Electromagnetic Testing

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The ASTM/ASME OD EC testing of tubes is usually accomplished using only one frequency, typically within a range of 25 KHz to 100 KHz. As the magnetic field penetrates the metal, the ability to receive a signal lessens or attenuates. This phenomenon is called standard depth of penetration or alternatively, the “skin effect”. The depth of penetration decreases with increasing frequency, conductivity and magnetic permeability. As a result, the signal returning from an imperfection near the OD will be stronger than an identically sized imperfection away from the OD surface. The specifications do not address the imperfection’s location. Rejection is typically decided on a go/no-go signal amplitude criteria from an artificial defect described in the general specification or in the supplementary requirements of the product specifications. Magnetic properties or anomalies can be created in non-magnetic materials through minor parent metal alloy excursions, manufacturing, welding, strain-induced cold work and other processes and may not be detected using conventional OD saturation. These signals are defined as anomalies or discontinuities and are not considered a manufacturing defect. This magnetic coupling is achieved by using encircling coils to create a saturating magnetic field. This magnetic saturation does not necessarily improve the testing sensitivity or repeatability but does allow penetration of eddy currents in magnetic materials. Charlie Chong/ Fion Zhang http://www.heatexchange.org/pdf/techsheets/TechSheet132.pdf
One additional advantage of OD ECT inspection is that the tubing can be fully magnetically saturated during testing to ensure the maximum level of sensitivity and repeatability, vastly reducing the occurrence of false indications on those materials which have ferromagnetic domains. As noted earlier, carbon and alloy steels, stainless steels and some nickel alloys may contain small magnetic domains that must be magnetically coupled during testing to minimize “noise” providing for “quiet” or higher signal to noise inspection with eddy currents. Even austenitic stainless steels which are considered to be non-magnetic, may have small magnetic regions from residual delta ferrite formed during the welding process or strain induced martensite from cold working. Special tube configurations such as integral ID and/or OD fins will require unique technologies that are not covered in this document but should be reviewed with the manufacturer prior to the onset of testing. Charlie Chong/ Fion Zhang http://www.heatexchange.org/pdf/techsheets/TechSheet132.pdf
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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
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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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Page 439 and 440: These eddy currents, in turn, produ
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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
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Page 457 and 458: American Society for Testing and Ma
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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
Page 477 and 478: More Reading http://www.allaboutcir
Page 479 and 480: Discussion Subject: discuss on the
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Page 483 and 484: Inspection from the Tube OD Most AS
Page 485: Approximately 25 years ago, the AST
Page 489 and 490: The baseline eddy current test The
Page 491 and 492: There is no standard accept/reject
Page 493 and 494: Pulsed Eddy Currents Systems Charli
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Page 499 and 500: Gap Point : Similar to the LOI, the
Page 501 and 502: Driving Coil Charlie Chong/ Fion Zh
Page 503 and 504: Hall effect sensors In opposition t
Page 505 and 506: Crack Detection using Pulsed Eddy C
Page 507 and 508: Fig. 1 (a) ARMANDA - Automated scan
Page 509 and 510: Fig. 2. Images of the Eddy current
Page 511 and 512: Reading 2: 4.9.2.3 Pulsed Eddy Curr
Page 513 and 514: Good Luck Charlie Chong/ Fion Zhang
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Electromagnetic Testing

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