Electromagnetic Testing

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The sensing area of a probe is the physical diameter of the coil plus an extended area governed by magnetic field spread. Hence, it is common to use ferrite cores/shields (high permeability and low conductivity) to contain the lateral extent of magnetic fields without affecting the depth of penetration. It is essential to operate EC probes below the probe/cable resonance frequency, especially while using long probe cables and at very high frequencies. The probe bodies are usually made of non-conducting plastics. Wear of probes is normally be reduced by giving wear resistant coating to the probe heads or tips. It must be noted here that such coatings add to the builtin lift-off of probes and tend to reduce signal amplitudes. Temperature stability of probes is usually accomplished by using coil holder material with poor heat transfer characteristics. Most common commercial copper wires are used up to about 150º C. For temperatures above this, silver or aluminum wires with ceramic or high temperature silicon insulation or MIC are used. The probe material must be chemically compatible with the component. Charlie Chong/ Fion Zhang http://www.geocities.ws/raobpc/Probes.html
In brief, probe design is usually done considering the following: • Geometry of the component e.g. rod, tube, plate etc. • Type of discontinuity expected e.g. fatigue cracks, conductivity variation etc. • Likely location of defect e.g. surface, sub-surface. • Coil impedance and its matching with the bridge circuit of the EC instrument. • Frequency range of the probe i.e. for simultaneous multi-frequency excitation • Inspection requirement e.g. detection, evaluation of length, depth etc. • Material characteristics e.g. ferromagnetic or non-ferromagnetic. • Coil response to a notch, drilled hole or other reference discontinuity. • Field distribution in space and eddy current flow distribution in the material. • Shape and dimensions of core, coil /coils and lift-off characteristics. • Environmental characteristics such as wear, temperature and chemical attack. As many factors need to be considered, three different approaches viz. experimental, analytical and numerical are often resorted to for designing eddy current probes. Charlie Chong/ Fion Zhang http://www.geocities.ws/raobpc/Probes.html
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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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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
Page 207 and 208: Signal-to-Noise Ratio Signal-to-noi
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Page 211 and 212: Q.4.4 A (?) prime factor affecting
Page 213 and 214: Q.4.10 Temperature changes, vibrati
Page 215 and 216: Test Frequencies It is the responsi
Page 217 and 218: Single Frequency Systems Unfortunat
Page 219 and 220: Eddy Current Density Since the sens
Page 221 and 222: Applicable Scenario Eddy Current De
Page 223 and 224: Standard Depth δ Formula The depth
Page 225 and 226: Example 1: As an example of how thi
Page 227 and 228: Frequency Selection - Ferromagnetic
Page 229 and 230: A frequency can always selected to
Page 231 and 232: Figure 5.1(a) shows the effect on p
Page 233 and 234: Figure 5.1: Effects of frequency ch
Page 235 and 236: Figure 5.2: Normalized impedance di
Page 237 and 238: Figure 5.3: Impedance variations ca
Page 239 and 240: Figure 5.4: Impedance variations ca
Page 241 and 242: Multiparameter Techniques It become
Page 243 and 244: Multiparameter Techniques - Multipl
Page 245 and 246: First, a frequency is selected to g
Page 247 and 248: More Reading on Characteristic Para
Page 249 and 250: Figure 1: Eddy Current Testing Char
Page 251 and 252: Figure 2: Types of Probes Charlie C
Page 253 and 254: Surface (Pancake) Probes Surface pr
Page 255 and 256: Encircling Probes Encircling probes
Page 257: Design of eddy current probes In mo
Page 261 and 262: Analytical Approach (Pc & f g ) Ana
Page 263 and 264: RECENT TRENDS IN EDDY CURRENT PROBE
Page 265 and 266: Pressurized Heavy Water Reactors (P
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Page 269 and 270: Q.5.4 Calculate the limit frequency
Page 271 and 272: Q.5.7 Primary resistance is subtrac
Page 273 and 274: Q5.9 A 25% deep crack open to the n
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Page 277 and 278: Eddy Current Instrumentation Most o
Page 279 and 280: Figure 6.1: Internal functions of t
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Page 283 and 284: Figure 6.2: Four types of simple ed
Page 285 and 286: Figure 6.2(b) shows an impedance br
Page 287 and 288: Figure 6.2(d) illustrates a balanci
Page 289 and 290: Eddy current testing - Signal Analy
Page 291 and 292: Impedance Testing With impedance ma
Page 293 and 294: Phase Analysis Testing - Vector Poi
Page 295 and 296: Phase Analysis Testing - Ellipse As
Page 297 and 298: Figure 6.4: Cathode ray tube displa
Page 299 and 300: Figure 6.5: Screen image of a linea
Page 301 and 302: Impedance Plane Testing - Mode of O
Page 303 and 304: Figure 6.6: Null balance instrument
Page 305 and 306: Figure 6.7: Typical surface riding
Page 307 and 308: 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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Figure 6.1: Internal functions of t
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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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Figure 6.1: Internal functions of t
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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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Electromagnetic Testing

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