Electromagnetic Testing - Eddy Current Testing Applications Chapter 5 & 6

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Generally, to detect small flaws, coils with a small diameter, no greater than the length of flaw required to be detected, need to be used. In addition, inservice cracking most often occurs in a change of section, slot, or thread root. Therefore, small diameter pencil probes give good access to such test surfaces and are most commonly used, although spot probes with a small diameter coil can be used on flat surfaces or where the curvature of the test surface is constant and not too great. If only relatively large flaws are sought, larger diameter probes can be used, with a consequent reduction in the number of passes required to scan a given test area. Absolute probes are almost always used for surface flaw detection, with differential probes being used only for special applications such as testing holes, discussed later. The probe can be shielded or unshielded. Shielded probes should be used for testing around holes. Keywords: Absolute probes are almost always used for surface flaw detection Charlie Chong/ Fion Zhang
If the fastener is not removed, cracks will normally be detected only if they extend beyond the fastener. To detect cracks under fasteners, a ring probe or sliding probe should be used. These are discussed later under the heading ‘Detection of subsurface flaws’. Shielded probes should also be used for testing near edges, at changes in the section, such as in slots, grooves, and thread roots, and, if testing non-ferromagnetic material, where there is an adjacent ferromagnetic material. Also, because the eddy current field of shielded probes is much more confined than that of an unshielded probe with the same diameter coil, shielded probes are capable of detecting smaller cracks, and so should be used whenever very small cracks are required to be detected. Unshielded probes can be used in other situations, and have the advantage that, because of the greater lateral spread of the eddy currents, fewer passes are required to scan a given test area. Charlie Chong/ Fion Zhang
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Electromagnetic Testing - Eddy Curr
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http://igor113.livejournal.com/5121
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Charlie Chong/ Fion Zhang
Page 7 and 8: 同桌的你 Charlie Chong/ Fion
Page 9 and 10: Fion Zhang at Shanghai 2014/Novembe
Page 11 and 12: 5.0 APPLICATIONS 5.1. Surface testi
Page 13 and 14: FIG. 5.1. Schematic diagram showing
Page 15 and 16: Eddy current field extends laterall
Page 17 and 18: Depth of Penetration & Current Dens
Page 19 and 20: Please also comment on this illustr
Page 21 and 22: FIG. 5.2 Directional properties of
Page 23 and 24: The depth of surface flaws (the dis
Page 25 and 26: Case Discussion: The corresponding
Page 27 and 28: 5.1.2.2 Types of standard surface t
Page 29 and 30: (b) Spot probes Spot probes are pro
Page 31 and 32: FIG. 5.6. A spring loaded probe. Ch
Page 33 and 34: FIG. 5.5. (a) The core and coil of
Page 35 and 36: Although it is usually evident by i
Page 37 and 38: FIG. 5.7. Effects of cores and shie
Page 39 and 40: 5.1.2.3 Other types of surface prob
Page 41 and 42: FIG. 5.8. A tangential probe showin
Page 43 and 44: Compare vertical probe with the FIG
Page 45 and 46: Discussion Topic- Why in the tangen
Page 47 and 48: FIG. 5.9. A gap (horseshoe) probe.
