ACFM Nondestructive testing

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The <strong>ACFM</strong> probe induces a uniform alternating current in the area under test and detects magnetic field of the resulting current near the surface. The AC currents under the probe are uniform in direction and strength. They do not penetrate deep into the plate but instead run in a very thin skin (
The uniform alternating current in the area under test is aligned perpendicularly to the expected crack direction known as Y axis. An array of sensors is located across the weld and monitors any disturbances in the magnetic field. There are two sensor types: B z sensors, which measure the disturbance to the current flowing around the ends of a crack, and B x sensors, which measure the reduction in density above the deepest part of the defect. If there is no abnormality only B x magnetic flux is induced. If there is a surface breaking defect, The above two components of the magnetic field are induced and measured; B x , parallel to the input field and expected defect orientation, responds to changes in surface current density and gives an indication of depth, while B z , normal to the surface, gives negative and positive responses at either end of the defect caused by current generated poles and thus gives an indication of length. Charlie Chong/ Fion Zhang http://en.wikipedia.org/wiki/Alternating_current_field_measurement
Page 1 and 2: Electromagnetic Testing MFLT/ ECT/
Page 3 and 4: Charlie Chong/ Fion Zhang
Page 21 and 22: 苏州太湖 2014 Fion Zhang at
Page 23 and 24: Alternating Current Field Measureme
Page 25: The simplification in mathematical
Page 29 and 30: Mathematical model display of Bx &
Page 31 and 32: Keywords: ■ By using mathematical
Page 33 and 34: 10.0.3 Prime Advantages: Non Contac
Page 35 and 36: 10.0.4 Limitation Simple Semi Ellip
Page 37 and 38: The B x & B z Display Charlie Chong
Page 39 and 40: FIGURE 16. Probability of detection
Page 41 and 42: Actual Fatigue cracks Charlie Chong
Page 43 and 44: Actual Fatigue cracks - Figure 16:
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Page 51 and 52: Actual Fatigue cracks- Fractographi
Page 53 and 54: Actual Fatigue cracks- Micrographs
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Page 57 and 58: Stress Corrosion Cracking Charlie C
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Page 61 and 62: In the 1980s, there were moves to d
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Page 67 and 68: 10.1.3 Magnetic Field Measurement W
Page 69 and 70: Keywords: ■ Alternating current f
Page 71 and 72: ACFM Charlie Chong/ Fion Zhang http
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Page 75 and 76: Encoded Probe (XYZ) Charlie Chong/
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Array Probe with multi-sensors Char
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Probe Arrays give the opportunity f
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Probes with different geometries Ch
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Probes with different geometries Ch
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Ovality Probe Charlie Chong/ Fion Z
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This feature of alternating current
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Crack- Fatigue Charlie Chong/ Fion
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The sizing tables have been produce
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FIGURE 1. Uniform magnetic field ge
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FIGURE 2. Coordinates conventionall
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B x will have a constant positive v
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Figure 3 shows the effect of a surf
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Keywords: • Counter clockwise cur
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FIGURE 4. Data from longitudinal di
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Software algorithms The actual para
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0 A measurement unit is needed to q
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Charlie Chong/ Fion Zhang In ACFM:
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10.2.3 Uniform Field The alternatin
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10.2.3.1 Advantages (I) Testing thr
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Keywords: The Current Field • Ind
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10.2.3.2 Disadvantages (I) Reduced
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Geometry Changes. Charlie Chong/ Fi
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Geometry Changes - Simple leg weldm
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The uniform field theoretical model
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Crack Charlie Chong/ Fion Zhang htt
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ACFM currents flowing around a defe
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The maximum coating thickness throu
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FIGURE 6. Effect of coating thickne
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Effect of coating thickness on Bx f
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Discussion Subject: “FIGURE 7. Co
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Keywords: The points at which the c
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The Eddy Current Standard Depth & P
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Discussion: when the coil is larger
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FIGURE 9. Comparison of 5 kHz and 5
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Discussion: Compare Figure 9 & Figu
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In this way, the changing signal fr
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FIGURE 12. Estimation of background
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This combination results in an upwa
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For discontinuities within about 30
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FIGURE 13. Magnetic flux density si
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FIGURE 14. Magnetic flux density fr
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More Reading on: Data Display The p
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10.2.9 Restrictions in Theoretical
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Practical alternating current field
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Keywords: • Calibrated once, at t
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The restriction to semielliptical c
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Liftoff The signal intensity reduce
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FIGURE 15. Amplitude of magnetic fl
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Trials with alternating current fie
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FIGURE 16. Probability of detection
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Another independent evaluation of t
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Remotely operated vehicle. ROV Char
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Remotely operated vehicle. ROV Char
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Further tests were carried out blin
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FIGURE 17. Experimental probability
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10.3.2 Influences on Sizing Accurac
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Crack Inclination Charlie Chong/ Fi
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10.3.2.2 Morphology On the other ha
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Rail Track Charlie Chong/ Fion Zhan
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10.3.2.4 Geometry Effects Geometric
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10.3.3 Sensor Coverage and Lateral
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FIGURE 18. Lateral displacement at
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Figure 19 shows the experimental ef
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FIGURE 19. Decrease in predicted de
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FIGURE 13. Magnetic flux density si
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10.4 PART 4. Alternating Current Fi
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Fatigue Crack Charlie Chong/ Fion Z
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10.4.1.2 Stress Corrosion Cracking
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Sulfide stress concentration cracks
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10.4.2 Corrosion Pitting The unidir
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ACFM systems have been used for a r
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Figure: Array Probe Display Charlie
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Figure: ACFM Underwater Application
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10.5.2.2 Application of the ACFM in
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Figure: Above Ground Storage Tank C
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Figure: Above Ground Storage Tank f
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Why ACFM Leakage due to cracking at
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Figure: Encoder array probe used to
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Figure: High speed inspection of wa
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Figure: Compliant array probe inspe
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Figure: Compliant array probe inspe
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ACFM Inspection Result- Tank#1 On o
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Figure: Defective region Charlie Ch
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Figure: Localised corrosion under w
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Conclusions The ability to inspect
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Other sample result display Charlie
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Figure 1: An actual ACFM screen cap
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Charlie Chong/ Fion Zhang
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Subsea Structures Charlie Chong/ Fi
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Offshore lift Charlie Chong/ Fion Z
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Expert at Works Charlie Chong/ Fion
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2015- 学习总是开心事 C
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2015- 学习总是开心事 C
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上海老照片 Charlie Chong/
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Shanghai 南浦大桥 -4 2015-
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ACFM Nondestructive testing

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