall thickness as a stronger alternating current magnetic field cutting across the pick up coil. This induces a stronger voltage in the coil. Discontinuities of larger volume increase the amplitude of the signal while smaller volume discontinuities produce small amplitude signals, but the signal phase still represents the wall loss at the discontinuity. Signal location (at or near a support versus in free span tube) goes a long way to assisting in signal interpretation. The use of specialized voltage dependent phase analysis curves can also improve discontinuity resolution. Because some of the primary magnetic field extends out beyond the tube outside diameter tube support plates or baffles interfere with the magnetic field distribution. Any metallic material on the tube outside diameter will tend to block the energy transfer down the length of the tube. Because of the spacing between exciter and pick up coils this could lead to decreased sensitivity at these locations. Remote field testing is capable of detecting both small and large volume discontinuities in most ferromagnetic tubing found in a wide range of tubes and pipes such as heat exchangers, boilers, piping and pipelines. Some limitations do exist, for example in fin fan tubing found in air fin coolers. 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
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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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Page 381 and 382: Some other technologies that have b
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Page 385 and 386: Figure 8.1 shows the basic principl
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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
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Page 403 and 404: The most commonly used inservice in
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Page 407 and 408: The magnetization curve is not retr
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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: Remote Field Zone - The third defin
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Page 433 and 434: The Remote Field Technique is an el
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
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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
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Page 473 and 474: Q.9.4 Military Standards are design
Page 475 and 476: Q.9.10 The system in QA3 is calibra
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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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