Page 49 and 50: Horseshoe probe - maximum sensitivi
Page 51 and 52: A gap (horseshoe) probe - Magnetic
Page 53 and 54: 5.1.3 Testing for surface-breaking
Page 55 and 56: Eddy Current Testing over painted s
Page 57: Testing Frequency: • 200 kHz to 5
Page 61 and 62: Following are some examples of spec
Page 63 and 64: Threaded Probe Charlie Chong/ Fion
Page 65 and 66: Eddy Current Testing- Hole fatigue
Page 67 and 68: Hand operated or manual hole probes
Page 69 and 70: If motor driven probes are to be us
Page 71 and 72: FIG. 5.12. Typical rotating hole pr
Page 73 and 74: Bolt hole probes Charlie Chong/ Fio
Page 75 and 76: (c) Aircraft wheels: Aircraft wheel
Page 77 and 78: Aircraft wheels Charlie Chong/ Fion
Page 79 and 80: Automated equipment which will perf
Page 81 and 82: Tangential probe - used in electron
Page 83 and 84: FIG. 5.3 Charlie Chong/ Fion Zhang
Page 85 and 86: Although these blocks can be used f
Page 87 and 88: (f) Scan over the appropriate disco
Page 89 and 90: 4.1.3.5 Testing in-service welds in
Page 91 and 92: FIG. 5.14 a. Typical weld testing p
Page 93 and 94: Since the eddy currents produced at
Page 95 and 96: For testing, the instrument should
Page 97 and 98: Charlie Chong/ Fion Zhang
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Page 101 and 102: Keywords: Typically, the magnetic f
Page 103 and 104: Multilayer structures - of flaws in
Page 105 and 106: 5.1.4.2 Probe and frequency selecti
Page 107 and 108: An acceptable compromise which give
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FIG. 5.15. Eddy current signals fro
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FIG. 5.16. Spot probes testing a la
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) Sliding probes Sliding probes are
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5.1.4.4 Reference samples Reference
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5.1.5 Conductivity testing and mate
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5.1.5.3 Factors which affect conduc
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(b) Alloying. Dissolving any elemen
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(d) Cold work Plastic deformation o
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(b) Test part thickness The conduct
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(c) Edge effect Probes dedicated to
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5.1.5.6 Frequency selection The fre
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FIG. 5.19. Impedance diagrams and t
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The Characteristic Parameter (PC) i
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Example: Calculate the optimum freq
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When eddy current conductivity mete
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(d) Perform conductivity measuremen
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5.1.5.9 Heat treatment of aluminium
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5.1.5.10 Sorting materials by magne
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5.1.6 Thickness measurement of non-
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FIG. 5.22. Methods of obtaining sta
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Non-conducting coating thickness me
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A typical operating frequency to me
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5.1.6.4 Measurement procedure (a) C
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(k) (l) Alternatively, if the measu
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5.1.7 Thickness measurement of cond
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5.1.7.2 Probe and frequency selecti
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5.1.7.3 Signals from variations in
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FIG. 5.26. Part of the display show
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5.1.7.5 Measurement procedure (a) C
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(j) (k) Alternatively, if the measu
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5.1.8 Thickness measurement of cond
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FIG. 5.28 shows the impedance curve
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5.2.1.1 Tube testing probes and the
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The coil(s) in bobbin probes produc
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Bobbin probe eddy current the orien
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To obtain adequate sensitivity to f
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As for surface testing, the test se
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5.2.1.2 Selection of test frequency
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The basis for the selection of test
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FIG. 5.32. Impedance diagram showin
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5.2.1.4 Flaw signals from absolute
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At f 90 , all flaw signals appear i
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5.2.1.5 Absolute probe signals from
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Wobble - A-go-go Charlie Chong/ Fio
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Discussion Topic- Discuss on the fo
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(c) Ferromagnetic conditions at the
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A signal from a ferromagnetic condi
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FIG. 5.36 shows the signal from a f
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Tube Sheet: Baffle Plate Charlie Ch
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Tube Sheet: Baffle Plate Charlie Ch
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(e) Non-ferromagnetic support or ba
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This signal will be modified by any
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(f) Ferromagnetic support or baffle
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FIG. 5.37. The signals from a carbo
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FIG. 5.38. Absolute and differentia
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5.2.1.7 Correlating flaw depth and
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FIG. 5.39. Graph showing the correl
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5.2.1.8 Correlating flaw depth and
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5.2.2 Bar and tube testing using en
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Discussion Topic: This means that p
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FIG. 5.41. The eddy current intensi
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5.2.2.2 Selection of frequency For
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Associated with the f/f g concept i
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The optimum operating point depends
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5.2.2.3 Specific test applications
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(c) Flaw detection Surface flaw ind
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5.2.2.4 Testing ferromagnetic bars
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Ferromagnetic material can be teste
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5.3.2 Equipment Most modern eddy cu
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These standards cover such topics a
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The following example is taken from
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The content of written procedures d
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6.5. Records and reports 6.5.1 Test
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6.5.2 Test reports A formal test re
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Records Charlie Chong/ Fion Zhang
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Calibration Standard A test standar
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Coil, probe A small coil or coil as
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Discontinuity Artificial Reference
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Electromagnetic Testing That non de
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IACS σ IACS . International Anneal
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Material, Diamagnetic A material ha
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Parameter A material property or in
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Phase Lag β (beta), radians or deg
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Resistivity ρ (ro), microhm centim
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Signal A change in eddy current ins
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Space Station Charlie Chong/ Fion Z
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Charlie https://www.yumpu.com/en/br
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Good Luck! Charlie Chong/ Fion Zhan
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Electromagnetic Testing - Eddy Current Testing Applications Chapter 5 & 6

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